Organization and General Plan of the Body PDF

01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 4 Copyright © 2007 by F. A. Davis. 4 Organization and General Plan of the Body T he human body is a precisely structured container of chemical reactions. Have you ever thought of your- that your knowledge of anatomy and physiology will become the basis for your further study in the health self in this way? Probably not, and yet, in the strictly professions. physical sense, that is what each of us is. The body consists of trillions of atoms in speciﬁc arrangements and thousands of chemical reactions proceeding in LEVELS OF ORGANIZATION a very orderly manner. That literally describes us, and yet it is clearly not the whole story. The keys The human body is organized into structural and to understanding human consciousness and self- functional levels of increasing complexity. Each higher awareness are still beyond our grasp. We do not yet level incorporates the structures and functions of the know what enables us to study ourselves—no other previous level, as you will see. We will begin with the animals do, as far as we know—but we have accumu- simplest level, which is the chemical level, and pro- lated a great deal of knowledge about what we are ceed to cells, tissues, organs, and organ systems. All of made of and how it all works. Some of this knowledge the levels of organization are depicted in Fig. 1–1. makes up the course you are about to take, a course in basic human anatomy and physiology. CHEMICALS Anatomy is the study of body structure, which The chemicals that make up the body may be divided includes size, shape, composition, and perhaps even into two major categories: inorganic and organic. coloration. Physiology is the study of how the body Inorganic chemicals are usually simple molecules functions. The physiology of red blood cells, for exam- made of one or two elements other than carbon (with ple, includes what these cells do, how they do it, and a few exceptions). Examples of inorganic chemicals are how this is related to the functioning of the rest of the water (H2O); oxygen (O2); one of the exceptions, car- body. Physiology is directly related to anatomy. For bon dioxide (CO2); and minerals such as iron (Fe), cal- example, red blood cells contain the mineral iron in cium (Ca), and sodium (Na). Organic chemicals are molecules of the protein called hemoglobin; this is an often very complex and always contain the elements aspect of their anatomy. The presence of iron enables carbon and hydrogen. In this category of organic red blood cells to carry oxygen, which is their function. chemicals are carbohydrates, fats, proteins, and All cells in the body must receive oxygen in order to nucleic acids. The chemical organization of the body function properly, so the physiology of red blood cells is the subject of Chapter 2. is essential to the physiology of the body as a whole. Pathophysiology is the study of disorders of func- CELLS tioning, and a knowledge of normal physiology makes such disorders easier to understand. For example, you The smallest living units of structure and function are are probably familiar with the anemia called iron- cells. There are many different types of human cells, deﬁciency anemia. With insufficient iron in the diet, though they all have certain similarities. Each type of there will not be enough iron in the hemoglobin of cell is made of chemicals and carries out speciﬁc red blood cells, and hence less oxygen will be trans- chemical reactions. Cell structure and function are ported throughout the body, resulting in the symp- discussed in Chapter 3. toms of the iron-deﬁciency disorder. This example shows the relationship between anatomy, physiology, TISSUES and pathophysiology. A tissue is a group of cells with similar structure and The purpose of this text is to enable you to gain function. There are four groups of tissues: an understanding of anatomy and physiology with the emphasis on normal structure and function. Many Epithelial tissues—cover or line body surfaces; some examples of pathophysiology have been included, are capable of producing secretions with speciﬁc however, to illustrate the relationship of disease to functions. The outer layer of the skin and sweat normal physiology and to describe some of the proce- glands are examples of epithelial tissues. Internal dures used in the diagnosis of disease. Many of the epithelial tissues include the walls of capillaries examples are clinical applications that will help you (squamous epithelium) and the kidney tubules begin to apply what you have learned and demonstrate (cuboidal epithelium), as shown in Fig. 1–1. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 5 Copyright © 2007 by F. A. Davis. 1. Chemical Level 2. Cellular Level Cuboidal epithelium Squamous epithelium Smooth muscle 3. Tissue Level Kidney Urinary bladder 4. Organ Level Urinary system 6. Organism Level 5. Organ System Level Figure 1–1. Levels of structural organization of the human body, depicted from the simplest (chemical) to the most complex (organism). The organ system shown here is the urinary system. QUESTION: What other organ system seems to work directly with the urinary system? 5 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 6 Copyright © 2007 by F. A. Davis. 6 Organization and General Plan of the Body Connective tissues—connect and support parts of and stomach. The kidneys contain several kinds of the body; some transport or store materials. Blood, epithelial, or surface tissues, for their work of absorp- bone, cartilage, and adipose tissue are examples of tion. The stomach is lined with epithelial tissue that this group. secretes gastric juice for digestion. Smooth muscle Muscle tissues—specialized for contraction, which tissue in the wall of the stomach contracts to mix brings about movement. Our skeletal muscles and food with gastric juice and propel it to the small intes- the heart are examples of muscle tissue. In Fig. 1–1, tine. Nerve tissue carries impulses that increase or you see smooth muscle tissue, which is found in decrease the contractions of the stomach (see Box 1–1: organs such as the urinary bladder and stomach. Replacing Tissues and Organs). Nerve tissue—specialized to generate and transmit ORGAN SYSTEMS electrochemical impulses that regulate body func- tions. The brain and optic nerves are examples of An organ system is a group of organs that all con- nerve tissue. tribute to a particular function. Examples are the uri- nary system, digestive system, and respiratory system. The types of tissues in these four groups, as well as In Fig. 1–1 you see the urinary system, which consists their speciﬁc functions, are the subject of Chapter 4. of the kidneys, ureters, urinary bladder, and urethra. These organs all contribute to the formation and ORGANS elimination of urine. An organ is a group of tissues precisely arranged so as As a starting point, Table 1–1 lists the organ sys- to accomplish speciﬁc functions. Examples of organs tems of the human body with their general functions, are the kidneys, individual bones, the liver, lungs, and some representative organs, and Fig. 1–2 depicts BOX 1–1 REPLACING TISSUES AND ORGANS Blood transfusions are probably the most familiar eventually be used to cover a large surface. Other and frequent form of “replacement parts” for peo- cells grown in culture include cartilage, bone, pan- ple. Blood is a tissue, and when properly typed and creas, and liver. Much research is being done on cross-matched (blood types will be discussed in liver implants (not transplants), clusters of func- Chapter 11) may safely be given to someone with tional liver cells grown in a lab. Such implants the same or a compatible blood type. would reduce or eliminate the need for human Organs, however, are much more complex struc- donors. Tissue engineering is also being used to cre- tures. When a patient receives an organ transplant, ate arteries and urinary bladders. there is always the possibility of rejection (destruc- Many artiﬁcial replacement parts have also been tion) of the organ by the recipient’s immune sys- developed. These are made of plastic or metal and tem (Chapter 14). With the discovery and use of are not rejected as foreign by the recipient’s more effective immune-suppressing medications, immune system. Damaged heart valves, for exam- however, the success rate for many types of organ ple, may be replaced by artiﬁcial ones, and sections transplants has increased. Organs that may be trans- of arteries may be replaced by tubular grafts made planted include corneas, kidneys, the heart, the of synthetic materials. Artiﬁcial joints are available liver, and the lungs. for every joint in the body, as is artiﬁcial bone for The skin is also an organ, but skin transplanted reconstructive surgery. Cochlear implants are tiny from another person will not survive very long. instruments that convert sound waves to electrical Several kinds of artiﬁcial skin are now available to impulses the brain can learn to interpret, and have temporarily cover large areas of damaged skin. provided some sense of hearing for people with cer- Patients with severe burns, for example, will even- tain types of deafness. Work is also progressing on tually need skin grafts from their own unburned the use of a featherweight computer chip as an arti- skin to form permanent new skin over the burn ﬁcial retina, on devices that help damaged hearts sites. It is possible to “grow” a patient’s skin in lab- pump blood more efficiently, and on small, self- oratory culture, so that a small patch of skin may contained artiﬁcial hearts. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 7 Copyright © 2007 by F. A. Davis. Organization and General Plan of the Body 7 Table 1–1 THE ORGAN SYSTEMS System Functions Organs* Integumentary Is a barrier to pathogens and chemicals skin, subcutaneous tissue Prevents excessive water loss Skeletal Supports the body bones, ligaments Protects internal organs and red bone marrow Provides a framework to be moved by muscles Muscular Moves the skeleton muscles, tendons Produces heat Nervous Interprets sensory information brain, nerves, eyes, ears Regulates body functions such as movement by means of electrochemical impulses Endocrine Regulates body functions such as growth and reproduc- thyroid gland, pituitary tion by means of hormones gland, pancreas Regulates day-to-day metabolism by means of hormones Circulatory Transports oxygen and nutrients to tissues and removes heart, blood, arteries waste products Lymphatic Returns tissue ﬂuid to the blood spleen, lymph nodes Destroys pathogens that enter the body and provides immunity Respiratory Exchanges oxygen and carbon dioxide between the air lungs, trachea, larynx, and blood diaphragm Digestive Changes food to simple chemicals that can be absorbed stomach, colon, liver, and used by the body pancreas Urinary Removes waste products from the blood kidneys, urinary bladder, Regulates volume and pH of blood and tissue ﬂuid urethra Reproductive Produces eggs or sperm Female: ovaries, uterus In women, provides a site for the developing Male: testes, prostate gland embryo-fetus *These are simply representative organs, not an all-inclusive list. all of the organ systems. Some organs are part of two of life. The pumping of the heart, the digestion of organ systems; the pancreas, for example, is both a food in the stomach, the diffusion of gases in the lungs digestive and an endocrine organ, and the diaphragm and tissues, and the production of energy in each cell is part of both the muscular and respiratory systems. of the body are just a few of the thousands of aspects All of the organ systems make up an individual person. of metabolism. Metabolism comes from a Greek word The balance of this text discusses each system in more meaning “change,” and the body is always changing in detail. visible ways (walking down the street), microscopic ways (cells dividing in the skin to produce new epider- mis), and submicroscopic or molecular ways (RNA METABOLISM AND HOMEOSTASIS and enzymes constructing new proteins). A related concept, metabolic rate, is most often used to mean Metabolism is a collective noun; it is all of the chem- the speed at which the body produces energy and heat, ical reactions and physical processes that take place or, put another way, energy production per unit of within the body. Metabolism includes growing, repair- time, such as 24 hours. Metabolic rate, therefore, is ing, reacting, and reproducing—all the characteristics one aspect of metabolism. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 8 Copyright © 2007 by F. A. Davis. Muscular system Nervous system Skeletal system Integumentary system Circulatory system Figure 1–2. Organ systems. Compare the depiction of each system to its description in Table 1–1. QUESTION: Name at least one organ shown in each system. 8 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 9 Copyright © 2007 by F. A. Davis. Urinary system Endocrine system Respiratory system Digestive system Lymphatic system Reproductive system Figure 1–2. (Continued) 9 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 10 Copyright © 2007 by F. A. Davis. 10 Organization and General Plan of the Body A person who is in good health may be said to be in heat production is detected by the brain and pituitary a state of homeostasis. Homeostasis reﬂects the abil- gland. They then decrease secretion of their hor- ity of the body to maintain a relatively stable metabo- mones, which in turn inhibits any further secretion of lism and to function normally despite many constant thyroxine until the metabolic rate decreases again. changes. The changes that are part of normal metab- Metabolic rate does rise and fall, but is kept within olism may be internal or external, and the body must normal limits. respond appropriately. You may be wondering if there is such a thing as a Eating breakfast, for example, brings about an positive feedback mechanism. There is, but they are internal change. Suddenly there is food in the stom- rare in the body and quite different from a negative ach, and something must be done with it. What hap- feedback mechanism. In a positive feedback mecha- pens? The food is digested or broken down into nism, the response to the stimulus does not stop or simple chemicals that the body can use. The protein in reverse the stimulus, but instead keeps the sequence of a hard-boiled egg is digested into amino acids, its basic events going. A good example is childbirth, in which chemical building blocks; these amino acids can then the sequence of events, simply stated, is as follows: be used by the cells of the body to produce their own Stretching of the uterine cervix stimulates secretion of specialized proteins. the hormone oxytocin by the posterior pituitary gland. An example of an external change is a rise in envi- Oxytocin stimulates contraction of the uterine muscle, ronmental temperature. On a hot day, the body tem- which causes more stretching, which stimulates more perature would also tend to rise. However, body oxytocin and, hence, more contractions. The mecha- temperature must be kept within its normal range of nism stops with the delivery of the baby and the pla- about 97⬚ to 99⬚F (36⬚ to 38⬚C) in order to support centa. This is the “brake,” the interrupting event. normal functioning. What happens? One of the body’s Any positive feedback mechanism requires an responses to the external temperature rise is to external “brake,” something to interrupt it. Blood increase sweating so that excess body heat can be lost clotting is such a mechanism, and without external by the evaporation of sweat on the surface of the skin. controls, clotting may become a vicious cycle of clot- This response, however, may bring about an undesir- ting and more clotting, doing far more harm than able internal change, dehydration. What happens? As good (discussed in Chapter 11). Inﬂammation follow- body water decreases, we feel the sensation of thirst ing an injury is beneﬁcial and necessary for repair to and drink ﬂuids to replace the water lost in sweating. begin, but the process may evolve into a cycle of dam- Notice that when certain body responses occur, they age and more damage. The rise of a fever may also reverse the event that triggered them. In the preced- trigger a positive feedback mechanism. Notice in Fig. ing example a rising body temperature stimulates 1–3 that bacteria have affected the body’s thermostat increased sweating, which lowers body temperature, in the hypothalamus and caused a fever. The rising which in turn decreases sweating. Unnecessary sweat- body temperature increases the metabolic rate, which ing that would be wasteful of water is prevented. This increases body temperature even more, becoming a is an example of a negative feedback mechanism, in cycle. Where is the inhibition, the brake? For this which the body’s response reverses the stimulus (in infection, the brake is white blood cells destroying the effect, turning it off for a while) and keeps some aspect bacteria that caused the fever. An interruption from of the body metabolism within its normal range. outside the cycle is necessary. It is for this reason, Look at Fig. 1–3 for another negative feedback because positive feedback mechanisms have the poten- mechanism, one in which the hormone thyroxine reg- tial to be self-perpetuating and cause harm, that they ulates the metabolic rate of the body. As metabolic are rare in the body. rate decreases, the hypothalamus (part of the brain) Negative feedback mechanisms, however, contain and pituitary gland detect this decrease and secrete their own brakes in that inhibition is a natural part of hormones to stimulate the thyroid gland (on the front the cycle, and the body has many of them. The secre- of the neck just below the larynx) to secrete the hor- tion of most hormones (Chapter 10) is regulated by mone thyroxine. Thyroxine stimulates the cellular negative feedback mechanisms. The regulation of enzyme systems that produce energy from food, which heart rate (Chapter 12) and blood pressure (Chapter increases the metabolic rate. The rise in energy and 13) involves several negative feedback mechanisms. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 11 Copyright © 2007 by F. A. Davis. Organization and General Plan of the Body 11 A Hypothalamus Thyroid gland and pituitary gland Cells decrease No longer Metabolic Thyroxine energy stimulates rate decreases production thyroid gland increases Hypothalamus and pituitary gland Thyroid gland Metabolic Stimulates Cells increase Thyroxine rate thyroid energy increases decreases gland production B Hypothalamus Cells increase Metabolic heat Fever rate production increases Heat gain Bacteria mechanisms White blood cells Key: Stimulates Inhibits Leads to Figure 1–3. Feedback mechanisms. (A) The negative feedback mechanism of regulation of metabolic rate by thyroxine. (B) The positive feedback mechanism triggered by a fever. See text for description. QUESTION: For each mechanism, where is the source of the “brake” or inhibition? The result of all of these mechanisms working to- of the human body, keep in mind that the proper func- gether is that all aspects of body functioning, that is, of tioning of each organ and organ system contributes to metabolism, are kept within normal limits, a steady homeostasis. Keep in mind as well that what we call state or equilibrium. This is homeostasis. the normal values of metabolism are often ranges, not In the chapters to come, you will ﬁnd many more single numbers. Recall that normal body temperature examples of homeostasis. As you continue your study is a range: 97⬚ to 99⬚F (36⬚ to 38⬚C). Normal pulse 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 12 Copyright © 2007 by F. A. Davis. 12 Organization and General Plan of the Body rate, another example, is 60 to 80 beats per minute; a Table 1–2 DESCRIPTIVE TERMS FOR normal respiratory rate is 12 to 20 breaths per minute. BODY PARTS AND AREAS Variations within the normal range are part of normal metabolism. Term Deﬁnition (Refers to) Antebrachial forearm Antecubital front of elbow TERMINOLOGY AND GENERAL Axillary armpit PLAN OF THE BODY Brachial upper arm Buccal (oral) mouth As part of your course in anatomy and physiology, Cardiac heart Cervical neck you will learn many new words or terms. At times you Cranial head may feel that you are learning a second language, and Cutaneous skin indeed you are. Each term has a precise meaning, Deltoid shoulder which is understood by everyone else who has learned Femoral thigh the language. Mastering the terminology of your pro- Frontal forehead Gastric stomach fession is essential to enable you to communicate effec- Gluteal buttocks tively with your coworkers and your future patients. Hepatic liver Although the number of new terms may seem a bit Iliac hip overwhelming at ﬁrst, you will ﬁnd that their use soon Inguinal groin becomes second nature to you. Lumbar small of back Mammary breast The terminology presented in this chapter will be Nasal nose used throughout the text in the discussion of the organ Occipital back of head systems. This will help to reinforce the meanings of Orbital eye these terms and will transform these new words into Parietal crown of head knowledge. Patellar kneecap Pectoral chest Pedal foot BODY PARTS AND AREAS Perineal pelvic ﬂoor Plantar sole of foot Each of the terms listed in Table 1–2 and shown in Popliteal back of knee Fig. 1–4 refers to a speciﬁc part or area of the body. Pulmonary lungs For example, the term femoral always refers to the Renal kidney thigh. The femoral artery is a blood vessel that passes Sacral base of spine through the thigh, and the quadriceps femoris is a Scapular shoulder blade Sternal breastbone large muscle group of the thigh. Temporal side of head Another example is pulmonary, which always refers Umbilical navel to the lungs, as in pulmonary artery, pulmonary edema, Volar (palmar) palm and pulmonary embolism. Although you may not know the exact meaning of each of these terms now, you do know that each has something to do with the lungs. these are pairs of terms and that each pair is a set of opposites. This will help you recall the terms and their TERMS OF LOCATION AND POSITION meanings. When describing relative locations, the body is always BODY CAVITIES AND assumed to be in anatomic position: standing upright THEIR MEMBRANES facing forward, arms at the sides with palms forward, and the feet slightly apart. The terms of location are The body has two major cavities: the dorsal cavity listed in Table 1–3, with a deﬁnition and example for (posterior) and the ventral cavity (anterior). Each of each. As you read each term, ﬁnd the body parts used these cavities has further subdivisions, which are as examples in Figs. 1–4 and 1–5. Notice also that shown in Fig. 1–5. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 13 Copyright © 2007 by F. A. Davis. Organization and General Plan of the Body 13 Body Parts and Areas Anatomic position Cranial Frontal Parietal Orbital Temporal Nasal Occipital Buccal Cervical Sternal Deltoid Pectoral Scapular Axillary Mammary Brachial Antecubital Antebrachial Lumbar Umbilical Iliac Sacral Inguinal Femoral Gluteal Volar Perineal Popliteal Patellar Pedal Plantar A B Figure 1–4. Body parts and areas. The body is shown in anatomic position. (A) Anterior view. (B) Posterior view. (Compare with Table 1–2.) QUESTION: Name a body area that contains a bone with a similar name. Can you name two more? Dorsal Cavity Ventral Cavity The dorsal cavity contains the central nervous system, The ventral cavity consists of two compartments, the and consists of the cranial cavity and the vertebral or thoracic cavity and the abdominal cavity, which are spinal cavity. The dorsal cavity is a continuous one; separated by the diaphragm. The diaphragm is a large, that is, no wall or boundary separates its subdivisions. dome-shaped respiratory muscle. It has openings for The cranial cavity is formed by the skull and contains the esophagus and for large blood vessels, but other- the brain. The spinal cavity is formed by the backbone wise is a wall between the thoracic and abdominal cav- (spine) and contains the spinal cord. The membranes ities. The pelvic cavity may be considered a that line these cavities and cover the brain and spinal subdivision of the abdominal cavity (there is no wall cord are called the meninges. between them) or as a separate cavity. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 14 Copyright © 2007 by F. A. Davis. Table 1–3 TERMS OF LOCATION AND POSITION Term Deﬁnition Example Superior above, or higher The heart is superior to the liver. Inferior below, or lower The liver is inferior to the lungs. Anterior toward the front The chest is on the anterior side of the body. Posterior toward the back The lumbar area is posterior to the umbilical area. Ventral toward the front The mammary area is on the ventral side of the body. Dorsal toward the back The buttocks are on the dorsal side of the body. Medial toward the midline The heart is medial to the lungs. Lateral away from the midline The shoulders are lateral to the neck. Internal within, or interior to The brain is internal to the skull. External outside, or exterior to The ribs are external to the lungs. Superﬁcial toward the surface The skin is the most superﬁcial organ. Deep within, or interior to The deep veins of the legs are surrounded by muscles. Central the main part The brain is part of the central nervous system. Peripheral extending from the main part Nerves in the arm are part of the peripheral nervous system. Proximal closer to the origin The knee is proximal to the foot. Distal farther from the origin The palm is distal to the elbow. Parietal pertaining to the wall of a cavity The parietal pleura lines the chest cavity. Visceral pertaining to the organs within a cavity The visceral pleura covers the lungs. Cranial cavity Foramen magnum Dorsal cavity Spinal cavity Thoracic cavity Figure 1–5. Body cavities (lateral view from the left side). Diaphragm QUESTION: Which of these cavities are surrounded by bone? Ventral Abdominal cavity cavity Sacral promontory Pelvic cavity Symphysis pubis 14 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 15 Copyright © 2007 by F. A. Davis. Organization and General Plan of the Body 15 Organs in the thoracic cavity include the heart and folded around and covering the outer surfaces of the lungs. The membranes of the thoracic cavity are abdominal organs. serous membranes called the pleural membranes. The pelvic cavity is inferior to the abdominal cav- The parietal pleura lines the chest wall, and the vis- ity. Although the peritoneum does not line the pelvic ceral pleura covers the lungs. The heart has its own set cavity, it covers the free surfaces of several pelvic of serous membranes called the pericardial mem- organs. Within the pelvic cavity are the urinary blad- branes. The parietal pericardium lines the ﬁbrous der and reproductive organs such as the uterus in pericardial sac, and the visceral pericardium covers the women and the prostate gland in men. heart muscle. Organs in the abdominal cavity include the liver, PLANES AND SECTIONS stomach, and intestines. The membranes of the abdominal cavity are also serous membranes called the When internal anatomy is described, the body or an peritoneum and mesentery. The peritoneum is the organ is often cut or sectioned in a speciﬁc way so as membrane that lines the entire abdominal wall, and to make particular structures easily visible. A plane is the mesentery is the continuation of this membrane, an imaginary ﬂat surface that separates two portions of - B A Figure 1–6. (A) Planes and sections of the body. (B) Cross-section and longitudinal sec- tion of the small intestine. QUESTION: What other organs would have sections that look like those of the small intes- tine? 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 16 Copyright © 2007 by F. A. Davis. 16 Organization and General Plan of the Body Front Stomach Liver Pancreas Gallbladder Colon Duodenum Spleen Ribs Aorta Left kidney Vertebra Inferior vena cava Spinal cord Right kidney Back Muscle C Figure 1–6. (Continued) (C) Transverse section through the upper abdomen. the body or an organ. These planes and sections are cian or nurse would want to know more precisely shown in Fig. 1–6 (see Box 1–2: Visualizing the where the pain was. To determine this, the abdomen Interior of the Body). may be divided into smaller regions or areas, which are shown in Fig. 1–7. Frontal (coronal) section—a plane from side to side separates the body into front and back portions. Quadrants—a transverse plane and a midsagittal Sagittal section—a plane from front to back separates plane that cross at the umbilicus will divide the the body into right and left portions. A midsagittal abdomen into four quadrants. Clinically, this is section creates equal right and left halves. probably the division used more frequently. The pain of gallstones might then be described as in the Transverse section—a horizontal plane separates the right upper quadrant. body into upper and lower portions. Nine areas—two transverse planes and two sagittal Cross-section—a plane perpendicular to the long planes divide the abdomen into nine areas: axis of an organ. A cross-section of the small intes- Upper areas—above the level of the rib cartilages are tine (which is a tube) would look like a circle with the left hypochondriac, epigastric, and right the cavity of the intestine in the center. hypochondriac. Longitudinal section—a plane along the long axis of Middle areas—the left lumbar, umbilical, and right an organ. A longitudinal section of the intestine is lumbar. shown in Fig. 1–6, and a frontal section of the Lower areas—below the level of the top of the pelvic femur (thigh bone) would also be a longitudinal bone are the left iliac, hypogastric, and right section (see Fig. 6–1 in Chapter 6). iliac. These divisions are often used in anatomic studies AREAS OF THE ABDOMEN to describe the location of organs. The liver, for exam- The abdomen is a large area of the lower trunk of the ple, is located in the epigastric and right hypochon- body. If a patient reported abdominal pain, the physi- driac areas. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 17 Copyright © 2007 by F. A. Davis. Organization and General Plan of the Body 17 A B Figure 1–7. Areas of the abdomen. (A) Four quadrants. (B) Nine regions. QUESTION: Are there any organs found in all four abdominal quadrants? nal changes. In the chapters that follow, you will ﬁnd SUMMARY detailed descriptions of the physiology of each organ As you will see, the terminology presented in this and organ system, and how the metabolism of each is chapter is used throughout the text to describe the necessary to homeostasis. We will now return to a anatomy of organs and the names of their parts. All consideration of the structural organization of the organs of the body contribute to homeostasis, the body and to more extensive descriptions of its levels of healthy state of the body that is maintained by con- organization. The ﬁrst of these, the chemical level, is stant and appropriate responses to internal and exter- the subject of the next chapter. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 18 Copyright © 2007 by F. A. Davis. 18 Organization and General Plan of the Body BOX 1–2 VISUALIZING THE INTERIOR OF THE BODY In the past, the need for exploratory surgery possible using any other technique. The patient brought with it hospitalization, risk of infection, and is placed inside a strong magnetic ﬁeld, and the discomfort and pain for the patient. Today, how- tissues are pulsed with radio waves. Because ever, several technologies and the extensive use of each tissue has different proportions of various computers permit us to see the interior of the body atoms, which resonate or respond differently, without surgery. each tissue emits a characteristic signal. A com- Computed tomography (CT) scanning uses a puter then translates these signals into an image; narrowly focused x-ray beam that circles rapidly the entire procedure takes 30 to 45 minutes. around the body. A detector then measures how Positron emission tomography (PET) scanning much radiation passes through different tissues, creates images that depict the rates of physio- and a computer constructs an image of a thin logical processes such as blood ﬂow, oxygen slice through the body. Several images may be usage, or glucose metabolism. The comparative made at different levels—each takes only a few rates are depicted by colors: Red represents the seconds—to provide a more complete picture of highest rate, followed by yellow, then green, and an organ or part of the body. The images are ﬁnally blue representing the lowest rate. much more detailed than are those produced by One drawback of these technologies is their cost; conventional x-rays. they are expensive. However, the beneﬁts to Magnetic resonance imaging (MRI) is another patients are great: Highly detailed images of the diagnostic tool that is especially useful for visual- body are obtained without the risks of surgery and izing soft tissues, including the brain and spinal with virtually no discomfort in the procedures them- cord. Recent reﬁnements have produced images selves. of individual nerve bundles, which had not been A B C Box Figure 1–A Imaging techniques. (A) CT scan of eye in lateral view showing a tumor (arrow) below the optic nerve. (B) MRI of midsagittal section of head (compare with Figs. 8–6 and 15–1). (C) PET scan of brain in transverse section (frontal lobes at top) showing glucose metabolism. (From Mazziotta, JC, and Gilman, S: Clinical Brain Imaging: Principles and Applications. FA Davis, Philadelphia, 1992, pp 27 and 298, with permission.) STUDY OUTLINE Introduction Levels of Organization 1. Anatomy—the study of structure. 1. Chemical—inorganic and organic chemicals make 2. Physiology—the study of function. up all matter, both living and non-living. 3. Pathophysiology—the study of disorders of func- 2. Cells—the smallest living units of the body. tioning. 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 19 Copyright © 2007 by F. A. Davis. Organization and General Plan of the Body 19 3. Tissues—groups of cells with similar structure and 2. Terms of location and position—used to describe function. relationships of position (see Table 1–3 and Figs. 4. Organs—groups of tissues that contribute to spe- 1–4 and 1–5). ciﬁc functions. 3. Body cavities and their membranes (see Fig. 1–5). 5. Organ systems—groups of organs that work Dorsal cavity—lined with membranes called together to perform speciﬁc functions (see Table meninges; consists of the cranial and vertebral cavities. 1–1 and Fig. 1–2). Cranial cavity contains the brain. 6. Person—all the organ systems functioning prop- Vertebral cavity contains the spinal cord. erly. Ventral cavity—the diaphragm separates the tho- racic and abdominal cavities; the pelvic cavity is Metabolism and Homeostasis inferior to the abdominal cavity. 1. Metabolism is the sum of all of the chemical and Thoracic cavity—contains the lungs and heart. physical changes that take place in the body. — Pleural membranes line the chest wall and Metabolic rate is the amount of energy and heat cover the lungs. production per unit of time. — Pericardial membranes surround the 2. Homeostasis is a state of good health maintained heart. by the normal metabolism (functioning) of the Abdominal cavity—contains many organs organ systems. including the stomach, liver, and intestines. 3. The body constantly responds to internal and — The peritoneum lines the abdominal cav- external changes, yet remains stable; its many ity; the mesentery covers the abdominal aspects of metabolism are kept within normal lim- organs. its (usually a range of values, not a single value). Pelvic cavity—contains the urinary bladder 4. Negative feedback mechanism—a control system and reproductive organs. in which a stimulus initiates a response that 4. Planes and sections—cutting the body or an organ reverses or reduces the stimulus, thereby stopping in a speciﬁc way (see Fig. 1–6). the response until the stimulus occurs again and Frontal or coronal—separates front and back there is a need for the response (see Fig. 1–3). parts. 5. Positive feedback mechanism—a control system Sagittal—separates right and left parts. that requires an external interruption or brake. Has Transverse—separates upper and lower parts. the potential to become a self-perpetuating and Cross—a section perpendicular to the long axis. harmful cycle, therefore is rare in the body (see Fig. Longitudinal—a section along the long axis. 1–3). 5. Areas of the abdomen—permits easier description of locations: Terminology and General Plan of the Body Quadrants—see Fig. 1–7. 1. Body parts and areas—see Table 1–2 and Fig. 1–4. Nine areas—see Fig. 1–7. REVIEW QUESTIONS 1. Explain how the physiology of a bone is related to a. Moves the skeleton its anatomy. Explain how the physiology of the b. Regulates body functions by means of hormones hand is related to its anatomy. (p. 4) c. Covers the body and prevents entry of 2. Describe anatomic position. Why is this knowl- pathogens edge important? (p. 12) d. Destroys pathogens that enter the body 3. Name the organ system with each of the following e. Exchanges oxygen and carbon dioxide between functions: (p. 7) the air and blood 01Scanlon(p3)-ch01 8/17/06 10:41 AM Page 20 Copyright © 2007 by F. A. Davis. 20 Organization and General Plan of the Body 4. Name the two major body cavities and their subdi- 9. Deﬁne organ. When a group of organs works visions. Name the cavity lined by the peritoneum, together, what name is it given? (p. 6) meninges, and parietal pleura. (pp. 13, 15) 10. Define metabolism, metabolic rate, and ho- 5. Name the four quadrants of the abdomen. Name at meostasis. (pp. 7, 10) least one organ in each quadrant. (p. 17) a. Give an example of an external change and 6. Name the section through the body that would explain how the body responds to maintain result in each of the following: equal right and left homeostasis halves, anterior and posterior parts, superior and b. Give an example of an internal change and inferior parts. (pp. 15–16) explain how the body responds to maintain homeostasis 7. Review Table 1–2, and try to ﬁnd each external area c. Brieﬂy explain how a negative feedback mech- on your own body. (pp. 12–13) anism works, and how a positive feedback 8. Deﬁne cell. When similar cells work together, what mechanism differs name are they given? (p. 4) FOR FURTHER THOUGHT 1. The human foot is similar to the human hand, but abdominal quadrant? (If you’re not sure, take a does have anatomic differences. Describe two of look at Fig. 16–1 in Chapter 16.) Surgery is usually these differences, and explain how they are related necessary to remove an inﬂamed appendix before it to the physiology of the hand and the foot. ruptures and causes peritonitis. Using your knowl- edge of the location of the peritoneum, explain why 2. Complete each statement using the everyday term peritonitis is a very serious condition. for the body part. a. The distal femoral area is immediately superior 5. Keep in mind your answer to Question 4, and to the ____. explain why bacterial meningitis can be a very seri- b. The proximal brachial area is immediately infe- ous infection. rior to the ____. c. The patellar area is directly proximal to the 6. Use a mental picture to cut the following sections. ____. Then describe in simple words what each section d. The volar area is directly distal to the ____. looks like, and give each a proper anatomic name. 3. Name a structure or organ that is both superior and First: a tree trunk cut top to bottom, then cut side inferior to the brain. Name one that is both ante- to side. rior and posterior. Second: a grapefruit cut top to bottom (straight 4. If a person has appendicitis (inﬂammation of the down from where the stem was attached), then appendix caused by bacteria), pain is felt in which sliced through its equator. 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 24 Copyright © 2007 by F. A. Davis. 24 Some Basic Chemistry W hen you hear or see the word chemistry, you may think of test tubes and Bunsen burners in a laboratory Table 2–1 ELEMENTS IN THE HUMAN BODY experiment. However, literally everything in our phys- Percent of ical world is made of chemicals. The paper used for Atomic the Body Elements Symbol Number* by Weight this book, which was once the wood of a tree, is made of chemicals. The air we breathe is a mixture of chem- Hydrogen H 1 9.5 icals in the form of gases. Water, gasoline, and diet Carbon C 6 18.5 soda are chemicals in liquid form. Our foods are Nitrogen N 7 3.3 Oxygen O 8 65.0 chemicals, and our bodies are complex arrangements Fluorine F 9 Trace of thousands of chemicals. Recall from Chapter 1 that Sodium Na 11 0.2 the simplest level of organization of the body is the Magnesium Mg 12 0.1 chemical level. Phosphorus P 15 1.0 This chapter covers some very basic aspects of Sulfur S 16 0.3 Chlorine Cl 17 0.2 chemistry as they are related to living organisms, and Potassium K 19 0.4 most especially as they are related to our understand- Calcium Ca 20 1.5 ing of the human body. So try to think of chemistry Manganese Mn 25 Trace not as a complicated science, but as the air, water, and Iron Fe 26 Trace food we need, and every substance that is part of us. Cobalt Co 27 Trace Copper Cu 29 Trace Zinc Zn 30 Trace Iodine I 53 Trace ELEMENTS * Atomic number is the number of protons in the nucleus of All matter, both living and not living, is made of ele- the atom. It also represents the number of electrons that ments, the simplest chemicals. An element is a sub- orbit the nucleus. stance made of only one type of atom (therefore, an atom is the smallest part of an element). There are 92 naturally occurring elements in the world around us. Examples are hydrogen (H), iron (Fe), oxygen (O), books, articles, hospital lab reports, and so on. Notice calcium (Ca), nitrogen (N), and carbon (C). In nature, that if a two-letter symbol is used for an element, the an element does not usually exist by itself but rather second letter is always lowercase, not a capital. For combines with the atoms of other elements to form example, the symbol for calcium is Ca, not CA. CA is compounds. Examples of some compounds important an abbreviation often used for cancer. to our study of the human body are water (H2O), in which two atoms of hydrogen combine with one atom of oxygen; carbon dioxide (CO2), in which an atom of ATOMS carbon combines with two atoms of oxygen; and glu- cose (C6H12O6), in which six carbon atoms and six Atoms are the smallest parts of an element that have oxygen atoms combine with 12 hydrogen atoms. the characteristics of that element. An atom consists of The elements carbon, hydrogen, oxygen, nitrogen, three major subunits or particles: protons, neutrons, phosphorus, and sulfur are found in all living things. If and electrons (Fig. 2–1). A proton has a positive elec- calcium is included, these seven elements make up trical charge and is found in the nucleus (or center) of approximately 99% of the human body (weight). the atom. A neutron is electrically neutral (has no More than 20 different elements are found, in vary- charge) and is also found in the nucleus. An electron ing amounts, in the human body. Some of these are has a negative electrical charge and is found outside listed in Table 2–1. As you can see, each element has a the nucleus orbiting in what may be called an electron standard chemical symbol. This is simply the ﬁrst (and cloud or shell around the nucleus. sometimes the second) letter of the element’s English The number of protons in an atom gives it its or Latin name. You should know the symbols of the atomic number. Protons and neutrons have mass and elements in this table, because they are used in text- weight; they give an atom its atomic weight. In an 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 25 Copyright © 2007 by F. A. Davis. Some Basic Chemistry 25 Second energy level atoms. In this way, the atom becomes stable, because First energy level its outermost shell of electrons has been ﬁlled. It is these reactive atoms that are of interest in our study of anatomy and physiology. Proton [+] Nucleus Neutron CHEMICAL BONDS A chemical bond is not a structure, but rather a force or attraction between positive and negative electrical charges that keeps two or more atoms closely associ- ated with each other to form a molecule. By way of comparison, think of gravity. We know that gravity is Electrons [--] not a “thing,” but rather the force that keeps our feet on the ﬂoor and allows us to pour coffee with consis- Figure 2–1. An atom of carbon. The nucleus contains tent success. Molecules formed by chemical bonding six protons and six neutrons (not all are visible here). Six often have physical characteristics different from those electrons orbit the nucleus, two in the ﬁrst energy level of the atoms of the original elements. For example, and four in the second energy level. the elements hydrogen and oxygen are gases, but QUESTION: What is the electrical charge of this atom as a whole? atoms of each may chemically bond to form molecules of water, which is a liquid. The type of chemical bonding depends upon the tendencies of the electrons of atoms involved, as you atom, the number of protons (⫹) equals the number of will see. Four kinds of bonds are very important to the electrons (⫺); therefore, an atom is electrically neu- chemistry of the body: ionic bonds, covalent bonds, tral. The electrons, however, are important in that disulﬁde bonds, and hydrogen bonds. they may enable an atom to connect, or bond, to other atoms to form molecules. A molecule is a combina- IONIC BONDS tion of atoms (usually of more than one element) that are so tightly bound together that the molecule An ionic bond involves the loss of one or more elec- behaves as a single unit. trons by one atom and the gain of the electron(s) by Each atom is capable of bonding in only very spe- another atom or atoms. Refer to Fig. 2–2 as you read ciﬁc ways. This capability depends on the number and the following. the arrangement of the electrons of the atom. An atom of sodium (Na) has one electron in its out- Electrons orbit the nucleus of an atom in shells or ermost shell, and in order to become stable, it tends to energy levels. The ﬁrst, or innermost, energy level lose that electron. When it does so, the sodium atom can contain a maximum of two electrons and is then has one more proton than it has electrons. Therefore, considered stable. The second energy level is stable it now has an electrical charge (or valence) of ⫹1 and when it contains its maximum of eight electrons. The is called a sodium ion (Na⫹). An atom of chlorine has remaining energy levels, more distant from the seven electrons in its outermost shell, and in order to nucleus, are also most stable when they contain eight become stable tends to gain one electron. When it electrons, or a multiple of eight. does so, the chlorine atom has one more electron than A few atoms (elements) are naturally stable, or it has protons, and now has a charge (valence) of ⫺1. uninterested in reacting, because their outermost It is called a chloride ion (Cl⫺). energy level already contains the maximum number of When an atom of sodium loses an electron to an electrons. The gases helium and neon are examples of atom of chlorine, their ions have unlike charges (pos- these stable atoms, which do not usually react with itive and negative) and are thus attracted to one other atoms. Most atoms are not stable, however, and another. The result is the formation of a molecule of tend to gain, lose, or share electrons in order to ﬁll sodium chloride: NaCl, or common table salt. The their outermost shell. By doing so, an atom is capable bond that holds these ions together is called an ionic of forming one or more chemical bonds with other bond. 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 26 Copyright © 2007 by F. A. Davis. 26 Some Basic Chemistry Na + Cl = NaCl + – Figure 2–2. Formation of an ionic bond. An atom of sodium loses an electron to an atom of chlorine. The two ions formed have unlike charges, are attracted to one another, and form a molecule of sodium chloride. QUESTION: Why is the charge of a sodium ion ⫹1? Another example is the bonding of chlorine to cal- part in another reaction since it is tightly bound to the cium. An atom of calcium has two electrons in its out- sodium atom. However, the Cl⫺ ions available from ermost shell and tends to lose those electrons in order ionized NaCl in the cellular water can be used for the to become stable. If two atoms of chlorine each gain synthesis, or chemical manufacture, of HCl in the one of those electrons, they become chloride ions. stomach. The positive and negative ions are then attracted to one another, forming a molecule of calcium chloride, CaCl2, which is also a salt. A salt is a molecule made COVALENT BONDS of ions other than hydrogen (H⫹) ions or hydroxyl Covalent bonds involve the sharing of electrons (OH⫺) ions. between atoms. As shown in Fig. 2–3, an atom of oxy- Ions with positive charges are called cations. These gen needs two electrons to become stable. It may include Na⫹, Ca⫹2, K⫹, Fe⫹2, and Mg⫹2. Ions with share two of its electrons with another atom of oxy- negative charges are called anions, which include Cl⫺, gen, also sharing two electrons. Together they form a SO4⫺2 (sulfate), and HCO3⫺ (bicarbonate). The types molecule of oxygen gas (O2), which is the form in of compounds formed by ionic bonding are salts, which oxygen exists in the atmosphere. acids, and bases. (Acids and bases are discussed later in An atom of oxygen may also share two of its elec- this chapter.) trons with two atoms of hydrogen, each sharing its In the solid state, ionic bonds are relatively strong. single electron (see Fig. 2–3). Together they form a Our bones, for example, contain the salt calcium car- molecule of water (H2O). When writing structural bonate (CaCO3), which helps give bone its strength. formulas for chemical molecules, a pair of shared elec- However, in an aqueous (water) solution, many ionic trons is indicated by a single line, as shown in the for- bonds are weakened. The bonds may become so weak mula for water; this is a single covalent bond. A double that the bound ions of a molecule separate, creating a covalent bond is indicated by two lines, as in the for- solution of free positive and negative ions. For exam- mula for oxygen; this represents two pairs of shared ple, if sodium chloride is put in water, it dissolves, then electrons. ionizes. The water now contains Na⫹ ions and Cl⫺ The element carbon always forms covalent bonds; ions. Ionization, also called dissociation, is important an atom of carbon has four electrons to share with to living organisms because once dissociated, the ions other atoms. If these four electrons are shared with are free to take part in other chemical reactions within four atoms of hydrogen, each sharing its one electron, the body. Cells in the stomach lining produce a molecule of methane gas (CH4) is formed. Carbon hydrochloric acid (HCl) and must have Cl⫺ ions to do may form covalent bonds with other carbons, hydro- so. The chloride in NaCl would not be free to take gen, oxygen, nitrogen, or other elements. Organic 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 27 Copyright © 2007 by F. A. Davis. Some Basic Chemistry 27 O + O = O2 O=O A 8+ + 8+ = 8+ 8+ O + H+H = H2O O H H 1+ 1+ 1+ B 8+ + = 1+ 8+ Figure 2–3. Formation of covalent bonds. (A) Two atoms of oxygen share two electrons each, forming a molecule of oxygen gas. (B) An atom of oxygen shares one electron with each of two hydrogen atoms, each sharing its electron. A molecule of water is formed. QUESTION: Which of the bonds shown here is a double covalent bond? compounds such as proteins and carbohydrates are hydrogen bonds. Disulﬁde bonds are found in some complex and precise arrangements of these atoms proteins. Hydrogen bonds are part of many different covalently bonded to one another. Covalent bonds are molecules. relatively strong and are not weakened in an aqueous A disulﬁde bond (also called a disulﬁde bridge) is a solution. This is important because the proteins pro- covalent bond formed between two atoms of sulfur, duced by the body, for example, must remain intact in usually within the same large protein molecule. The order to function properly in the water of our cells and hormone insulin, for example, is a protein that must blood. The functions of organic compounds will be have a very speciﬁc three-dimensional shape in order considered later in this chapter. to function properly to regulate the blood glucose level. Each molecule of insulin has two disulﬁde bonds that help maintain its proper shape and function (see DISULFIDE BONDS AND Box Fig. 10–A). Other proteins with shapes that HYDROGEN BONDS depend upon disulﬁde bonds are antibodies of the Two other types of bonds that are important to immune system (see Fig. 14–8) and keratin of the skin the chemistry of the body are disulﬁde bonds and and hair. 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 28 Copyright © 2007 by F. A. Davis. 28 Some Basic Chemistry A strand of hair maintains its shape (a genetic char- In a decomposition reaction, bonds are broken, acteristic) because of disulﬁde bonds. When naturally and a large molecule is changed to two or more curly hair is straightened, the disulﬁde bonds in the smaller ones. One example is the digestion of large keratin molecules are broken. When naturally straight molecules of starch into many smaller glucose mole- hair is “permed” or curled, the disulﬁde bonds in the cules. Some decomposition reactions release energy; keratin are ﬁrst broken, then re-formed in the curled this is described in a later section on cell respiration. hair. Neither process affects the living part of the hair, In this and future chapters, keep in mind that the the hair root, so the hair will grow out in its original term reaction refers to the making or breaking of shape. We would not want such a process affecting our chemical bonds and thus to changes in the physical insulin or antibody molecules, for that would destroy and chemical characteristics of the molecules their functioning. involved. A hydrogen bond does not involve the sharing or exchange of electrons, but rather results because of a property of hydrogen atoms. When a hydrogen atom INORGANIC COMPOUNDS shares its one electron in a covalent bond with another OF IMPORTANCE atom, its proton has a slight positive charge and may then be attracted to a nearby oxygen or nitrogen atom, Inorganic compounds are usually simple molecules which has a slight negative charge. that often consist of only one or two different ele- Although they are weak bonds, hydrogen bonds are ments. Despite their simplicity, however, some inor- important in several ways. Large organic molecules ganic compounds are essential to normal structure and such as proteins and DNA have very speciﬁc functions functioning of the body. that depend upon their three-dimensional shapes. The shapes of these molecules, so crucial to their proper WATER functioning, are often maintained by hydrogen bonds. Water makes up 60% to 75% of the human body, and Hydrogen bonds also make water cohesive; that is, is essential to life for several reasons: each water molecule is attracted to nearby water mol- ecules. Such cohesiveness can be seen if water is 1. Water is a solvent; that is, many substances (called dropped onto clean glass; the surface tension created solutes) can dissolve in water. Nutrients such as by the hydrogen bonds makes the water form three- glucose are dissolved in blood plasma (which is dimensional beads. Within the body, the cohesiveness largely water) to be transported to cells throughout of water helps keep blood a continuous stream as it the body. The sense of taste depends upon the sol- ﬂows within the blood vessels, and keeps tissue ﬂuid vent ability of saliva; dissolved food stimulates the continuous around cells. These hydrogen bonds are receptors in taste buds. The excretion of waste also responsible for the other important characteris- products is possible because they are dissolved in tics of water, which are discussed in a later section. the water of urine. 2. Water is a lubricant, which prevents friction where surfaces meet and move. In the digestive tract, CHEMICAL REACTIONS swallowing depends upon the presence of saliva, and mucus is a slippery ﬂuid that permits the A chemical reaction is a change brought about by the smooth passage of food through the intestines. formation or breaking of chemical bonds. Two general Synovial ﬂuid within joint cavities prevents friction types of reactions are synthesis reactions and decom- as bones move. position reactions. 3. Water changes temperature slowly. Water has a high In a synthesis reaction, bonds are formed to join heat capacity, which means that it will absorb a two or more atoms or molecules to make a new com- great deal of heat before its temperature rises sig- pound. The production of the protein hemoglobin in niﬁcantly, or it must lose a great deal of heat before potential red blood cells is an example of a synthesis its temperature drops signiﬁcantly. This is one of reaction. Proteins are synthesized by the bonding of the factors that helps the body maintain a constant many amino acids, their smaller subunits. Synthesis temperature. Water also has a high heat of vapor- reactions require energy for the formation of bonds. ization, which is important for the process of 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 29 Copyright © 2007 by F. A. Davis. Some Basic Chemistry 29 Intracellular fluid Cell Fluid movement Capillary Lymph Interstitial Lymph (tissue) fluid capillary Plasma Figure 2–4. Water compartments, showing the names water is given in its different loca- tions and the ways in which water moves between compartments. QUESTION: Which of the ﬂuids shown are extracellular ﬂuids? sweating. Excess body heat evaporates sweat on the the body and the functions of the specialized ﬂuids skin surfaces, rather than overheating the body’s will be discussed in later chapters. cells, and because of water’s high heat of vaporiza- tion, a great deal of heat can be given off with the OXYGEN loss of a relatively small amount of water. Oxygen in the form of a gas (O2) is approximately 21% of the atmosphere, which we inhale. We all know WATER COMPARTMENTS that without oxygen we wouldn’t survive very long, All water within the body is continually moving, but but exactly what does it do? Oxygen is important to us water is given different names when it is in speciﬁc because it is essential for a process called cell respira- body locations, which are called compartments (Fig. tion, in which cells break down simple nutrients such 2–4). as glucose in order to release energy. The reason we breathe is to obtain oxygen for cell respiration and to Intracellular ﬂuid (ICF)—the water within cells; exhale the carbon dioxide produced in cell respiration about 65% of the total body water (this will be discussed in the next section). Biologically Extracellular ﬂuid (ECF)—all the rest of the water useful energy that is released by the reactions of cell in the body; about 35% of the total. More speciﬁc respiration is trapped in a molecule called ATP compartments of extracellular ﬂuid include: (adenosine triphosphate). ATP can then be used for Plasma—water found in blood vessels cellular processes that require energy. Lymph—water found in lymphatic vessels Tissue ﬂuid or interstitial ﬂuid—water found in CARBON DIOXIDE the small spaces between cells Carbon dioxide (CO2) is produced by cells as a waste Specialized ﬂuids—synovial ﬂuid, cerebrospinal product of cell respiration. You may ask why a waste ﬂuid, aqueous humor in the eye, and others product is considered important. Keep in mind that The movement of water between compartments in “important” does not always mean “beneﬁcial,” but it 02Scanlon(p3)-ch02 8/17/06 10:42 AM Page 30 Copyright © 2007 by F. A. Davis. 30 Some Basic Chemistry BOX 2–1 BLOOD GASES A patient is admitted to the emergency room with oxygen falls below the normal range, oxygen will a possible heart attack, and the doctor in charge be administered; if blood carbon dioxide rises orders “blood gases.” Another patient hospitalized above the normal range, blood pH will be corrected with pneumonia has “blood gases” monitored at to prevent serious acidosis. frequent intervals. What are blood gases, and what Damage to the heart may also bring about a does measurement of them tell us? The blood gases change in blood gases, especially oxygen. Oxygen are oxygen and carbon dioxide, and their levels is picked up by red blood cells as they circulate in arterial blood provide information about the through lung capillaries; as red blood cells circulate functioning of the respiratory and circulatory through the body, they release oxygen to tissues. systems. Arterial blood normally has a high con- What keeps the blood circulating or moving? The centration of oxygen and a low concentration of pumping of the heart. carbon dioxide. These levels are maintained by A mild heart attack, when heart failure is unlikely, gas exchange in the lungs and by the proper circu- is often characterized by a blood oxygen level that lation of blood. is low but still within normal limits. A more severe A pulmonary disease such as pneumonia inter- heart attack that seriously impairs the pump

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