Chapter 1: The Human Organism PDF

1 C h a P T e r The Human Organism Learn TO PreDiCT renzo, the dancer in the photo, is perfectly balanced, yet a slight movement in any direction would cause him to adjust his position. The human...

1 C h a P T e r The Human Organism Learn TO PreDiCT renzo, the dancer in the photo, is perfectly balanced, yet a slight movement in any 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 before this photo was taken, he’d eaten an energy bar. as an energy bar is digested, blood sugar rises. normally, tiny collections of cells embedded in the pancreas respond to the rise in blood sugar by secreting the chemical insulin. insulin increases the movement of sugar from the blood into the cells. however, renzo did not feel satisfied from his energy bar. he felt dizzy and was still hungry, all symptoms he worried could be due to a family history of diabetes. Fortunately, the on-site trainer tested his blood sugar and noted that it was much higher than normal. after a visit to his regular physician, renzo was outfitted with an insulin pump and his blood sugar levels are more consistent. after reading about homeostasis in this chapter, create an explanation for renzo’s blood sugar levels before and after his visit to the doctor. Module 1 Body Orientation 1.1 anaTOmy Knowing human anatomy and physiology also provides the Learning Outcomes After reading this section, you should be able to basis for understanding disease. The study of human anatomy A. Define anatomy and describe the levels at which anatomy and physiology is important for students who plan a career in can be studied. the health sciences because health professionals need a sound B. explain the importance of the relationship between knowledge of structure and function in order to perform their structure and function. duties. In addition, understanding anatomy and physiology pre- pares all of us to evaluate recommended treatments, critically Human anatomy and physiology is the study of the structure and review advertisements and reports in the popular literature, and function of the human body. The human body has many intricate rationally discuss the human body with health professionals parts with coordinated functions maintained by a complex system and nonprofessionals. of checks and balances. The coordinated function of all the parts Anatomy (ă-nat′ŏ-mē) is the scientific discipline that inves- of the human body allows us to detect changes or stimuli, respond tigates the structure of the body. The word anatomy means to to stimuli, and perform many other actions. dissect, or cut apart and separate, the parts of the body for study. 1 2 Chapter 1 Anatomy covers a wide range of studies, including the structure of Chemical Level body parts, their microscopic organization, and the processes by The structural and functional characteristics of all organisms are which they develop. In addition, anatomy examines the relation- determined by their chemical makeup. The chemical level of ship between the structure of a body part and its function. Just organization involves how atoms, such as hydrogen and carbon, as the structure of a hammer makes it well suited for pounding interact and combine into molecules. The function of a molecule nails, the structure of body parts allows them to perform specific is intimately related to its structure. For example, collagen mol- functions effectively. For example, bones can provide strength and ecules are strong, ropelike fibers that give skin structural strength support because bone cells secrete a hard, mineralized substance. and flexibility. With old age, the structure of collagen changes, and Under­standing the relationship between structure and function the skin becomes fragile and more easily torn. A brief overview makes it easier to understand and appreciate anatomy. of chemistry is presented in chapter 2. Two basic approaches to the study of anatomy are systemic anatomy and regional anatomy. Systemic anatomy is the study of Cell Level the body by systems, such as the cardiovascular, nervous, skeletal, Cells are the basic structural and functional units of organisms, such and muscular systems. It is the approach taken in this and most as plants and animals. Molecules can combine to form organelles introductory textbooks. Regional anatomy is the study of the orga- (or′gă-nelz; little organs), which are the small structures that make nization of the body by areas. Within each region, such as the head, up some cells. For example, the nucleus contains the cell’s hereditary abdomen, or arm, all systems are studied simultaneously. This is information, and mitochondria manufacture adenosine triphosphate the approach taken in most medical and dental schools. (ATP), a molecule cells use for a source of energy. Although cell Anatomists have two general ways to examine the internal types differ in their structure and function, they have many charac- structures of a living person: surface anatomy and anatomical teristics in common. Knowledge of these ­characteristics and their imaging. Surface anatomy is the study of external features, such variations is essential to a basic understanding of anatomy and as bony projections, which serve as landmarks for locating deeper physiology. The cell is discussed in chapter 3. structures (for examples, see chapters 6 and 7). Anatomical imaging involves the use of x-rays, ultrasound, magnetic resonance imag- ing (MRI), and other technologies to create pictures of internal Tissue Level structures. Both surface anatomy and anatomical imaging provide A tissue (tish′ū) is a group of similar cells and the materials surround- important information for diagnosing disease. ing them. The characteristics of the cells and surrounding materials determine the functions of the tissue. The many tissues that make up the body are classified into four primary types: epithelial, con- 1.2 Physiology nective, muscle, and nervous. Tissues are discussed in chapter 4. Learning Outcomes After reading this section, you should be able to Organ Level A. Define physiology. An organ (ōr′găn; a tool) is composed of two or more tissue types B. State two major goals of physiology. that together perform one or more common functions. The ­urinary bladder, skin, stomach, and heart are examples of organs (figure 1.2). Physiology (fiz-ē-ol′ō-jē; the study of nature) is the scientific dis- cipline that deals with the processes or functions of living things. It is important in physiology to recognize structures as dynamic Organ System Level rather than fixed and unchanging. The major goals of physiology An organ system is a group of organs classified as a unit because are (1) to understand and predict the body’s responses to stimuli of a common function or set of functions. For example, the urinary and (2) to understand how the body maintains conditions within system consists of the kidneys, ureter, urinary bladder, and urethra. a narrow range of values in the presence of continually changing The kidneys produce urine, which is transported by the ureters internal and external environments. Human physiology is the study to the urinary bladder, where it is stored until eliminated from of a specific organism, the human, whereas cellular physiology the body by passing through the urethra. In this text, we consider and systemic physiology are subdivisions that emphasize specific eleven major organ systems: integumentary, skeletal, muscular, organizational levels. lymphatic, respiratory, digestive, nervous, endocrine, cardiovascular, urinary, and reproductive (figure 1.3). The coordinated activity of the organ systems is necessary for 1.3 Structural and Functional normal function. For example, the digestive system takes in and Organization of the Human Body processes food, which is carried by the blood of the cardiovascular system to the cells of the other systems. These cells use the food Learning Outcomes After reading this section, you should be able to and produce waste products that are carried by the blood to the kid- A. Describe the six levels of organization of the body, and neys of the urinary system, which removes waste products from the describe the major characteristics of each level. blood. Because the organ systems are so interrelated, dysfunction B. List the eleven organ systems, identify their components, in one organ system can have profound effects on other systems. and describe the major functions of each system. For example, a heart attack can result in inadequate circulation of blood. Consequently, the organs of other systems, such as the The body can be studied at six structural levels: chemical, cell, tissue, brain and kidneys, can malfunction. Throughout this text, Systems organ, organ system, and organism (figure 1.1). Pathology essays consider the interactions of the organ systems.  The human Organism 3 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 Organism Level highly organized. All organisms are composed of one or An organism is any living thing considered as a whole, whether more cells. Some cells, in turn, are composed of highly composed of one cell, such as a bacterium, or of trillions of cells, specialized organelles, which depend on the precise such as a human. The human organism is a complex of organ functions of large molecules. Disruption of this organized systems that are mutually dependent on one another (figure 1.3). state can result in loss of function and death. 2. Metabolism (mĕ-tab′ō-lizm) is the ability to use energy to perform vital functions, such as growth, movement, 1.4 CharaCTeriSTiCS OF LiFe and reproduction. Plants capture energy from sunlight, Learning Outcome After reading this section, you should be able to and humans obtain energy from food. 3. Responsiveness is the ability of an organism to sense A. List and define six characteristics of life. changes in the environment and make the adjustments that help maintain its life. Responses include movement toward Humans are organisms sharing characteristics with other organ- food or water and away from danger or poor environmental isms. The most important common feature of all organisms is life. conditions. Organisms can also make adjustments that This text recognizes six essential characteristics of life: maintain their internal environment. For example, if body 1. Organization refers to the specific interrelationships temperature increases in a hot environment, sweat glands among the parts of an organism and how those parts produce sweat, which can lower body temperature down interact to perform specific functions. Living things are to the normal level. 4 Chapter 1 MICROBES IN YOUR BODY Getting to Know Your Bacteria Did you know that you have sequenced over 20 million unique micro- a detriment, this variation may actually more microbial cells than human cells in bial genes. be very useful for at least one major your body? astoundingly, for every cell in What did scientists learn from the reason. There seems to be a correlation your body, there are ten microbial cells. human microbiome Project? human health between certain diseases and a “charac- That’s as many as 100 trillion microbial is dependent upon the health of our micro- teristic microbiome community,” especially cells, which can collectively account for biota, especially the “good” bacteria. in for autoimmune and inflammatory diseases anywhere between 2 and 6 pounds of your fact, it seems that our microbiota are so (Crohn’s, asthma, multiple sclerosis), which body weight! a microbe is any living thing completely intertwined with human cells have become more prevalent. Scientists are that cannot be seen with the naked eye that in a 2013 New York Times article, beginning to believe that any significant (for example, bacteria, viruses, fungi, and Dr. David relman of Stanford university sug- change in the profile of the microbiome protozoa). The total population of micro- gested that humans are like corals. Corals of the human gut may increase a person’s bial cells on the human body is referred to are marine organisms that are collections susceptibility to autoimmune diseases. it as the microbiota, while the combination of different life forms all existing together. has been proposed that these changes may of these microbial cells and their genes more specifically, the human microbiome is be associated with exposure to antibiotics, is known as the microbiome. The micro- intimately involved in the development and particularly in infancy. Fortunately, newer biota includes so-called “good” bacteria maintenance of the immune system. and studies of microbial transplantations have that do not cause disease and may even more evidence is mounting for a correlation shown that the protective and other func- help us. it also includes pathogenic, or between a host’s microbiota, digestion, and tions of bacteria can be transferred from “bad” bacteria. metabolism. researchers have suggested one person to the next. however, this work With that many microbes in and on that microbial genes are more responsible is all very new and much research remains our bodies, you might wonder how they for our survival than human genes. There to be done. affect our health. To answer that question, are even a few consistent pathogens that Throughout the remainder of this text, in October 2007 the national institute of are present without causing disease, sug- we will highlight specific instances where health (nih) initiated the 5-year human gesting that their presence may be good our microbes influence our body systems. microbiome Project, the largest study of its for us. however, there does not seem to in light of the importance of our body’s kind. Five significant regions of the human be a universal healthy human microbiome. bacteria and other microbes, the preva- body were examined: airway, skin, mouth, rather, the human microbiome varies across lence of antibacterial soap and hand gel gastrointestinal tract, and vagina. This lifespan, ethnicity, nationality, culture, and usage in everyday life may be something project identified over 5000 species and geographical location. instead of being to think about. 4. Growth refers to an increase in size of all or part of the 1.5 hOmeOSTaSiS organism. It can result from an increase in cell number, cell size, or the amount of substance surrounding cells. For Learning Outcomes After reading this section, you should be able to example, bones become larger as the number of bone cells A. Define homeostasis, and explain why it is important for increases and they become surrounded by bone matrix. proper body function. 5. Development includes the changes an organism undergoes B. Describe a negative-feedback mechanism and give through time; it begins with fertilization and ends at death. an example. The greatest developmental changes occur before birth, C. Describe a positive-feedback mechanism and give but many changes continue after birth, and some continue an example. throughout life. Development usually involves growth, but it also involves differentiation. Differentiation is change in Homeostasis (hō′mē-ō-stā′sis; homeo-, the same) is the existence cell structure and function from generalized to specialized. and maintenance of a relatively constant environment within the For example, following fertilization, generalized cells body despite fluctuations in either the external environment or the specialize to become specific cell types, such as skin, bone, internal environment. Most body cells are surrounded by a small muscle, or nerve cells. These differentiated cells form amount of fluid, and normal cell functions depend on the mainte- tissues and organs. nance of the cells’ fluid environment within a narrow range of con- 6. Reproduction is the formation of new cells or new ditions, including temperature, volume, and chemical content. These organisms. Without reproduction of cells, growth and conditions are called variables because their values can change. For tissue repair are impossible. Without reproduction of example, body temperature is a variable that can increase in a hot the organism, the species becomes extinct. environment or decrease in a cold environment.  The human Organism 5 CLINICAL IMPACT Cadavers and the Law The study of human bodies medical schools. Because the bodies were Today, in the united States, it is quite is the foundation of medical education, not easy to obtain and were not always in simple to donate your body for scientific and for much of history, anatomists have the best condition, two enterprising men study. The uniform anatomical gift act used the bodies of people who have died, named William Burke and William hare allows individuals to donate their organs called cadavers, for these studies. however, went one step further. Over a period of or entire cadaver by putting a notation public sentiment has often made it difficult time, they murdered seventeen people in on their driver’s license. you need only for anatomists to obtain human bodies for Scotland and sold their bodies to a medi- to contact a medical school or private dissection. in the early 1800s, the benefits cal school. When discovered, hare testified agency to file the forms that give them of human dissection for training physicians against Burke and went free. Burke was the rights to your cadaver. Once the donor had become very apparent, and the need convicted, hanged, and publicly dissected. dies, the family of the deceased usually for cadavers increased beyond the ability Discovery of Burke’s activities so outraged pays only the transportation costs for the to acquire them legally. Thus arose the the public that sensible laws regulating the remains. after dissection, the body is cre- resurrectionists, or body snatchers. For a acquisition of cadavers were soon passed, mated, and the cremains can be returned fee and no questions asked, they removed and this dark chapter in the history of to the family. bodies from graves and provided them to anatomy was closed. 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 6 Chapter 1 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 body Produces body movements, maintains prevents water loss, and helps produce movements, produces blood cells, and stores posture, and produces body heat. Consists of vitamin D. Consists of skin, hair, nails, and minerals and adipose tissue. Consists of bones, muscles attached to the skeleton by tendons. sweat glands. associated cartilages, ligaments, and joints. Nasal Pharynx Tonsils cavity (throat) Nose Cervical Pharynx Salivary Oral cavity lymph (throat) glands (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 dietary fats blood pH. Consists of the lungs and nutrients, and elimination of wastes. Consists from the digestive tract. Consists of the respiratory passages. of the mouth, esophagus, stomach, lymphatic vessels, lymph nodes, and other intestines, and accessory organs. lymphatic organs. Figure 1.3 Organ Systems of the Body  The Human Organism 7 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) Kidney Seminal Uterine vesicle tube Ureter 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, uterine tubes, uterus, vagina, ducts, and penis. mammary glands, and associated structures. Figure 1.3 Organ Systems of the Body (continued) 8 Chapter 1 such as body temperature; (2) a control center, such as part of the brain, establishes the set point around which the variable is 98.8°F maintained; and (3) an effector (ē-fek′tŏr), such as the sweat Body temperature (normal range) glands, can change the value of the variable. A changed variable 98.6°F Set point is a stimulus because it initiates a homeostatic mechanism. Normal body temperature depends on the coordination of multiple structures, which are regulated by the control center, 98.4°F or hypothalamus, in the brain. If body temperature rises, sweat glands (the effectors) produce sweat and the body cools. If body temperature falls, sweat glands do not produce sweat (figure 1.5). Time (min) The stepwise process that regulates body temperature involves the interaction of receptors, the control center, and effectors. Figure 1.4 Homeostasis Often, there is more than one effector and the control center Homeostasis is the maintenance of a variable, such as body temperature, must integrate them. In the case of elevated body temperature, around an ideal normal value, or set point. The value of the variable thermoreceptors in the skin and hypothalamus detect the increase fluctuates around the set point to establish a normal range of values. in temperature and send the information to the hypothalamus con- trol center. In turn, the hypothalamus stimulates blood vessels in the skin to relax and sweat glands to produce sweat, which sends Homeostatic mechanisms, such as sweating or shivering, more blood to the body’s surface for radiation of heat away from normally maintain body temperature near an ideal normal value, the body. The sweat glands and skin blood vessels are the effec- or set point (figure 1.4). Most homeostatic mechanisms are gov- tors in this scenario. Once body temperature returns to normal, erned by the nervous system or the endocrine system. Note that the control center signals the sweat glands to reduce sweat pro- homeostatic mechanisms are not able to maintain body temperature duction and the blood vessels constrict to their normal diameter. precisely at the set point. Instead, body temperature increases and On the other hand, if body temperature drops, the control center decreases slightly around the set point, producing a normal range does not stimulate the sweat glands. Instead, the skin blood ves- of values. As long as body ­temperatures remain within this normal sels constrict more than normal and blood is directed to deeper range, homeostasis is ­maintained. regions of the body, conserving heat in the interior of the body. The organ systems help control the internal environment so In addition, the hypothalamus stimulates shivering, quick cycles that it remains relatively constant. For example, the digestive, of skeletal muscle contractions, which generates a great amount respiratory, cardiovascular, and urinary systems function together of heat. Again, once the body temperature returns to normal, the so that each cell in the body receives adequate oxygen and nutri- effectors stop. In both cases, the effectors do not produce their ents and so that waste products do not accumulate to a toxic level. responses indefinitely and are controlled by negative feedback. If the fluid surrounding cells deviates from homeostasis, the cells Negative feedback acts to return the variable to its normal range do not function normally and may even die. Disease disrupts (figure 1.6). homeostasis and sometimes results in death. Modern medicine attempts to understand disturbances in homeostasis and works to Predict 2 reestablish a normal range of values. What effect would swimming in cool water have on body temperature regulation mechanisms? What would happen if a negative-feedback mechanism did not return the value Negative Feedback of a variable, such as body temperature, to its normal range? Most systems of the body are regulated by negative-feedback mechanisms, which maintain homeostasis. Negative means that any deviation from the set point is made smaller or is resisted. Positive Feedback Negative feedback does not prevent variation but maintains varia- Positive-feedback mechanisms occur when the initial stimulus tion within a normal range. further stimulates the response. In other words, the deviation The maintenance of normal body temperature is an example from the set point becomes even greater. At times, this type of of a negative-feedback mechanism. Normal body temperature response is required to re-achieve homeostasis. For example, is important because it allows molecules and enzymes to keep during blood loss, a chemical responsible for clot formation their normal shape so they can function optimally. An optimal stimulates production of itself. In this way, a disruption in homeo- body temperature prevents molecules from being permanently stasis is resolved through a positive-feedback mechanism. What destroyed. Picture the change in appearance of egg whites as prevents the entire vascular system from clotting? The clot forma- they are cooked; a similar phenomenon can happen to molecules tion process is self-limiting. Eventually, the components needed in our body if the temperature becomes too high. Thus, normal to form a clot will be depleted in the damaged area and more clot body temperature is required to ensure that tissue homeostasis material cannot be formed (figure 1.7). is maintained. Birth is another example of a normally occurring positive- Many negative-feedback mechanisms, such as the one that feedback mechanism. Near the end of pregnancy, the uterus is maintains normal body temperature, have three components: (1) A stretched by the baby’s large size. This stretching, especially receptor (rē-sep′tŏr, rē-sep′tōr) monitors the value of a variable, around the opening of the uterus, stimulates contractions of the  The human Organism 9 CLINICALIMPACT Humors and Homeostasis The idea that the body main- vessels, but sometimes they applied leeches, had been removed to restore a healthy bal- tains a balance (homeostasis) can be traced blood-eating organisms, to the skin. ance of the body’s juices. Thus, the obvious back to ancient greece. early physicians Tragically, in the eighteenth and solution was to let still more blood, undoubt- believed that the body supported four juic- nineteenth centuries, bloodletting went to edly causing many deaths. eventually, the es, or humors: the red juice of blood, the extremes. During this period, a physician failure of this approach became obvious, yellow juice of bile, the white juice secreted might recommend bloodletting, but barbers and the practice was abandoned. from the nose and lungs, and a black juice conducted the actual procedure. in fact, The modern term for bloodletting is in the pancreas. They also thought that the traditional red-and-white-striped barber phlebotomy (fle-bot′o--me-), but it is prac- health resulted from a proper balance of pole originated as a symbol for bloodletting. ticed in a controlled setting and removes these juices and that an excess of any one The brass basin on top of the pole represent- only small volumes of blood, usually for of them caused disease. normally, they ed the bowl for leeches, and the bowl on the laboratory testing. There are some diseases in believed, the body would attempt to heal bottom represented the basin for collecting which bloodletting is still useful—for exam- itself by expelling the excess juice, as when blood. The stripes represented the bandages ple, polycythemia (pol′e- -sı- -the-′me--ă), mucus runs from the nose of a person with a used as tourniquets, and the pole itself stood an overabundance of red blood cells. cold. This belief led to the practice of blood- for the wooden staff patients gripped during however, bloodletting in these patients letting to restore the body’s normal balance the procedure. The fact that bloodletting does not continue until the patient faints or of juices. Typically, physicians used sharp did not improve the patient’s condition was dies. Fortunately, we now understand more instruments to puncture the larger, external taken as evidence that not enough blood about how the body maintains homeostasis. 1 Receptors monitor the value of a variable. In this case, receptors in the skin monitor body temperature. 1 Receptors monitor 2 Information about the value 2 body temperature. of the variable is sent to a control center. In this case, nerves send information to the part of the brain Nerves responsible for regulating 5 body temperature. 3 Effector (sweat gland) 3 The control center Control center 4 responds to changes compares the value of the (brain) in body temperature. Sweat gland variable against the set point. 4 If a response is necessary to 5 An effector produces a maintain homeostasis, the response that maintains control center causes an homeostasis. In this case, effector to respond. In this stimulating sweat glands case, nerves send information lowers body temperature. to the sweat glands. Figure 1.5 Negative-Feedback Mechanism: Body Temperature uterine muscles. The uterine contractions push the baby against (heart) muscle. Contraction of cardiac muscle generates blood pres- the opening of the uterus, stretching it further. This stimulates sure and moves blood through the blood vessels to the tissues. A additional contractions, which result in additional stretching. This system of blood vessels on the outside of the heart provides cardiac positive-feedback sequence ends when the baby is delivered from muscle with a blood supply sufficient to allow normal contractions the uterus and the stretching stimulus is eliminated. to occur. In effect, the heart pumps blood to itself. Just as with On the other hand, occasionally a positive-feedback mecha- other tissues, blood pressure must be maintained to ensure adequate nism can be detrimental. One example of a detrimental positive- delivery of blood to the cardiac muscle. Following extreme blood feedback mechanism is inadequate delivery of blood to cardiac loss, blood pressure decreases to the point that the delivery of blood 10 Chapter 1 3 4 Actions Reactions Control centers in the brain increase stimulation of sweat glands and relax blood vessels in the skin when Effectors receptors detect increased body Respond: temperature. Sweat glands produce Sweat gland sweat; blood vessels in the skin dilate. Homeostasis Disturbed: Homeostasis Restored: 2 5 Body temperature decreases. Body temperature increases. Body temperature Body temperature (normal range) (normal range) 1 Start Here 6 Homeostasis Disturbed: Homeostasis Restored: Body temperature decreases. Body temperature increases. Actions Reactions Control centers in the brain decrease stimulation of sweat glands and constrict blood vessels in the skin Effectors Respond: when receptors detect decreased Sweat glands cease body temperature. sweat production; blood vessels in the skin constrict; Sweat gland skeletal muscle contracts (shivering). Homeostasis Figure 1.6 Negative-Feedback Control of Body Temperature 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) Body temperature is within its normal range. (2) Body temperature increases outside the normal range, which causes homeostasis to be disturbed. (3) The body temperature control center in the brain responds to the change in body temperature. (4) The control center causes sweat glands to produce sweat and blood vessels in the skin to dilate. (5) These changes cause body temperature to decrease. (6) Body temperature returns to its normal range, and homeostasis is restored. Observe the responses to a decrease in body temperature outside its normal range by following the red arrows.  The Human Organism 11 When you begin to study anatomy and physiology, the number SUBSTRATE SUBSTRATE of new words may seem overwhelming. Learning is easier and Enzyme A Enzyme A more interesting if you pay attention to the origin, or etymology Inactive intermediate 1 Inactive intermediate 1 (et′ ĕ-mol′o-jē), of new words. Most of the terms are derived from Latin or Greek. For example, anterior in Latin means “to go Enzyme B Enzyme B – + before.” Therefore, the anterior surface of the body is the one that Inactive intermediate 2 Inactive intermediate 2 goes before when we are walking. Words are often modified by adding a prefix or suffix. For Enzyme C Enzyme C example, the suffix -itis means an inflammation, so appendicitis Active product Active product is an inflammation of the appendix. As new terms are introduced (a) Negative feedback (b) Positive feedback in this text, their meanings are often explained. The glossary and the list of word roots, prefixes, and suffixes on the inside back cover of the textbook also provide additional information about Figure 1.7 Comparison of Negative-feedback and the new terms. Positive-feedback Mechanisms (a) In negative feedback, the response stops the effector. (b) In positive Body Positions feedback, the response keeps the reaction going. For example, during blood The anatomical position refers to a person standing erect clotting, the "active product" represents thrombin, which triggers, "enzyme A," the first step in the cascade that leads to the production of thrombin. with the face directed forward, the upper limbs hanging to the sides, and the palms of the hands facing forward (figure 1.8). A person is supine when lying face upward and prone when lying to cardiac muscle is inadequate. As a result, cardiac muscle homeo- face downward. stasis is disrupted, and cardiac muscle does not function normally. The position of the body can affect the description of body The heart pumps less blood, which causes the blood pressure to parts relative to each other. In the anatomical position, the elbow is drop even lower. The additional decrease in blood pressure further above the hand, but in the supine or prone position, the elbow and reduces blood delivery to cardiac muscle, and the heart pumps even hand are at the same level. To avoid confusion, relational descrip- less blood, which again decreases the blood pressure. The process tions are always based on the anatomical position, no matter the continues until the blood pressure is too low to sustain the cardiac actual position of the body. muscle, the heart stops beating, and death results. Following a moderate amount of blood loss (e.g., after donating a Directional Terms pint of blood), negative-feedback mechanisms result in an increase Directional terms describe parts of the body relative to each in heart rate that restores blood pressure. However, if blood loss is other (figure 1.8 and table 1.1). It is important to become familiar severe, negative-feedback mechanisms may not be able to maintain with these directional terms as soon as possible because you will homeostasis, and the positive-feedback effect of an ever-decreasing see them repeatedly throughout the text. Right and left are used blood pressure can develop. as directional terms in anatomical terminology. Up is replaced A basic principle to remember is that many disease states by superior, down by inferior, front by anterior, and back result from the failure of negative-feedback mechanisms to main- by posterior. tain homeostasis. The purpose of medical therapy is to overcome As previously mentioned, the word anterior means that which illness by aiding negative-feedback mechanisms. For example, a goes before; the word ventral means belly. Therefore, the anterior transfusion can reverse a constantly decreasing blood pressure and surface of the human body is also called the ventral surface, or restore homeostasis. belly, because the belly “goes first” when we are walking. The word posterior means that which follows, and dorsal means back. Predict 3 Thus, the posterior surface of the body is the dorsal surface, or Is the sensation of thirst associated with a negative- or a positive- back, which follows as we are walking. feedback mechanism? Explain. (Hint: What is being regulated when Proximal means nearest, whereas distal means distant. These you become thirsty?) terms are used to refer to linear structures, such as the limbs, in which one end is near another structure and the other end is farther 1.6 Terminology and the Body Plan away. Each limb is attached at its proximal end to the body, and the distal end, such as the hand, is farther away. Learning Outcomes After reading this section, you should be able to Medial means toward the midline, and lateral means away A. Describe a person in anatomical position. from the midline. The nose is located in a medial position on the B. Define the directional terms for the human body, and face, and the ears are lateral to the nose. The term superficial use them to locate specific body structures. refers to a structure close to the surface of the body, and deep is C. Know the terms for the parts and regions of the body. toward the interior of the body. For example, the skin is superficial D. Name and describe the three major planes of the body to muscle and bone. and the body organs. E. Describe the major trunk cavities and their divisions. Predict 4 F. Describe the serous membranes, their locations, and Provide the correct directional term for the following statement: their functions. When a boy is standing on his head, his nose is ______ to his mouth. 12 Chapter 1 Superior Right Left (cephalic) Superior (cephalic) Midline Proximal Anterior Posterior Inferior Medial (dorsal) (caudal) (ventral) Distal Lateral Inferior (caudal) Proximal Distal Distal Proximal Figure 1.8 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. TABLE 1.1 Directional Terms for the Human Body Term Etymology Definition* Example right Toward the body’s right side The right ear Left Toward the body’s left side The left ear inferior Lower Below The nose is inferior to the forehead. Superior higher above The mouth is superior to the chin. anterior To go before Toward the front of the body The teeth are anterior to the throat. Posterior Posterus, following Toward the back of the body The brain is posterior to the eyes. Dorsal Dorsum, back Toward the back (synonymous with posterior) The spine is dorsal to the breastbone. Ventral Venter, belly Toward the belly (synonymous with anterior) The navel is ventral to the spine. Proximal Proximus, nearest Closer to a point of attachment The elbow is proximal to the wrist. Distal di + sto, to be distant Farther from a point of attachment The knee is distal to the hip. Lateral Latus, side away from the midline of the body The nipple is lateral to the breastbone. medial Medialis, middle Toward the middle or midline of the body The bridge of the nose is medial to the eye. Superficial Superficialis, surface Toward or on the surface The skin is superficial to muscle. Deep Deop, deep away from the surface, internal The lungs are deep to the ribs. *all directional terms refer to a human in the anatomical position.  The Human Organism 13 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) Manual (hand) Digital (fingers) Coxal (hip) Femoral (thigh) Patellar (kneecap) Crural (leg) Lower limb (a) Figure 1.9 Body Parts and Regions Talus (ankle) The anatomical and common (in parentheses) names are indicated Dorsum (top of foot) Pedal (foot) for some parts and regions of the body. (a) Anterior view. Digital (toes) Body Parts and Regions (hı̄-pō-kon′drē-ak), umbilical (ŭm-bil′i-kăl), right and left lumbar Health professionals use a number of terms when referring to dif- (lŭm′bar), hypogastric (hı̄-pō-gas′trik), and right and left iliac ferent regions or parts of the body. Figure 1.9 shows the anatomical (il′ē-ak) (figure 1.10b). Clinicians use the quadrants or regions as terms, with the common terms in parentheses. The central region reference points for locating the underlying organs. For example, of the body consists of the head, neck, and trunk. The trunk can the appendix is in the right-lower quadrant, and the pain of an be divided into the thorax (chest), abdomen (region between acute appendicitis is usually felt there. the thorax and pelvis), and pelvis (the inferior end of the trunk Predict 5 associated with the hips). The upper limb is divided into the arm, Using figures 1.2 and 1.10a, determine in which quadrant each of forearm, wrist, and hand. The arm extends from the shoulder to the the following organs is located: spleen, gallbladder, kidneys, most elbow, and the forearm extends from the elbow to the wrist. The of the stomach, and most of the liver. lower limb is divided into the thigh, leg, ankle, and 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 terms arm and A CASE IN POINT leg refer to only a part of the respective limb. Epigastric Pain The abdomen is often subdivided superficially into four Wilby Hurtt has pain in the epigastric region (figure 1.10b), which sections, or quadrants, by two imaginary lines—one horizontal is most noticeable following meals and at night when he is lying and one vertical—that intersect at the navel (figure 1.10a). The in bed. He probably has gastroesophageal reflux disease (GERD), quadrants formed are the right-upper, left-upper, right-lower, and in which stomach acid improperly moves into the esophagus, left-lower quadrants. In addition to these quadrants, the abdo- damaging and irritating its lining. Epigastric pain, however, can have men is sometimes subdivided into regions by four imaginary many causes and should be evaluated by a physician. For example, lines—two horizontal and two vertical. These four lines create gallstones, stomach or small intestine ulcers, inflammation of the an imaginary tic-tac-toe figure on the abdomen, resulting in nine pancreas, and heart disease can also cause epigastric pain. regions: epigastric (ep-i-gas′trik), right and left hypochondriac 14 Chapter 1 Cranial (skull) Occipital (base of skull) Nuchal (back of neck) Acromial (point of shoulder) Scapular (shoulder blade) Dorsal Vertebral (spinal column) (back) Olecranon (point of elbow) Upper limb Lumbar (loin) Trunk Sacral (between hips) Dorsum (back of hand) Gluteal (buttock) Perineal (perineum) Popliteal (hollow behind knee) Sural (calf) (b) Lower limb Figure 1.9 Body Parts and Regions (continued) Plantar (sole) (b) Posterior view. Calcaneal (heel) Right Left hypochondriac Epigastric hypochondriac region region region Right-upper Left-upper quadrant quadrant Right Left lumbar Umbilical lumbar region region region Right-lower Left-lower quadrant quadrant Right Left iliac Hypogastric iliac region region region (a) (b) Figure 1.10 Subdivisions of the Abdomen Lines are superimposed over internal organs to demonstrate the relationship of the organs to the subdivisions. (a) Abdominal quadrants consist of four subdivisions. (b) Abdominal regions consist of nine subdivisions.  The Human Organism 15 Cerebrum Cerebellum Nasal cavity Brainstem Tongue Spinal cord Pharynx (throat) Vertebral column Trachea (b) Sagittal section of the head Sagittal plane Transverse, or horizontal, plane Stomach Liver Large intestine Spleen Kidney Vertebra Spinal Kidney cord Frontal, or coronal, plane (c) Transverse section through the abdomen Skin Adipose tisse Hip muscle (a) Coxal bone (hipbone) Femur (thighbone) Thigh muscles Figure 1.11 Planes of Section of the Body (d) Frontal section through the right hip (a) Planes of section through the body are indicated by “glass” sheets. Also shown are actual sections through (b) the head (viewed from the right), (c) the abdomen (inferior view; liver is on the right), and (d) the hip (anterior view). 16 Chapter 1 Planes At times, it is conceptually useful to discuss the body in reference to a series of planes (imaginary flat surfaces) passing through it Longitudinal section (figure 1.11). Sectioning the body is a way to “look inside” and observe the body’s structures. A sagittal (saj′i-tăl) plane runs ­vertically through the body and separates it into right and left parts. The word sagittal literally means the flight of an arrow and refers to the way the body would be split by an arrow passing ante- riorly to posteriorly. A median plane is a sagittal plane that passes Intestine through the midline of the body, dividing it into equal right and left halves. A transverse (trans-vers′) plane, or horizontal plane, runs parallel to the surface of the ground, dividing the body into superior and inferior parts. A frontal plane, or coronal (kōr′ ŏ-năl, kō-rō′nal; crown) plane, runs vertically from right to left and divides the body into anterior and posterior parts. Organs are often sectioned to reveal their internal structure (figure 1.12). A cut through the long axis of the organ is a longi­ tudinal section, and a cut at a right angle to the long axis is a transverse section, or cross section. If a cut is made across the long axis at other than a right angle, it is called an oblique section. Body Cavities Transverse Oblique section section The body contains many cavities. Some of these cavities, such as the nasal cavity, open to the outside of the body, and some do Figure 1.12 Planes of Section Through an Organ not. The trunk contains three large cavities that do not open to the outside of the body: the thoracic cavity, the abdominal cavity, and Planes of section through the small intestine are indicated by “glass” sheets. The views of the small intestine after sectioning are also shown. the pelvic cavity (figure 1.13). The thoracic cavity is surrounded Although the small intestine is basically a tube, the sections appear quite by the rib cage and is separated from the abdominal cavity by different in shape. the muscular diaphragm. It is divided into right and left parts Esophagus Trachea Mediastinum (divides Blood vessels thoracic cavity) Thymus Thoracic cavity Heart Abdominal cavity Diaphragm Abdominal Abdominopelvic cavity cavity Pelvic cavity Pelvic Symphysis cavity pubis (a) (b) Figure 1.13 Trunk Cavities (a) Anterior view showing the major trunk cavities. The diaphragm separates the thoracic cavity from the abdominal cavity. The mediastinum, which includes the heart, is a partition of organs dividing the thoracic cavity. (b) Sagittal section of the trunk cavities viewed from the left. The dashed line shows the division between the abdominal and pelvic cavities. The mediastinum has been removed to show the thoracic cavity.  The human Organism 17 by a median structure called the mediastinum (me′dē-as-tı̄′nŭm; A pleural (ploor′ ăl; associated with the ribs) cavity surrounds wall). The mediastinum is a partition containing the heart, the each lung, which is covered by visceral pleura (figure 1.15b). thymus, the trachea, the esophagus, and other structures. The two Parietal pleura lines the inner surface of the thoracic wall, the lateral lungs are located on each side of the mediastinum. surfaces of the mediastinum, and the superior surface of the dia- The abdominal cavity is bounded primarily by the abdomi- phragm. The pleural cavity is located between the visceral pleura nal muscles and contains the stomach, the intestines, the liver, the and the parietal pleura and contains pleural fluid. spleen, the pancreas, and the kidneys. The pelvic (pel′vik) cavity The abdominopelvic cavity contains a serous membrane-lined is a small space enclosed by the bones of the pelvis and contains cavity called the peritoneal (per′i-tō-nē′ ăl; to stretch over) cavity the urinary bladder, part of the large intestine, and the internal (figure 1.15c). Visceral peritoneum covers many of the organs of reproductive organs. The abdominal and pelvic cavities are not the abdominopelvic cavity. Parietal peritoneum lines the wall of the physically separated and sometimes are called the abdominopelvic abdominopelvic cavity and the inferior surface of the diaphragm. (ab-dom′i-nō-pel′vik) cavity. The peritoneal cavity is located between the visceral peritoneum and the parietal peritoneum and contains peritoneal fluid. Serous membranes The serous membranes can become inflamed—usually as a result of an infection. Pericarditis (per′i-kar-dı̄′tis) is inflammation Serous (sēr′ ŭs) membranes line the trunk cavities and cover the of the pericardium, pleurisy (ploor′i-sē) is inflammation of the pleu- organs of these cavities. To understand the relationship between ra, and peritonitis (per′i-tō-nı̄′tis) is inflammation of the peritoneum. serous membranes and an organ, imagine pushing your fist into an inflated balloon. The inner balloon wall in contact with your fist (organ) represents the visceral (vis′er-ăl; organ) serous membrane, a CaSe in POinT and the outer part of the balloon wall represents the parietal (pă-rı̄′ ĕ- tăl; wall) serous membrane (figure 1.14). The cavity, or space, Peritonitis between the visceral and parietal serous membranes is normally filled may Day is rushed to the hospital emergency room. earlier today, with a thin, lubricating film of serous fluid produced by the mem- she experienced diffuse abdominal pain, but no fever. Then branes. As an organ rubs against another organ or against the body the pain became more intense and shifted to her right-lower wall, the serous fluid and smooth serous membranes reduce friction. quadrant. She also developed a fever. The examining physician concludes that may Day has appendicitis, an inflammation of the The thoracic cavity contains three serous membrane-lined appendix that is usually caused by an infection. The appendix is cavities: a pericardial cavity and two pleural cavities. The peri- a small, wormlike sac attached to the large intestine. The outer cardial (per-i-kar′dē-ăl; around the heart) cavity surrounds the surface of the appendix is visceral peritoneum. an infection of heart (figure 1.15a). The visceral pericardium covers the heart, the appendix can rupture its wall, releasing bacteria into the which is contained within a connective tissue sac lined with the peritoneal cavity and causing peritonitis. appendicitis is the most parietal pericardium. The pericardial cavity, which contains peri- common cause of emergency abdominal surgery in children, and cardial fluid, is located between the visceral pericardium and the it often leads to peritonitis if not treated. may has her appendix parietal pericardium. removed, is treated with antibiotics, and makes a full recovery. Outer balloon wall Outer balloon wall (parietal serous membrane) Inner balloon wall Inner balloon wall (visceral serous Cavity membrane) Fist (organ)