Transcript for:
Human Anatomy and Physiology Overview

Welcome to this module in which you will be provided with an overview of the human body and the physiology of its various systems. Once completed with this module, you should be able to: Identify the topographical anatomy and directional terms utilized by the EMT. List the components of each of the major body systems. List the elements of the life support chain. Acquire a basic understanding of common Latin medical terminology. First and foremost, this module will be looking at the structure of the human body and its function. The study of the body’s structure is called anatomy. The study of its function is called physiology. Thus, one could say that this module is a cursory study of anatomy and physiology. Before we begin our discussion of the human body, it is important to ensure we are speaking the same language. There must be a standardized way we view the human body, and this standardized view provides the basis for any discussion regarding human anatomy. Within the health care professions, that standard is referred to as normal anatomical position. All descriptions of the human body use this position as the starting point. As you see from the illustration, this position is a person standing, facing forward, with palms forward. Again, all descriptions of the human body, even if your specific patient at the time is nowhere close to being in this position, are made from this common reference point. From this starting position, we can now identify some landmarks. The first thing we will do is divide the body into planes. Given the normal anatomical position, splitting the body down the middle from top to bottom generates sagittal, medial, or lateral planes. (The terms are used interchangeably; you may see one used over another in various textbooks.) The line we just drew to produce the sagittal/median/lateral planes is referred to as the midline. This also breaks the body up into both a right and a left side. With the normal anatomical position as our reference, right and left always refer to the patient’s right and left, not the provider’s (which is opposite when looking at the patient from the front). Using this midline for a reference, items closer to the midline are considered medial, while those away from the midline, toward the periphery, are referred to as lateral. Your arms, for instance, have both a medial and a lateral side. Along similar lines, we also can refer to things on a relative basis by using the terms proximal and distal. Body parts and structures that are closer to the midline or torso than other body parts and structures are said to be proximal. Inversely, body parts and structures that are further from the midline or torso than other body parts and structures are said to be distal. For instance, the elbow is distal from the shoulder, but proximal from the wrist. Your collarbones are called clavicles. Mid-clavicular refers to a vertical line drawn across the middle of the clavicle. When viewed from the normal anatomical position, there is a great deal of symmetry between the right and left sides of the body. If a body part or structure is present on both sides of the body, such as a person’s eyes, they are said to be bilateral. Inversely, something located on a single side of the body is said to be unilateral. If we were to split the body in half, top and bottom, along the pelvic girdle, we would create transverse or axial planes. Given the normal anatomical position, the term superior refers to anything above something else and inferior refers to anything below something else. The terms are relative. For instance, the nose may be superior to the mouth, but it is inferior to the eyes. When viewing the human body from the side, we begin with the middle of the armpit as our landmark. The armpit is called the axilla. If we draw a line from the middle of the axilla to the ankle, the result is the mid-axillary line. This line then creates the frontal or coronal planes. When referring to the front half of the body, the terms anterior or ventral are used. When referring to the back half of the body, the terms posterior or dorsal are used. Given the many positions in which you may find a patient, it is important to remember that these terms are not relative, they are absolute. Thus, an individual’s posterior side is the same, regardless of whether the patient is face-up, face-down, or somewhere in the middle. When abdominal emergencies are discussed later in this course, it will be important to know the anatomical structures within each quadrant. In discussing a patient’s abdomen, we divide the abdomen into quarters, or quadrants, by imaginary horizontal and vertical lines that intersect at the belly button (navel). Again, our reference is that of the patient’s perspective, so the quadrants on the right-hand side of the patient are called right upper and right lower quadrants (with the upper quadrant obviously superior to the lower, or the lower quadrant inferior to the upper, depending on your perspective). Given that, the quadrants on the left-hand side of the patient are called the left upper and left lower quadrants. Hands and feet are very important to the human body and have their own terms as well. Plantar refers to the sole of the foot and palmar refers to the palm of the hand. In addition to a knowledge of common landmarks, it is also important to be familiar with various positions in which a patient may be found or transported. A person on his or her back (face-up) is in a supine position. A person on his or her abdomen (face-down) is in a prone position. A person on his or her side is in a lateral recumbent position. Because this is a common position in which to transport unconscious, non-trauma patients (given the repositioning of the mouth to allow for the drainage of fluid or vomit), this position is often times referred to as the recovery position. In many instances, it is preferable to transport patients in a sitting position. Such a position is called the Fowlers Position. If the patient is in a semi-sitting position, the position is called Semi-Fowlers. Exactly when Fowlers becomes Semi-Fowlers and vice-versa is a grey area with no specific definition. Some consider a 45° angle to still be Fowlers, while many would call it Semi-Fowlers. Ultimately, the more upright someone is sitting, the closer it is to Fowlers; the more someone is reclining, the closer it is to Semi-Fowlers. There is also a position called the Trendelenburg position in which the patient’s feet are elevated above his or her head. First Aid teaches that a person in shock should have his or her feet elevated so gravity can assist in keeping blood up in the head and torso. As a result, this position is also referred to as the Shock Position. With our introduction to anatomical landmarks and positional terms completed, we can now begin focusing on the different systems within the body. We will begin by first discussing the six major body systems: Skeletal, Muscular, Respiratory, Circulatory, Nervous, and Integumentary. We will then continue by discussing the remaining systems: Digestive, Endocrine, Renal, and Reproductive. The first body system we will be discussing is the skeletal system. The skeletal system is comprised of bones, 206 in all for an adult. Joints are formed where bones meet (and will be discussed in greater detail later in this course). The skeletal system provides infrastructure for the human body. Think of the skeletal system as the framing for a building. Without the 2’x4’s underneath, drywall and paint are useless. Without our bones, there would be no structure for our other systems and tissues. Our bones also provide critical protection for many of our organs, such as the heart, lungs, kidneys, spleen, etc. Our joints make it possible for us to move (in conjunction with the muscular system) and the bones themselves create blood cells (in the bone marrow) and store minerals. Working our way from the top to the bottom, we first encounter the skull. The skull is the bony structure of the head. It’s main purpose is to enclose and protect the brain. On the anterior side is the face. There are several bones that make up the face. The function of the face is obvious. The eyes are protected by the facial bones, as are the superior portions of our respiratory and digestive systems (which we will discuss later). Beneath the head is our spinal or vertebral column. Our spine consists of 33 separate vertebrae, all designed to keep us upright, provide for motion, and protect our central nervous system and spinal cord. The spine is divided into five parts. The first the is the cervical spine. Consisting of seven vertebrae, this is the portion of the spine laymen would describe as the neck. Proceeding inferior are the 12 vertebrae of the thoracic spine. These vertebrae form the upper back and also are connected to the posterior rib cage. Inferior to the thoracic spine are the five vertebrae of the lumbar spine, which form the small of the back. Inferior to the lumbar spine is the sacral spine, which is actually five separate vertebrae fused together to form a structure known as the sacrum. Lastly, we come to the coccygeal spine, which contains four vertebrae fused together to form the coccyx. To tell the difference between the various vertebrae, they are named based on their relative position within these spinal regions. Cervical vertebrae are labeled with a capital C, followed by the number one through seven with C1 being superior and C7 being inferior. The same is done for the thoracic vertebrae, using the letter T and the numbers one through twelve. The lumbar vertebrae use an L and the numbers one through five, and the sacral vertebrae use an S and the numbers one through five as well. The spine is so very important to the health of the body given its protection of our spinal cord. Significant injuries to the spine can result in chronic pain, paralysis, or even death. As a result, spinal precautions for trauma patients will be covered in tremendous depth later within this course. Anterior to the vertebral column, inferior to the skull and face, sits the thorax. In lay terms, the thorax is a person’s chest. The ribs and other bones of the thorax serve primarily to protect our vital organs and major blood vessels. In conjunction with the diaphragm and intercostal muscles, the thorax also produces both negative and positive thoracic pressure that results in ventilation (breathing). Inferior to the thorax sits the pelvis. The pelvis consists of three separate bones that are fused together and it serves as the foundation (the basement floor, if you will) for the organs located above it, such as the intestines, bladder, and female reproductive organs. It also provides varying levels of protection for those organs as well. Continuing down, we encounter the lower extremities. Otherwise known as the legs and feet. The large bone connected to the pelvis is the femur. Inferior to the femur are the tibia and fibula, which form the lower leg. (To differentiate the two bones, the tibia is commonly called the shin bone.) The patella is the bone that covers the knee joint between the femur and the tibia. On the bottom of the lower extremities are the tarsals, metatarsals, calcaneus, and phalanges of the ankle, heel, feet, and toes. Lastly, we need to move back up the body to discuss our upper extremities. Connected to the thorax are our shoulders, arms, and hands. The shoulder consists predominantly of the clavicle, our collarbone; the scapula, the flat bone on the posterior side; and, the proximal humerus. The upper arm is therefore called the humerus. Distal is the elbow joint that joins the humerus with the distal arm bones, the radius and ulna. (The radius is the lateral bone of the forearm. It is always aligned with the thumb.) Distal from the radius and ulna are the carpals, metacarpals, and phalanges of the wrists, hands, and fingers. Remember that bones are rigid and do not bend. So that we can move, our skeletal system also contains joints where these rigid bones meet. Some joints work like hinges, such as the knee and elbow. The joints between vertebrae allow for rotational movement so we can twist and turn our bodies, in addition to allowing us a certain amount of flexibility to bend over and backward. Ball and socket joints, such as the hips and shoulders, provide for tremendous articulation and range of motion. Ligaments, cartilage, bones, muscles, and tendons all work in concert to provide for movement. Injuries to the skeletal system can have dire consequences given its role in protecting organs, providing structure, and allowing for movement and range of motion. Addressing issues pertinent to the skeletal system is a vital component of practicing emergency medicine. Integral to the skeletal system is the muscular system. The two are so intertwined that some refer to both systems as a single musculoskeletal system. For our purposes as emergency medicine providers, however, we will consider the two as separate systems. The muscles in our body perform some very important functions. First and foremost, the muscles provide for movement. This movement is not just that associated with gross and fine motor functions, such as standing, sitting, walking, and manipulating objects in our environment, but the muscles are also responsible for the movement of blood within our body and air in and out of our lungs. Our muscles give our bodies their shape; they provide additional protection for our vital organs and vessels; and, because muscles consume a lot of calories, they also generate our body heat. It is important to recognize that not all muscle is created equal. There are actually three different types of muscle cells within the human body: skeletal, smooth, and cardiac. Skeletal muscle cells are also called voluntary muscles as these are the muscles that we control through conscious thought. These are the muscles responsible for gross movement and fine motor functions. By their very name, skeletal muscles are those we commonly think of when discussing the muscular system. They exist attached to our bones, to our skeletal system, the shape and outlines of which are commonly visible under the body’s skin. By contracting and relaxing in concert with each other, these muscles help us stand, walk, write, grab, push, pull, etc. Smooth muscle cells are responsible for movement that is not a result of conscious thought. Such movement includes that of the gastrointestinal system, respiratory system, cardiac system (with the exception of the heart), and renal system. These muscles respond directly to impulses from the brain without any intent or conscious thought on the part of the individual. As a result, these cells are also called involuntary muscle cells because they cannot be voluntarily controlled by the person. We do not have to think about digesting food or breathing. No conscious thought is given to constricting or relaxing blood vessels to regulate blood pressure. Given their function, smooth muscles are obviously vital to the proper functioning of the human body. The last type of muscle cells to be discussed are actually a type or subset of involuntary cells. The heart is a muscular organ built from cardiac muscle cells. These cells are very specialized and do a lot of work. Imagine doing 60 to 100 (or more) pushups per minute from before we are born until the day we die. Seems unfathomable. That is exactly what the cardiac muscle in the heart does. The heart beats by contracting and relaxing its cardiac muscle cells once a second (or more) for decades. These cells are also very unique in that the heart has the ability to generate and conduct electrical impulses on its own. (This property is called automaticity.) Given the importance of the heart to the survivability of the body and the specialized work of the cardiac cells, the heart (and its cardiac cells) needs a constant supply of oxygen and has its own blood supply. (We will be covering the heart and its functioning comprehensively in another course module.) Our next system to discuss is the respiratory system. Before we delve into the function of the respiratory system, we will first identify the structures of the respiratory system, beginning with the upper airway, continuing with the lower airway, and concluding with the other structures that support ventilation. Starting at the top of the respiratory system and working our way down, we first encounter the nasal cavity. The nasal cavity does more than just give us a pathway for air to enter the respiratory system; it also cleanses, warms and humidifies our inhaled air. Just below the nasal cavity is our oral cavity, which contains the mouth, teeth, tongue, and jaw. In many instances, EMS providers must manipulate the mouth, jaw, and tongue to ensure a patent airway in an unconscious patient, so it is important to be familiar with the structures in the oral cavity. (These structures, their significance, and their manipulation by the EMT will be discussed in greater depth during the module pertinent to airway management.) The posterior of the airway in the head and neck is called the pharynx. The pharynx is divided into three separate areas. The nasopharynx is located posterior to the nasal cavity. The oropharynx is posterior to the oral cavity. Inferior to the oropharynx is the laryngopharynx, which connects the airway to the larynx and esophagus. The epiglottis lies superior to the larynx, anterior to the pharynx. It is a structure of elastic cartilage covered with a mucous membrane and is designed to cover the larynx when we swallow to protect the lower airway from foreign bodies, such as food or beverages. The last upper airway structure is the larynx. Commonly referred to as the voice box, the larynx contains the vocal cords and serves as the connecting structure between the pharynx and the trachea. Inferior to the larynx lies the lower airway and its structures. The first structure is the trachea, which is essentially the tube through with air passes from the upper airway down into bronchi, where the air is then diverted to both the left and right lungs. The bronchi continue to branch off while diminishing in size to route the air throughout the entire lung. When the bronchi diminish in size to the point where they no longer contain cartilage or glands, they become bronchioles. At the end of the bronchioles are the alveoli. It is in the alveoli, these little sacs, that gas exchange actually occurs between the air and our bloodstream. In addition to the structures that comprise our upper and lower airways, there are other structures within our body that are essential to supporting ventilation. We have muscles that exist between our ribs. These muscles are called intercostal muscles. We also have a diaphragm, which is a large muscle that sits inferior to the lungs. These muscles work in conjunction with our chest wall to produce both positive and negative pressure in our lungs. When we need to breathe, it is the phrenic nerve that carries messages back-and-forth between the respiratory control center in the spinal cord and the diaphragm. Because our lungs need to expand and contract within the chest cavity, both the lungs and the chest cavity are covered with a membrane known as the pleura. Given the existence of pleural fluid between these two layers of membranes, the inner and outer pleura can glide effortlessly against each other, thus facilitating the mechanical process of breathing. Lastly, the respiratory system has to connect with the circulatory system at some point so that oxygen and carbon dioxide can be exchanged. This process occurs in the alveoli, which are covered by pulmonary capillaries. As you will find throughout the course, not all patients are the same. This is especially true when discussing the respiratory system of a pediatric patient. When managing the airway of a pediatric patient, it is important to recognize the following differences in the pediatric airway: Mouth and nose are smaller. The tongue is proportionally larger, taking up more relative space in the oral cavity. Trachea is narrower. Cricoid cartilage is less rigid and developed. Airway structures are more anterior and the head is proportionally larger than the rest of the body, making airway maintenance more difficult. Given that the airway structures are smaller than in an adult, obstructions occur with greater ease. This includes foreign bodies, as well as airway restriction or obstruction due to mucous or inflammation. Airway management considerations and techniques for pediatrics will be discussed in greater depth in a different course module. Now that we are familiar with the components of the respiratory system, it is time to identify the system’s functions. To a layperson, the respiratory system is responsible for breathing. For an EMT, however, the respiratory system is much more complicated than that. The respiratory system makes both ventilation and respiration possible. While these terms are sometimes used interchangeably, doing so is actually incorrect as they mean two very different things. Ventilation is the mechanical process of moving air into and out of the lungs. Picture a balloon inflating and deflating. That movement of air into and out of the balloon is ventilation. Just moving air into and out of the lungs is not enough, however. Somehow, we need the oxygen in that air to enter our bloodstream. We then need that oxygen in the bloodstream to enter individual cells. As a part of doing work, our cells produce waste products, such as carbon dioxide. That carbon dioxide needs to leave the cells, enter the bloodstream, and then somehow be expelled from the body in the air we exhale. The process by which oxygen and carbon dioxide pass between the bloodstream and cells is called respiration (or cellular respiration). Within the lungs themselves, oxygen and carbon dioxide move between the alveoli and the bloodstream by a process known as diffusion. For additional reference, perfusion will also be mentioned throughout this course. Perfusion is defined as the circulation of blood through the capillaries, which is where respiration occurs. Without perfusion, there could be no diffusion or respiration. As a result, the moving of gasses, nutrients, and waste products through the capillaries to and from the cells of the body is sometimes called perfusion instead of respiration, depending on the textbook author. There are texts that are even more specific in their definition of perfusion, using the word to describe the passing of oxygen from the capillaries into cells (without any mention to the need for carbon dioxide to also pass from the cells back into the capillaries). When discussing shock later in this course, the ability of the body to deliver oxygen to its cells is referred to as perfusion, or the ability to perfuse. The difference between ventilation and respiration is important to understand as a patient may be ventilating adequately, but due to some ailment, is unable to respirate or perfuse. Inversely, compression-only CPR works because of respiration, not ventilation. Moving air in-and-out of the lungs is not as important as circulating the oxygen already existing within the body so that the process of cellular respiration can occur. Obviously, without some ventilation, some fresh oxygen in the lungs, respiration will eventually cease even if adequate compressions are being performed as there is no oxygen left in the blood to supply the cells. As a result, maintaining an adequate airway and ventilating a patient is an important part of performing CPR. Hopefully this example illustrates the difference between ventilation and respiration. Another function of the respiratory system deals with something called the acid-base balance within our bodies. Our cells are constantly producing hydrogen ions, which become acids within the body. Too much or too little acid within the body is a bad thing, so the body regulates its acid-base balance through several mechanisms, one of which is through the respiratory system. Carbon dioxide is a byproduct of cellular metabolism and we expel carbon dioxide from our body by exhaling. Carbon dioxide is also acidic. As a result, an increase in respiratory rate results in more carbon dioxide being expelled, making the body more alkaline. A decrease in respiratory rate, on the other hand, retains carbon dioxide, making the body more acidic. This process works in conjunction with something called the buffer (or bicarbonate buffer) system and the kidneys to regulate our body’s acid-base balance, and is yet another important function of the respiratory system. While all of our body systems are important, the circulatory system (or cardiovascular system, as it is also called) receives significant focus within EMS. Many of the interventions you will learn within this course pertain directly to the circulatory system. Whether the EMT is performing CPR, controlling bleeding, or administering medications for chest pain, the circulatory system is a crucial body system that cannot be overlooked. As with the respiratory system, we will begin our discussion of the circulatory system by identifying the structures within the system, we will examine our blood and its components, and we will conclude with information pertaining to the functions of the circulatory system. The best place to start when examining the circulatory system is the heart. When discussing the anatomy of the heart, we begin by dividing the heart in to a right and left side. (Because the heart sits at a slight angle within the body, the line we drew is not completely vertical.) Each side of the heart has two chambers. The superior chamber on each side is called the atrium. We differentiate between the two by the side on which each respective atrium sits. Thus, we have a right atrium, as well as a left atrium. The inferior chambers of the heart are the ventricles. As before, we differentiate between the two by referring to the right and left sides, resulting in a right ventricle and a left ventricle. These chambers within the heart are separated by a series of valves that prevent blood from flowing backward. The tricuspid valve lies between the right atrium and the right ventricle. The pulmonary valve is between the right ventricle and the pulmonary artery (which we will identify in just a bit). On the left side of the heart, the left atrium and left ventricle are separated by the mitral valve. The aortic valve then lies between the left ventricle and the aorta (which we will be identifying soon as well). Essentially, deoxygenated blood enters the heart from the rest of the body through the right atrium. From the right atrium, the blood moves into the right ventricle where it is pumped out through the pulmonary arteries to the lungs. Oxygenated blood returns from the lungs through the pulmonary veins into the left atrium. From the left atrium, blood enters the main pumping chamber of the heart, the left ventricle, where the blood is then pumped out to the rest of the body. Now, do not worry if that description went a little fast. We will be discussing the functioning of the heart and its chambers in much greater depth in a different module of this course. The heart also has an electrical system with which the EMT must be familiar. The heart’s electrical system will be a topic of discussion in another module as well. For the time being, just know that the heart has four chambers: the right atrium, right ventricle, left atrium, and left ventricle. When we discussed muscles before, it was said that the heart is such an important muscle that it has its own blood supply. While the heart itself is filled with blood, the blood within the heart does not supply the muscle of the heart with oxygen. Rather, the heart receives its supply of oxygen through the coronary arteries. The red arteries on this computer model are the coronary arteries. These arteries branch off from the aorta to provide the heart with fresh, oxygenated blood. They are labeled right and left based upon the side of the heart to which they supply blood. When someone has a heart attack, it is commonly due to a blockage in a coronary artery, which reduces or stops the flow of blood (and, as a result, oxygen) distal to the blockage. By definition, arteries are the vessels that take blood away from the heart. There are two main arteries that leave the heart. The first is the pulmonary artery, which takes oxygen-depleted blood from the right ventricle to the lungs. Because blood returns to the heart from the body through the right atrium, into the right ventricle, and then through the pulmonary artery before going to the lungs to exchange carbon dioxide for oxygen, the pulmonary artery is the only artery in the body that carries oxygen-depleted blood. The other main artery leaving the heart also happens to be the largest artery in the body. It is the aorta. Once blood is oxygenated in the lungs, it returns to the heart through the left atrium, into the left ventricle, and then into the aorta for distribution throughout the body. The aorta extends superior to the heart, providing blood to the coronary arties and the head before traveling inferiorly to provide blood to the rest of the body. Beyond the aorta lie the remaining arteries. The anatomical locations of the main arteries are important to know as these are the locations in which the EMT will check for a patient’s pulse. The carotid arteries (one on each side of the neck, left and right) supply blood to the head and its organs. They are located on the neck, inferior to the jaw, lateral to the thorax. The brachial artery is located in each arm, on the anterior crease of the elbow, along the medial aspect of the upper arm. This artery is commonly used for a pulse check on infants and it is also the location for stethoscope placement when taking a blood pressure. The radial artery is located on the anterior side of each wrist, proximal from the thumb. The radial artery is adjacent to the radius in the lower arm, thus its name. It is very common for EMS providers to obtain a patient’s pulse by palpating the radial artery in either the patient’s left or right wrist. There are two femoral arteries, one for both the left and right legs. These arteries can be palpated in the crease between the abdomen and the groin. Proceeding down the lower extremities, there are two other pulse locations commonly used by EMS providers. The first is the posterior tibial artery, which is on the posterior aspect of the medial malleous. (Stated another way, it is on the inside of the ankle, toward the heel.) The second is the dorsalis pedis artery, which is on the dorsal part of the foot (the top), lateral to the large tendon of the big toe. These arteries exist in both the right and left leg, and they are commonly palpated to confirm circulation to the lower extremities. As the arteries extend from the heart, they narrow in size. Eventually, we reach the smallest branch of an artery, called an arteriole. These small vessels then lead to capillaries. When we discussed respiration and perfusion associated with the respiratory system, capillaries were an important component. The pulmonary capillaries are where the circulatory system meets the respiratory system. It is through these capillaries that gasses are exchanged between the air in our lungs and our bloodstream. The other capillaries in our body (not associated with the lungs and alveoli) perform a similar function with the other cells in our body, exchanging gases, nutrients, and waste products between the circulatory system and those cells. To accomplish this exchange, capillaries are very small (the width of a single blood cell). With that gaseous exchange completed with the cells of our body, the blood then enters the venous system. The entry point for which is the venule, the smallest part of the vein that connects the capillaries to the rest of the venous system. The network of veins throughout the human body is very similar to the network of arteries. If the arteries carry blood away from the heart, something has to carry it back. Thus, wherever the arteries go, the veins must go as well. The veins close the proverbial loop of the circulatory system. The veins return blood from the extremities, torso, and head to the heart. When someone initiates an IV (intravenous therapy), they are accessing the circulatory system through the venous, not arterial, blood supply. Ultimately, blood returns to the heart from the venous system through the vena cava. There is both a superior vena cava, which returns blood from the head and upper body, and an inferior vena cava, which returns blood from the lower body and extremities. The blood from the vena cava enters the right atrium, where the blood begins its journey through the circulatory system once again. Once the blood is infused with oxygen in the lungs, it returns to the heart through the pulmonary veins. Because the pulmonary veins return to the heart from the lungs, they are the only veins in the body that carry oxygenated blood. All other veins return to the heart with a depleted oxygen supply. (When looking at illustrations of the circulatory system, arteries are typically drawn as red because the blood they carry are oxygen-rich, thus making the blood a bright shade of red. Veins, on the other hand, carry blood saturated with carbon dioxide instead of oxygen, resulting in a much darker red color. Veins look blue under our skin, so veins are typically illustrated as being blue in color. The pulmonary arteries and veins are colored inversely to what other arteries and veins are colored given their position between the heart and the lungs.) The last vital component to the circulatory system is one with which everyone is familiar, our blood. Blood is responsible for moving gasses, nutrients, and waste products through the body. If the circulatory system is the body’s plumbing system, the blood is the fluid that fills it. Our blood is composed of several different types of cells; all of which have a specific function. Red blood cells, or erythrocytes, carry oxygen and carbon dioxide. The shape of the cells is vital in carrying these gasses. Sickle cell disease, for instances, is a disease where the red blood cells are deformed, thus reducing the ability to carry oxygen and carbon dioxide. Red blood cells are also responsible for giving blood its red color. Also known as leukocytes, our white blood cells are essential in keeping us healthy. These specialized cells produce antibodies that help us resist infection. White blood cells also destroy invading microorganisms (germs) as well. There are five primary types of white blood cells. At this point in the course, however, it is not necessary to know the names and function of each. Platelets are very important in that they have the ability to release a chemical known as a clotting factor. As the name implies, these clotting factors are responsible for producing blood clots. Clotting is important in stopping bleeding from cuts, scrapes, and other trauma. Without platelets and clotting factors, even a small laceration could prove problematic as there would be no way to stop the bleeding. These clots produce scabs, under which the body grows new skin. In some instances, these clotting factors can be a major problem if they accumulate in an area within the blood supply. We will discuss many of these conditions later in the course. Approximately 45% of our blood is comprised of these three cells (about 44% is red blood cells and 1% or less are white blood cells and platelets). The remaining portion of our blood is called plasma. Plasma is a watery, salty, yellowish, somewhat translucent fluid that carries the red blood cells, white blood cells, and platelets throughout our body. Located in the upper left quadrant of the abdomen, toward the lateral aspect of the body, is the spleen. (The spleen is part of the lymphatic system, which is commonly considered to be part of the circulatory system. While we will not be discussing the lymphatic system as it plays little role in the practice of emergency medicine, the spleen is a special organ with which the EMT must be familiar.) The spleen supports the body’s immune system and also serves as a reservoir for blood. It is a very vascular organ, about the size of your palm. While very well protected within the rib cage by bones, the spine, and muscles, it is also considered to be the body’s most fragile abdominal organ. Injuries to the spleen are typically a result of blunt or penetrating trauma. Such injuries can result in tremendous internal bleeding from the spleen, posing a true emergency for the patient if significant injury was sustained. Now that we are familiar with the structures that comprise our circulatory system, some of the functions performed by the circulatory system should not be a surprise. The circulatory system is responsible for the movement of nutrients, gases, and waste products throughout our bodies. Through the process of cellular respiration, we are able to exchange gasses between the cells in our bodies and the red blood cells within the circulatory system. Where the circulatory system meets the respiratory system, diffusion allows us to exchange those gasses with the air in our lungs. The circulatory system also provides a reservoir for blood. An adult carries approximately five liters of blood within his or her circulatory system, which can accommodate instances in which some blood is lost, typically due to trauma or some type of internal hemorrhage. That additional blood, that reservoir, allows our bodies to compensate when blood volume is lost. (As more blood is lost, however, our bodies lose the ability to adequately perfuse to the periphery and, eventually, vital organs. This type of emergency will be discussed later in the course.) As mentioned with the respiratory system, the circulatory system also plays a part in regulating the body’s acid-base balance. Through mechanisms known as the bicarbonate and phosphate buffer systems, our circulatory system works to ensure a healthy pH balance within the body. Unlike the respiratory system, it takes longer for the circulatory system to regulate pH. On the other hand, the effects of the blood buffer system on pH within the body are much more persistent; it lasts longer. The white blood cells within the circulatory system are integral to infectious response and our platelets are responsible for coagulation. Together, the blood and the organs of the circulatory system ensure the health of the body’s cells through these various and important functions. The next major body system to analyze is the nervous system. The nervous system is broken down into two primary components. The first is the central nervous system, which includes the brain and spinal cord. Everything else branches off from the central nervous system and is a part of the peripheral nervous system. Within the peripheral nervous system are sensory and motor nerves that help the body interact with its environment. Our nervous system performs several vital functions for the body. The first is referred to as autonomic control or response. These are the things our bodies do without any conscious thought. We do not need to think to breathe or to blink our eyes, for instance. This is all automatic. This autonomic control is integral in the body’s fight-or-flight and feed-or-breed responses with the sympathetic and parasympathetic nervous systems, which we will be discussing in a few moments. The central nervous system is the center of our consciousness, our thoughts, personality, and essential being. Located within the brain are areas for logic, language, intuition, reasoning, and analytic thought, to name a few. This is why brain injury, from trauma, a stroke, or some other disease process can be so debilitating as such injury has the potential to strike at the very core of the person’s own identity and abilities. Within our consciousness is also something called the reticular activating system, which is responsible for regulating our sleep-wake cycle and also plays a part in transitioning between periods of conscious relaxation and heightened attention. While not an all-inclusive list, the reticular activating system is a complex mechanism that has been linked to schizophrenia, narcolepsy, depression, autism, Alzheimer’s, Parkinson’s, attention deficit, and post-traumatic stress pathologies. The nervous system allows us to receive feedback from the environment in which we live through the body’s senses of hearing, smell, taste, sight, and touch. Sensations of both pleasure and pain have cursory effects on the other parts of the central nervous system, which can trigger the sympathetic or parasympathetic nervous systems, impact our consciousness, and provoke an involuntary motor response (which just so happens to be the last function of the nervous system that needs to be identified). Motor function, that is the flexion or relaxation of skeletal muscles to produce movement, is a function of our nervous system as well. While these functions are listed separately, they are all related and, in many instances, interdependent. Sensory input, such as an alarm clock, can trigger the reticular activating system to wake us from sleep. During that process, the person may consciously decide to stretch, thus triggering a motor response. When the person realizes that she hit the snooze button once too many times, there is a sympathetic response when she realizes she is late for work. Within a few moments, however, she realizes it’s a Saturday and the alarm should not have been on in the first place, triggering the parasympathetic nervous system and, if she’s lucky, the reticular activating system that allows her to grab an extra hour of sleep. To understand how the nervous system performs autonomic functions, it is important to have familiarity with the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is responsible for what is known as the “fight or flight” reaction. It is the system that kicks in when we are threatened or when we need to be aggressive. Stated another way, this is the system that helps our bodies respond to stress. It is the system responsible for that “jolt” you feel when you narrowly miss being in a car accident, go bungee jumping, or become involved in an altercation. This response is designed to heighten our senses and improve the ability to respond for the sake of preserving ourselves. This is a primal response that does not even involve the brain. In simple terms, this is the body’s gas pedal. Push it and the engine revs up. At the EMT level, it is not necessary to know the fine intricacies of how the sympathetic nervous system works. On a simplistic level, our body receives feedback from the environment that activates neurons in the spinal cord (within the T1 to L2 region). These signals proceed through bundles of nerves, known as ganglia, to various target organs. Of great importance is the effect on the endocrine system. The sympathetic nervous system directly stimulates the adrenal medulla (in the adrenal gland, located on top of the kidneys). This causes the release of the hormones norepinephrine and epinephrine into the circulatory system. Where the nerves of the sympathetic nervous system do not reach, the hormones do, and these hormones have a direct impact on our circulatory and respiratory systems. When active, the sympathetic nervous system recognizes the need for the body to respond quickly. As a result, blood flow is increased to vital organs and decreased to those that are less vital to immediate survival. Our eyes dilate to receive more light; our heart rate increases to move more blood and, subsequently, more oxygen to our muscles; the bronchi relax to allow for greater air exchange into and out of the lungs; and, the liver converts an increased level of glycogen to glucose (to supply additional sugar to the brain and active muscles). Inversely, the digestive and renal systems slow down substantially (the last thing you need to do when fighting or running for your life, so to speak, is stop for a bathroom break). If we called the sympathetic nervous system the body’s gas pedal, the the parasympathetic nervous system would be the brake. This is the system that turns off the sympathetic nervous system. It is also the system that works to regulate vegetative functions, such as maintaining a normal heart rate or blood pressure. Because this system slows us down, so to speak, it is often referred to as the “feed or breed” system. While we have not talked a great deal about how nerves function, it is important to know that chemicals are used as neurotransmitters to transmit messages from nerve cell to nerve cell. In the case of the sympathetic nervous system, those chemicals are norepinephrine and epinephrine. In the parasympathetic nervous system, however, the chemical used as a neurotransmitter is acetylcholine. When activated, impulses originating from the brainstem and the neurons in the S2 to S4 spinal cord travel throughout the parasympathetic nerve fibers (using acetylcholine as a neurotransmitter) to facilitate the processing of food, energy absorption, relaxation, and reproduction. The effect is obviously quite the opposite of the sympathetic nervous system. With the parasympathetic nervous system in control, our heart rate slows, blood pressure is reduced, pupils constrict, and digestive system activity increases. Thus far, every body system discussed has been labeled as important or integral to the body’s functioning, and the nervous system is no exception. Our next body system is the integumentary system, which is ultimately a very fancy way of describing our skin. Our skin is actually considered to be an organ, and it is the largest organ in (or, arguably, on) our bodies. The skin is comprised of three major layers. The first is the outermost, called the epidermis. The skin cells within the epidermis divide rapidly, resulting in the movement of skin cells up, away from the body. As the cells progress away from the skin’s blood supply, those cells die and are eventually shed away from the body. Believe it or not, the skin we see with our eyes are actually dead skin cells that will soon (within two to four weeks) be washed or brushed away to be replaced by other dying cells. This process helps protect the body against bacterial infection as the outermost skin layer is constantly moving cells out away from the body. Note that there are no nerves or vasculature within the epidermis. The prefix “epi” is derived from a Greek preposition meaning, on, above, or over. Thus it makes sense that the epidermis sits above the dermis, the skin’s second major layer. The dermis is far more busy, if you will, than the epidermis. Within the dermis are blood vessels, nerve endings, glands, and other structures. Given the existence of these structures, injuries exposing the dermis can lead to significant bleeding, intense pain, and infection. It is within the dermis that our bodies will begin an assault on foreign materials, including organisms and damaged cells, with the white blood cells within our immune system. It is also the area where platelets within the circulatory system will work to repair damage to the skin, such as cuts and abrasions. The dermis is also the layer that experiences the most degradation over time. As we age, our glands produce less sweat and natural oils, thus drying out the skin; then, some of the vasculature within the dermis is lost, and the skin becomes thinner and more prone to injury. The innermost layer of the skin is called the subcutaneous layer. This layer contains fatty (also called adipose) and soft tissue. It, too, is rich in blood supply, nerves, and other structures, just like the dermis. Injuries that extend down to the subcutaneous skin layer (or beyond, for that matter) are prone to infection, are associated with significant pain, and can generate a great deal of bleeding. If not evident thus far, one of the primary purposes of the skin is to protect the body from infection. The skin is a protective envelope for our bodies. It is our first line of defense against bacteria, viruses, foreign bodies, and other microorganisms that would harm us. Additionally, the skin serves a significant role in regulating the body’s temperature. The subcutaneous layer provides a great deal of insulation. Heat passes through this layer of the skin three times slower than it does through muscle or the other layers of the skin, which helps conserve body heat. The sweat glands within the skin also help cool the body through the evaporative process (the evaporation of sweat on the skin helps cool the body). While arguably not an essential function, the skin also serves at the basis for what we consider to be appealing or beautiful. Unfortunately for some, the skin can also be the basis for bias and prejudice given ethnic variations in skin pigmentation and other features. Because sight is such an important sense for human beings, our skin is one of the first things people notice about us; it presents us to the world. As an EMS student, you will eventually learn how to form an initial impression on your patient’s condition based, in part, upon how the patient’s skin looks. Next on our list is the digestive system. The purpose of the digestive system is pretty simple, it supplies our bodies with nutrients. We consume food and drink, the digestive system absorbs fats, proteins, carbohydrates, vitamins, minerals, and other nutrients, and it then dispels of the waste. Food and beverages enter the body through the mouth and oral cavity. Processing of our food begins right away as we chew the food, which is mixed with saliva. As we swallow, our food and drink hopefully bypass the trachea, which leads to the lungs, and enters the esophagus, a smooth-muscle tube that carries food down into a hollow organ known as the stomach. The environment within the stomach is not a pleasant one. Protected by a layer of mucous, the stomach mixes our food with hydrochloric acid and enzymes to produce a thick fluid called chyme. While we are discussing the stomach, please take note of its location within the body. The stomach lies in the upper left abdominal quadrant. This is important because patients will often complain of “stomach pain” when the pain is located somewhere else in their abdomen, nowhere near the stomach. From the stomach, the chyme is passed through a tube called the duodenum before it finds its way into the bowels. While in the duodenum, chyme is mixed with bile, which is produced by the liver and stored in the gallbladder, and pancreatic digestive juices. These substances help the body break down the food even further, while also increasing the pH of the chyme so that it is less acidic. Once in the small intestines, the nutrients contained within the food are absorbed through the intestinal wall into the bloodstream, where a pass is made through the liver to detoxify the blood before distribution through the remainder of the circulatory system. Thus, the liver not only produces bile to assist in digestion, but it also serves as a filter for the blood, removing toxins (such as alcohol) that enter through the digestive process. The liver also removes damaged red blood cells from our system, which are then used to make bile. After the small intestines are the large intestines. During this part of the journey, bacteria (intestinal flora, as they are sometimes called) assist in releasing vitamins and fluid while the bowel absorbs that fluid back into the blood stream. Anything left over becomes waste product (stool or feces) that is passed outside the body through the rectum and anus during excretion/defecation. One additional structure in the digestive system with which an EMT must be familiar is the appendix (or vermiform appendix, if you want to be proper). Located in the lower right quadrant, the appendix is believed to have served an evolutionary purpose that no longer exists by housing bacteria that broke down cellulose molecules found in plants. Whether or not that is the actual case is irrelevant when a patient is complaining of abdominal pain in that area as appendicitis can prove to be a significant medical emergency. That will be discussed more in a later module, though. As you may have noticed, some of our organs are considered to be parts of multiple body systems. The lungs are respiratory, but they also have a circulatory component. Our oral cavity is used by the both the respiratory and digestive systems. If there is one system in particular that seems to have numerous organs that also serve a role in another system, it would be the endocrine system. The endocrine system is a system that regulates bodily functions through the use of chemicals called hormones. We have many organs, usually called glands, responsible for producing these hormones. The testes and ovaries, collectively referred to as gonads, regulate the male and female reproductive systems, respectively. The pancreas regulates our blood sugar and will be discussed in greater depth in just a bit. We have some familiarity with the adrenal glands as they work with the sympathetic nervous system. They also serve a role in regulating water and electrolyte levels within the body. The thymus gland is integral in the development of our immune system. The thyroid (medial) and parathyroid (lateral) glands regulate metabolic rate and blood calcium levels. The pineal gland regulates our body’s internal clock, known as our circadian clock or circadian rhythm. The pituitary gland, though small (about the size of a pea) is powerful in that it governs some of the functions of many other glands. It is also regulates or impacts our growth, metabolism, blood pressure, reproductive organs, water balance, and thyroid gland function, to name a few. As EMS providers, there are a few organs in the endocrine system that are of particular importance. The first such organ is the pancreas. Located posterior to the stomach, resting superior to the bowels, the pancreas is important because it plays a very important role in the regulation of blood sugar. As we will discuss in a few slides, sugar is vital to the proper functioning of our cells and, thus, our bodies. The pancreas works in regulating our blood sugar by producing two critical hormones, glucagon and insulin. Glucagon is a hormone responsible for breaking down glycogen, a complex carbohydrate, into a simpler form of sugar, or glucose. By breaking glycogen down into individual glucose molecules, glucagon increases the blood sugar concentration within the blood stream. Because the liver is the largest and heaviest organ in the body, and an average liver can store five to eight percent of its weight as glycogen, a lot of the work being done by glucagon is in the liver. In addition to breaking down glycogen into glucose, glucagon also stimulates the liver into breaking down proteins and fats into glucose as well. One of the skills you will be learning as an EMT is how to administer glucagon to a person suffering from hypoglycemia (low blood sugar). In administering this medication, the EMT is hoping to raise the patient’s blood sugar by converting stored glycogen in the liver into glucose. In addition to increasing blood sugar concentration through the release of glucagon, the pancreas also produces a hormone called insulin that is responsible for lowering a person’s blood sugar. Imagine, for a minute, that your cells have little doorways in their membrane walls that allow sugar to pass into the cell. Insulin is essentially the “key” for those doors. When introduced into the bloodstream, insulin increases the uptake of glucose into our cells, thus resulting in a decrease of the concentration of glucose within the bloodstream. Insulin also promotes the creation of glycogen, protein, and fat to store energy within the body. You will delve into greater detail regarding diabetic emergencies and complications later within this course. While already discussed as part of the sympathetic nervous system, the adrenal glands deserve special recognition within this endocrine system discussion given their importance in the functioning of the sympathetic nervous system by the production of the hormones norepinephrine and epinephrine. As a quick refresher, norepinephrine and epinephrine are neurotransmitters that engage the sympathetic nervous system. These hormones are released from presynaptic cells for activation of receptors in post synaptic cells. Within the lungs, norepinephrine and epinephrine activate what are known as beta 2 receptors in the lungs that stimulate the bronchioles to dilate, thus allowing more air into the lungs themselves. The receptor sites in the heart are called alpha 1 receptors. When activated by norepinephrine and epinephrine, the alpha 1 receptors in the heart increase the heart rate and the force of contraction, which results in more blood and, by extension, more oxygen, being moved around the body to fuel our organs for that ever-so-vital fight or flight response. The renal system is also called the urinary system. Comprised of four primary structures, the kidneys, ureters, bladder, and urethra, the renal system is designed to primarily regulate fluid and electrolyte levels in the body, filter chemicals from our blood stream, and also maintain the acid-base balance within the body. An average adult will excrete 1.5 liters of urine per day. If a person is dehydrated, the renal system will compensate by retaining fluid, thus reducing the frequency of urination and quantity of urine expelled. Inversely, what happens when you drink a lot of fluids over a short period of time? The renal system increases urine production, resulting in much more frequent urination. The kidneys manage this by regulating the flow of electrolytes, such as sodium (salt), bicarbonate, potassium, hydrogen, and chloride. In managing hydrogen in particular, the kidneys help to ensure a proper acid-base balance within the body. For lack of a better term, the kidneys serve as filters for our bloodstream. The kidneys filter all the blood in our circulatory system approximately 60 times a day, which makes them very efficient at removing waste products in the blood. These waste products are commonly a substance called urea, which is the substance responsible for giving urine its yellow color. The kidneys are also responsible for removing other toxins, including drug metabolites, which is why individuals on certain prescription medications must have their kidney function monitored routinely to ensure the kidneys are not being damaged by the medication. The renal system also helps to manage our blood sugar by excreting glucose in our urine if the concentration of glucose in the blood exceeds a certain threshold and it even plays a part in regulating our blood pressure by controlling the fluid levels within the body and releasing an enzyme called renin that ultimately results in elevating our blood pressure. If not already evident, the urethra is shorter in women than in men given that it must pass through the male penis. As a result, women are much more susceptible to bladder and urinary tract infections than men. The last body system we need to cover is the reproductive system. By its very name, it should be evident that the main purpose of the reproductive system is reproduction, the making of babies to ensure the survival of the species. The reproductive system also serves an additional purpose by producing hormones that affect our emotions, mood, and physical development. Ovaries in females produce estrogen, which is essential in the development of secondary sexual characteristics, such as breasts, and the regulation of the menstrual cycle. Estrogen can also accelerate the metabolism, increase fat stores, and increase bone formation. Men also have low levels of estrogen in their bodies (compared to women) given some production in the liver and adrenal glands, which serves various functions related to the male reproductive system. In men, the testes produce testosterone, which is vital to the development of male reproductive organs. Testosterone also contributes to increasing muscle mass, bone mass, and the growth of hair. Women also have low levels of testosterone in their systems (approximately seven to eight times less than men) given some production in the ovaries and adrenal glands. Lastly, given the inclusion of the urethra (part of the renal system) within the penis (a reproductive organ), the male reproductive system is also involved in the process of urination. As the reproductive systems vary between men and women, we will look at each independently. Beginning with the female reproductive system, we will first identify the ovaries. These are the female sex glands. They produce the hormones estrogen and progesterone. They are also responsible for the development and release of eggs for reproduction. The fallopian tubes, also called uterine tubes, are thin, flexible tubes that extend from the ovaries to the uterus. The purpose of these tubes is to deliver the eggs produced in the ovaries to the uterus. If fertilization of an egg occurs, it usually does so while the egg is still in the fallopian tube. If the fertilized egg fails to move down into the uterus, an ectopic pregnancy will result. This is a significant medical emergency that will be discussed in greater depth later in this course. The uterus is where fetal development occurs. It is a hollow, thick-walled, muscular organ superior to the vagina. The vagina is located just below the uterus and serves several purposes. It receives the penis during intercourse, it provides a route for the discharge of menstrual blood and tissues, and it is also called the birth canal as it is the final passageway from the uterus to the outside world for a baby during delivery. Lastly are the external genitalia. Structures such as the perineum, mons pubis, labia, and clitoris protect the opening to the vagina and serve a role in sexual functioning. While not absolutely essential in the process of reproduction, female breasts are commonly included within the reproductive system as they do assist in the reproductive process by producing stimulus to both the male and female in varying degrees during the reproductive process. The breasts also contain mammary glands that provide breast milk (nourishment) to newborns and infants. As women age, ovarian function diminishes, menstrual periods cease, external genitalia (the labia and clitoris) become smaller, the vagina narrows and shortens, the lining of the vagina becomes thinner and dry, and the ovaries and uterus decrease in size. By comparison, the male carries his sex glands, his testes, on the outside of his body within a muscular sac known as the scrotum. The testes produce hormones and, most importantly to reproduction, sperm. Sperm produced in the testes is stored in the epididymis until needed. During intercourse, sperm moves from the epididymis through a tube called the vas deferens to an area in the prostate gland where the sperm is combined with seminal fluid to produce semen. The semen is then routed into the urethra, located within the penis, for ejaculation. The penis itself is a spongy organ that, when engorged with blood, becomes erect. As you may notice from the diagram, the urethra passes from the bladder through the prostate gland, before entering the penis. As a result, an enlarged prostate can lead to urinary problems in men, which typically becomes more common with age. Along those lines, men also experience a reduction in the size of their penis and their testes hang lower in the scrotum as they age. Given that you should now have some understanding of the systems within the body, their structures, and functioning, we can now talk about something known as the life support chain. Combined, the circulatory and respiratory systems form the cardiopulmonary system. The proper functioning of this system creates something called the life support chain. So long as all the elements of the chain are in place, the organism should continue living. Remove an element of the chain, however, and death is inevitable. There are three main components within this life support chain: oxygenation, perfusion, and the cellular environment itself. Focusing on oxygenation, our first primary concern is being able to exchange gases in the lungs. This means the body must be able to breathe, to ventilate itself, moving atmospheric air (containing 21% oxygen) into and out of the lungs. Given this supply of air in the lungs, it is then necessary for gas exchange to occur within the alveoli. Oxygen from the air must diffuse into the alveolar capillaries and carbon dioxide must diffuse from the alveolar capillaries into the air within the lungs to be exhaled. Even if this process is working within the lungs, we must also recognize the need for cellular respiration throughout the body. Our cells must expel carbon dioxide into the bloodstream so there is room, so to speak, for oxygen to enter. Inherent in this process is also the fact that the circulatory system is working; that the heart is pumping blood throughout the body. Having this gaseous exchange occur at the cellular level or within the alveoli is no longer beneficial if the blood in those locations does not make the trip throughout the body. The freshly oxygenated blood in the lungs needs to move to the cells to deliver that oxygen, and it needs to return to the lungs to expel the waste carbon dioxide. Within that process, perfusion into the individual cells of the body is important. Within this context, perfusion means the ability to move gases and nutrients between the bloodstream and the cells. We obviously want oxygen to enter the cells and carbon dioxide to leave the cells. We also need glucose (sugar) to enter the cells as well. For that to happen, our body needs insulin to open the proverbial door into the cell for the glucose. Our cells also produce other waste products that must be removed as well, otherwise the cells will die in their own waste. These are all important components of adequate perfusion into the cells. Lastly, we need to look at the cellular environment itself. Up to this point, we have not discussed how the cells within our bodies actually work. The cell is the basic building block within the body. Cells form tissues, which form organs, which forms systems, that eventually result in the full organism or, in our case, the human body itself. Ultimately, our cells are living things. They need energy to do work, and they need a way to expel the waste products produced by doing that work. Within a healthy environment, our cells have an ample supply of oxygen. When a cell is producing energy with oxygen, it is said to be functioning with aerobic metabolism. In aerobic metabolism, the cell has ample oxygen that allows it to break sugar down into a chemical called adenosine triphosphate (ATP) very efficiently. Given the inclusion of oxygen into the process, the cell can produce a great deal of energy with the rather innocuous byproducts of water and carbon dioxide. When the cells are deprived of oxygen, however, they enter into a state knows as anaerobic metabolism. Without oxygen, the cells cannot process glucose very efficiently, resulting in low ATP (low energy) production and the waste product of lactic acid. If a supply of oxygen is not restored to the cell, it will continue to function producing low energy and lactic acid until the pH of the cell becomes too acidic and the cell dies. As more cells suffer the same fate, the tissues and organs in the affected area become compromised, which may very well threaten the health of the organism, the body, itself. From our discussion thus far, it may be clear that the functioning of a single body system is rather complex. As soon as it is apparent that multiple systems rely on others, the complexity surrounding the functioning of our bodies reaches an entirely new level. For this reason, the life support chain can be a fragile thing and a break in one link of the proverbial chain can spell disaster for the entire system. This life support chain relies on the air we breathe, a patent airway, the ability to ventilate, the ability to respirate, the movement of gasses throughout our bodies, the amount of blood in our circulatory system (especially when compared to the relative capacity of the circulatory system itself), the health of the heart, and the maintenance of the body’s acid-base balance. Our life support chain begins outside the body with the air we breathe. Common ambient air contains 21% oxygen, 78% nitrogen, and 1% other gases. This 21% oxygen is of critical importance. A lack of oxygen in the air we breathe can have a profound impact on the body. The brain itself uses approximately 20% of the oxygen within the body and does not respond well to a reduction in available oxygen. If we see a reduction of just 1.5% to 19.5% oxygen in the air, the ability to work strenuously is impaired; we may see coordination suffer; and, people who are unhealthy to begin with, such as those with circulatory or respiratory problems, may begin to experience symptoms associated with their disease. It is important to keep in mind as well that, for every 1.5% of oxygen reduced in the air, approximately 7.5% of other stuff takes its place (as the oxygen is not only being displaced, but so too is the nitrogen). That which displaces the oxygen may have negative repercussions for the body on its own as well. Thus, an oxygen deficient atmosphere, such as that which exists in a confined space, typically brings a multitude of hazards. As the oxygen saturation in the air is decreased to 15%, coordination, perception, and judgment is impaired. At 12%, our body can no longer provide enough oxygen to adequately perfuse our extremities, resulting in cyanosis (where the skin turns blue due to the lack of oxygen). The impact is even more pronounced at 10% with nausea, vomiting, mental failure, and unconsciousness. At 8%, half the people in that environment for eight minutes will be dead. (A quarter are dead after only six minutes.) If the atmosphere has less than 6% oxygen in it, the person is dead within seconds. A patent airway is an established, affirmative airway. It is an airway that works; an airway that allows us to move air into and out of our lungs. If the airway is blocked or restricted, it becomes difficult or impossible to exchange the air in our lungs with the ambient air in the atmosphere. A person choking or suffering from asthma would be an example of an airway problem. If we are unable to bring air into the lungs, there is no oxygen available within the lungs to enter our bloodstream. Somewhat related to having a patent airway is the ability to ventilate, the ability to physically move air into and out of the lungs. Having a patent airway does no good if the person is unable to breathe on his or her own. Have you ever fallen on your back and had the “wind knocked out of you?” That uncomfortable feeling of not being able to take a breath is actually a result of a diaphragm spasm. If the diaphragm is not working, ventilation becomes a significant challenge. There are other things that can cause a ventilation problem as well. A neurological disorder or trauma to the spinal cord may disrupt the impulses that prompt our diaphragm to constrict. A drug overdose, especially of a narcotic substance, may depress the body’s central nervous system to the point where it no longer remembers to breathe, resulting in death. A pneumothorax (a collapsed lung) can greatly reduce the ability to move air as well. A crushing injury, such as a heavy object on the chest, may not allow for chest wall expansion, which would negatively impact the ability to ventilate. If you have ever been snorkeling, does it feel harder to breathe through the snorkel tube? The reason is because water has weight (approximately eight pounds per gallon). As you place water on top of your body, it reduces the ability to expand your chest, just like any other heavy object. For more proof, take the same snorkel and breathe through it without being in the water. You should be able to breathe without a problem. The deeper you go in the water, however, the more difficult it is to breathe, which is why snorkels have a limited length. SCUBA divers can breathe regulated air under water because that air is pressurized; it pushes the lungs open and overcomes the tremendous pressure placed on the thoracic cavity by the water above the diver. This is also why it feels more difficult to breathe at higher altitudes. The process of creating negative pressure in the thoracic cavity is not that difficult at high altitudes. The problem, though, is that the air (or barometric pressure) is less, meaning that the air has less push into our lungs. As a result, the “push” of oxygen into our blood stream through the alveoli is not as great, meaning we have to work harder to saturate our bodies at higher altitudes where there is less air pressure than at lower altitudes where there is more air pressure. Trench rescue is a special discipline in which victims are rescued (or recovered) from trenches that have collapsed. Falling dirt has weight and just three inches of dirt on top of a person’s chest is enough to overpower the body’s muscles of ventilation. Even with a patent airway and readily accessible ambient air with 21% oxygen, the ability to ventilate, to move that air into and out of the lungs, is absolutely critical. Assuming the air has 21% oxygen, our airway is patent, and we are able to move that air into the lungs, we still have to move the oxygen in the air into our bloodstream. That process begins in the alveoli. Damaged alveoli, due to diseases like pneumonia, emphysema, or asbestosis can greatly reduce the ability to exchange gases through the alveolar wall. Having an adequate supply of blood to the lungs is important as well. A blockage in a pulmonary artery, called a pulmonary embolism, can be just as bad as air not entering the lungs in the first place. Depending on the size of the embolism, a great deal of the lung may lose its capacity to exchange gases because there is no blood flowing to that area of the lung. Once the oxygen is in the bloodstream, we must also be able to move the gases between the capillaries and the individual cells. Within the cell, it is also imperative that the cellular environment contain the electrolytes and nutrients necessary to function, including glucose. Using the words respiration and perfusion interchangeably, if we ventilate adequately, but do not perfuse, or are perfusing without adequate ventilations, we have what is known as a ventilation/perfusion mismatch. V/Q mismatch (where V equals ventilation and Q equals perfusion) is the terminology used to delineate a difference in the amount of oxygen-containing air in the lungs and the amount of oxygen within the blood stream. Air in the lungs does not matter if it cannot enter the bloodstream (or the cells). Inversely, being able to perfuse does not matter if our lungs are somehow deprived of oxygen. Just because the oxygen in the lungs is able to enter the bloodstream does not necessarily mean it is being carried where it needs to go. There are diseases, such as sickle cell anemia, that impair the ability of the body’s red blood cells to transport oxygen throughout the body. There are also gases, such as carbon monoxide, that can displace oxygen within our bloodstream. Thus, another important link in the life support chain is the ability of the blood to carry oxygen, nutrients, electrolytes, and waste products. Of equal importance to the life support chain is having adequate blood within our circulatory system. An adult human has about four and one-half to five liters of blood within his or her circulatory system. (There is obviously some variance depending on the size of the person and the textbook being referenced.) That same body can typically withstand a 15 to 20% drop in blood volume (approximately one liter) before the life support chain is significantly impacted. The body experiences different levels of hypovolemic shock between 15 and 40% blood loss. At or beyond 40% blood loss, death becomes increasingly probable. We will talk about shock later in this course. For the time being, however, know that the body works to protect the organism by sacrificing, if you will, non-vital parts of itself. Given severe shock, the sympathetic nervous system shuts down the blood supply to extremities, trying to shunt as much blood (and, therefore, oxygen) as possible to the heart, lungs, and brain. As the volume of circulating blood within a person dwindles, however, the life support chain becomes more difficult to sustain. Now picture, for a minute, the vessels of the circulatory system and the amount of blood they can contain at any one time. We also have organs, such as the liver and spleen, that contain reservoirs of blood as well. Combined, that system holds up to five liters of blood. What would happen if our circulatory system (our arteries and veins, predominantly) suddenly increased in size without increasing the amount of blood to circulate within it? Increase the size of the container without increasing the volume of fluid within it and there is no longer enough fluid to fill the container. Systemic vascular resistance is a fancy way of saying blood pressure. Ultimately, we have to maintain a healthy blood pressure to maintain perfusion to our cells. Our veins and arteries are lined with muscles that allow them to expand and contract. This is what allows our sympathetic and parasympathetic nervous systems to restrict or reestablish blood flow to a given area. Our bodies function with many of these vessels somewhat constricted. If we happen to lose too much blood or our vessels all dilate at the same time, we can no longer maintain a perfusing blood pressure; there is not enough blood to fill is the vessels of our circulatory system. On the previous slide, we discussed how the loss of circulating blood volume negatively impacts the body. If we reduce the circulating blood volume, it is important for the body to be able to constrict blood vessels to conserve blood for critical organs, such as the heart, lungs, and brains. Whether we increase the size of the container or reduce the amount of fluid within the container, the result is the same… Too little blood in the circulatory system is problematic. Just 23 days after conception, our hearts began beating and circulating blood. From that time until right now, your heart has been maintaining the persistent rhythm of muscular contraction and relaxation to move blood around the body. So what happens if the heart begins to fail, as occurs with age or a disease process? Obviously, the heart is critical to the life support chain and a failing heart can quickly lead to the deterioration and eventual collapse of that chain. The failure can be a gradual process, or something more catastrophic, such as sudden-onset myocardial infarction (heart attack). One last item that can break the life support chain is related to the functioning of the cell itself. More specifically, the acid-base balance within the body and its cells. As we already discussed, cells produce energy. They do so by breaking down oxygen and glucose to produce adenosine triphosphate (ATP). When the cells have access to oxygen, this process is very efficient with a lot of energy produced. The byproducts are carbon dioxide and water. If the cells are starved of oxygen, however, they function anaerobically. This process produces substantially less energy and the ultimate byproduct is lactic acid. As this lactic acid begins to build without a source of oxygen being established, the body itself becomes acidotic, meaning the acid-base balance is shifting, making the body more acidic. This is called acidosis and it has a negative impact on the body. Too much acid and the cell will die. How quickly depends on the area affected, whether oxygen availability is simply reduced or is completely halted, the types of cells impacted, and the amount of time those cells have to function with reduced or no oxygen. Brain cells, for instance, are not at all tolerant of oxygen deprivation. Remove oxygen from brain cells and they begin to die within six to eight minutes. On the other hand, skeletal muscles and tissues can survive a longer time, typically up to hours, without adequate perfusion. Up to this point, we have covered some medical terminology to facilitate our discussion about the structures within the human body. It is now time to delve a little deeper in medical terminology to start pulling everything together and serve as a foundation for upcoming course modules. Medical words are built from three different parts, if you will. There is a root word, which commonly refers to the organ, system, or tissues involved. The root is then joined with a prefix before the root, a suffix after the root, or both. The prefixes and suffixes are designed to describe the root, to give it greater definition. Within the medical field, there are numerous roots for virtually every part and component of the body. For an EMS provider, some of the most common are: Cardi or Cardium, which refers to the heart. Neur, referring to a nerve or the nervous system. Pnea, related to breathing. Pneumo, referring to the lung. Nas refers to nose or nasal. Or refers to mouth or oral. Hem or hemat refers to the blood. Osteo refers to bone. Arthr refers to joints. Myo refers to muscles. Prefixes are added to the beginning of roots to modify or qualify their meaning. Some common prefixes include: Hyper, for fast, high, or above normal. Hypo, for slow, low, or below normal. Tachy, for rapid or above normal rate. Brady, for slow or below normal rate. Dys is difficult or painful. A is without. Cyan is blue. Intra means inside or within. Quad refers to four. Bi refers to two. There are also suffixes, added to the end of roots, that complete their meaning. For instance: ac or al means “pertaining to.” ology is the study of something. ist refers to one who specializes in something. osis is a disease condition. Ultimately, these prefixes, suffixes, and roots are combined to form medical terms that have significant meaning for the healthcare provider. For instance, adding tachy to cardi forms the word tachycardia, meaning a fast heart rate. Neur and ology is neurology, the study of nerves and the neurological system. Cardi plus ology and ist is cardiologist, one who specializes in the study of the heart. A is without and pnea is breathing. Combining the two is apnea, or the absence of breathing. Similarly, dys plus pnea is dyspnea, which means difficulty breathing. The list provided here is far from inclusive, and you may find yourself using other prefixes, roots, and suffixes with greater frequency in your eventual practice of emergency medicine. The important takeaway from this slide is that, once you identify a common prefix, suffix, or root, its meaning does not fluctuate and you can use the combination of those three word parts to describe patients, organs, diseases, tissues, signs, symptoms, and conditions. If confronted with a medical term that you do not understand, first see if you can break the word apart into its components (prefix, root, and suffix). For instance, hematoma is a common medical word used in EMS. Hemat refers to blood and oma means tumor. Thus, hematoma is a tumor (a swelling or growth) containing blood. Hematoma is a fancy way of saying bruise. When we delve deeper into medical terminology, one might wonder how these words developed, how they came to be. Ultimately, we go back to ancient Rome and Greece where the study of the human body has some recognized origins. When describing the body’s anatomical structure, we use Latin words. Other words pertaining to diseases, conditions, treatments, or diagnosis have Greek roots. We also find that it is possible to divide the terms up by their subject matter. Some terms are associated with body structure, some are related to the body systems we already discussed, and others pertain to body direction or position. For instance, epigastric and superficial are medical terms related to the body’s structure. Ocul refers to the eye and bronchiol refers to bronchial tubes, both are associated with body systems. Bilaterial and flexion are terms pertaining to the body’s direction or position. At this point, including pertinent medical terms and definitions would be counter-productive as there are so many of them. Medical dictionaries are very thick books and there is not enough time in the day to cover all of the medical terms you may encounter through your practice in EMS. With that being the case, it is recognized that much of the medical terminology you will need to know as a newly-licensed EMS provider will be included within subsequent modules of this course. Additionally, if confronted with a medical term to which you do not know the definition or meaning, you are encouraged to look it up. EMT textbooks, medical dictionaries, and the internet are all readily available resources for finding the definition of various medical terms. Another factor to consider regarding medical terminology is that you, as an EMT, must remember your audience when using such terms. If you are giving a report to the hospital, they will know what a myocardial infarction is. When speaking with a patient, however, that term may be completely foreign to him or her. Speak in plain, lay person terms when dealing with patients and the public. Using a word like “epistaxis” may sound impressive, but the average person has no idea that word is medical terminology for a nosebleed. Do not assume the patient knows what you mean when using medical terminology as communication problems can lead to errors in formulating a field impression and the delivery of proper emergency care to that patient. Additionally, do not go out of your way to use verbose medical terminology when simple words or descriptions will work just fine, even with other health care providers. The last thing you want when ensuring continuity of care for your patient is a communication problem because you used a fancy term incorrectly or the person to whom you were speaking did not understand the term and was embarrassed to ask for clarification. Lastly, given the complexity and length of many medical terms, health care providers will occasionally use abbreviations and acronyms in both oral communications as well as written documentation. The problem with the use of acronyms and abbreviations, however, is that they are not always standardized or universally recognized between various health care providers and systems. True, there are some abbreviations and acronyms that are used by virtually everyone. Some examples include: CHF for congestive heart failure. BVM for bag-valve mask. MI for myocardial infarction. CMS for circulation, motion, and sensation. IV for intravenous. JVD for jugular vein distension. There are also numerous acronyms and abbreviations that that can mean multiple things. For instance: BS can be breath sounds, bowel sounds, or blood sugar. CO routinely means complaining of, but can also be carbon monoxide. min can refer to minutes as a measure of time or can also mean minimum. HR is heart rate or hour. w/o can be wide open or without. If you are positive that an acronym or abbreviation is universally used and accepted within the healthcare community, then its use in conversation or reports may be acceptable. On the other hand, using acronyms or abbreviations that may not be widely used or that require the receiver of the message to consider the acronym or abbreviation in context to know what you are saying or writing is not a good idea. Additionally, if you make it a habit of using acronyms and abbreviations in your normal communications, you may do so as well when dealing with others outside the healthcare profession, such as patients, their families, or the public at-large. If a patient cannot understand you due to the use of acronyms and abbreviations in your speech, that is a problem. Lastly, many systems actually have protocols that define proper acronyms and abbreviations. If you are using an acronym or abbreviation incorrectly, or are using an acronym or abbreviation that is not approved by your local protocols, that is also an area of concern. For these reasons, it is not a bad idea to communicate without using acronyms or abbreviations wherever possible. Ultimately, follow your local protocols and exercise some common sense in your communications with other professionals as well as the lay public. With that, we are completed with this module. You should now be able to: Identify the topographical anatomy and directional terms utilized by the EMT. List the components of each of the major body systems. List the elements of the life support chain. Have acquired a basic understanding of common Latin medical terminology. That concludes this module on the overview of the human body and physiology. If need be, do not hesitate to play this presentation again. Please contact your course instructor with any questions you may have regarding the material in this module. This presentation was created by Waukesha County Technical College with grant funding from the Wisconsin Technical College System.