PCAT Anatomy and Physiology

Things you will learn in this section...

  • The different systems that make up the body
  • The different substances we secrete
  • Major structural systems

This section encompasses a generalized view of human anatomy and physiology, and how this relates and is useful to potential pharmacy students. Lots of pharmacy students ask, why is the study of human anatomy important to the science of pharmacy? The short answer is, many of the medicines that are given by a pharmacist have real life consequences to health and human physiology in different ways. For instance, a common medicine given from pharmacies is Vitamin D in combination with calcium. This common medicine is given for a condition known as osteoporosis, which is basically the demineralization of bones in the elderly. This drug helps to reduce the breakdown of bones, and it is useful for a pharmacist to know the anatomical, physiological, and mechanical features, which this affects, so that patients can be appropriately counselled. 

There are some common prefixes which are good to know before you start learning about the bodies anatomy, many of these terms come from Latin and Greek, so if you have any prior knowledge of these languages this can be extremely useful.

  • Cardio- "like cardiovascular”, which means the heart and blood vessels.
  • Cyto- "of the cell”, like cytoplasm which is the main area in a cell. Derm - "means of the skin, like dermatology which means the science of skin.
  • Haem- "means of the blood”, like haemoglobin which is part of red blood cells that transport oxygen in the blood.
  • Hepa- "means of the liver”, like hepatitis which is a viral disease effecting the liver.
  • Myo- "means of the muscle”, like myocardial which means the muscle in the heart.
  • Neuro- "means of the nerve”, like neuromuscular junction which is a transmission gap between neurons.
  • Nephro- means of the kidneys, like nephrons which are little tubules with the kidney itself.

A few suffixes hat are good to know include:

  • -aemia of the blood, an example of this is anaemia which means lack of blood
  • -itis means inflammation, which is a red, itchy reaction
  • -uria means of the urine, ketonuria which happens in diabetes

The body is dynamic, in that some systems cause an increase in something whilst other systems cause an increase this is called antagonism. One side is pulling called the agonist and the other side is pushing called the antagonist, the have the opposite effect.

  • Brady- slowing of the heart whereas tachy- is speeding of the heart.
  • Hyper- means in excess whereas hypo- mean lacking, below, under.
  • Endo- means of the inside whereas exo- means of the outside of the body or cell.

The Building Blocks of Organisms

Every living thing, plant, animal, or human being, is fundamentally constructed from the same basic building block, a cell. In the human body, there are over fifty trillion cells. For your body to function, it uses different cells and cell groups. For example, human skin is made up of many different cell groups. Some of these groups specialize in monitoring and reacting to the air temperature around you, while others are focused on your internal temperature.

Sometimes, these cell groups will join forces. If you've ever shivered, you are feeling the effect of the outer temperature cells reporting cold, and the internal cells reacting to the report by notifying your muscles to produce some extra heat through shivering. As these reports are being received by your brain, many other cell groups might react. Your brain might send out a message that tells you to rub your arms for added warmth, or the cell groups associated with appetite might trigger your desire for a warm cup of tea or soup.

Sometimes, cell groups co-operate in ways that might appear to be incorrect to you. When someone faints, this sudden, short-term loss of consciousness is their body's response to a lack of oxygen in the brain. When the cell group in your brain notices that it is not receiving enough oxygen, these cells jump to defend the brain. They do this by sending out a signal to your body that it needs to shut down most other functions and that it is better served if you are no longer standing up or sitting down.

Fainting seems like a poor response because people can be injured in the ensuing fall, but the cell group that protects your brain and other core organs has a lot of authority and it will override other groups. This includes the group of cells in your brain that doesn't think falling and hitting your head is a good idea.

These are just a couple examples of cell groups and how they may or may not work together for the common good of a human body. In an instant, billions of cells are monitoring, reporting and responding based on their particular jobs.

The cells that produce electrical activity in the heart are really exciting. If you've seen someone's heartbeat recorded on a hospital monitor, that jumping line is recording the electrical pattern of all of the heart's electrical cell groups hopefully working in unison. What makes these cells particularly unique is something called excitability. Most cells need some type of stimulus to do what they do, like skin cells feeling cold. But, excitable heart cells can actually create their own activity without any outer stimuli.

The cell membrane and phospholipids

Each cell has an outer "skin” that is known as a membrane. Think of this as a grocery bag, the bag and a cell can have their shape changed by pressure. If you squeeze the grocery bag, it won't stop holding the groceries, but will simply adjust to the pressure you put on it. Cells do this too.

But, the cells in the human body are a bit more advanced than your average the shopping bag, as they are semi-permeable, meaning they selectively let things in (absorption), and throw certain things out (excretion). If you think about the difference in how water would affect a paper bag versus a plastic bag, you can easily start to understand the differences in the cell membranes of different cells. The paper bag will want to absorb the water for a while before allowing the water to touch the groceries, however the plastic bag will repel the water.

Cells have differences in the amount of proteins, enzymes and other chemical building blocks they allow to pass in and out of themselves. Some cells, like the cells that make up the blood in your body, will allow high levels of inflows and outflows, while others, including the cells that make up human bones, allow minimal movement through their membranes.

Phospholipids are the key component in cell membranes. They have two parts that allow cells to be more similar to a mesh bag than a plastic bag. One component of a phospholipid is known as hydrophilic, meaning that it loves water. The part that hates water is known as hydrophobic. You might have friends that fall into one group or the other, but phospholipids are both lovers and haters. By alternating which part of the phospholipid is facing the outside of the cell, the cell can either allow fluid to pass through its membrane or not.

The ability of a cell to allow fluid to pass back and forth through its outer layer is known as its permeability. This means that the cell is able to maintain an organized structure while still allowing fluid to pass through its membrane in either direction.

A window screen could be considered semi permeable, because it will allow raindrops to pass through, you could also squirt water into the outdoors through the screen. Yet the screen doesn't change shape or move out of the way to allow the passing of water.

Tissues

A clump of cells and its supporting architecture is known as a tissue. Cells, like high school and college sports teams, prefer to be around their own teammates. In the cellular world, cells prefer other cells that have a similar job and/or a similar form (see figure 10-1). When these cells pack together, they become a tissue. Kidney cells are clumped together with other kidney cells and arterial cells clump together with other arterial cells.

Usually, human tissues are grouped into six different types. These types include epithelium, connective, nervous, cardiac muscle, smooth muscle and skeletal tissues. Each tissue group handles important and unique human body functions.

Human Tissues

Figure 10-1: The different human body tissues.

Epithelial tissues

Epithelial tissues provide several body functions. First, they can act as filters, like a gas mask or a water filter. This tissue group also includes the tissues that help your body to absorb things like sunlight and nutrients. Epithelial tissues also work to protect us from the world around us and include your skin. Finally, this tissue group is also responsible for secretions, including a stuffy nose. So, epithelial tissues are most notable for their work with fluids. Other functions include:

  • Secretion- of hormones into the blood vascular system, and/or the secretion of sweat, mucus, enzymes, and other products that are delivered by glandular epithelial ducts.
  • Selective absorption - the regulation and exchange of chemicals between the underlying tissues and a body cavity.
  • Protection- from radiation, desiccation, toxins, invasion by pathogens, and physical trauma.
  • Detection of sensation - one function you are constantly aware of, allowing for detection of external stimuli.

Cells in the epithelium are very closely packed together, one next to each other like bricks in a wall, leaving very little intracellular space. These cells can form continuous sheets which are attached to each other at many locations by tight junctions, desmosomes, and adherens junctions. Skin is an organ comprised of specialized epithelium and connective tissues that has two main layers:

Epidermis, made of epithelial cells, it provides waterproofing and serves as a barrier to infection.

Dermis, made of connective tissue which serves as a location for the appendages of skin.

The epidermis is composed of the outermost layers of the skin. It forms a protective barrier over the body's surface, responsible for keeping water in the body and preventing pathogens from entering. Figure 10-2, depicts the different layers in sequence, the epidermis can be subdivided into:

  • Stratum corneum aka the "horned layer” is the outermost layer of the epidermis, consisting of dead cells (corneocytes) that lack nuclei and organelles.
  • Stratum lucidum - a layer below which can be found only on palms and soles where a thicker skin is needed.
  • Stratum granulosum - a thin layer containing keratinocytes migrating from the underlying stratum spinosum that become known as granular cells in this layer
  • Stratum spinosum - the next layer down located below the granulosum, this is where keratinization begins.
  • Stratum germinativum aka the "stratum basale” is the deepest layer of the epidermis, which often only contains a single layer of cells. The stratum basale is primarily made up of basal keratinocyte cells, which can be considered the stem cells of the epidermis.

Skin layers 

Figure 10-2: The different layers of the epidermis.

90% of the cells found in the outermost layer of the skin are calledkeratinocytesand are considered the predominant cell type in the epidermis. The primary function of keratinocytes is the formation of a barrier against environmental harms such as pathogens, heat, UV radiation, and water loss. Keratinocytes are formed first by differentiation from epidermal stem cells (transit amplifying cells), residing in the lower part of the stratum basale of the epidermis, then they migrate upwards towards the stratum corneum.

Connective tissues

Very much like their group name, connective tissues create the ability for the body to stay connected as a unit. Even skin would not be enough to form a human body by itself, as we would all look more like our friendly grocery bag. Connective tissues are grouped into teams called loose, dense and special connective tissue. Loose connective tissue is good for creating the structure of some organs, as well as for storing things like nutrients that the body will need in the future or for creating a cushion between organs and other body structures. Most loose connective tissue is hidden in the human body. Dense connective tissue is more visible, because it includes tendons, ligaments and the skin itself. Tendons attach muscle to bone and ligaments attach bones to bones as well as keep joints together. Your knee will have tendons connecting your leg muscles to your femur, tibia and fibula, but it also has ligaments to keep the knee joint together.

Special connective tissues are tissues that "connect” things in the body, but don't obviously fit into the loose or dense family. This group includes blood, cartilage and bone. Cartilage is a tissue that gives the human body flexibility while protecting bones from rubbing together. Arthritis is simply a loss of cartilage between bones that creates inflammation in the patient's joints.

Skeletal Muscle

Each muscle is made of bundles of muscle fibers surrounded by connective tissue. Each individual muscle fiber has the following:

  • Numerous nuclei - a muscle fiber develops from the fusion of many cells
  • Sarcoplasm(muscle cell cytoplasm) filled by parallel myofibrils
  • Sarcolemma(surface membrane) forms deep tubes (T tubules) into the sarcoplasm (similar to the ER) along its length

The most important aspects to remember about muscles, is how they generate their effect. In essence, the brain sends out an electrical signal, which is transmitted along neurons to the muscle. At the muscle there is a neuromuscular junction, which converts the electrical signal into a chemical signal, which then electrically activates muscle.

Muscle action 

Figure 10-3: The sliding filament system - how muscles contract.

Once the muscle has been signaled to contract, the sliding filament system(depicted in figure 10-3) starts to operate. The first stage is that tiny filament-like structures called myosin-heads hydrolyse ATP to obtain a higher energy status and attaches itself to actin myofilaments, which are in close proximity. The myosin head then works as a piston and pulls the actin filament towards the M line flipping it into a low energy configuration. The collective bending of numerous myosin heads (all in the same direction), combine together to move the actin filament relative to the myosin filament. This results in muscle contraction. 

Cardiac muscle

Cardiac muscle is different from other muscles as it is involuntary, meaning that you don't consciously control it. Microscopically, it looks different from smooth muscle as it is striated (covered in lines) and had loads of mitochondria that it needs to produce enough energy for its rigorous pumping. These muscles act together to propel blood through the atrium and ventricles of the hearts towards the rest of the body and the lungs. The contraction that propels blood in this way is called systole. The cells that comprise cardiac muscle, called myocardiocytes, only contain one, unique nucleus. Like all cells, cardiac muscle requires oxygen, but its presence is more important than to other cells as oxygen deficiency, called ischaemia (lack of oxygen in the tissue) or hypoxia (lack of oxygen supply) can lead to the impairment of heart muscle function, which can be extremely detrimental.

Smooth muscle

Like cardiac muscle, smooth muscle too is involuntarily controlled and you are not aware that you are keeping them going. However, unlike cardiac muscle, smooth muscle under a microscope is non-striated. Smooth muscle can be found in your gastrointestinal tract comprising the walls of these hollow organs. Smooth muscle does all you internal "housekeeping”, taking care of functions like peristalsis - getting your intestines contracting to push food through your body, contracting your bladder when you're urinating.

The adult human body has 206 bones, more than half are in the hands and feet. An infant may have from 300-350 bones at birth. The PCAT examiners don't want you to know all of them just the most important ones.

Nervous tissue

Nervous tissue is only nervous part of the time. This group operates like the telephone wires or cell phone towers to carry information to and from various body parts. Nervous tissues are found in the brain, nerves and spinal cord. The reason we said that these tissues are only nervous part of the time is because they can sit quietly, like fireman in a firehouse, until the bell rings. Then, nervous tissues dive into action, alerting different body parts in response to a pleasure, a threat, or some other piece of sensory information. If you really love or really hate chocolate, putting a piece in your mouth will trigger alarm bells. Your taste buds will alert your brain to the presence of chocolate and your brain will send out several rapid-fire messages. First, whether you love it or hate it, the brain needs to let your stomach know that you are eating. If you love chocolate, your brain will also send out messages of relaxation and excited pleasure so that you can fully enjoy your snack. If you hate it, your brain might send other messages and your stomach might react by having you almost vomit in an attempt to repel the evil chocolate. Your nerves also work within this group. Nerves tend to be pretty excitable, as you know if you've ever touched a hot stove. The nerves in your hand immediately send out screaming messages for you to lift your hand away from the heat. Assuming your body reacts correctly, you quickly withdraw your hand to assess the damage and a new group of nerves announces their displeasure with what has happened in the form of pain.

Last, but certainly not least in the tissue groups, is muscle tissue. If you can remember the letter that muscle begins with, you can always remember what this group does. Muscle tissues provide the human body's mechanics. You can't move, eat, or live, without them, because muscle tissues are found in the heart, arteries, and veins, as well as the muscles you can see when you lift a heavy object.

Organs

Now that you understand tissues and tissue groups, organs should be a breeze. But, before we review various individual organs, you need to understand the major organ groups. Organ groups, or systems as they are usually called, include the endocrine system, digestive system, circulatory system, nervous system, reproductive system, and immune system, among others.

If you bunch lots of certain tissues together, you will end up with organs. Organs will typically be a group of tissues that gets something done. More often than not, organs are dependent on other organs to complete body functions.

The circulatory system is one organ group. These organs include the blood vessels and the heart. Their job is to move blood through the body in order to transport oxygen and nutrients. Blood vessels, in order of largest diameter to smallest, are arteries, veins, and capillaries. Arteries transfer oxygen rich bright red blood away from the heart whereas veins return blue black blood that needs to be reoxygenated, back to the heart. Capillaries are tiny blood vessels where oxygen and nutrients are traded for carbon dioxide and waste throughout the body at the tissue level.

The endocrine system is the body's main communication system. Glands, including the thyroid and adrenal glands, use hormones to communicate information to the brain, heart, and other organs or tissues. So, if you have swollen glands in your neck, hormones are being sent throughout your body, activating defensive and healing systems to fight the infection that is causing the inflammation.

We won't spend a lot of your time discussing the reproductive system since hopefully you are already familiar with the parts and pieces. We will say that each organ in the male or female reproductive system provides a unique function and reproduction requires that all of these organs are working together.

The nervous system, not surprisingly after our conversation earlier about nervous tissue, is responsible for evaluating information it collects and notifying other organ systems when needed. With the nerves, the spinal cord, and the brain as members, you can see that the nervous system is the human body's hard drive. Millions of messages are being sensed by your body every second and all of this information is being forwarded to your brain via your spinal cord with reply and action messages being sent in response by the brain to all parts of your body.

The human body's immune system is designed to fight disease. It works with other systems, including the digestive system, and will immediately launch chemical fighters to attack any threat. The immune system includes the lymph nodes, spleen, tonsils, thymus, and leukocytes.

The digestive system is a workhorse that the body uses to consume and process foods and fluids, as well as discharging waste. From the glands in your mouth that make you salivate, to the glands in the rectum that produce mucus, the digestive system's sole purpose is input and output. The liver, stomach, pancreas, intestines, and gallbladder, are all members of this important group.

Skeletal/Muscular System

Your house or apartment was built using wood as a framework. Your body also depends on a framework and it's the skeletal/muscular system. If your house didn't have this framework, it would look like a pile of nothing, so would the human body without this system.

For another example, a plastic shopping bag. You can flatten an empty shopping bag because there is nothing for it to form around. But, as soon as you put a box or bottle into the bag, it can no longer be flattened (at least without making a mess). The bottle or box is providing a structure that the bag supports. The human body's structure includes bones, muscles, tendons, ligaments, and cartilage, all contained inside a person's skin.

Defining the bodies infrastructure

Because the base building material in this structure is bone, the structure of a human being will decide how tall they are and there's not much anyone can do about it. The body can grow lean, muscular, or obese, laterally from the effects of good or bad exercise, lifestyle, and diet. Muscles can be developed and the supporting tissues will continue to support the body.

As we age, gravity and deterioration will start to affect the structure of the body, resulting in a loss of height or the stooping posture that usually accompanies old age.

The opposite happens when we are young. As we grow through childhood, our bones grow, forcing the supporting structure of ligaments, tendons, and muscles, to grow alongside them. Usually, our bodies stop growing after puberty and the body shifts from growing to maintaining throughout our adult lives.

Skeleton learning for the pCAT

Figure 10-4: The human skeleton.

The skelly quiz, depicted in figure 10-4, is not there just to provide you with rigid support so you don't fall down into a big pile of jelly, it also functions to:

  • Produce Blood Cells - This process takes place in the red bone marrow inside some larger bones.
  • Protection from harm - The skeleton provides mechanical protection for many of the body's internal organs, reducing risk of injury to them. For example, cranial bones protect the brain, vertebrae protect the spinal cord, and the ribcage protects the heart lungs and liver.
  • Assisting in Movement - Skeletal muscles are attached to bones, therefore when the associated muscles contract they cause bones, and inevitably your body, to move.
  • Storage of Minerals - Bone tissues store several minerals, including calcium (Ca) and phosphorus (P). When required, bone releases minerals into the blood - facilitating the balance of minerals in the body.
  • Storage of Chemical Energy - With increasing age, some bone marrow changes from 'red bone marrow' to 'yellow bone marrow'. Both of which are an important chemical energy reserve.

This is all to do with the macrostructure of the skeleton, however you also need to know the microscopic structure as well.

 Bone structure

Figure 10-5: Compact and spongy bone.

Key structures illustrated in Figure 10-5, include:

          Haversian canals -these canals surround blood vessels and nerve cells throughout the bone and communicate with osteocytes in lacunae

Periosteum - is a membrane that lines the outermost layer of all bones, except at the joints of long bones.

Endosteum  - lines the inner surface of all bones.

Red Bone Marrow and Yellow Bone Marrow - consists mainly of adipose cells, and a few blood cells.

Agonistic and Antagonistic Relationships

If you want to pick up a cup, your brain receives the request and sends a message to your arm and hand that a cup needs to be grabbed. As you close your hand around the cup, you are experiencing the antagonistic, or contracting side of muscles. All muscles typically have an antagonistic side that activates when we want to do something. To take a few steps, the antagonistic side of several muscles needs to be activated so you can move, stop, and retain your balance.

When you want to release the cup, the other retracting side, or agonistic side of the muscle, becomes active. Muscle relaxation uses the agonistic side of the muscle. This is a simple example and it is highly possible that many body movements are using muscles that are acting in opposite ways in order to create the movement. Balance is a good example of this, because balance requires multiple muscles, some contracting, and some relaxing during the act of balancing.

Nervous System

Your body is one big electrical system. The central nervous system is the epicenter, sending out electrical signals from the tip of your toes to the top of the skin on your head. The nerve cells within the body's nervous system, also known as neurons, have some very special talents. First, they can react when they are stimulated by light, sound. or touch. Neurons can also communicate with each other, getting each other excited when there is stimulation. Once they get excited, they can then communicate with other tissues, organs and systems, such as muscles in order to gain an action or reaction.

If you touch a hot stove, neurons in your hand get excited by the combination of heat and pressure, and then send messages to the muscles in your arm to pull away, while simultaneously notifying the brain that something bad is happening. Your body is constantly carrying electricity. Ever been shocked when touching a metal doorknob? This is because the sole of your shoes are brushing against a man-made fabric which moves electrons causing friction, and you actually become electrically charged like a thunder cloud. You build up this charge and as always, the electricity is looking for a way to escape. So, touching an object allows the static electricity to discharge, giving you a shock as it exits.

All electrical signals originate, from the nerve center, pardon the pun, which is called the Central Nervous System (CNS) which physically comprises of the brain and the spinal chord.

Simple CNS structure

Figure 10-6: A simplified version of the CNS structural layout.

The main parts of the CNS (illustrated in Figure 10-6) include:

  • The brain- the center of the nervous system in all vertebrate and most invertebrate animals. It serves as the centralized control center over the other organs of the body. The brain acts on the rest of the body both by generating patterns of muscle activity and by driving secretion of chemicals called hormones.
  • The brain stem - the posterior (back) part of the brain, adjoining and structurally continuous with the spinal cord.

The CNS is the control center our neurological activity and is structurally isolated as it is protected by the bone of spine and skull, or by the blood-brain barrier which is a chemical barrier in the blood which excludes small potentially harmful molecules. The CNS then branches out into the peripheral nervous system (PNS). The PNS can be considered as any part of the nervous system, which transmits electrical signal out side the CNS (i.e. anything other than the brain and the brain stem). 

Note that some cranial nerves are part of the PNS with the exception of cranial nerve II, the optic nerve, along with the retina. You can see that the dark black is the CNS whilst the light grey spindles emanating from the CNS is the PNS. The PNS is divided into the somatic nervous system and the autonomic nervous system (see figure 10-8).

CNS Breakdown 

Figure 10-8: the breakdown of the different parts of the nervous system.

The Autonomic Nervous System (ANS) in general is responsible for control of involuntary (outside your consciousness control) or visceral (involuntary organ movements) bodily functions including:

  • Cardiovascular - heart rate
  • Respiratory - breathing rate
  • Digestive - salivation
  • Urinary - called micturition in medical lingo
  • Reproductive functions - sexual arousal
  • Key role in the body's response to stress

Although, in general most of these functions are involuntary, some can be temporarily overridden such as breathing, sexual arousal and in some cases even heart rate so it is not a exclusive feature. The autonomic nervous system can be broken down into the Sympathetic (governed by Norepinephrine neurotransmitter) and Parasympathetic (governed by Acetylcholine) nervous systems, which work both cooperatively and independently. The Sympathetic nervous system allows body to function under stress and is responsible for "fight or flight" quick responses. The other branch is the parasympathetic nervous system, which pretty much does, the opposite and controls vegetative functions sometimes called "rest and digest" and works as a slowly activated "dampening” system. This part of the nervous system is responsible for feed or breed or rest and repose and is usually in constant opposition to sympathetic system functioning.

Both the parasympathetic and sympathetic work together providing ANS functionality can generally be divided into sensory (afferent) and motor (efferent) subsystems.

A useful way to remember afferent and efferent and what the mean is to remember what the word effect and affect mean. Affect is a verb, meaning to cause something to happen. Effect is a noun, which is the result of having happened. So the afferent subsystem receives information, which causes the efferent nerve to cause the effect.

Affector muscle 

Figure 10-9: Affector/effector neuro-muscular pathways.

There is a distinct anatomical difference between the two systems, the sympathetic system has thoracolumbar outflow, meaning that the neurons begin at the thoracic and lumbar (T1-L2/3) portions of the spinal cord. The parasympathetic division has craniosacral "outflow”, meaning that the neurons begin at the cranial nerves (CN 3, CN7, CN 9, CN10) and sacral (S2-S4) spinal cord.

Nerves and electrical conduction

Electricity is important as an information transportation mechanism throughout the body, just as a computer receives the internet from a server. By utilizing the pathways of the nervous system, electrical messages, like Morse code, are constantly being shuttled through the human body, resulting in millions of small adjustments. You don't notice many of these, like a very slight increase in your heart rate or an increased secretion in your pancreas, as they are involuntary and automatically controlled by a part of the brain called the medulla oblongata.

But, sometimes you do notice the changes brought on by the electrical messages. If you suddenly notice your heartbeat or suddenly feel hot or cold, this is the result of all of tiny electrical communication between cells. Most of the time, your body won't ask you how you feel about the changes because it is preprogrammed to maintain a certain predetermined stasis, or maintenance level for every function in the human body.

Unlike an appliance, however, the body creates its own internal electrical power. Electrical cells in the heart are the most unique sources of electrical party. This is because an electrical heart cell can stimulate itself, creating its own stimulation in order to work. This is a great design feature, because it means that your heart's electrical activity is not based on anything except the heart cell's perception of the needs and wants of the heart. Like an appliance, the pumping group of heart cells, or those that compose the heart muscle, are stimulated by outside stimuli and they pump, fast or slow, accordingly.

Occasionally, the electrical signals and the pump get out of sync. This is called an arrhythmia. Most of the time, an acute, or one-time arrhythmia can be fixed with medical intervention and chronic disconnects between the electrical and pumping system can be managed with medication, surgery or the placement of a pacemaker. A pacemaker is like the drummer in a band, setting the beat for the other instruments, except the pacemaker is implanted to ensure that the electrical and pumping cell groups within the heart stay in synch with each other.


Figure 10-10: A neuron.

Figure 10-10 shows an entire neuron, important structures to note include:

  • Cell body (or soma). This is the control center of the neuron; it is also where neuronal proteins are synthesized.
  • Axon, carries outgoing signals to other neurons flows along.
  • Dendrites, can number in their thousands per neuron, but it will have only one axon.
  • Axon terminals, lies at the very end of the axon, these are the structures that contain neurotransmitters. Neurotransmitters are the chemical medium through which signals flow from one neuron to the next at chemical synapses.

Myelin sheath - insulating your very own electrical cables

All of the human body's electrical activity needs a smooth and fast pathway. Nerves that conduct electricity have a layer of insulation that facilitates the transmission clarity and speed of electrical impulses.

There are diseases and illnesses that can slow this transmission. Multiple sclerosis is a disease that tricks the immune system into attacking its own nerves. Some viruses, including HIV, measles and even chickenpox can disrupt the myelin sheath. Severe liver damage can also create problems for the myelin sheath, as can conditions that disrupt or slow blood supply movement through the body. Some of these include carbon monoxide poisoning, heart attack and drug overdose.

The brain and its control mechanisms

We love the brain and we expect that you do to. The brain never stops working and it does a lot for you. The brain has two control mechanisms for thought. One of the controls is the brain's ability to "think slow”. Thinking slow gives humans the ability to rationally process thoughts, apply their own experiences and reasoning and develop a solution or action plan associated with the thought.

Many scientists think that this key feature of our brains is what separates us from almost all animals. Slow thinking is activated in our brains when an immediate solution doesn't appear to be available. For example, if a friend asks you where you want to go for lunch, it's highly likely that you'll employ slow thinking to make a decision. Your brain will search for known inputs, including past experience, restaurant reviews you read a month ago, things someone told you about a particular restaurant and other data that's been stored away. The brain will also send out a quick poll to your body to ask how hungry you might be. Your stomach might reply back that it is empty and your brain will factor this into your decision-making process.

What's interesting about slow thinking is how deeply it can be affected by outside information. This is seen in real life with the importance of customer ratings and comments on social media and how they affect buying behavior.

Your brain also has a "quick draw” thought process. This process is running all of the time and largely behind the scenes, but this thought pattern can also be corrupted by bad data. If you've ever seen an optical illusion, this is an example of your thoughts being "tricked”. This trickery may be from past experiences, lack of education or even bad sensory information. If your eyes send a signal that they are looking at two identical objects and your brain decides that your eyes are never wrong, you will immediately decide that the two objects are exactly alike.

There are even examples where groups of people get it wrong. Your state government announces that it is replacing a bridge in an important commuter area. In the announcement, all of the designers, architects, contractors and accountants have reviewed and certified the cost estimate for the new bridge, yet the bridge ends up costing ten times the original quoted amount.

The cause of this disconnect is often associated with problems in the slow thinking process of everyone involved. Sometimes, this is because of optimism or ego. Other times, the brains of the group are just grabbing the most recent relevant data, no matter how flawed that data might be. There can and are many other causes for flawed long and short thinking. There is probably not a group that pays money to exploit these thinking flaws more often or in greater amounts than the advertising industry and their clients. There are no accidents in mainstream advertising, because extensive research has already been completed. The order in which products are presented, the color of the package and the demographics of the spokesperson are all ingredients that are carefully calculated. Now, you've been warned.

The are many layers to the brains anatomy, you do not need to know it fully in-depth however, you will be expected to know the fundamental parts of the brain.

Brain anatomy

Figure 10-11: Brain anatomy.

The different parts of the brain, shown in figure 10-11, are responsible for different functions:

  • Hindbrain, which includes the medulla, pons, and cerebellum, controls circulation, respiration and balance.
  • Midbrain, located below the cerebral cortex, and above the hindbrain placing it near the center of the brain this part is responsible for visual and auditory reflexes.
  • Forebrain, is the largest brain area and comprises of parts of the cerebellum, this area controls higher functions such a thought and comprehension.

Circulatory System

For the PCAT you do not have to know the entire anatomy of the heart in depth, however you will be expected to know the mechanisms of its actions. The hearts main function is to pump blood around the body, it does this by contracting almost 120 times per minute, which is coincidently the same speed as disco music!


Figure 10-12: The circulatory system in respect to oxygenated and deoxygenated blood.

The image above is a simplified version of how the heart deals with the circulatory system. You can see the two different types of blood; the red blood is oxygenatedblood which is pumped from the lungs, via the pulmonary vein to all of the organs around the body. The blue blood is deoxygenatedand brings blood into the lungs via the pulmonary artery for oxygenation. The most important artery in the heart is the Aorta, this is the largest artery in the body and has to be, as it carries the highest amount of blood pressure as it is the beginning of the oxygenated bloods journey around the body. The most important vein in the heart is the Inferior Vena Cava that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart.

A useful way to remember the difference between and artery and a vein is simple. An Artery brings blood out of the heart at high pressure, the A in artery looks like an upwards arrow. The downward V in Vein means that they bring blood down into the heart.

Keeping your blood pressure and pulse in check

We've already mentioned the circulatory system. The heart pumps blood throughout the human body at a consistent rate and pressure. Blood pressure, as a measurement, is simply the numeric value of two pumping pressures.

Diastolic blood pressure is simply the minimum pressure in the circulatory system just prior to the heart beginning another pumping cycle. Systolic blood pressure is the maximum pressure at the end of the heart's pumping cycle. You've probably seen a blood pressure represented like this- 130/80. This is the systolic pressure over the diastolic pressure. In case you're a little extra curious, that cuff that nurses and physicians wrap around your arm and pump up and down to measure your blood pressure has a very unusual name. It's called a sphygmomanomter, but most people just call it a blood pressure cuff.

It is very important for humans to monitor and measure their blood pressure frequently. Often, a higher or lower than usual blood pressure reading is a sign that something is not right, even if there are no other symptoms. Very high or very low blood pressure can be life-threatening.

The human pulse is simply a measurement of how many times the heart beats in a minute. The pulse works in concert with blood pressure, so if there is a rise in blood pressure, there will typically be a decline in pulse rate. The opposite is also true.

The Spleen

This is probably as good a place to introduce the spleen as any. The spleen is a primary filter and secondary storage vessel for the circulatory system. Red blood cells eventually wear out and need to be recycled and the spleen handles the recycling efforts.

In addition, new white blood cells and blood platelets are stored in the spleen and released when needed. Finally, the spleen is a defender against blood borne bacteria that can cause meningitis or pneumonia.

When Circulation Goes Wrong

There are several causes and effects of circulation problems. The causes can include obesity or anorexia, trauma, genetic system problems, stroke, heart attack and others. In all cases, the circulatory system is being to asked too much or has been breached so it's losing blood faster than it can be replaced.

A heart attack is caused when the heart muscle doesn't receive enough oxygen over a period of time. The heart muscle reacts by sending out pain messages. The brain, reacting to these messages, tells the blood vessels in the arms and legs to squeeze, or constrict, to cut down the amount of blood and the amount of work the heart is doing. This is called shunting.

A common cause of heart attack is a narrowing of the arteries surrounding the heart. This narrowing is usually caused by a build-up of plaque, a sticky substance similar to the plaque that builds up on your teeth, causing a disruption in blood flow. This disruption is similar to what happens if you step on a garden hose someone is using to wash the car. If you maintain your pressure on the hose, the amount of water coming out the end will slow to a trickle or stop. That's not good for the car wash, but it's even worse for your heart. Conventional medicine battles arterial narrowing with medication and a procedure called angioplasty.

Angioplasty is the procedure used by doctors to expand the narrowed area in the bloodflow system. Using a very small tube that is inserted into the patient's groin and the femoral artery, a balloon is moved into the blocked location. As the balloon fills, it forces the plaque to release back into the blood stream.

Sometimes, the balloon isn't enough and doctors will use a device called a stint to keep the artery open. The stint attaches to the walls of the artery, refusing to allow plaque to pile up in that section of artery. As a last resort, a heart surgeon will cut out bad sections of artery and replace them with either sections of artery from other parts of the body or possibly artificial or animal artery section replacements.

If the heart is denied proper oxygenation, parts of the heart muscle can and will die. This heart muscle death is almost always permanent. Patients who have had a heart attack will usually be placed on medications for the rest of their life and encouraged to improve their diet, exercise, quit smoking or all of the above.

A stroke can be a byproduct of a heart attack, but a heart attack is not necessary for a stroke to occur. A stroke happens when a blood clot gets stuck in a blood vessel in the brain, causing symptoms that will usually include partial paralysis, speech impairment or loss of other body functions. A small stroke, called a transient ischemic attack, or TIA can create the symptoms as a full stroke, but the symptoms will often resolve with medication, rest and time. TIA's are usually a warning, from the brain, that a major stroke is brewing and doctors will focus on finding possible sources of the clots and the patient will be placed on blood thinning drugs, sometimes indefinitely.

Many people suffer from high blood pressure. Genetics and lifestyle are the two most common causes. High blood pressure can lead to heart attack and stroke, so these people are placed on medications, dietary restrictions, exercise regimens and other programs to reduce their blood pressure to acceptable levels.

Cholesterol is another source of medical problems. There are two types of cholesterol. LDL, often called "bad cholesterol” will contribute to plaque buildup in the arteries. HDL, called "good cholesterol,” helps cells to maintain their semi permeable state.

Genetics and lifestyle, especially diet, are the key contributors to the levels of both cholesterol types. Although many patients can lower bad cholesterol and raise good cholesterol with changes in their diet, some will require medication. The big payoff in cholesterol maintenance is the reduction in likelihood of a heart attack or stroke.

Respiratory System

Now we'll take a spin around the pleural space. The pleural space is simply the sack where the lungs live. Two inflatable bags operate within a larger bag. This larger bag, or cavity, also contains two membranes, called pleura that surround each lung a small amount of lubricating fluid known as pleural fluid.

The lungs don't decide to breathe. They are prompted by the diaphragm. The diaphragm is a muscle, shaped like a dome that triggers breathing based on signals from the brain. When the diaphragm relaxes, the lungs have the space and pressure to accept air. The exact opposite happens when the diaphragm contracts.

Incidentally, if the diaphragm doesn't smoothly relax, you get the hiccups. No one has been able to figure out the purpose or benefit of hiccups, but we do know that they were originally called hiccoughs and everyone seems to have a personal way to cure them, including breathing into a bag and trying to be scared. For our money, the easiest cure seems to be simply gulping in a big breath, then quickly following with a small gulp, then holding your breath with a long, slow exhale.

The internal air bags

Your lungs are not identical twins. If you are looking down at your own chest, the right lung has an extra section, or lobe. The left lung has two lobes and there are three lobes making up the right lung. This difference is simple to explain... The left lung sits above the heart, so there isn't room for the third lobe.

Internal gas exchange

When a human and most mammals inhale, the outside air rushes into the lungs because the pressure in the lungs is lower than the outside pressure. The opposite happens during an exhalation, quite a few muscles cause this but the main one is called the diaphragm which lies under the lungs, going up and down like an accordion. During this air rush, the incoming air is humidified and filtered. The air is humidified to ensure that the air is at roughly the same temperature as the body's internal temperature. Otherwise, the very act of breathing would be considered a threat or everyone would at least get Slurpee brain freeze with every inhale. The incoming air is also filtered by hairs and mucous lining the nose, mouth and trachea, or windpipe. These filters are catching small foreign particles, bacteria and viruses that might otherwise lead to infection or disease.

When the windpipe gets close to the lungs, it bifurcates (see figure10-13), or splits into two smaller pipes called bronchi. The bronchi then divide in each lung into structures that look like trees. The main tree branches are called bronchial tubes and the much smaller branches are called bronchioles. Each bronchiole ends in little bags called alveoli. It is with the alveoli that the human body starts using the air.

Biforcation of the lings

Figure 10-13: Biforcation of the lungs.

Alveoli (shown below) allow oxygen to pass through their thin walls and into the bloodstream where it is picked up by hemoglobin in red blood cells. As the blood moves through the body, it loses most of the oxygen as cells need it for respiration. Whilst on its travels, hemoglobin picks up carbon dioxide that it hands back through the alveoli to be exhaled. So, while oxygen is offloading from the air, carbon dioxide is simultaneously being loading up for the trip out of the body. When a human body is in motion, the rate of inhaling and exhaling increases.


The amount of air that is inhaled is called the tidal volume. It's the combination of inhalation rate and tidal volume that gives the human body the oxygen it needs. But, there are many things that can cause problems for the respiratory system.

Common Respiratory Diseases

If the alveoli produce too much mucous because of disease or illness, the transfer of oxygen is slowed. So, when you have some type of virus or infection that is causing your alveoli to produce too much mucous, you will breath heavier and more often as the body seeks to maintain the oxygen levels it needs.

Alveoli can also be inhibited by foreign invaders. Asbestos is a good example. Asbestos is constructed with very tiny glass fibers. Even with the body's filtering mechanisms working overtime, glass fibers sneak past and lodge in the bronchioles. Prolonged exposure to these types of threats can cause permanent and sometimes fatal respiratory failure.

Asthma is another common reason for breathing problems. Genetics and some environmental factors including prolonged exposure to certain chemicals or mold and poor general air quality can cause chronic asthma. Continued inflammation of the airways, by any means, is the root cause of asthma.

Asthma sufferers are often prone to sudden asthma attacks. The causes of these attacks vary, but can include stress, smoke, infection and even exercise can bring on an asthma attack. Experienced asthma sufferers will often carry an inhaler. An inhaler is a device that delivers medications into the lungs when activated. These medications often include a bronchodilator that works to open all airways to their largest possible diameter, greatly improving breathing.

Chronic Obstructed Pulmonary Disease, or COPD, is another respiratory ailment. Almost always caused by smoking or prolonged exposure to unhealthy air, COPD affects breathing in a few possible ways.

First, COPD causes the airways to produce too much mucus, clogging the airways. Or, the walls of the airways thicken or aren't able to stretch. Also, the walls of the air sacs can be damaged or destroyed. Any or all of these will be the medical reason behind COPD.

COPD can and will get progressively worse, however the progression of the disease can be slowed with smoking cessation, exercise, some diet changes and medication.

Emphysema is also a disease that worsens with time. The leading cause of Emphysema is smoking. In emphysema, air sacs in the lungs become misshapen and torn, reducing the amount of oxygen that will be transferred into the bloodstream as well as the amount of carbon dioxide that can leave the body. Like COPD, Emphysema can be controlled, but not cured.

There are other ailments that can make breathing difficult, but most will be acute, as is the case with a virus and can be cured with medication, environmental changes and rest.

We don't want to gross anyone out, but boogers and snot are a good thing as they show that the body's natural filters are working. In increase can show that the person is working in unhealthy air and a very dry nose is suggesting that the surrounding air needs more moisture. Either way, everyone picks their nose. It's a fact.

Excretory/Digestive System

The human body cannot survive on air alone. Our bodies need nourishment in the form of food and fluids. Our bodies do amazing things with food and humans can make dramatic changes in their health with simple changes to what they put in their mouths. There are two systems directly involved in processing food and discharging the leftovers, the digestive system and the excretory system.

The digestive system is complex, but involves a few key organs. When you take a bite of food or a drink, digestion begins immediately. Chewing food breaks it down into little pieces while adding saliva to the mix. Saliva is also added to whatever you drink.

Enter via the esophagus

Your nose is indirectly involved in the early stages of digestion because you hopefully breathe through your nose while you are chewing, adding air to the food and saliva mix. Your taste buds use the air to tell you if something tastes good and removing the air reducing their ability to report good versus bad. You can test this by holding your nose while you eat, if you didn't already as a child.

Chewed food, fluids and saliva move to the back of your mouth and a flap closes over the windpipe so food and fluids can be directed into the esophagus. As the mixture nears your stomach, there is a "door,” called the lower esophageal sphincter that opens to allow food to pass into the stomach, but closes so that food from the stomach doesn't travel back up the esophagus. The esophagus moves food with a series of contractions. If you've ever watched a snake consume its dinner, the contractions it makes are similar to the contractions in the absorption esophagus.

Your stomach works like a blender, mixing food and grinding it into a liquid while also adding acid and enzymes to break the food down even further. Once the liquid has the consistency of a paste, it is sent to the small intestine for additional digestion and the first level of nutrient.

Acid Regulation in the Stomach

Acid in the stomach is called gastric acid and includes hydrochloric acid, sodium chloride and potassium chloride. Different stomach cells produce bicarbonate to keep the acid in check. This acid is produced as needed by cells that line the entire stomach interior and the bicarbonate producing cells also produce mucus to protect the stomach's interior.

The nervous system monitors and regulates the stomach's acid production. However, if you have ever had "heartburn,” you know that the regulation of the stomach does not always work as designed. You shouldn't blame the nervous system, because heartburn is actually caused when partially digested food sneaks back past a weakened or slow lower esophageal sphincter.

Heartburn is most likely to happen soon after consuming a big meal or a meal with a large volume of spicy foods and is often started by lying down, lifting something heavy or by exercising too soon after eating.

Heartburn is usually acute and can be controlled with an antacid, but chronic heartburn may be a sign of something more serious.

The small intestine, also known as the duodenum, has three areas, called the duodenum, the jejunum and the ileum. When stretched out straight, the small instestine is over fifteen feet long, but it is coiled into a small area in the abdomen. Within the small intestine, additional chemicals produced by the pancreas and liver are added to further break down the paste and help with absorbing nutrients.

The liver is the largest organ, other than the skin, in the human body. It is also the largest gland in the human body. The liver is made up of four lobes of differing shapes and sizes and it's not a particularly pretty organ, but it is powerful.

In addition to producing bile for digestion, the liver also handles cholesterol usage. Remember earlier that we spoke about good cholesterol and bad cholesterol. The liver handles the processes for using cholesterol within the human body.

The liver also breaks down insulin and tries to metabolize substances that are toxic and this last function can get the liver into trouble.

The bile produced in the liver is extremely important to digestion and low bile production from an injured or damaged liver is a serious medical condition. Some conditions are severe enough to warrant liver dialysis or a liver transplant.

The liver can be damaged by trauma, hepatitis, illnesses including cancer and the chronic ingestion of toxins, most notably alcohol. You will often be able to notice someone with severe liver damage because they will display jaundice, or a yellowish appearance, especially on their face and in the white portions of the eyes.

It's not all bad news for the liver, because it has a special super power. The liver can re-grow itself if it needs to. This doesn't mean that the liver can grow a new lobe if one needs to be removed or can reverse the effects of alcoholism by reproducing a healthy version of itself. What it means is that a healthy liver can expand its existing lobes, through cellular growth, to meet the workload it needs to handle.

This ability to re-grow is most often utilized in a liver transplant where both donor and recipient are alive. The donor loses a lobe of their liver, yet both patients will ultimately end up with a full size liver as the organ in each body grows to handle proper bile production and other needed functions. The key organs you need to know include:

The Gallbladder - a small organ that stores bile that the liver produces. The liver is almost always producing bile, even if there's no digestion happening and the gallbladder holds this bile until it is needed. After a meal, the gallbladder will be empty as all of the stored bile is used.

The most common ailment for the gallbladder is gallstones. Scientists aren't completely sure why some gallbladders allow certain bile ingredients to form stones, but everyone agrees that gallstones can become painful and this discomfort is usually treated by removing the gallbladder completely. 

The Pancreas - as partially digested food leaves the stomach and enters the small intestine, it becomes known as chyme. The pancreas adds more enzymes to the chyme to aid in nutrient absorption, including proteins, fats called lipids and carbohydrates, as well as prepping unneeded or unwanted substances in the chyme for waste product removal.

Digestive enzymes

We have mentioned enzymes a few times in our look at the digestive system, but what are these enzymes and what do they do? Digestive enzymes work in teams to focus on specific digestive functions. One team focuses on proteins, one on converting fat to fatty acids and one to convert sugar and starch.

As we mentioned earlier, there are digestive enzymes in the mouth, pancreas, small intestine and stomach. Without digestive enzymes, the human body would have no way to convert food and fluids into a usable fuel.

A car provides a good example of this importance. A car needs gasoline to run and gasoline is made primarily from oil, but you can't fill your gas tank with oil and expect a good outcome. Oil is refined, including additives, into gasoline so that it can be "digested” by your car and used as fuel. The opposite is also true in both examples because you couldn't pour gasoline into your car's oil supply and have a good outcome and you wouldn't want to try to re-eat food that has been fully broken down by enzymes. The most important enzymes you should know include:

  • Proteases (peptidases) split proteins into small peptides and amino acids.
  • Nucleases split nucleic acids into nucleotides.
  • Lipases split fat into three fatty acids and a glycerol molecule.
  • Carbohydrases like amylase, which is found in your saliva, can split carbohydrates such as starch and sugars into simple sugars such as glucose.

Exit via the...

The large intestine is the last stop for digestion before waste is stored and ejected from the human body. The large intestine has one apparently simple job and that is to absorb all of the water out of the chyme.

Organs of the GIT

Figure 10-14: The different parts of the gastrointestinal tract (GIT).

The large intestine's section nearest to the small intestine is known as the cecum and the large intestine ends at the anal canal. The large intestine will typically work on digesting a meal for twelve to twenty-four hours, slowly absorbing water and nutrients and compacting waste into feces.

Vitamins are created in the large intestine when certain bacteria in the colon feed on certain components of the chyme. There are lots of other bacteria types that are regularly present in the large intestine and it uses a layer of mucus to protect itself.

If the large intestine's ability to absorb water is impeded in some way, you will know in the form of diarrhea. To the opposite extreme is constipation or the absorption of too much water or a lack of appropriate water levels in a human being's diet.

Simple causes of diarrhea are too much sugar or too much salt. Frequently, travelers to Mexico and South America who complain about "Montezuma's revenge” are actually the victim of too much fresh fruit, too much salt and too much sugar via increased alcohol consumption. The colon can adjust to these increases, but it needs time to adjust and a vacation is not enough time.

Diarrhea can also be caused by parasites, bacterial infection and viruses. Acute diarrhea is usually treated with over-the-counter medications, but chronic diarrhea requires that the underlying medical problem be diagnosed and treated in order for the diarrhea to stop.

Irritable bowel syndrome is a condition that creates abdominal pain and either constipation or diarrhea. IBS, as it is commonly known, is usually treated with diet changes and medication.

Inflammatory bowel disease has two distinct types. The first, ulcerative colitis, is an inflammation of the colon that causes bloody diarrhea and rectal inflammation. Crohn's disease, the second type of inflammatory bowel disease, attacks the intestine only at certain places, causing abdominal pain, bloody stool, ulcers and diarrhea. Although science has not yet determined the cause of either version of inflammatory bowel disease, doctors are able to control and end the symptoms with medicine and dietary changes.

We will end our joyous tour through the digestive system with a few words about waste management. The system doesn't need any help to work as it is one hundred percent passive, but we all do learn how to control WHEN waste is expelled from the body.

Waste material sitting at the end of the large intestine is joined by waste from the bloodstream that has been filtered out by the kidneys. Although the liquid waste is expelled by different "fixtures” in males and females, the urethra is the tube that connects the liquid waste storage container, known as the bladder, to the outside world.

Solid waste is held in the rectal canal until it is expelled through the rectum via the anus.

The Kidneys

Most human beings have two kidneys, but can function with just one. As we just said, the kidney is responsible for removing waste from the bloodstream. But, because they also monitor and maintain the balance of salt and water, the kidneys also have a significant impact on blood pressure. Kidneys, like the gallbladder, can unfortunately also develop stones made up of crystallized waste. Kidney stones are typically uncomfortable, especially if they get stuck in the urethra and can be removed by outpatient external removal, surgery or blown into passable smaller stones using shock waves. You should think of the kidneys as a filtration organ for liquids that the body wants to get rid of. Its structure can be seen below:

Renal PCAT

Figure 10-16: The macro-structure of the kidneys.

The journey through the kidneys, a bit of sightseeing, these are the highlights:

  • Renal Hilium is where blood enters the kidneys and begins its journey. The liquid in the blood is filtered throughout the different kidney tubules and is either reabsorbed or excreted into the bladder.
  • Renal capsule is a protective membrane around kidneys, it is transparent, smooth, and fibrous that surrounds and encloses the kidneys. Each kidney has it's own outer layer, which helps to maintain the shape of the kidney as well as protecting it from physical damage. The renal capsule is itself surrounded by a mass of fatty tissue, which offers further physical protection by cushioning it in cases of impact or sudden movement.
  • Renal cortex, located just inside of the renal capsule, this reddish colored part is considered the outer part of the functional kidney. It has a smooth texture and is the location of the Bowman's Capsules and the glomeruli, in addition to the proximal and distal convoluted tubules and their associated blood supplies.
  • Renal medulla is the inner part of the kidney. "Medulla" means "inner portion". This area is a striated (striped) red-brown color.
  • The Duct of Bellini or papillary collecting duct is an anatomical structure of the kidneys which commences in the radiate part of the renal cortex, where they receive the curved ends of the distal convoluted tubules. They unite at short intervals with one another, the resulting tubes presenting a considerable increase in caliber, so that a series of comparatively large tubes passes from the bases of the medullary rays into the renal pyramids.
  • Renal pyramids, there are approximately 5 to 20 triangular structures called "Renal Pyramids" within the renal medulla of each kidney.
  • Renal pelvis is a funnel-shaped basin (cavity) that receives the urine drained from the kidney nephrons via the collecting ducts and then the (larger) papillary ducts.
  • Renal artery is what delivers oxygenated blood to the kidney. This main artery, like branches on a tree divides into many smaller branches as it enters the kidney via the renal hilus. These smaller arteries divide into vessels such as the segmental artery, the interlobar artery, the arcuate artery and the interlobular artery. These eventually separate into afferent arterioles, one of which serves each nephron in the kidney.
  • Renal vein is what receives deoxygenated blood from the peritubular veins within the kidney. These merge into the interlobular, arcuate, interlobar and segmental veins, which, in turn, deliver deoxygenated blood to the renal vein, through which it is returned to the systemic blood circulation system.
  • Interlobular artery is the artery, which delivers oxygenated blood at high pressure to the glomerular capillaries.
  • Interlobular vein receives deoxygenated blood (at lower pressure) that it drains away from the glomerular filtration units and from the Loops of Henle.
  • Kidney nephrons are the smallest functional units of the kidneys. Although they are miniscule, there are millions of them and in unison, it is here that the kidneys perform their main filtration function. The two main purposes of the nephrons is to remove excess water, wastes and other substances from your blood and to subsequently return substances like sodium, potassium or phosphorus whenever any of these substances run low in your body.

The image below shows the general structure of a nephron:

Microfiltration in the renal ducts.

Figure 10-17: The microscopic structure of the kidneys.

Each nephron is composed of two main structures: the glomerulus and renal (kidney) tubule. Everything starts at the glomerulus, which is a tiny blood vessel or capillary, that looks like a ball of yarn. The actual filtration of your blood occurs in the glomerulus. Each of your glomeruli acts like a sieve that helps keep normal proteins and cells in your bloodstream and allows wastes, excess fluid and other substances to pass.

The tubule, also called renal or kidney tubule, is a tiny tube running parallel to the unfiltered blood. This is where the wastes, extra fluid and other recyclable substances like sodium and potassium filtered out from the glomerulus pass through. Your kidneys measure out chemicals like sodium, phosphorus, and potassium and release them back to the blood to return to the body when need arises. In this way, your kidneys regulate the your body's level of these substances. The right balance is necessary for you to function properly.

The Loop of Henle is a part of a nephron located after the glomerulus that leads from the proximal convoluted tubule to the distal convoluted tubule. By means of a countercurrent multiplier system, which utilizes electrolyte pumps, the loop of Henle creates an area of high urine concentration deep in the medulla, near the collecting duct. Water present in the filtrate in the collecting duct flows through aquaporin channels out of the collecting duct, moving passively down its concentration gradient. This process reabsorbs water and creates concentrated urine for excretion.

To understand this, lets work backwards, starting with the thick ascending limb (of the Loop of Henle) - this limb actively transports Na+ (Cl- will passively follow) out of the tubule and into the surrounding tissue fluid. This thick limb is NOT permeable to water, so the diffusion of water does not follow Na and Cl out of the tubule. The reabsorption of Na and Cl by the surrounding tissue fluid will raise it's concentration.

The Loop of Henle is extremely important and PCAT examiner love to ask questions about it so you need to know it back to front. The descending limb is permeable to water, but not Na or Cl ions. Since the surrounding fluid has been made more concentrated, water leaves the tubule by osmosis. As a result, the fluid in the descending limb becomes more concentrated as it flows towards the bottom of the medulla (because more water is leaving, but can't get rid of the Na or Cl!) 

So, the thin ascending limb is NOT permeable to water. It is permeable to Na and Cl. Since the tubule fluid is more concentrated than the surrounding tissue, Na and Cl will diffuse out. Not all of it leaves and the thick ascending tube will move the remained up (towards the medulla by active transport) 

As a result of this process, the tubule fluid reaching the distal convulted tube is less concentrated than the blood plasma, and the solutes that have been left behind in the renal medulla have a concentrated gradient in the surrounding tissue fluid.

Since the fluid entering the distal convulted tube is less concentrated than the surrounding cortex, the tubule looses water osmotically as it flows towards the collecting duct.

As the collecting duct descends from the cortex, the concentration gradient established by the loop of Henle increases. This increasing solute concentration causes more water to be absorbed by the fluid, thus concentrating the urine in the collecting duct.

What the hell is a countercurrent multiplier system?

It sounds complicated but its not. Countercurrent multiplier systems are found widely in nature and especially in mammalian organs. In the kidneys, it means the process underlying the process of urine concentration, that is, the production of hyperosmotic urine by the mammalian kidney by taking advantage of concentration gradients between the medulla and cortex.

The end of the line is the Ureter, this is where the urine is conveyed from the kidney to the urinary bladder, where it is left to be excreted as urine.

The Reproductive System

The reproductive system, otherwise know as the genital system is a group of organs within an organism which work together for the purpose of reproducing itself. Unlike most organ systems, the two genders often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.

Female & Male Reproduction

The female reproductive system in a human being has two main portions, the uterus and the ovaries. The outermost portion of the female anatomy is the vagina. The vagina has two main structures, shaped like vertical lips, known as the labia majora and the labia minora. The vagina is connected to the uterus by the cervix. The cervix can actually be considered the lower portion of the uterus and is shaped like a cylinder. The uterus is also known as the womb and is the major organ in the female reproductive anatomy since it is responsible for the care, feeding and protection of a human embryo. The embryo becomes a fetus and ultimately leaves the uterus through childbirth. The ovaries are connected to the uterus by the fallopian tubes. Ovaries are the source of eggs and these eggs, when fertilized, will drop down through the fallopian tubes and attach to the wall of the uterus.

The male reproductive anatomy includes the penis, scrotum and testicles on the outside and the epididymis, vas deferens, seminal vesicles and the prostate gland. The penis has cartilage that fills with blood when the penis is erect. The scrotum is a sack that holds the testicles. The testicles produce sperm for reproduction, but also produce testosterone. The epididymis is a coil of tubes that stores sperm until it is needed. The vas deferens is a small tube that transports sperm as the male human body prepares to ejaculate. The sperm transported by the vas deferens is mixed with fluid in the seminal vesicles. This fluid gives the sperm energy. The prostate gland takes this mixture and adds calcium, giving male human ejaculatory fluid a milky white color and a sticky texture.

Menstruation

Human reproduction usually involves sexual intercourse where a male's erect penis enters a woman's vagina and ejaculates, fertilizing an available egg. Human females present eggs, known as ovum, every 28 days that are ready for fertilization.

One common misunderstanding is that a human female does not "produce” eggs. A woman is born with several hundred thousand eggs already in her body. Eggs are released on a cycle so the female body has time to recognize that an egg has been fertilized and is attached to the uterus. Otherwise, a human female could have multiple embryos and fetus' in various stages of development at the same time.

The fertilized egg, known as a zygote, will stay attached to the wall of the uterus via the placenta and umbilical cord. The placenta is responsible for converting the mother's blood into products that the zygote, then embryo, then fetus needs to grow, including oxygen. These important ingredients are transported to the growing child by the umbilical cord. Waste is filtered back through the cord to be discharged by the placenta.

If the egg that is presented is not fertilized, then menstruation will occur. During menstruation, the unfertilized egg will be expelled from the female body. Menstruation for many woman is sometimes painful. This pain is caused by her body that was prepared to foster a fertilized ovum, returning to normal by thinning the walls of the uterus. As the uterus is contracting, nearby tissues are not receiving normal oxygen levels and the combination causes mild to severe cramping.

Sometimes, an egg will not complete its journey through the fallopian tubes, but will still be fertilized, resulting in an ectopic pregnancy. This type of pregnancy is not survivable for the zygote and is dangerous for the mother. The female body will often terminate the pregnancy by itself without outside aid and this is called a spontaneous abortion.

A miscarriage means that for some reason, the body terminates the pregnancy. This can happen if the placenta becomes detached from the uterus, for example. Miscarriage is most likely to happen early in the pregnancy and the risk drops dramatically after the first 3 months.

There are a few other conditions that may develop during the 9 month pregnancy that can affect the viability of the fetus. One is the problem of the umbilical cord wrapping around the fetus' neck, which can cause suffocation during a prolonged childbirth.

Another possible problem is placenta previa. What has happened is that the placenta is physically too close to the cervix. This placement can cause many complications during childbirth, including severe bleeding, but the outcome can be successful with lots of rest and a caesarean section.

A caesarean section, also known as a C-section, is a childbirth where doctors cut into the uterus through the abdomen and remove the fetus. In normal childbirth, the fetus leaves the female's body through the vagina, but this is sometimes not practical or safe.

Although rare, there are times when the placenta will exit the vagina before the fetus. This is a life-threatening emergency and the child must be immediately removed from the womb.

Contraception

The only form of contraception that is one hundred percent successful is abstinence. All other contraceptives have some form or pregnancy risk, usually less than three percent.

Female Contraception

Female contraception works by either blocking the union of sperm and ovum or by eliminating the possibility that a fertilized ovum can attach to the uterus successfully. The blocking, or barrier method, often includes a spermicide to further reduce the likelihood of a living sperm finding an ovum.

Barrier methods include the male and female condom, the diaphragm (cervical cap, cervical shield) or contraceptive sponge. These devices are usually deployed just prior to intercourse and are limited in how long they will remain effective.

Oral contraceptives typically provide longer pregnancy protection and they work by adding hormones that reduce or eliminate viable ovum production while also often changing the lining of the uterus to keep an accidently fertilized ovum from attaching to the uterus.

Male Contraception

Contraception for men is also available in barrier or chemical forms. Barrier contraception for men is found from using a condom. Some condoms increase protection by also adding a spermicide or a spermicide gel can be used by both partners during sexual intercourse.

Pregnancy - 9 months of Pure Bliss

If a fertilized egg successfully attaches to the uterus, a pregnancy begins. The pregnancy cycle of a woman is approximately nine months and is divided into three sections, or trimesters.

The first trimester is a busy physiological time for mother and child. The mother will be experiencing many different mild to severe symptoms as her body adjusts to hosting the fetus. Hormones specially designed for pregnancy are being released and the symptoms vary wildly, but often include fatigue, unusual digestive disturbances including constipation or diarrhea, cramping and appetite increase or nausea and breast growth accompanied by tenderness or tingling. The vast majority of the symptoms will reduce or disappear as the woman's body settles into its new role.

For the zygote, life is happening at a very rapid pace. By the end of the first trimester, the zygote will have formed into an embryo, then into a fetus roughly the size of a baseball. The fetus will develop anatomy, including arms, legs, toes and fingers and the fetus starts moving.

The second trimester finds the fetus becoming male or female. The fetus is also converting tissues to bone, organs and other structures and systems. The fetus is able to move its eyes and mouth, Fat is forming to provide cushioning around organs and the skin is thickening. Late in the second trimester, the fetus can hear and respond to noises and the mother will begin to notice periods where the fetus is awake and asleep.

For the mother, the second trimester usually marks the end of most of the bad first trimester symptoms. Her body "quiets” somewhat and she probably feels more energetic. Her abdomen is growing distended as the fetus requires more space.

But, the second trimester doesn't mean that there are no discomforts. Some women feel dizzy as blood flow is being diverted to the fetus. Slight nose bleeds or bleeding after brushing her teeth is normal because her body's blood flow has increased to allow for increased oxygen and nutrient needs.

Some women experience cramping, as if the body is "practicing” for childbirth. These "exercising” contractions are called Braxton Hicks contractions and are typically normal. Other parts of her body may also cramp, including her legs.

The third trimester is the home stretch and mother and fetus' body are both actively preparing for childbirth. The fetus' eyes are open. The fetus is noticing and reacting to light. The fetus will also start practicing breathing as the lungs are now fully developed. Although the fetus has all of its bones, they remain soft to allow the fetus' body to contort during childbirth.

For the mother, the third trimester marks the return of exhaustion. Females may develop back aches from carrying the fetus' weight. Since the uterus is expanding and reducing the space available to the diaphragm, shortness of breath is common. The same is true of eliminating waste as the uterus also affects the bladder's ability to store waste, so the mother is urinating more frequently.

As the mother's body is growing to create space for the fetus, she may notice changes to her skin, hair and veins. Varicose veins, spider veins and hemorrhoids are common. The mother's arms, legs, hands and feet may tingle or become numb as her swelling body and growing fetus demand more work from veins and squeeze nerves in her extremities.

Childbirth

We mentioned earlier that a caesarean section may be required in some child births, but most infants are born vaginally. The childbirth process is marked by cervical dilation, fetal descent into the birth canal to exit through the vagina and the same journey for the placenta.

Most child births will activate naturally, but about one in four U.S. births will be "induced” by a doctor. Reasons for induction can include a concern for the well being of the fetus or mother. This can be as simple as the fetus staying in the uterus too long, but can also include the birth of twins (or more).

When it is time for childbirth, the mother will usually notice increasingly uncomfortable and regular contractions. Her cervix will begin dilating. Medical professionals will begin assessing the progression of labor using something called the Bishop Score. The mother will probably begin to also notice vaginal discharge, including slight bleeding.

The fetus will be rotating and adjusting so that its head is usually below its body and the fetus is facing the mother's rectum. The head will begin applying pressure to the cervix, accelerating constriction and probably increasing the frequency and severity of cramping. The fetus will also rotate its shoulders into a more narrow, or hunched position to allow the fetus to travel through the cervix.

The fetus has developed in a bag of fluid called the amniotic sac. This sac maintains temperature, cushions the fetus and delivers nutrients to the fetus through the fluid contained in the sac. At some point, the amniotic sac will tear and the amniotic fluid will leak from the woman's vagina. Some women report a "gush” while others see a slow and steady leaking. In any case, once the amniotic sac breaks, the fetus will need to leave its mother's body.

The cervix will continue to thin and stretch and contractions become "productive” as they produce a motion to expel the fetus. The fetus begins its journey through the cervix and this journey can be short or take several ours.

As the head appears at the vaginal opening, often called "crowning,” the vaginal muscles will stretch to allow the fetus to leave the mother's body. Once the head is fully outside, the rest of the fetus' body will usually quickly follow.

The fetus will usually be covered by a sticky white coating called vernix. Vernix provided insulation to the fetus as well as protecting the fetus from the normal electrical activity of the mother's body. It also acts to moisturize the fetal skin.

In some cases, the fetus may be born with a green or brown substance mixed with the vernix. This substance is called merconium and represents the fetus' first bowel movement while still inside the mother. Merconium will also be present in the infant's bowel movements for a few days until its body has finished expelling all of the waste from its time in the uterus. Merconium is what makes a newborn child's stool very sticky and dark.

The placenta has remained attached to the uterus, but will slowly detach as the newly born baby's air breathing begins and it's heart rate climbs. Doctors will usually cut the umbilical cord soon after the fetus is born, which will also stimulate the placenta's detachment from the uterus. At a point after the baby is born, the placenta and remaining umbilical cord will follow the same path and leave the mother's body.

The placenta will have a rough side and a smooth side. The rough side was attached to the uterus and the smooth side faced the fetus and was made smooth by fetal and amniotic fluid movement.

Some mother's choose to retain remaining blood from the placenta and umbilical cord, usually called "cord blood” for donation to research institutions or in case it is needed by the baby in the near future. The placenta is usually reviewed, then discarded.

Occasionally, the fetus' head will not be the first body part to present at the vaginal opening. Instead, the fetus will exit feet or buttocks first, called a breech birth. In some cases, doctors may try to manipulate the fetus to rotate it into a head first birth position as a breech position increases the odds that the fetus will not smoothly travel through the birth canal.

The fetus will initially appear blue or grey, but this usually quickly passes as oxygen enters its lungs and the newborn will quickly become pink in color. Medical professionals will often blow pure oxygen near the baby's nose and mouth to increase the oxygen percentage the baby is breathing while it adjusts to life outside the womb.

Sexually Transmitted Disease (STDs)

STDs are also known as venereal disease (VD) and sexually transmitted infections (STIs). Although many STDs can also be transmitted through illegal intravenous drug use, childbirth or breastfeeding, the most common transmission route for STDs is sexual contact or intercourse. Acquired Immune Deficiency (AIDs), gonorrhea, chlamydia, herpes and syphilis are the most common STDs.

AIDS can be shared from person to person through serum (blood, semen, breast milk, vaginal fluid or ejaculate), urine or saliva. AIDs itself is harmful because it suppresses the human body's ability to fight bacterial and viral infections. So, a simple virus can be fatal to someone afflicted with HIV.

Gonorrhea, also known as the "clap,” is a bacterial infection. Women can have no symptoms or may present pelvic pain or an unusual discharge from the vagina. Men will experience an unusual discharge from their penis and a burning sensation when they urinate. Gonorrhea is typically terminated with medicine.

Herpes is a virus. The herpes virus will often show blisters on the mouth (oral herpes) and/or the genitals (genital herpes). There is no cure for the herpes virus, so an infected human will carry the virus for life, but the virus, with or without medical intervention, has periods where it is inactive (remission) or active.

Syphilis is transmitted by a bacteria. It can be transmitted from a mother to her fetus as well as through sexual contact. The challenge with diagnosing syphilis, as its "great imitator” nickname suggests, is that it will give the human a variety of symptoms that can also be caused by a multitude of other medical problems. Syphilis, however, can be clearly diagnosed with a blood test and treated with a single or multiple doses of penicillin.

Chlamydia is one of the most prevalent STDs worldwide. It can transmitted to a fetus during vaginal childbirth as well as through sexual contact. Chlamydia has a variety of symptoms because it can he hosted by every form of bacteria. Chlamydia is also known as the "silent epidemic,” because women will most often not have any symptoms. Once diagnosed, chlamydia can be effectively treated with antibiotics aimed at the underlying bacterial infection.

Male impotence

The inability of a male penis to become or maintain erect is commonly known as impotence. Impotence can be caused by acute or chronic medical conditions, chemical abnormalities, medications, stress, drug use, smoking or psychological factors.

Male impotence can often be reversed with medications, including Viagra. Other medical or chemical conditions can also be controlled through various means, resolving the impotence. Psychological and stress factors can be controlled or eliminated with stress management training, medication or psychological counseling and treatment.

Endocrinology - the Science of Secretions

Endocrinology is the science and study of the endocrine system. This system is made up of glands that secrete chemicals into the bloodstream, most notably hormones.

Endocrine system glands are responsible for regulating growth and development, sleep, mood and metabolism. Although the heart and other organs have endocrine functions, this section will focus on the structures whose primary or singular focus is hormone secretion.

Glands can work with each other and a sequence of organized hormone secretion is known as an axis. However, some glands work largely alone. All glands receive signals to secrete from the brain, but different glands may receive their signals from different portions of the brain. This system includes the pituitary gland, the thyroid, the adrenal glands and the parathyroid as its primary members. It also includes the skin, bone marrow, testes in men, ovaries in women and adipose tissue as members who have other functions.

The Different systems and what secretes what

The pituitary gland is also known as the hypophysis. It is located near the base of the brain. This pea-sized gland is made up of three lobes. The pituitary gland is responsible for promoting human body growth, primarily through growth hormones also known as human growth hormone or HGH.

The pituitary gland also regulates blood pressure, sex organ function, water balance, breast milk production, body temperature regulation, pain relief and overall body metabolism. That's a lot of job description for such a small structure! Because of its long list of functions, the pituitary gland is also known as the Master Gland.

The pituitary is subject to a couple of negative ailments. First, there is hypopituitarism or hyperpituitarism. This is the unnecessary over or under production and release of hormones from the pituitary gland and can cause a human to be unusually tall or short, as an example.

The pituitary gland can also develop cancerous or non-cancerous tumors that will affect hormone production and release. In most cases, problems with the pituitary gland will be treated with medication or surgery.

Sugar Problems

The human body needs sugar to function, usually in the form of carbohydrates in the same way that a vehicle needs gasoline. The body uses insulin, produced by the pancreas, to maintain how much sugar is being stored for fuel. When a human eats, the pancreas releases lots of insulin, called an insulin bolus, to handle the expected increase in sugar coming into the body. In between meals, the pancreas produces low to moderate insulin to maintain sugar storage levels.

During digestion, sugar is turned into glucose that is absorbed by the stomach and intestines then added to the bloodstream. Once in the bloodstream, glucose can be used for sudden energy needs, like a workout or stored for later use. The human body adjusts how it uses and stores glucose based on our eating habits, including frequency and volume.

Some humans have a reduced or lost ability to produce insulin. This is known as diabetes. A diabetic has a lost or diminished ability to retain sugar. Someone who is diagnosed with diabetes will be very focused on how much sugar they consume and can control many of the symptoms of diabetes with diet changes or insulin injections.

Diabetes is usually broken into two classes: 

  1. Type I diabetes, often known as diet-controlled diabetes is marked by fatigue, mood swings, extreme hunger and thirst and unusual weight loss. This makes sense because the body is reflecting its inability to store energy. 
  2. Type 2 diabetes, also known as insulin-controlled diabetes, can have all of the symptoms of Type 1, plus blurred vision and dizziness, slow to heal bruising, infections and extremity numbness or tingling. Again, this makes sense because the body is showing more severe results from its lack of insulin production.

Pancreas structure

Figure 10-19: The structure of the pancreas.

Although diabetes can usually be controlled, it can also lead to a whole host of health problems ranging from mental health issues to kidney or heart problems. It can also lead to hearing or vision loss, high blood pressure, skin conditions and even necessitate extremity amputation due to long term reduction in blood flow to the arms and legs.

Adrenals: The "Fight or flight” gland

The glands charged with stress management, kidney function and blood sugar level management are the adrenal glands. As the adrenal glands sense stressors, low or high blood sugar or a need for increased or decreased kidney function, they will release hormones to regulate these functions. The adrenal glands are located on both sides of the human body near the kidneys. The human body's "fight or flight” response controlled by signals the brain receives from the adrenal glands. The circulatory system and much of the human body, works on a system that is frequently called "fight or flight.” When the human body is exposed to a high level of stress, the adrenal glands release a secretion that increases pulse and blood pressure, makes the hands sweaty, dilates the pupils and makes hairs stand straight (such as the hairs on the back of your neck). The body is putting itself in the best possible position to fight the cause of the stress or run away.

Darwin was not only responsible for figuring out the theory of evolution he also thought a lot about the bodies innate ability to override conscious control. He would often visit London zoo, where he liked to visit an exhibition, which has an aggressive snake behind thick glass. He would often visit the snake and stare at it through the glass, whilst the snake was poised to attack Darwin would try convince himself that there was no danger as he was behind glass and try make it so that he would not react. After many attempts he could not suppress his innate reaction to the snake when it hit the glass.

"My will and reason were powerless against the imagination of a danger which had never been experienced.”

If you were taking a hike through the woods and you suddenly encountered a bear, your whole body would go on high alert. Alarms would sound in your brain and every system in your body would go into a hyper state of excitement. While this is all happening, your brain is doing an analysis on the best way to avoid being a bear snack. If you are armed and the bear is clearly preparing to charge at you, you might decide to fight, hoping to wound or kill the bear. If not, you might be choosing to climb the nearest tree, slowly back away or just run for your life.

This entire evaluation process takes a second, or less. But, by the time that second has passed, your body has already increased your blood pressure and heart rate to give you the best odds of beating the stress no matter what response you choose.

Being suddenly frightened by a friend is another example of fight or flight. Even though you quickly realize that there is no real danger, your body has already assumed the danger is very real and prepped you to react. You can often feel your heart rate and breathing slowing back down long after the threat has been determined to be a joke.

Adrenal glands are also subject to tumors and over or under production. Cushing's Syndrome is a condition where the adrenal glands are producing too much cortisol. Too much of this hormone will result in very rapid weight gains, excessive sweating, high blood pressure, joint aches, thinning of the skin, impotence and infertility. Interestingly, dogs and horses are also at risk for developing Cushing's Syndrome. This syndrome is often caused by the use of prescribed or illegal steroid use and can be controlled or eliminated by reduction in steroid prescription or discontinued use. Sometimes, surgery to remove the adrenal glands is used as a last resort to eliminate dangerous over-production of cortisol.

Thyroid: Regulating everyday functions

The thyroid gland is one of the largest glands in the human body. The thyroid lives in the human neck, just below the laryngeal prominence, or Adam's apple. The thyroid is responsible for controlling how the human body uses energy and the body's use of and sensitivity to other hormones.

Large and in charge, the thyroid controls heart, liver, spleen and kidneys. The thyroid can also develop tumors, but if it is not functioning correctly, it will often release too much (hyperthyroidism) or too little (hypothyroidism) hormone, causing problems throughout the body.

A more rare condition known as Addison's disease is caused by abnormally and chronic cortisol production. The symptoms of Addison's disease develop slowly, causing dizziness, digestive problems, mood swings, muscle aches and fatigue. But, Addison's disease can usually be controlled by controlled hormone therapy.

The parathyroid glands usually reside in the neck but will sometimes develop in the chest area. The amount of calcium contained in bones and maintained in the bloodstream is regulated by the parathyroid glands.

Cholesterol: The good, the bad, and the downright ugly

We spoke earlier about cholesterol, but its important that you have a deeper understanding of the good, the bad and the downright ugly affects of healthy or poor cholesterol management.

Cholesterol provides three important roles in the human body. First, cholesterol allows the human body to produce hormones and Vitamin D. Second, cholesterol helps to construct the bile our intestines use for digestion. Finally and no less important, cholesterol is a key ingredient in the outer shell of cells. So, cholesterol is a good thing, right? Yes, and no.

Cholesterol is a lipid, or a fat and it also the substance that steroids are made from. Cholesterol and human blood have a love-hate relationship. If you dropped cholesterol onto a drop of blood, they would not combine, like olive oil and water. But, during digestion, cholesterol is remade into something called a lipoprotein, or cholesterol with a protein coating. This coating allows cholesterol to climb into blood cells for transportation and usage in the human body. This sounds good, right? Not so fast, young grasshopper.

The action item in these newly repackaged cholesterol packets are triglycerides. The human body uses triglycerides as an energy source, but the heart and arteries aren't big fans of triglycerides.

There are two types of lipoproteins produced in the human body. The first is high-density lipoproteins, also known as HDL and the second is low-density, or LDL.

Before we go any further, we need to briefly talk about fat. Fat can be saturated or unsaturated. Saturated fat is not good for the human body, largely because being saturated means that this fat is filled with hydrogen and our bodies don't have a good use for hydrogen, other than to create health problems.

Unsaturated fat can be used or stored by the body for a back-up energy source and as a cushion to protect our body from the outside world and to protect organs from other organs, bones, etc.

You should also know that the body will make the EXACT amount of good cholesterol it needs without the presence of any in the food you eat. You can eat a 100% cholesterol free diet (good luck) and still produce the cholesterol your body requires with very rare and usually genetic exceptions. Now, back to the fat.

Saturated fat is heavy. In fact, it is so heavy that it is made up largely of HDL, or bad cholesterol. This heaviness is because HDL has more protein (that's the saturated part). As blood cells carry this heavy cholesterol around, they get tired and dump the bad cholesterol into the surrounding arteries. This would be like you dropping a couple books into your school locker to lower the weight of your backpack.

The arteries don't have any use for HDL, but they're "stuck” with it, literally. Over time, these HDL dumping sites grow larger and they will eventually fill arteries to the point where blood has problems pushing through and, viola, a heart attack or other serious circulatory system failure happens.

Good cholesterol, on the other hand, is much lighter. It gets where it is supposed to get, creating strong cell coatings, stimulating healthy hormone creation, etc. So, by understanding how this all works, we think it's pretty easy to understand why too much bad cholesterol is so dangerous. The great news in all of this is that the amount of bad cholesterol in a human body can be completely controlled by dietary choices.

Integumentary system: The body armor

Beginning with the skin, the human integumentary system provides protection, temperature regulation, cushioning, sensory detection and respiratory gas exchange. The human body would look like a bag of rocks, would not be able to maintain an internal temperature of 98.7 degrees Fahrenheit, survive road rash or enjoy airplane rides without the integumentary system.

Epidermis

The outermost layer of human skin is the epidermis. If you're dialing in your medical terminology, that would be epi- for outside, over or upon and -dermis for involving the skin. The epidermis covers the entire human body, including the eyes and protects the body against all types of invaders. These invaders can include low or high temperature, puncture, bacteria, blunt force trauma and other stuff that the body doesn't want or need.

The epidermis is composed of five layers. These layers will vary in thickness depending on what part of the body they are protecting. The outermost layer, or stratum corneum, is filled with proteins for flexibility and water retention. The ingredients of the stratum corneum are loosely packed. The thickest stratum corneum layers are found on human palms and the soles of human feet.

The second epidermal layer is called the stratum lucidum and is mostly clear. it adds further cushioning and is only found on the hands and feet.

The stratum granulosum layer is the middle epidermal layer. This layer is the transitional layer for the other four and it contains much of the skin's barrier properties because of the lipids and proteins it contains.

The "prickle-cell” or "spinous” next epidermal layer is called the stratum spinosum and gets its nickname from the spiky appearance of its cells. These spiky defenders provide most of the skin's protection against bacteria, germs and microbes.

The inner most layer is the stratum basale (base layer if you're taking notes). This layer is located most proximate to nerves and it transfers pressure to the nerves. You'll find more of this layer in the lips, fingertips and toes.

Dermis

The dermis, or dermal skin layer is the primary shock absorber for the skin. This shock absorbancy is created by elastic fibers and collagen that will flex to absorb or deflect physical pressure on the skin.

The combination of the epidermis and dermis is known as the cutis. When you press on one of your fingernails, the nail itself doesn't absorb the pressure, but rather depends on the cutis below it to fend off the pressure and protect the tissue and bone below. But, there is only so much energy the cutis can absorb. You know this if you have accidently struck your finger with a hammer.
Hypodermis

You'll hear the hypodermis also called subcutaneous tissue or the subcutis. This skin layer only has one function and that is to store fat, another shock absorption tool. Note that your eye and a couple other body parts, such as the nipple and areola, don't store fat, but the hypodermis is present because the hypodermis is also where most of the body's nerves are located.

Many medication injections are given into the hypodermis because it provides excellent medicinal storage when a slow medicine absorption rate is needed, as it is with insulin for a diabetic. As an aside, the other three injection depths where the majority of medications are injected are intramuscular (IM) and interosseous (IS or OS). Intramuscular injections are more painful than their subcutaneous counterparts because the needle is driving deeper and encountering more nerves along the way. Interosseous injections are usually performed on children and the injection is directed through a bone and into the bone marrow. This is usually a life-saving, last resort as even the flexibility of a child's bones doesn't make this injection painful.

The final medication injection option is intravenous injection (IV). IV drug and fluid therapy uses a catheter tube to introduce fluids and/or medications directly into a vein for rapid use by the body. Even in cases where fluids aren't needed, they will be used as the transporter of medication and to keep the catheter open and free of clotting that would prevent additional medication dosing.

Skin Diseases and injuries

The skin is susceptible to all sorts of maladies. From mosquito bites to blisters and from psoriasis to cancer, skin takes the brunt of the environmental abuse for the human body. For many of these, the skin will heal itself and any treatment will surround personal comfort. A few, such as severe acne, psoriasis or cancer will require medical intervention to heal.


PCAT Practice Human Anatomy and Physiology Questions

1. Which relation is right?

A. Nail & Hair - Collagen

B. Artery  - Elastin

C. Milk - Albumin

D. Muscle - Keratin


2. Blood entering the kidneys starts off at the glomerulus and then descends in to the loop of Henle. Which of the following is its final destination within the kidneys?

A. Distal convoluted tubule

B. Peritbular capillary

C. Afferent arteriole

D. Descending limb

3. Another name for a sphygmomanomter is which of the following?

A. Temperature gauge

B. MRI

C. Stethoscope

D. Blood pressure cuff

4. Which of the following structures within a neuron insulates electrical conductivity?

A. Dendrite

B. Schwann cell

C. Axon

D. Myelin sheath

5. The somatic nervous system is part of which of the following?

A. Autonomic nervous system (ANS)

B. Parasympathetic nervous system

C. Sympathetic nervous system

D. Peripheral nervous system (PNS)

6. Which of the following is the lowest layer of the skin?

A. Stratum lucidum

B. Stratum granulosum

C. Stratum spinosum

D. Stratum basale

7. The largest blood vessel in the body is which of the following?

A. Pulmonary artey

B. Aorta

C. Pulmonary vein

D. Vena cava

Answers and explanation

1.B

Elastin is the right answer here, as it is what arteries are mainly comprises of. (A) Hair and nails is not made of collagen as this is more relation to ski. The correct association for hair and nails would be keratin.

2.A

The final pitstop for blood which enters the kidneys is the Distal convoluted tubule which is option (A). Option (c) the Afferent arteriole actually feeds into the glomerulus, so this is before so you can rule that out. The descending limb which is located just after the glomerulus is before the option (A). Option (B) Peritbular capillary is a little more ambiguous, as this capillary moves deoxygenated blood away from the kidneys but is located before (A).

3.A

A temperature gauge is otherwise known as a thermometer. (B) An MRI means a magnetic resonance imager which is a large machine which generate magnetic fields to produce an image of inside the body. (c) A stethoscope is used by doctors to listen to the heart beat of patients. This leaves option D which is a blood pressure cuff, sphygmomanomter is an old word for this but is sometimes still used by medical professionals.

4.D

Myelin is dielectric meaning that it is electrically insulating. The sheath material that forms a layer, the myelin sheath, usually around only the axon of a neuron helping electrical signals transmit from one end to the other.

5.D

The PNS is divided into the somatic nervous system and the autonomic nervous system so the best answer here would be (D). The ANS divides into the parasympathetic and sympathetic nervous systems. Overall, all of these parts are part of the peripheral nervous system.

6.D

The best option here is option (D) as the stratum basale is the deepest layer of the epithelial layers, which often only contains a line of cells one cell thick.

7. B

The Aorta is the largest artery in the body. The aorta arises from the left ventricle of the heart, forms an arch, then extends down to the abdomen, where it branches off into two smaller arteries.

Last modified: Friday, 3 March 2017, 4:40 AM