Seeley's Anatomy & Physiology, 10th Edition - Human Organism PDF

1 learn to Predict...

1 learn to Predict Renzo, the dancer in the photo, is perfectly balanced, yet a slight movement in any The Human Organism direction would cause him to adjust his position. The human body adjusts its balance among all its parts through a process called homeostasis. let’s imagine that Renzo is suffering from a blood sugar disorder. earlier, just w before this photo was taken, he’d eaten an hat lies ahead is an astounding adventure—learning about the structure and energy bar. as an energy bar is digested, function of the human body and the intricate checks and balances that regu- blood sugar rises. Normally, tiny collections late it. Renzo’s response to eating the energy bar is a good example of how of cells embedded in the pancreas respond important this system of checks and balances is in the body. Perhaps you have had a similar experience, but with a different outcome. You have overslept, rushed to your to the rise in blood sugar by secreting 8 a.m. class, and missed breakfast. Afterwards, on the way to Anatomy & Physiology the chemical insulin. Insulin increases the class, you bought an energy bar from the vending machine. Eating the energy bar movement of sugar from the blood into his helped you feel better. The explanation for these experiences is the process of homeo- cells. However, Renzo did not feel satisfied stasis; for you, homeostasis was maintained, but for Renzo, there was a disruption in from his energy bar. He felt dizzy and was homeostasis. Throughout this book, the major underlying theme is homeostasis. As you still hungry, all symptoms he worried could think about Renzo’s case, you will come to realize just how capable the human body is be due to a family history of diabetes. of an incredible coordination of thousands upon thousands of processes. Knowing Fortunately, the on-site trainer tested his human anatomy and physiology is also the basis for understanding disease. The study blood sugar and noted that it was much of human anatomy and physiology is important for students who plan a career in the higher than normal. after a visit to his health sciences because health professionals need a sound knowledge of structure and regular physician, Renzo was outfitted with function in order to perform their duties. In addition, understanding anatomy and an insulin pump, and his blood sugar levels physiology prepares all of us to evaluate recommended treatments, critically review are more consistent. advertisements and reports in the popular literature, and rationally discuss the human after reading about homeostasis body with health professionals and nonprofessionals. in this chapter, create an explanation for Renzo’s blood sugar levels before and after his visit to the doctor. Module 1 Body Orientation 1 van03636_ch01.indd 1 12-09-07 3:13 PM  2 PART 1 Organization of the Human Body 1.1 Anatomy and Physiology surgery. Although most of the technology used in anatomical imaging is very new, the concept and earliest technology are quite old. In 1895, Wilhelm Roentgen (1845–1923) became the first med- LEARNING OUTCOMES ical scientist to use x-rays to see inside the body. The rays were After reading this section, you should be able to called x-rays because no one knew what they were. Whenever the human body is exposed to x-rays, ultrasound, electromagnetic A. Define anatomy and describe the levels at which anatomy fields, or radioactively labeled substances, a potential risk exists. can be studied. This risk must be weighed against the medical benefit. Numerous B. Define physiology and describe the levels at which studies have been conducted and are still being done to determine physiology can be studied. the effects of diagnostic and therapeutic exposure to x-rays. The C. Explain the importance of the relationship between risk of anatomical imaging is minimized by using the lowest possible structure and function. doses providing the necessary information. No known risks exist from ultrasound or electromagnetic fields at the levels used for Anatomy is the scientific discipline that investigates the body’s diagnosis. Both surface anatomy and anatomical imaging provide structure—for example, the shape and size of bones. In addi- important information for diagnosing disease. tion, anatomy examines the relationship between the structure However, no two humans are structurally identical. of a body part and its function. Thus, the fact that bone cells are Anatomical anomalies are physical characteristics that differ surrounded by a hard, mineralized substance enables the bones from the normal pattern. Anatomical anomalies can vary in to provide strength and support. Understanding the relationship severity from relatively harmless to life-threatening. For example, between structure and function makes it easier to understand and each kidney is normally supplied by one blood vessel, but in some appreciate anatomy. Anatomy can be considered at different levels. individuals a kidney is supplied by two blood vessels. Either way, Developmental anatomy studies the structural changes that occur the kidney receives adequate blood. On the other hand, in the con- between conception and adulthood. Embryology (em-brē-ol′ō-jē), dition called “blue baby” syndrome, certain blood vessels arising a subspecialty of developmental anatomy, considers changes from an infant’s heart are not attached in their correct locations; from conception to the end of the eighth week of development. blood is not effectively pumped to the lungs, and so the tissues do Some structures, such as cells, are so small that they must be not receive adequate oxygen. studied using a microscope. Cytology (sī-tol′ō-jē) examines the Physiology is the scientific investigation of the processes or structural features of cells, and histology (his-tol′ō-jē) examines functions of living things. The major goals when studying human tissues, which are composed of cells and the materials surround- physiology are to understand and predict the body’s responses to ing them. stimuli and to understand how the body maintains conditions within Gross anatomy, the study of structures that can be examined a narrow range of values in a constantly changing environment. without the aid of a microscope, can be approached from either a Like anatomy, physiology can be considered at many levels. systemic or a regional perspective. In systemic anatomy, the body Cell physiology examines the processes occurring in cells, and is studied system by system. A system is a group of structures that systemic physiology considers the functions of organ systems. have one or more common functions, such as the cardiovascular, Neurophysiology focuses on the nervous system, and cardio- nervous, respiratory, skeletal, or muscular system. The systemic vascular physiology deals with the heart and blood vessels. approach is taken in this and most other introductory textbooks. Physiology often examines systems rather than regions because a In regional anatomy, the body is studied area by area. Within each particular function can involve portions of a system in more than region, such as the head, abdomen, or arm, all systems are studied one region. simultaneously. The regional approach is taken in most graduate Studies of the human body must encompass both anatomy programs at medical and dental schools. and physiology because structures, functions, and processes Surface anatomy is the study of the external form of the body are interwoven. Pathology (pa-thol′ō-jē) is the medical science and its relation to deeper structures. For example, the sternum dealing with all aspects of disease, with an emphasis on the cause (breastbone) and parts of the ribs can be seen and palpated (felt) and development of abnormal conditions, as well as the struc- on the front of the chest. Health professionals use these structures tural and functional changes resulting from disease. Exercise as anatomical landmarks to identify regions of the heart and physiology focuses on the changes in function and structure points on the chest where certain heart sounds can best be heard. caused by exercise. Anatomical imaging uses radiographs (x-rays), ultrasound, mag- netic resonance imaging (MRI), and other technologies to create ASSESS YOUR PROGRESS pictures of internal structures (table 1.1). Anatomical imaging has revolutionized medical science. Some scientists estimate that the 1. How does the study of anatomy differ from the study of physiology? past 20 years have seen as much progress in clinical medicine as occurred in all of medicine’s previous history. Anatomical imag- 2. What is studied in gross anatomy? In surface anatomy? ing has made a major contribution to that progress. Anatomical 3. What type of physiology is employed when studying the imaging allows medical personnel to look inside the body with endocrine system? amazing accuracy and without the trauma and risk of exploratory 4. Why are anatomy and physiology normally studied together? van03636_ch01.indd 2 12-09-07 3:13 PM  CHAPTER 1   The Human Organism 3 Table 1.1 Anatomical Imaging Imaging Technique Image Clinical Examples X-ray This extremely shortwave electromagnetic radiation (see chapter 2) moves through the body, exposing a photographic plate to form a radiograph (rā′dē- ō-graf ). Bones and radiopaque dyes absorb the rays and create underexposed areas that appear white on the photographic film. Almost everyone has had a radiograph taken, either to visualize a broken bone or to check for a cavity in a tooth. However, a major limitation of radiographs is that they give only flat, two-dimensional (2-D) images of the body. Ultrasound Ultrasound, the second oldest imaging technique, was first developed in the early 1950s as an extension of World War II sonar technology. It uses high-frequency sound waves, which are emitted from a transmitter-receiver placed on the skin over the area to be scanned. The sound waves strike internal organs and bounce back to the receiver on the skin. Even though the basic technology is fairly old, the most important advances in the field occurred only after it became possible to analyze the reflected sound waves by computer. Once a computer analyzes the pattern of sound waves, the information is transferred to a monitor and visualized as a sonogram (son′ō-gram) image. One of the more recent advances in ultrasound technology is the ability of more advanced computers to analyze changes in position through “real-time” movements. Among other medical applications, ultra- sound is commonly used to evaluate the condition of the fetus during pregnancy. Computed Tomography Computed tomographic (tō′mō-graf′ik) (CT) scans, developed in 1972 and (CT) originally called computerized axial tomographic (CAT) scans, are computer- analyzed x-ray images. A low-intensity x-ray tube is rotated through a 360-degree arc around the patient, and the images are fed into a computer. The computer then constructs the image of a “slice” through the body at the point where the x-ray beam was focused and rotated (a). Some computers are able to take several scans short distances apart and stack the slices to produce a 3-D image of a body part (b). (a) (b) Dynamic Subtraction Digital subtraction angiography (an-jē-og′ră-fē) (DSA) is one step beyond CT Angiography (DSA) scanning. A 3-D radiographic image of an organ, such as the brain, is made and stored in a computer. Then a radiopaque dye is injected into the blood, and a second radiographic computer image is made. The first image is subtracted from the second one, greatly enhancing the differences revealed by the injected dye. These dynamic computer images can be used, for example, to guide a catheter into a carotid artery during angioplasty, a procedure by which a tiny balloon compresses the material clogging the artery. Magnetic Resonance Magnetic resonance imaging (MRI) directs radio waves at a person lying inside Imaging (MRI) a large electromagnetic field. The magnetic field causes the protons of various atoms to align (see chapter 2). Because of the large amounts of water in the body, the alignment of hydrogen atom protons is most important in this imaging system. Radio waves of certain frequencies, which change the alignment of the hydrogen atoms, then are directed at the patient. When the radio waves are turned off, the hydrogen atoms realign in accordance with the magnetic field. The time it takes the hydrogen atoms to realign is different for various body tissues. These differences can be analyzed by computer to produce very clear sections through the body. The technique is also very sensitive in detecting some forms of cancer far more readily than can a CT scan. Positron Emission Positron emission tomographic (PET) scans can identify the metabolic states Tomography (PET) of various tissues. This technique is particularly useful in analyzing the brain. When cells are active, they are using energy. The energy they need is supplied by the breakdown of glucose (blood sugar). If radioactively treated (“labeled”) glucose is given to a patient, the active cells take up the labeled glucose. As the radioactivity in the glucose decays, positively charged subatomic particles called positrons are emitted. When the positrons collide with electrons, the two particles annihilate each other and gamma rays are given off. The gamma rays can be detected, pinpointing the cells that are metabolically active. van03636_ch01.indd 3 12-09-07 3:13 PM  4 PART 1 Organization of the Human Body 1.2 Structural and Functional 6. Organism level. An organism is any living thing considered as a whole—whether composed of one cell, such as a bacte- Organization of the Human Body rium, or of trillions of cells, such as a human. The human organism is a complex of organ systems, all mutually depen- dent on one another. LEARNING OUTCOMES After reading this section, you should be able to ASSESS YOUR PROGRESS A. Name the six levels of organization of the body, and 5. From simplest to complex, list and define the body’s six levels describe the major characteristics of each level. of organization. B. List the 11 organ systems, identify their components, 6. What are the four basic types of tissues? and describe the major functions of each system. 7. Referring to figure 1.3, which two organ systems are responsible The body can be studied at six levels of organization: the chemi- for regulating the other organ systems? Which two are responsible cal, cell, tissue, organ, organ system, and whole organism levels for support and movement? (figure 1.1). 1. Chemical level. The chemical level involves interactions Predict 2 between atoms, which are tiny building blocks of matter. In one type of diabetes, the pancreas fails to produce insulin, a chemical Atoms combine to form molecules, such as water, sugar, fats, normally made by pancreatic cells and released into the blood. list as many and proteins. The function of a molecule is intimately related levels of organization as you can at which this disorder could be corrected. to its structure. For example, collagen molecules are ropelike protein fibers that give skin structural strength and flexibility. With old age, the structure of collagen changes, and the skin becomes fragile and more easily torn. We present a brief over- 1.3 Characteristics of Life view of chemistry in chapter 2. 2. Cell level. Cells are the basic structural and functional units LEARNING OUTCOME of plants and animals. Molecules combine to form organelles After reading this section, you should be able to (or′gă-nelz; little organs), which are the small structures that A. List and define the six characteristics of life. make up cells. For example, the nucleus is an organelle that contains the cell’s hereditary information, and mitochon- Humans are organisms, sharing characteristics with other organ- dria are organelles that manufacture adenosine triphosphate isms. The most important common feature of all organisms is life. (ATP), a molecule cells use for energy. Although cell types This text recognizes six essential characteristics of life: differ in their structure and function, they have many char- acteristics in common. Knowledge of these characteristics, as 1. Organization refers to the specific interrelationships among well as their variations, is essential to understanding anatomy the parts of an organism and how those parts interact to and physiology. We discuss the cell in chapter 3. perform specific functions. Living things are highly orga- 3. Tissue level. A tissue is composed of a group of similar cells nized. All organisms are composed of one or more cells. and the materials surrounding them. The characteristics of Cells in turn are composed of highly specialized organelles, the cells and surrounding materials determine the functions which depend on the precise organization of large molecules. of the tissue. The numerous tissues that make up the body are Disruption of this organized state can result in loss of func- classified into four basic types: epithelial, connective, muscle, tions, or even death. and nervous. We discuss tissues in chapter 4. 2. Metabolism (mĕ-tab′ō-lizm) refers to all of the chemical reac- 4. Organ level. An organ is composed of two or more tissue types tions taking place in an organism. It includes an organism’s that perform one or more common functions. The urinary blad- ability to break down food molecules, which the organism der, heart, stomach, and lung are examples of organs (figure 1.2). uses as a source of energy and raw materials to synthesize its 5. Organ system level. An organ system is a group of organs own molecules. Energy is also used when one part of a molecule that together perform a common function or set of functions moves relative to another part, changing the shape of the and are therefore viewed as a unit. For example, the urinary molecule. Changes in molecular shape can lead to changes in system consists of the kidneys, ureter, urinary bladder, and cellular shape, which can produce movement of the organism. urethra. The kidneys produce urine, which the ureters trans- Metabolism is necessary for vital functions, such as respon- port to the urinary bladder, where it is stored until being siveness, growth, development, and reproduction. eliminated from the body through the urethra. In this text, we 3. Responsiveness is an organism’s ability to sense changes consider 11 major organ systems: the integumentary, skeletal, in its external or internal environment and adjust to those muscular, nervous, endocrine, cardiovascular, lymphatic, changes. Responses include such actions as moving toward respiratory, digestive, urinary, and reproductive systems. food or water and moving away from danger or poor envi- Figure 1.3 presents a brief summary of these organ systems ronmental conditions. Organisms can also make adjustments and their functions. that maintain their internal environment. For example, if the van03636_ch01.indd 4 12-09-07 3:13 PM  FUNDaMeNTal Figure 1 Chemical level. Atoms (colored balls) combine to form molecules. 1 2 Cell level. Molecules form organelles, such as the nucleus and mitochondria, which make up cells. Atoms Mitochondria 3 Tissue level. Similar cells and surrounding materials 2 Nucleus make up tissues. Molecule (DNA) 4 Organ level. Different tissues combine to form organs, such as the urinary bladder. Smooth muscle cell 5 Organ system level. Organs, such as the Smooth urinary bladder and muscle 3 kidneys, make up an tissue organ system. 6 Organism level. Organ systems make up an organism. 4 Urinary Epithelium bladder Connective tissue Smooth muscle tissue Kidney Connective tissue 5 6 Ureter Wall of urinary bladder Urinary bladder Urethra Urinary system Organism PROCESS FIGURE 1.1 Levels of Organization for the Human Body external environment causes the body temperature to rise, The greatest developmental changes occur before birth, but sweat glands produce sweat, which can lower body tempera- many changes continue after birth, and some go on through- ture back toward its normal range. out life. Development usually involves growth, but it also 4. Growth refers to an increase in the size or number of cells, involves differentiation and morphogenesis. Differentiation which produces an overall enlargement of all or part of an is change in cell structure and function from generalized to organism. For example, a muscle enlarged by exercise is specialized, and morphogenesis (mōr-fō-jen′ĕ-sis) is change composed of larger muscle cells than those of an untrained in the shape of tissues, organs, and the entire organism. For muscle, and the skin of an adult has more cells than the skin example, following fertilization, generalized cells specialize to of an infant. An increase in the materials surrounding cells can become specific cell types, such as skin, bone, muscle, or nerve also contribute to growth. For instance, bone grows because of cells. These differentiated cells form the tissues and organs. an increase in cell number and the deposition of mineralized 6. Reproduction is the formation of new cells or new organ- materials around the cells. isms. Without reproduction of cells, growth and development 5. Development includes the changes an organism undergoes are not possible. Without reproduction of organisms, species through time, beginning with fertilization and ending at death. become extinct. 5 van03636_ch01.indd 5 12-09-07 3:13 PM  6 PART 1 Organization of the Human Body Brain Spinal cord Carotid Larynx artery Trachea Esophagus Aortic arch Lung Heart Diaphragm Liver Spleen Pancreas (behind (behind stomach) stomach) Stomach Gallbladder Kidney Kidney (behind stomach) (behind intestine) Small intestine Large intestine Ureter (behind small intestine) Urinary bladder Urethra Figure 1.2 Major Organs of the Body ASSESS YOUR PROGRESS evidenced by the great progress in open heart surgery and kidney 8. What are the six characteristics of living things? Briefly transplantation made possible by perfecting surgical techniques explain each. on other mammals before attempting them on humans. Strict laws 9. How does differentiation differ from morphogenesis? govern the use of animals in biomedical research; these laws are designed to ensure minimal suffering on the part of the animal and to discourage unnecessary experimentation. 1.4 Biomedical Research Although much can be learned from studying other organ- isms, the ultimate answers to questions about humans can be obtained only from humans because other organisms differ from LEARNING OUTCOME humans in significant ways. A failure to appreciate the differences After reading this section, you should be able to between humans and other animals led to many misconceptions A. Explain why it is important to study other organisms by early scientists. One of the first great anatomists was a Greek along with humans. physician, Claudius Galen (ca. 130–201). Galen described a large number of anatomical structures supposedly present in humans Studying other organisms has increased our knowledge about but observed only in other animals. For example, he described the humans because humans share many characteristics with other liver as having five lobes. This is true for rats, but not for humans, organisms. For example, studying single-celled bacteria provides who have four-lobed livers. The errors introduced by Galen much information about human cells. However, some biomedical persisted for more than 1300 years until a Flemish anatomist, research cannot be accomplished using single-celled organisms Andreas Vesalius (1514–1564), who is considered the first mod- or isolated cells. Sometimes other mammals must be studied, as ern anatomist, carefully examined human cadavers and began van03636_ch01.indd 6 12-09-07 3:13 PM  CHAPTER 1   The Human Organism 7 Hair Skull Temporalis Pectoralis Clavicle major Sternum Ribs Skin Humerus Biceps Vertebral brachii column Rectus Pelvis Radius abdominis Ulna Sartorius Femur Quadriceps femoris Tibia Gastrocnemius Fibula Integumentary System Skeletal System Muscular System Provides protection, regulates temperature, Provides protection and support, allows Produces body movements, maintains prevents water loss, and helps produce body movements, produces blood cells, and posture, and produces body heat. Consists of vitamin D. Consists of skin, hair, nails, and stores minerals and fat. Consists of bones, muscles attached to the skeleton by tendons. sweat glands. associated cartilages, ligaments, and joints. Nasal Pharynx Tonsils cavity (throat) Nose Pharynx Salivary Cervical Oral cavity (throat) glands lymph (mouth) Thymus node Larynx Esophagus Trachea Stomach Axillary Mammary Bronchi lymph plexus Pancreas Lungs node Small Thoracic intestine duct Liver Gallbladder Large Lymphatic Spleen intestine vessel Inguinal lymph node Appendix Rectum Anus Lymphatic System Respiratory System Digestive System Removes foreign substances from the blood Exchanges oxygen and carbon dioxide Performs the mechanical and chemical and lymph, combats disease, maintains between the blood and air and regulates processes of digestion, absorption of tissue fluid balance, and absorbs fats from blood pH. Consists of the lungs and nutrients, and elimination of wastes. Consists the digestive tract. Consists of the lymphatic respiratory passages. of the mouth, esophagus, stomach, vessels, lymph nodes, and other lymphatic intestines, and accessory organs. organs. Figure 1.3 Organ Systems of the Body to correct the textbooks. This example should serve as a word of ASSESS YOUR PROGRESS caution: Some current knowledge in molecular biology and physi- 10. Why is it important to recognize that humans share many, but ology has not been confirmed in humans. not all, characteristics with other animals? van03636_ch01.indd 7 12-09-07 3:13 PM  8 PART 1 Organization of the Human Body Hypothalamus Brain Pineal Carotid Pituitary gland artery Superior Parathyroids Jugular vena cava Thyroid (posterior vein Spinal cord part of Pulmonary Thymus thyroid) trunk Nerve Heart Brachial Cauda Adrenals artery Aorta equina Pancreas (islets) Ovaries Inferior Femoral (female) Testes vena cava artery and (male) vein Nervous System Endocrine System Cardiovascular System A major regulatory system that detects A major regulatory system that influences Transports nutrients, waste products, gases, sensations and controls movements, metabolism, growth, reproduction, and many and hormones throughout the body; plays physiological processes, and intellectual other functions. Consists of glands, such as a role in the immune response and the functions. Consists of the brain, spinal cord, the pituitary, that secrete hormones. regulation of body temperature. Consists of nerves, and sensory receptors. the heart, blood vessels, and blood. Mammary gland (in breast) Seminal Kidney Uterine vesicle Ureter tube Prostate Ovary Ductus gland Urinary deferens bladder Testis Uterus Urethra Vagina Epididymis Penis Urinary System Female Reproductive System Male Reproductive System Removes waste products from the blood and Produces oocytes and is the site of fertilization Produces and transfers sperm cells to regulates blood pH, ion balance, and water and fetal development; produces milk for the the female and produces hormones that balance. Consists of the kidneys, urinary newborn; produces hormones that influence influence sexual functions and behaviors. bladder, and ducts that carry urine. sexual function and behaviors. Consists of the Consists of the testes, accessory structures, ovaries, vagina, uterus, mammary glands, and ducts, and penis. associated structures. Figure 1.3 (continued) van03636_ch01.indd 8 12-09-07 3:13 PM  CHAPTER 1 The Human Organism 9 1.5 Homeostasis from homeostasis, body cells do not function normally and can even die. Disease disrupts homeostasis and sometimes results in death. Modern medicine attempts to understand disturbances LEARNING OUTCOMES in homeostasis and works to reestablish a normal range of values. After reading this section, you should be able to A. Define homeostasis and explain why it is important Negative Feedback for proper body function. Most systems of the body are regulated by negative-feedback B. Describe a negative-feedback mechanism and give mechanisms, which maintain homeostasis. Negative means that an example. any deviation from the set point is made smaller or is resisted; C. Describe a positive-feedback mechanism and give therefore, in a negative-feedback mechanism, the response to the an example. original stimulus results in deviation from the set point, becoming smaller. An example of important negative-feedback mechanisms Homeostasis (hō′mē-ō-stā′sis) is the existence and maintenance of in the body are those maintaining normal blood pressure. Normal a relatively constant environment within the body. A small amount blood pressure is critical to our health because blood pressure helps of fluid surrounds each body cell. For cells to function normally, the move blood from the heart to tissues. The blood transports essential volume, temperature, and chemical content of this fluid—conditions materials to and from the tissues. Because a disruption of normal known as variables because their values can change—must remain blood pressure could result in a disease state, maintaining homeo- within a narrow range. Body temperature is a variable that can stasis through negative feedback is a critical activity. Most negative- increase in a hot environment or decrease in a cold one. feedback mechanisms have three components: (1) a receptor, which Homeostatic mechanisms, such as sweating or shivering, monitors the value of a variable; (2) a control center, which receives normally maintain body temperature near an ideal normal value, or set point (figure 1.4). Note that these mechanisms are not able to maintain body temperature precisely at the set point. Instead, body temperature increases and decreases slightly around the set point to produce a normal range of values. As long as body Case Orthostatic temperature remains within this normal range, homeostasis is maintained. Keep in mind that the fluctuations are minimal, how- STUDY Hypotension ever. Note in figure 1.4 that the normal body temperature range M is no more than 1 degree Fahrenheit above or below normal. Our olly is a 75-year-old widow who lives alone. For 2 days, average body temperature is 98.6 degrees Fahrenheit. Just as your she had a fever and chills and mainly stayed in bed. On home’s thermostat does not keep the air temperature exactly at rising to go to the bathroom, she felt dizzy, fainted, and 75 degrees Fahrenheit at all times, your body’s temperature does fell to the floor. Molly quickly regained consciousness and man- aged to call her son, who took her to the emergency room, where a not stay perfectly stable. physician diagnosed orthostatic hypotension. The organ systems help keep the body’s internal environ- Orthostasis literally means “to stand,” and hypotension refers ment relatively constant. For example, the digestive, respiratory, to low blood pressure; thus, orthostatic hypotension is a signifi- cardiovascular, and urinary systems work together, so that each cant drop in blood pressure upon standing. When a person moves cell in the body receives adequate oxygen and nutrients and waste from lying down to standing, blood “pools” within the veins below products do not accumulate to a toxic level. If body fluids deviate the heart because of gravity, and less blood returns to the heart. Consequently, blood pressure drops because the heart has less blood to pump. Predict 3 98.8°F although orthostatic hypotension has many causes, in the elderly Body temperature (normal range) it can be due to age-related decreases in neural and cardiovascular responses. Decreased fluid intake while feeling ill and sweating due 98.6°F Set point to a fever can result in dehydration. Dehydration can decrease blood volume and lower blood pressure, increasing the likelihood of ortho- static hypotension. Use figure 1.6 to answer the following: 98.4°F a. Describe the normal response to a decrease in blood pressure on standing. Time (min) b. What happened to Molly’s heart rate just before she fainted? Why did Molly faint? FIGURE 1.4 Homeostasis c. How did Molly’s fainting and falling to the floor help establish Homeostasis is the maintenance of a variable around an ideal normal value, or homeostasis (assuming she was not injured)? set point. The value of the variable fluctuates around the set point to establish a normal range of values. van03636_ch01.indd 9 12-09-07 3:13 PM  FUNDaMeNTal Figure 1 R Receptors Recept s monitor the value of a variable. In this case, receptors in the wall of a blood vessel monitor 1 blood pressure. Receptors monitor 2 blood pressure. 2 Information about the value of the variable is sent to a control center. In this case, nerves send information to Nerves the part of the brain responsible for regulating 5 blood pressure. 3 Effector (heart) Control center 4 responds to changes 3 The control center (brain) in blood pressure. compares the value of the variable against the set point. 4 If a response is necessary 5 An effector produces a to maintain homeostasis, response that maintains the control center causes homeostasis. In this case, an effector to respond. In changing heart rate this case, nerves send changes blood pressure. information to the heart. PROCESS FIGURE 1.5 Negative-Feedback Mechanism: Blood Pressure information about the variable from the receptor, establishes the set blood pressure increases delivery of blood to muscles during exer- point, and controls the effector; and (3) an effector, which produces cise, thereby increasing the delivery of oxygen and nutrients and responses that change the value of the variable. A changed variable the removal of waste products—ultimately maintaining muscle is a stimulus because it initiates a homeostatic mechanism. Several cell homeostasis. negative-feedback mechanisms regulate blood pressure, and they are described more fully in chapters 20 and 21. Here we describe Positive Feedback one of them: Receptors that monitor blood pressure are located Positive-feedback mechanisms occur when a response to the within large blood vessels near the heart and the head. A control original stimulus results in the deviation from the set point center in the brain receives signals sent through nerves from the becoming even greater. At times, this type of response is required receptors. The control center evaluates the information and sends to re-achieve homeostasis. For example, during blood loss, a signals through nerves to the heart. The heart is the effector, and chemical responsible for blood clot formation, called thrombin, the heart rate increases or decreases in response to signals from stimulates production of even more thrombin (figure 1.8). In this the brain (figure 1.5). way, a disruption in homeostasis is resolved through a positive- If blood pressure increases slightly, receptors detect that feedback mechanism. What prevents the entire vascular system change and send the information to the control center in the brain. from clotting? The clot formation process is self-limiting. The control center causes the heart rate to decrease, lowering blood Eventually, the components needed to form a clot will be depleted pressure. If blood pressure goes down slightly, the receptors inform in the damaged area and no more clot material can be formed. the control center, which elevates the heart rate, thereby producing Birth is another example of a normally occurring positive- an increase in blood pressure (figure 1.6). As a result, blood pressure feedback mechanism. Near the end of pregnancy, the baby’s larger constantly rises and falls within a normal range of values. size stretches the uterus. This stretching, especially around the open- Although homeostasis is the maintenance of a normal range ing of the uterus, stimulates contractions of the uterine muscles. of values, this does not mean that all variables remain within the The uterine contractions push the baby against the opening of the same narrow range of values at all times. Sometimes a deviation uterus and stretch it further. This stimulates additional contrac- from the usual range of values can be beneficial. For example, tions, which result in additional stretching. This positive-feedback during exercise the normal range for blood pressure differs from sequence ends only when the baby is delivered from the uterus the range under resting conditions and the blood pressure is and the stretching stimulus is eliminated. significantly elevated (figure 1.7). Muscle cells require increased Two basic principles to remember are that (1) many disease oxygen and nutrients and increased removal of waste products to states result from the failure of negative-feedback mechanisms to support their heightened level of activity during exercise. Elevated maintain homeostasis and (2) some positive-feedback mechanisms 10 van03636_ch01.indd 10 12-09-07 3:13 PM  CHAPTER 1 The Human Organism 11 3 4 Receptors detect an increase in Effectors Activated: blood pressure. Heart rate and stroke volume Control centers in the brain decrease decrease; blood vessels dilate. stimulation of heart and blood vessels. Blood pressure increases: Blood pressure decreases: 2 Homeostasis Disturbed 5 Homeostasis Restored Blood pressure (normal range) Blood pressure (normal range) 1 Start Here 6 Blood pressure decreases: Blood pressure increases: Homeostasis Disturbed Homeostasis Restored Receptors detect a decrease in Effectors Activated: blood pressure. Heart rate and stroke volume Control centers in the brain increase increase; blood vessels constrict. stimulation of heart and blood vessels. HOMEOSTASIS PROCESS FIGURE 1.6 Negative-Feedback Control of Blood Pressure Throughout this book, all homeostasis figures have the same format as shown here. The changes caused by the increase of a variable outside the normal range are shown in the green boxes, and the changes caused by a decrease are shown in the red boxes. To help you learn how to interpret homeostasis figures, some of the steps in this figure are numbered: (1) Blood pressure is within its normal range. (2) Blood pressure increases outside the normal range; this change is detected by receptors and causes homeostasis to be disturbed. (3) The blood pressure control center in the brain responds to the change in blood pressure. (4) The control center activates the effectors: heart rate and stroke volume decrease and blood vessels dilate. (5) These changes cause blood pressure to decrease. (6) Blood pressure returns to its normal range, and homeostasis is restored. Observe the responses to a decrease in blood pressure outside its normal range by following the red arrows. can be detrimental instead of helpful. One example of a detrimen- tissues, blood pressure must be maintained to ensure adequate tal positive-feedback mechanism is inadequate delivery of blood delivery of blood to the cardiac muscle. Following extreme blood to cardiac (heart) muscle. Contraction of cardiac muscle generates loss, blood pressure decreases to the point that the delivery of blood pressure and the heart pumps blood to itself through a sys- blood to cardiac muscle is inadequate. As a result, cardiac muscle tem of blood vessels on the outside of the heart. Just as with other does not function normally. The heart pumps less blood, which van03636_ch01.indd 11 12-09-07 3:13 PM  12 PART 1 Organization of the Human Body ASSESS YOUR PROGRESS 11. How do variables, set points, and normal ranges relate to homeostasis? 12. Distinguish between negative feedback and positive feedback. Blood pressure 13. What are the three components of a negative-feedback mechanism? 14. Give an example of how a negative-feedback mechanism maintains homeostasis. Normal BP during exercise 15. Give an example of a positive-feedback mechanism that Normal BP at rest Normal BP after exercise may be harmful to the body and an example of one that is not harmful. Time FIGURE 1.7 Changes in Blood Pressure During Exercise Predict 4 During exercise, muscle tissue demands more oxygen. To meet this demand, ashley is on the track team and is running an 800-meter race. Throughout blood pressure (BP) increases, resulting in an increase in blood flow to the tissues. the race, her respiratory rate increases rapidly. Does this represent negative The increased blood pressure is not an abnormal or nonhomeostatic condition or positive feedback? explain. but a resetting of the normal homeostatic range to meet the increased demand. The reset range is higher and broader than the resting range. after exercise ceases, the range returns to that of the resting condition. 1.6 Terminology and the Body Plan SUBSTRATE SUBSTRATE LEARNING OUTCOMES Enzyme A Enzyme A After reading this section, you should be able to Inactive intermediate 1 Inactive intermediate 1 A. Describe a person in anatomical position. Enzyme B Enzyme B B. Define the directional terms for the human body, and use – + Inactive intermediate 2 Inactive intermediate 2 them to locate specific body structures. C. know the terms for the parts and regions of the body. Enzyme C Enzyme C D. Name and describe the three major planes of the body. Active product Active product E. Name and describe the three major ways to cut an organ. (a) Negative feedback (b) Positive feedback F. Describe the major trunk cavities and their divisions. FIGURE 1.8 Comparison of Negative-Feedback and Positive- G. Locate organs in their specific cavity, abdominal quadrant, Feedback Mechanisms or region. (a) In negative feedback, the response stops the effector. (b) In positive H. Describe the serous membranes, their locations, and feedback, the response keeps the reaction going. For example, during blood their functions. clotting, the “active product” represents thrombin, which triggers “enzyme a,” the first step in the cascade that leads to the production of thrombin. As you study anatomy and physiology, you will be learning many new words. Knowing the derivation, or etymology (et′uh- causes the blood pressure to drop even further—a deviation further mol′ŏ-jē), of these words can make learning them easy and fun. from the setpoint. The additional decrease in blood pressure Most anatomical terms are derived from Latin or Greek. For further reduces blood delivery to cardiac muscle, and the heart example, foramen is a Latin word for “hole,” and magnum means pumps even less blood, which again decreases the blood pressure. “large.” The foramen magnum is therefore a large hole in the skull The process self-propagates until the blood pressure is too low through which the spinal cord attaches to the brain. to sustain the cardiac muscle, the heart stops beating, and death Prefixes and suffixes can be added to words to expand their results. In this example, we see the deviation from the heart rate meaning. For example, the suffix -itis means an inflammation, so set point becoming larger and larger—this is a positive-feedback appendicitis is an inflammation of the appendix. As new terms mechanism. Thus, if blood loss is severe, negative-feedback mech- are introduced in this text, their meanings are often explained. anisms may not be able to maintain homeostasis, and the postive The glossary and the list of word roots, prefixes, and suffixes on feedback of ever-decreasing blood pressure can develop. On the the inside back cover provide additional information about the other hand, following a moderate amount of blood loss (e.g., after new terms. donating a pint of blood), negative-feedback mechanisms result in It is very helpful to learn these new words, so that your message an increase in heart rate, which restores blood pressure. is clear and correct when you speak to colleagues or write reports. van03636_ch01.indd 12 12-09-07 3:13 PM  FUNDaMeNTal Figure Superior Right Left (cephalic) Superior (cephalic) Midline Proximal Anterior Posterior Inferior (dorsal) (caudal) Medial (ventral) Distal Lateral Inferior (caudal) Proximal Distal Distal Proximal FIGURE 1.9 Directional Terms all directional terms are in relation to the body in the anatomical position: a person standing erect with the face directed forward, the arms hanging to the sides, and the palms of the hands facing forward. Body Positions with these directional terms as soon as possible because you Anatomical position refers to a person standing erect with the face will see them repeatedly throughout this text. Right and left are directed forward, the upper limbs hanging to the sides, and the retained as directional terms in anatomical terminology. Up is palms of the hands facing forward (figure 1.9). A person is supine replaced by superior, down by inferior, front by anterior, and when lying face upward and prone when lying face downward. back by posterior. The position of the body can affect the description of body In humans, superior is synonymous with cephalic (se-fal′ik), parts relative to each other. In the anatomical position, the which means toward the head, because, when we are in the ana- elbow is above the hand but, in the supine or prone position, tomical position, the head is the highest point. In humans, the the elbow and hand are at the same level. To avoid confusion, term inferior is synonymous with caudal (kaw′dăl), which means relational descriptions are always based on the anatomical posi- toward the tail, which would be located at the end of the vertebral tion, no matter the actual position of the body. Thus, the elbow is column if humans had tails. The terms cephalic and caudal can be always described as being “above” (superior to) the wrist, whether used to describe directional movements on the trunk, but they are the person is lying down or is even upside down. not used to describe directional movements on the limbs. The word anterior means “that which goes before,” and ventral means “belly.” The anterior surface of the human body is Directional Terms therefore the ventral surface, or belly, because the belly “goes first” Directional terms describe parts of the body relative to each when we are walking. The word posterior means “that which fol- other. Important directional terms are illustrated in figure 1.9 lows,” and dorsal means “back.” The posterior surface of the body and summarized in table 1.2. It is important to become familiar is the dorsal surface, or back, which follows as we are walking. 13 van03636_ch01.indd 13 12-09-07 3:13 PM  14 PART 1 Organization of the Human Body Table 1.2 Directional Terms for Humans Terms Etymology* Definition Examples Right Toward the right side of the body Right ear Left Toward the left side of the body Left eye Superior L. higher A structure above another The chin is superior to the navel. Inferior L. lower A structure below another The navel is inferior to the chin. Cephalic G. kephale, head Closer to the head than another structure (usually The chin is cephalic to the navel. synonymous with superior) Caudal L. cauda, a tail Closer to the tail than another structure (usually The navel is caudal to the chin. synonymous with inferior) Anterior L. before The front of the body The navel is anterior to the spine. Posterior L. posterus, following The back of the body The spine is posterior to the breastbone. Ventral L. ventr-, belly Toward the belly (synonymous with anterior) The navel is ventral to the spine. Dorsal L. dorsum, back Toward the back (synonymous with posterior) The spine is dorsal to the breastbone. Proximal L. proximus, nearest Closer to the point of attachment to the body than The elbow is proximal to the wrist. another structure Distal L. di- plus sto, to stand Farther from the point of attachment to the body than The wrist is distal to the elbow. apart or be distant another structure Lateral L. latus, side Away from the midline of the body The nipple is lateral to the breastbone. Medial L. medialis, middle Toward the midline of the body The nose is medial to the eye. Superficial L. superficialis, toward Toward or on the surface (not shown in figure 1.10) The skin is superficial to muscle. the surface Deep O.E. deop, deep Away from the surface, internal (not shown in figure 1.10) The lungs are deep to the ribs. *Origin and meaning of the word: L., Latin; G., Greek; O.E., Old English. Predict 5 Predict 6 The anatomical position of a cat refers to the animal standing erect on all four Use as many directional terms as you can to describe the relationship limbs and facing forward. On the basis of the etymology of the directional between your kneecap and your heel. terms, which two terms indicate movement toward the cat’s head? What two terms mean movement toward the cat’s back? Compare these terms with those referring to a human in the anatomical position. Body Parts and Regions Health professionals use a number of terms when referring to dif- Proximal means “nearest,” whereas distal means “distant.” ferent parts or regions of the body. Figure 1.10 shows the anatomi- These terms are used to refer to linear structures, such as the cal terms, with the common terms in parentheses. limbs, in which one end is near another structure and the other The central region of the body consists of the head, neck, and end is farther away. Each limb is attached at its proximal end to the trunk. The trunk can be divided into the thorax (chest), abdomen body, and the distal end, such as the hand, is farther away. (region between the thorax and pelvis), and pelvis (the inferior end Medial means “toward the midline,” and lateral means “away of the trunk associated with the hips). The upper limb is divided from the midline.” The nose is in a medial position in the face, and into the arm, forearm, wrist, and hand. The arm extends from the the eyes are lateral to the nose. Superficial describes a structure shoulder to the elbow, and the forearm extends from the elbow to close to the surface of the body, and deep is toward the interior of the wrist. The lower limb is divided into the thigh, leg, ankle, and the body. The skin is superficial to muscle and bone. foot. The thigh extends from the hip to the knee, and the leg extends from the knee to the ankle. Note that, contrary to popular usage, the ASSESS YOUR PROGRESS terms arm and leg refer to only a part of the respective limb. The abdomen is often subdivided superficially into quadrants 16. What is anatomical position in humans? Why is it important? by two imaginary lines—one horizontal and one vertical—that 17. What two directional terms indicate “toward the head” in intersect at the navel (figure 1.11a). The quadrants formed are humans? What are the opposite terms? the right-upper, left-upper, right-lower, and left-lower quadrants. 18. What two directional terms indicate “the back” in humans? In addition to these quadrants, the abdomen is sometimes sub- What are the opposite terms? divided into regions by four imaginary lines: two horizontal and 19. Define the following directional terms and give the term that two vertical. These four lines create a “virtual” tic-tac-toe grid means the opposite: proximal, lateral, and superficial. on the abdomen, resulting in nine regions: epigastric, right and van03636_ch01.indd 14 12-09-07 3:13 PM  CHAPTER 1   The Human Organism 15 Frontal (forehead) Orbital (eye) Otic (ear) Head Nasal (nose) Buccal (cheek) Oral (mouth) Mental (chin) Neck Cervical Clavicular (collarbone) Pectoral (chest) Axillary (armpit) Thoracic Sternal (breastbone) (thorax) Brachial (arm) Mammary (breast) Antecubital (front of elbow) Trunk Abdominal (abdomen) Upper limb Umbilical (navel) Antebrachial (forearm) Pelvic (pelvis) Inguinal (groin) Carpal (wrist) Pubic (genital) Palmar (palm)