Discovering Your Health through Applied Anatomy & Physiology
Discovering Your Health through Applied Anatomy & Physiology

Discovering Your Health through Applied Anatomy & Physiology

Lead Author(s): Margaret Dobbs

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Focuses on structure and function of various human body systems, Real Life Applications, engaging questions and interactive format.

Discovering Your Health thru Applied Anatomy & Physiology

Margaret S. Dobbs

1.1 Introduction to Your Human Body

How will knowing about anatomy and physiology make a difference in your future profession?

Figure 1 Discover your own curiosity of the living body.​

​Welcome to an applied study of anatomy and physiology. The intent of this interactive text is to introduce you to the structure and function of various systems of the human body, to explore how the body can experience positive change from exercise and activity, and to identify how a variety of metabolic changes occur simultaneously in your body during every second of your life. Let's discover a level of curiosity about how your body functions. We can start with the question, "What makes our body work"? As you explore the content in the following pages, you are invited to think deeply, read widely, and ponder over fascinating topics that help in understanding the anatomy and physiology of your living body.

By the end of this Chapter, you will be able to:

  • ​Identify the significance of learning about human anatomy and physiology.
  • Describe the structural levels of organization, from simple to complex.
  • Recognize structure and function of key organ systems
  • Identify major characteristics of organisms.
  • Identify basic requirements for survival.
  • Explain homeostasis and its consequences in human body function.
  • Identify anatomical terminology for body structures, body regions, and directions.
  • Identify fundamental imaging techniques.

Figure 2 Anatomy of a Man

Figure 2 Internal organ structure within the male thoracic and abdominopelvic cavities.​

Figure 3​ Athlete suffering the pain of a pulled hamstring.

Have you ever wondered what causes a sneeze, a seizure, or those annoying hiccups? Ever thought about what causes a migraine headache immediately after a stressful office meeting with your boss? What exactly causes that painful cramp in your hamstring? (Fig. 3) For just-in-time learning to occur in this course, just click on the hyperlinks provided. Be curious. Do a little research on matters of the body that interest you! Find out!

Why does a middle-school student, who is running the mile in a P.E. class, suddenly collapse with unexpected exercise-induced asthma? Why would an 84-year old grandpa suddenly become allergic to poison ivy after years of working outside in the wilds, and in addition, randomly develop his first hyperthyroid condition? Why would a mid-life woman have an unforeseen reaction to an antibiotic? And, how do we ever begin to understand why a 23-year old NCAA division champion, who contributed so much to collegiate basketball history, would collapse on the floor during the final moments of the game and die moments later? 

Well, humans are rather complex biological organisms. (Fig. 2 & 4) Our bodies are made up of billions of cells that derive their structure from intricate human tissues that steadily contribute to your ability to breath in, to see out, to digest foods, to sense the world around you, to hear, to pump blood through vessels, and to help you move your legs. On one hand, human bodies naturally experience internal disruptions like fever, acute physical or mental disorders (depressive moments), emotional interludes, fatigue, and the inevitable external circumstances causing chemical changes that drive our body's chemistry. 

On the other hand, humans are hardwired to endure both internal and external circumstances, to adapt to pressure on our organs, to avert blunt physical impact to rigid bones, to deflect trauma away from our 'waterproofed' skin, to heal from accidental injury, to bear the unbearable hypothermic environment,  and to manage real pain. Unfortunately, humans also transform behaviors into habits that interfere with the body's working systems. Humans are creatures of desire. Most humans have for centuries learned to escape the mundane by resorting to the use of recreational substances, desiring leisure activities like watching the television for hours a day. Such unproductive habits, although providing a temporary outlet for boredom, favor robbing the human body of its natural potential. Other habits include smoking, being  sedentary, excessive alcohol intake, addiction, lack of exercise, eating too much sugar, and exposing the human body to the destructive consequences of metabolic syndrome, diabetes Type II, and obesity

As the Athenian philosopher Plato, c. 428-347 B.C., conveyed in his teaching...“Lack of activity destroys the good condition of every human being, while movement and methodical physical exercise save and preserve it.”  (Am J Prev Med 2009) Plato's historical rationale applies to humans today. What better way to learn about the health of our human body than to know something about how our own anatomy and physiology works?

Did You Know that science is now telling us that sitting is known to wreak the same hazards on the body as smoking? Sitting still in your chair or in your car throughout the day may lead to physical problems, lowered functional movements, being overweight or obese. Read deeper about the current population suffering from metabolic syndrome and risk factors that include high cholesterol and triglycerides, increased high blood pressure, and excess body fat. Know that the state of being sedentary may also contribute to your risk of death from cardiovascular disease and cancer. 

With that said, go take an exercise 'snack'. No, I don't mean to eat, I mean to go for a ten-minute walk, stretch with Rodney Yee, or swim a few laps. Release some natural endorphins and wake up your body!!

Figure 5​ Early artist's depiction of the brain.

Have you ever wondered about what part of your brain allows you to think about the very thoughts you are thinking right now? (Fig. 5) Is it possible to even control your thoughts? How does an individual begin to consider how to connect mind with body? How important is this idea to you?  Is it probable that an overweight or obese person, confronting the inevitably difficult loss of weight, can learn to meditate about that plate of food in front of her on the dinner plate? How would she know when she is 3/4's full? Ponder over these queries, and others that come to mind as you take the time to discover lessons in modern clinical or alternative treatments for chronic illness alongside the more rudimentary foundations of human anatomy and physiology.

There is value in understanding our body, as there is also value in understanding the mind. Let's begin to realize the significance of knowing something about how our own human body and mind work, so that we begin to know ourselves, can find optimal health and wellness, and are thus better prepared to share our knowledge with others in our personal lives and in our career paths. 

For starters, take a look at the first YouTube just below about the curious inner workings of the brain. This video will introduce us to what scientists know so far about this three-pound fatty substance (making up 2% of your body weight) that you carry around inside your skull everyday. Think of your brain as the great signaler, as it connects every part of your body together from your eyeballs to your ankle bones, allowing you to function as a whole. (A big Yawp! goes out to our corpus callosum!). Your brain plays a significant role in everything you do, most of the time without any thinking required, that is, because of your involuntarily controlled autonomic nervous system. 

To introduce you to our active learning platform, let's start with a 13-minute video about the anatomy of our brain brought to you from Mr. Bozeman. Click on the button in the middle of the image just below. When you have finished listening, respond to the Think Out Loud question box which follows. This is one example of how learning will take place in this interactive textbook. Let's Go!

Think Out Loud 1.0

Describe three significant or surprising things you learned from this video about the human brain.

Anatomy and Physiology are two disciplines that work closely together to help us understand our human body. Structures of our human body are directly related to function within our body. For example, it would be difficult to talk about the respiratory mechanism involved in your taking a breath of air (a basic human physiological function) without talking about the thoracic muscles, diaphragm, and lungs (anatomical parts of this system) which make your breathing possible. Likewise, it would be puzzling to demonstrate how a muscle contraction works to produce movement in your body so you can lift your groceries, without articulating how an action potential transfers an electrical impulse from your brain, down your spinal cord, and peripherally to your deltoid and your biceps brachii in your upper arms and back (not to mention how your obliques and rectus abdominus fire together deep within your abdominopelvic cavity to flex your spine).

In all of your learning about the disciplines of anatomy and physiology, it is fitting to pay tribute to the great Belgian-born Renaissance anatomist and physician, Andreas Vesalius, who is considered the Modern Father of Anatomy. Andreas Vesalius, c. 1514 – 1564, was an early 16th-century Flemish anatomist, doctor, and author of one of the most prominent books on human anatomy, De humani corporis fabrica (On the Fabric of the Human Body). Vesalius embarked on a mission for medical knowledge centuries ago in macabre vivisection viewing chambers, in his quest for understanding the inner workings of the human body. (Fig. 6) Since Vesalius' teachings, efforts to "bring our insides into view" have been more than moderately creative in teaching about human structure and function. 

Figure 6 De humani corporis fabrica; early dissection of human body ​

Moving forward into the 21st Century, we are observing a paradigm shift from the doddering and commonplace textbook to revolutionary, just-in-time learning for science, including our fascinating topics of anatomy and physiology. We presently have access to learning technologies such as  Google Body Browsers, providing oscillating views of anatomical structures, The Visible Body 3-D virtual dissection of a human heart; and the artistic and engaging Khan Academy , offering inventive whiteboard tutorials on human anatomy and physiology and a host of other scientific subjects.  In addition, video technology produced by Naked Science, allows learners like you to view biological stages of the human body portraying the moment of birth to the final heartbeat of death in a stunning video entitled The Living Body - Our Extraordinary LifeThese pioneering methods of teaching and learning valiantly flow from the quintessential works of Vesalius and his Greek predecessor, Herophilus of Alexandria (325-255 B.C.), nominated as the Father of Anatomy, who actually premiered as the first explorer in dissection of a real human body. (Fig 7)

Our interactive platform seeks to provide you, the learner, with a balance between new technologies like those described above, to short vignettes from the classic lectures, including relevant scientific and artistic images, and unique book recommendations designed to enrich your knowledge of the human body. Take the peculiar Stiff: The Curious Lives of Human Cadavers, by Mary Roach. Readers will become engrossed by this unusual book and will likely want to add it to their summer reading list. What an "unexpectedly hilarious take on learning about the history of cadavers", which by the way, has become one of your author's most favorite books.  (

Figure 7 Vesalius

​As Aristotle once said, “Knowing yourself is the beginning of all wisdom.” This phrase undeniably applies today, centuries after Aristotle's time. So, although we must leave history behind, let's not forget the intrepid pioneers who led us to the present. Let's learn from the past, revere history as we step aboard the knowledge train and move forward into the future. Let us begin our discovery of what is relevant, that which is based on good science, and learn how to apply our knowledge from the present into the burgeoning allied health fields and lifelong learning for tomorrow.

Why study Anatomy and Physiology? 

Knowledge of anatomy and physiology is paramount for work in allied health fields, in teaching fitness and health, and in 21st century physical education classes. A course in anatomy and physiology may be required for your chosen field of study, or you may just desire our subject to add another dimension to your future career.  Knowing something about how the body works can help trainers direct their clients to individualized fitness plans. Knowing about the relationship between health and human anatomy/physiology can assist practitioners and clinicians to determine a proper plan of action when signs of illness or acute injury occur. Being well informed about anatomy and physiology will help you understand better how to interpret popular trends, pseudo-scientific theories, and inaccuracies in health and wellness strategies. Gaining new knowledge will prepare you for a career in health, or for assisting a sick parent, friend, spouse, or child. 

A special language is used in anatomy and physiology.  Our study includes the identification of several characteristics that the body shares with all living things. For example, click on the button in the middle of the image just below to begin to identify how your body balances its internal milieu in the regulatory job of homeostasis.  Homeostasis is your body's vigorous biological framework. In response to considerable changes occurring, the body's ability to maintain a balanced equilibrium within normal limits contributes to your stable internal environment.

Think Out Loud 1.0

To begin our journey about anatomy and physiology, recall an experience you have had that interrupted the natural course of your body's normal physical or mental condition. Stop and think about the experience. How did it affect you? Describe your "normal state" before the occurrence. After the occurrence, were you mindful of your body's return to such normal state? How long did it take for your body to resume such normal state?

1.2 What is Anatomy? Physiology?

 By the end of this section, you will be able to: 

  • Distinguish between anatomy and physiology.

​Human anatomy and physiology is one area of the biological disciplines of biology. As you know, biology studies living organisms. Human anatomy is about body structure. Many structures are so small that observations require using a microscope. Most of our visible body structures are easily seen without magnification. Anatomy originates from Greek origin. Human anatomy was originally studied by observing deceased bodies and by managing illness and injury with some very unusual methods that were thought to heal. Doctors were supposed to help, but as some early historical accounts reveal, they often misled their patients into gruesome practices as they resorted to extreme measures. As noted in Stiff, early physicians were finally allowed after much hesitation, to dissect limbs, organs, and dead bodies to gain knowledge. Even the most well-known curious artist Leonardo DaVinci created precision sketchings of the inner workings of the developing human body. Dissection is the act of cutting a body or body parts for clinical observation. Features and elements of the body may be studied and charted to help in understanding the physical relationship of one body part to another. Society frowned on the unearthing of dead people for scientific discovery. But these grisly discoveries set in motion the key to learning anatomy.

When the bones of ten or more people were discovered in the basement of Benjamin Franklin’s British residence, citizens questioned such obscurity. "Franklin was keenly aware of the bodies buried in his basement, and also knew they weren’t the victims of violent acts. Rather, they were used for the purposes of an illegal anatomy school that helped to shape modern medicine." (OETA; 2017) Many medical schools today still practice dissection in organized scientific classrooms, under certified professionals.  Medical technology has vastly improved and now provides a clear view into cancerous tumors, fractured bones, and the growth of an embryo. See the last section of this chapter for studying various imaging techniques.

Gross anatomy is the specific study of structures observed with the unaided eye, like the brains on a dissection tray found in (Fig. 8a). Macroscopic anatomy imparts a larger view of the body whereas microscopic anatomy uses an electron microscope to learn about deeper structures. (Fig. 8b). Such observations include cytology, the study of cells, and histology, the study of various tissues that make up your organs. As technology continues moves forward, anatomists are now able to explore three-dimensional structures. Developmental anatomy is the study of structural changes; and pathological anatomy (pathology), investigates disease.

Figure 8a A human brain prepped for gross anatomy lab

Figure 8b bacteria observed via electron microscope​

Anatomists utilize two general strategies for studying body structure. Regional anatomy reveals important interrelationships of body structures, such as how organs from the abdominal and pelvic regions work together in the process of digestion, or how nerves, blood vessels, and other structures in the thoracic cavity work together to serve the specific functions of respiratory inspiration and expiration. 

Systemic anatomy teaches about more distinct body systems—ideally, how structures work together to carry out a specific body function. For example, studying the skeletal system includes observing a wide variety of active tissues such as bone, connective tissue, special fatty tissue and blood cell-forming tissues of the body.

Studying the human body.

How do scientists study the human body?

Anatomy is study of structure, where physiology is the study of how parts function.  Human physiology involves the subdisciplines of physics and chemistry that help us understand the body's natural inclination toward homeostasis. Advances in physiology depend on research that reveal a wide variety of dynamic functions of structures and chemical compounds that comprise our human body. 

Similar to the work of an anatomist, a physiologist typically specializes in a division of physiology. For example, Exercise Physiology is the study of physical exercise. It includes the study of acute responses and chronic adaptations to a wide range of exercise conditions. A sports physiologist is a type of exercise physiologist that works strictly with athletes in order to advance and maintain overall health including nutrition, fitness, endurance and strength. Physiologists' work may explore similarities at the organismic level to the chemical level (as in how neurotransmitters assist in delivering a braking action on the heart tissues in order to reduce increased levels of blood pressure). Discoveries in the field of physiology occur more frequently than do discoveries in the field of anatomy.

We can easily observe how structure is related to function in the living body. For example, your grooved molars are built so close to your jawbone joint (structure) providing powerful leverage in crushing and grinding your food (function). Deep abdominal muscles such as your transversus abdominis andinternal and external obliques groups work synergistically with more superficial rectus abdominis muscles to assist you in breathing, in the activation of your core musculature, and in stabilizing your body movements through extensive muscle attachments. The position of your thumb in opposition to your four fingers makes your hand a unique structure that allows you to grab the steering wheel, grasp a wooden spoon, and type text messages. 

A New Thumb Affliction

In a recent report noted in the Wall Street Journal, Geoffrey Fowler reveals an increasing anatomical problem for our thumbs. This predicament seems to be associated with the overuse of our thumbs in playing computer games (nintendothumb or nintendinitis), texting or text messaging injury (TMI), and computer work which more commonly is known to impair carpal nerve pathways found near the wrist (CTS) . Reports from the New England Journal of Medicine are causing such scrutiny today. (Fowler, GA. (April 17; 2002) Thumb Affliction. Wall Street Journal. p.1)

After reading this article, respond to the Think Out Loud box below.

Think Out Loud 1.02

After reading the Wall Street Journal article on Thumb Affliction, what are Chiropractors beginning to suggest to remedy such thumb issues? What is the name of the program offered to deal with this specific clinical issue?

Anatomy observes body structure. Physiology explains function. Knowledge has evolved through the years from the early ill-equipped dissection of cadavers to twenty-first century imaging techniques providing three dimensional views of the brain for clinical studies. These two disciplines provide voluminous knowledge about the systems of the body and how they work together. For our purposes, it makes more sense to study our subjects simultaneously for a richer learning experience. 

Anatomy and Physiology

Explain the difference between anatomy and physiology. Provide at least two examples to demonstrate your understanding.

the structure and composition of parts of the body

a stable internal environment

science that studies the chemistry, biochemistry, and physics of the body’s functions

1.2 Structural Organization of the Human Body

By the end of this section, you will be able to: 

  • Identify the levels of organization in the human body.
  • Identify the key organ systems of the human body.
  • Recognize organs and major functions of each organ system.

Levels of Organization

Your body is built from very basic biological and chemical levels of organization. Molecules combine from various atoms and are constructed into larger macromolecules that develop into basic units known as cells. Cells build into specific tissues of the body. Various tissues combine to form organs. Organs perform essential functions that build and maintain homeostasis. Organs combine into organ systems that make up our fully functioning organism. Recognize in the following image how human and animal levels of organization are similar.

Figure 9(a) Levels of Biological Organization

atoms => molecules => macromolecules => cells => tissues => organs => organ systems => organism

Key Organ Systems

We begin with your Integumentary System which confines and protects internal body structures, and plays a major role in body temperature regulation through a matrix of sensory receptors that trigger your brain on exposure to the cold. This system also includes the accessory organs of skin, hair, and nails. Your Skeletal System consists of bones and a wide assortment of connective tissues that bind body parts together. Your Muscular System is arranged with over 600 skeletal muscles providing your body with potential energy and heat. Smooth muscle tissues help in the fluid movement of nutrients throughout your organs, such as moving food through your digestive tract. Your Nervous System consists of your brain, your spinal cord, and peripheral nerves, such as the axon that carries a nerve impulse out to your pectorals, biceps, and triceps (and others) to perform pushups.  Your Endocrine System helps manage many body processes through glands and hormones. For example, when triggered by the autonomic nervous system, exocrine glands such as the pancreas secrete insulin to help in the regulation of blood glucose, parathyroid glands balance calcium levels, adrenal glands on the kidney release cortisol when you are stressed, and apocrine glands release fluids through your skin through sweat to help cool your body after a long run.

Figure 9(b) Body Systems

Your cardiovascular system consists of a pumping heart and a vast network of tubular blood vessels. As lower leg muscles contract and move, they help squeeze blood back toward your heart through capillary networks and veins, against gravitational forces, to help maintain proper blood flow. Your heart pumps this blood to your lungs, where your respiratory system uses nasal passages, the trachea, and pulmonary alveoli in the lungs to exchange deoxgygenated blood for a fresh supply of oxygenated blood, then transports it back to your heart for delivery through arteries to keep you alive.  

Figure 9(c) Body Systems II

Your lymphatic system helps drain fluids from your tissues back into the blood from the thymus and spleen. It absorbs and transports fatty acids and chyme from digestion of food and transports white blood cells to and from lymph nodes into your bones.  The digestive system consists of your stomach, liver, gall bladder, and your large and small intestine. Your reproductive system produces sex hormones and cells to produce and support an embryo until birth. Each system of your body has a specific group of organs that unite with other organ systems to meet life and health needs of the organism. The organism is the highest level of organization in the living body. 

Think Out Loud 1.2

Create a chart that describes structure and function of each organ system. Give examples of specific organs that comprise each system.

Click on the link directly below to review the relationship of the hierarchy of your body, levels of organization, and the differences between anatomy and physiology.

The human body is comprised of different levels of organization, each one building upon the other. Smaller structures assemble, forming larger structures that work together to make up the fully functioning human organ system. It is important to recognize how distinctive human elements including organs and tissues form in the development of each of our body systems.

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Structural Organization

List the following in correct sequence from the smallest to the largest in terms of the levels of an organism: cell, organ, tissue, molecule, organelle, atom, organism, macromolecule, organ system.

1.3 Functions of Human Life

By the end of this section, you will be able to:

  • Recognize the significance of organization of the human organism.
  • Identify examples of human metabolism.
  • Identify key characteristics of life. 


Your body is a dynamic organism that depends entirely on how your cells function. An average adult, between ages of 18 - 65 has about 100 trillion unique cells, all of which work together in order to nurture optimum health. Cells are your simplest organisms, built from various chemicals and mini-cell structures that contribute to your physiological function. The total of all chemical and hormonal reactions in the body that either build up or tear down cell tissues is called your metabolism. You may hear people talking about how they have a fast or a slow body metabolism. But, body metabolism includes much more than just digesting your food. Your body can be organized into several intricate units, or systems, that are uniquely designed to perform complex functions in addition to digestion, such as reproducing, repairing tissues, staying healthy and alive. 

​Each body organ system has a unique function and a distinct role to fulfill in the physiology of a living organism. The following functions will illustrate some vital characteristics that help describe and are similar in every living organism: organization, metabolism, responsiveness, movement, development, and reproduction. In this chapter we will introduce several characteristic reactions that contribute to our ability to sustain life, making up our body's metabolism. We begin with the highest level of organization and progress through smaller levels until we reach the cellular level. 


The first law of thermodynamics states that "energy can neither be created nor destroyed—it will only change form". Cells require energy and information to assemble and shape the body. Inside cells, a host of chemical series of events break down nutrients to release the energy in their chemical bonds and also to build larger molecules in order to store vital human energy. Cells use some of this energy to make a copy of the genetic material as it divides and to access genetic codes in order to construct proteins from the basic building blocks of amino acids. Anabolism and catabolism are two kinds of chemical reactions that carry out such human construction. 

Anabolism is the buildup of larger biomolecules from smaller ones.  Through this reaction, the body can synthesize intricate chemicals it needs by integrating small molecules extracted from the foods you eat, like carbohydrates and proteins. Catabolism is the breakdown of larger molecules into smaller ones, thereby releasing energy. Take about 10 minutes to view the following YouTube video on the comparison of the your body's two processes of anabolism and catabolism.

Metabolism is the sum of all chemical reactions that take place in the body. (Fig. 11) Both of these chemical reactions occur in unison and occur uninterrupted to keep you alive and kicking. However, most people use the term metabolism incorrectly for either anabolism or catabolism.

Human beings depend on four basic biomolecules known as macromolecules...proteins, fats, carbohydrates, and nucleic acids (DNA and RNA). As discussed in this video lesson, metabolism includes all the body's processes used to sustain these biomolecules through our use of food. Bodies break down foods into component parts, releasing energy, and then the body harnesses this energy to build and grow new tissues.  Metabolism will be covered in more detail later in Chapter 2.

Think Out Loud 1.3

Explain metabolism. Give examples.

Key Characteristics of Life


Responsiveness is your natural capacity to detect change and adapt to such change. An example of sensitivity to an external stimulus may include a flight (flee or bolt), fright (shock or panic), or fight (battle or confrontation) response, requiring the release of certain hormones. The body's autonomic nervous system controls such change by either sympathetic or parasympathetic responses. Perceived changes to your internal environment, such as an increase in body temperature will cause vasodilation of your blood vessels, causing a physiological reaction of perspiring or sweating in order to reduce your core temperature. Glands in the skin of runners (Fig. 10) secrete visible sweat from pores on the athletes' foreheads, chest, and appendages, cooling the body, allowing for internal mechanisms to keep body temperature within a constant range.

Figure 10 Runners demonstrate responsiveness in sweating during a run.


​You move constantly. Even in your sleep your body changes position. Fluids circulate. Body limbs shift around, flopping over pillows, to find more comfortable sleep in order to enter REM sleep so that you are rested for the next day. Movement of intestines is best described as the rhythmic or peristaltic action of smooth muscle during digestion. These examples demonstrate rather unconscious movements.  Many other such involuntary automatic functions occur at every interval throughout your day to help regulate your metabolism.  

Likewise, the voluntary action of your skeletal muscle groups empower you to breath deeper, naturally circulating better bloodflow by squeezing your muscles and pushing blood through your vessels, providing the oxygen you must have to function. Mindfully, you voluntarily contract your quadriceps muscles, which extend your leg bones to move you one more step forward in a road race. You activate abdominal stabilizer muscles when you rotate your torso when performing a Russian Twist You use tension in your brachialis and brachioradialis near your elbow joint to help you move your forearms as you perform a pull-up. 

Development, Growth, & Reproduction

Development can be described as the process of change within the organism. For example, when osteoprogenitor cells in cartilagenous tissue begin to grow and change into a more specialized form of osseous tissue, eventually cartilage becomes hardened bone. Cellular differentiation occurs many times and in various ways throughout the body and helps to illustrate the concept of human growth and development. Growth can be characterized by enlargement of an organ or its tissues from an increase in cell size. A good example of growth, in the health and fitness world, is how skeletal muscle can begin to increase in size of myofibrils  from an increase in intensity of resistance training exercises, creating a greater muscle mass, or increasing glycogen stores to develop more lean muscle mass. Glycogen is the primary storage form of glucose in animal cells. Most glycogen in the human body is stored in the liver (about 10%), whereas muscle contains a relatively low amount of glycogen (1%). Only small amounts can be found in certain glial cells of the brain. When you run, your body uses a mixture of carbohydrates and fats. Your body stores carbohydrate as glycogen. The fitter you are, the more glycogen your body will store, thus allowing for better breakdown when needed by the body.

Reproduction is the formation of a new organisms. Human reproduction is sustained by the male and female reproductive systems. Since death is inevitable in all living organisms, without reproduction, the series of organisms would end.

Digestion, Absorption and Excretion

Digestion is how your body utilizes the foods we ingest. For example, your body digests the proteins from the eggs and bacon you ate this morning into a more useable form called amino acids.  Amino acids that your body can synthesize are termed nonessential proteins; those that the body cannot synthesize and must obtain from your diet are essential amino acids. All twenty amino acids must be present in your body at the same time to provide the raw materials for growth and tissue repair. So, if just one type of essential amino acid is absent from your diet, normal protein synthesis cannot occur.

Absorption must occur in order for your body to actually build and repair tissues. In malabsorption, the small intestine will not absorb nutrients. This physical issue can occur for various reasons, one in particular from an abnormal reaction to gluten. Celiac disease may damage the microvilli in the intestine, reducing the surface area required for the normal absorption of food. Although the prevalence of celiac disease strikes only about 1% of people, many food companies are now providing a healthy alternative for people with products that do not contain wheat, barley, and rye.

Your small intestine bears the responsibility for absorbing most of the intake of food. Blending movements and peristaltic waves push and churn the contents squeezed from your stomach. Contractions fragment chyme into smaller portions and sweep the churned substances slowly through intestinal walls. There are several mechanisms in the human body which allow for the intestinal absorption by cells of food nutrients. We will discuss passive and active mechanisms for absorption in later chapters. 

Excretion is the removal of excessive or toxic fluids from the body. Your cells are vital to your metabolism and ensure your survival. But your cells also manufacture a range of toxic substances if allowed to accumulate inside of you. Blood and lymphtransport such waste from tissues that produce them and remove fluids to the outside of your body. Likewise, your respiratory system removes gaseous wastes from the blood where urine restores normal concentrations of water and electrolytes within body fluids, helping to maintain a proper pH.

Respiration, Circulation, and Assimilation

Your body cells require oxygen to break down nutrients in order to release energy and produce stores of ATP. Excreting carbon dioxide and obtaining vital oxygen are the key functions of the mechanism of respiration. The events of respiration will be covered in later chapters. Oxygenation of your blood and  removal of carbon dioxide assists all the other systems of your body by helping blood circulate. The structure of your upper respiratory tract includes your nose, nasal cavity, paranasal sinuses, pharynx, and larynx. The lower structure consists of your trachea, bronchial tree and lungs. Each serves a purpose in the movement of gases and the circulation of oxygenated blood. 

Assimilation is the incorporation of nutrients into your body system after absorption of nutrients from food takes place. After digestion, the intestines work to transform biological tissues and fluids. Assimilation occurs in every cell of your body to help develop new cells.

So, let's take a closer look at how anabolism and catabolism actually work in your body to sustain many of the characteristics of life discussed in this chapter.  Take about eight minutes to listen to this Khan Academy podcast. When you have finished, respond to the Let's Practice questions found below. 

​​Most metabolic processes that occur in the human body operate nonstop and in unconscious mode. These processes build, preserve, and sustain your life. Such operations include organization, maintenance of essential body boundaries, metabolism, energy transfer via anabolic and catabolic reactions, responsiveness, movement, growth, differentiation, respiration, reproduction, and renewal. Metabolism then, is the sum total of all the chemical reactions in a body that break substances down and build them up. The reactions of metabolism equip our bodies to acquire and apply energy to sustain all of life's processes.  


What site in the body is responsible for monitoring and regulating overall metabolic state?









maintenance of glucose levels

What organ is predominately the storage depot for glycogen, and responsible for maintaining normal blood glucose levels?








small intestine

dependence on glucose

What organ is solely dependent on blood glucose for its energy source?









stored energy

What is the site of the majority of your body's stored energy?






adipose tissue




Which type of tissue varies greatly in its tremendous energy needs?




adipose tissue






Where does the final place for digestion and absorption of dietary sources occur?




small intestine





anabolism - chemical reactions that synthesis molecules 

catabolism - biochemical reactions that break down molecules 

development - process of developing or being developed

growth - process of increasing in physical size

metabolism - all of the chemical processes that occur to maintain life

responsiveness - adaptability to changes in the immediate environment

(1) Image courtesy of author MADobbs photo collection.

(2) Image courtesy of Geralt under CC0 1.0 via Pixabay.

​(3) image courtesy of Shauking under CC0 1.0via Pixabay.

(4) Image courtesy of Geralt under CC0 1.0 via Pixabay.

(5) Image courtesy of ArtsyBee under CC0 1.0 via Pixabay.

(6) Image courtesy of Jan van Calcar under CC by 4.0 Wikimedia Commons

(7) Image courtesy of  Welcome Library  under CC0 by 4.0 Wikimedia commons

(8) a.) Image courtesy of Prylarer under CC0 1.0 via Pixabay.

  b.) Image courtesy of Skeeze under CC0 1.0 via Pixabay

(9)  a.) Image courtesy of Mikala14 for CC0-BY-SA for Creative Commons

       b.) Image courtesy of Connexions for CC0-BY-SA for Creative Commons

       c.) Image courtesy of Connexions for CC0-BY-SA for Creative Commons

(10) Image courtesy of Petterijokela for Pixabay CC0 1.0
Of, relating to, or being an anatomical structure that is between two other similar structures or that is midway in position; middle.
the tendency toward a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes.
The transverse abdominal muscle (TVA), also known as the transverse abdominis, transversalis muscle and transversus abdominis muscle, is a muscle layer of the anterior and lateral (front and side) abdominal wall which is deep to (layered below) the internal oblique muscle.
The internal oblique muscle is a muscle in the abdominal wall that lies below the external oblique and just above the transverse abdominal muscles.
each of a pair of long flat muscles at the front of the abdomen, joining the sternum to the pubis and acting to bend the whole body forward or sideways.
a milky fluid consisting of fat droplets and lymph. It drains from the lacteals of the small intestine into the lymphatic system during digestion.
An individual form of life, such as a plant, an animal, a bacterium, a protist, or a fungus; a body made up of organs, organelles, or other parts that work together to carry on the various processes of life
The whole range of biochemical processes that occur within a living organism. Metabolism consists of anabolism (the buildup of substances) and catabolism (the breakdown of substances). The term metabolism is commonly used to refer specifically to the breakdown of food and its transformation into energy.
The building up in the body of complex chemical compounds from smaller simpler compounds (for example, proteins from amino acids), usually with the use of energy.
destructive metabolism involving the release of energy and resulting in the breakdown of complex materials within the organism.
Four main types of organic molecules predominate in living organisms: carbohydrates (polymers of simple sugars) lipids (fatty acids linked by glycerol) polypeptides (made of amino acids) nucleic acids (DNA or RNA - polymers of nucleotides)
a kind of sleep that occurs at intervals during the night and is characterized by rapid eye movements, more dreaming and bodily movement, and faster pulse and breathing.
You probably know what the Russian twist looks like: Sit with your torso leaning back at a 45-degree angle, knees bent, and your feet either on the floor or elevated a few inches. In most variations you hold something in front of your chest, usually a medicine ball or weight plate.
The brachialis (brachialis anticus) is a muscle in the upper arm that flexes the elbow joint. It lies deeper than the biceps brachii, and makes up part of the floor of the region known as the cubital fossa.
The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm.
The study of the structural changes of an individual from fertilization to adulthood.
A mesenchymal stem cell that can undergo mitotic division and differentiate into an osteoblast. Osteoprogenitor cells are located in the inner cellular layer of the periosteum, the endosteum and lining osteonic canals. ... They also differentiate into osteoblasts during the continuous process of bone remodeling.
Cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. ... Differentiation occurs many times during the development of a multicellular organism. The organism changes from a single zygote to a complex system of tissues and cell types.
any of the elongated contractile threads found in striated muscle cells.
a substance deposited in bodily tissues as a store of carbohydrates. It is a polysaccharide that forms glucose on hydrolysis.
The sexual or asexual process by which organisms generate new individuals of the same kind; procreation
The process by which food is broken down into simple chemical compounds that can be absorbed and used as nutrients or eliminated by the body. In most animals, nutrients are obtained from food by the action of digestive enzymes. In humans and other higher vertebrates, digestion takes place mainly in the small intestine.
Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the various amino acids are produced from other compounds. The substrates for these processes are various compounds in the organism's diet or growth media
During digestion and absorption, protein passes through many organs. Once protein is digested, the body can utilize its nutrients to build and repair many of the cells in the body
a disease in which the small intestine is hypersensitive to gluten, leading to difficulty in digesting food.
the pulpy acidic fluid that passes from the stomach to the small intestine, consisting of gastric juices and partly digested food.
a colorless fluid containing white blood cells, that bathes the tissues and drains through the lymphatic system into the bloodstream.
the absorption and digestion of food or nutrients by the body or any biological system.