《医学生理学 Medical Physiology》参考教材资料（PDF电子书籍）Mader Understanding Human Anatomy and Physiology 5th edition

Mader: Understanding ② The McG Human Anatomy ysiology, Fifth Edition Figure 1.6 Clinical subdivisions of the abdomen into quadrants. these subdivisions help physicians identify the location of stomach lower quadrant quadrant urinary bladder The right and left portions of the thoracic cavity contain Clinically speaking the abdominopelvic cavity is divided the lungs. The lungs are surrounded by a serous membrane into four quadrants by running a transverse plane across the called the pleura. The parietal pleura lies next to the tho. midsagittal plane at the point of the navel(Fig. 1. 6a). Physi- raic wall, and the visceral pleura adheres to a lung. In be. cians commonly use these quadrants to identify the locations tween the two pleura, the pleural cavity is filled with pleural of patients' symptoms. The four quadrants are: (1)right upper fluid. Similarly, in the mediastinum, the heart is covered by quadrant, (2) left upper quadrant, (3)right lower quadrant, the two-layered membrane called the pericardium. The vis and(4)left lower quadrant ceral pericardium which adheres to the heart is separate Figure 1. 6b shows the organs that lie within these four from the parietal pericardium by a small space called the quadrants. pericardial cavity (Fig. 1.5b). This small space contains pericardial fluid. Table 1.1 Body Cavities and Membranes Abdominopelvic Cavity vity Contents Membranes The abdominopelvic cavity has two portions: the superior ab- dominal cavity and the inferior pelvic cavity. The stomach, POSTERIOR BODY CAVITY liver, spleen, gallbladder, and most of the small and large in-Cranial ca Meninges Vertebral canal Spinal cord ans, and the rest of the large intestine. Males have an external ANTERIOR BODY CAVITY extension of the abdominal wall, called the scrotum where the testes are found Thoracic Cavity Many of the organs of the abdominopelvic cavity are cov- Lung ered by the visceral peritoneum, while the wall of the ab- Pericardium dominal cavity is lined with the parietal peritoneum. Peri Abdominopelvic Cavity toneal fluid fills the cavity between the visceral and parietal peritoneum. Peritonitis, another serious condition, is an in liver kidne flammation of the peritoneum, again usually caused by an Pelvic cavity eCm Peritoneum fection. Table 1.1 summarizes our discussion of body cavities urinary bladder, and membranes Chapter 1 Organization of the Body7

Mader: Understanding Human Anatomy & Physiology, Fifth Edition I. Human Organization 1. Organization of the Body © The McGraw−Hill Companies, 2004 The right and left portions of the thoracic cavity contain the lungs. The lungs are surrounded by a serous membrane called the pleura. The parietal pleura lies next to the tho￾raic wall, and the visceral pleura adheres to a lung. In be￾tween the two pleura, the pleural cavity is filled with pleural fluid. Similarly, in the mediastinum, the heart is covered by the two-layered membrane called the pericardium. The vis￾ceral pericardium which adheres to the heart is separated from the parietal pericardium by a small space called the pericardial cavity (Fig. 1.5b). This small space contains pericardial fluid. Abdominopelvic Cavity The abdominopelvic cavity has two portions: the superior ab￾dominal cavity and the inferior pelvic cavity. The stomach, liver, spleen, gallbladder, and most of the small and large in￾testines are in the abdominal cavity. The pelvic cavity contains the rectum, the urinary bladder, the internal reproductive or￾gans, and the rest of the large intestine. Males have an external extension of the abdominal wall, called the scrotum, where the testes are found. Many of the organs of the abdominopelvic cavity are cov￾ered by the visceral peritoneum, while the wall of the ab￾dominal cavity is lined with the parietal peritoneum. Peri￾toneal fluid fills the cavity between the visceral and parietal peritoneum. Peritonitis, another serious condition, is an in- flammation of the peritoneum, again usually caused by an in￾fection. Table 1.1 summarizes our discussion of body cavities and membranes. Clinically speaking, the abdominopelvic cavity is divided into four quadrants by running a transverse plane across the midsagittal plane at the point of the navel (Fig. 1.6a). Physi￾cians commonly use these quadrants to identify the locations of patients’ symptoms. The four quadrants are: (1) right upper quadrant, (2) left upper quadrant, (3) right lower quadrant, and (4) left lower quadrant. Figure 1.6b shows the organs that lie within these four quadrants. Chapter 1 Organization of the Body 7 a. b. right upper quadrant left upper quadrant right lower quadrant left lower quadrant sternum lung stomach large intestine small intestine urinary bladder femur Figure 1.6 Clinical subdivisions of the abdomen into quadrants. These subdivisions help physicians identify the location of various symptoms. Table 1.1 Body Cavities and Membranes Name of Cavity Contents Membranes POSTERIOR BODY CAVITY Cranial cavity Brain Meninges Vertebral canal Spinal cord Meninges ANTERIOR BODY CAVITY Thoracic Cavity Lungs Pleura Heart Pericardium Abdominopelvic Cavity Abdominal cavity Digestive organs, Peritoneum liver, kidneys Pelvic cavity Reproductive organs, Peritoneum urinary bladder, rectum

Mader: Understanding ② The McG ysiology, Fifth Edition 1.4 Organ Systems tion is then processed by the brain and spinal cord, and the ndividual responds to environmental stimuli through the The organs of the body work together in systems. Today, cer- muscular system tain diseased organs can be replaced by organ transplanta- The endocrine system, discussed in Chapter 10, consists tion, during which a healthy organ is received from a donor. of the hormonal glands that secrete chemicals that serve as In the future, tissue engineering may provide organs for trans- messengers between body parts. Both the nervous and en- plant, as discussed in the Medical Focus on page 9 The reference figures in Appendix A can serve as an aid to environment by coordinating and regulating the functions of earning the ll organ systems and their placement. The type the bodys other systems. The nervous system acts quickly but of illustration that will be used at the end of each of the organ has a short-lived effect; the endocrine system acts more slowly system chapters is introduced on page 13. In this chapter, the but has a more sustained effect on body parts. The endocrine illustration demonstrates the general functions of the bod system also helps maintain the proper functioning of the organ systems. The corresponding illustrations in the organ male and female reproductive organs stem chapters will show how a particular organ system in tracts with all the other systems. In this text, the organ sys- Maintenance of the body tems of the body have been divided into four categories, as discussed next The internal environment of the body is the blood within the blood vessels and the tissue fluid that surrounds the cells. five Support, Movement, and Protection systems add substances to and/ or remove substances from the blood: the cardiovascular, lymphatic, respiratory, digestive, The integumentary system, discussed in Chapter 5, include nd urinary syst the skin and accessory organs, such as the hair, nails, sweat The cardiovascular system, discussed in Chapter 12, con- glands, and sebaceous glands. The skin protects underlying sists of the heart and the blood vessels that carry blood tissues, helps regulate body temperature, contains sense or- through the body. Blood transports nutrients and oxygen to gans, and even synthesizes certain chemicals that affect the the cells, and removes waste molecules to be excreted from rest of the body. the body. Blood also contains cells produced by the lym The skeletal system and the muscular system give the phatic system, discussed in Chapter 13. The lymphatic system ody support and are involved in the ability of the body and protects the body from di Its parts to move. The respiratory system, discussed in Chapter 14, consists The skeletal system, discussed in Chapter 6, consists of of the lungs and the tubes that take air to and from the lungs the bones of the skeleton and associated cartilage, as well as The respiratory system brings oxygen into the lungs and takes the ligaments that bind these structures together. The skeleton carbon dioxide out of the lungs protects body parts. For example, the skull forms a protective The digestive system( see Fig. 1.1), discussed in encasement for the brain, as does the rib cage for the heart 15, consists of the mouth, esophagus, stomach, small intes- and lungs. Some bones produce blood cells, and all bones are tine, and large intestine(colon), along with the accessory or a storage area for calcium and phosphorus salts. The skeleton gans: teeth, tongue, salivary glands, liver, gallbladder, and as a whole serves as a place of attachment for the muscles pancreas. This system receives food and digests it into nutri- Contraction of skeletal muscles, discussed in Chapter 7, ent molecules, which can enter the cells of the body. accounts for our ability to move voluntarily and to respond The urinary system, discussed in Chapter 16, contains to outside stimuli. These muscles also maintain posture and the kidneys and the urinary bladder. This system rids the body are responsible for the production of body heat. Cardiac mu of nitrogenous wastes and helps regulate the fluid level and le and smooth muscle are called involuntary muscles because chemical content of the bloo contract automatically. Cardiac muscle makes up the heart, and smooth muscle is found within the walls of inter- Reproduction and Development nal organs. The male and female reproductive systems, discussed in Integration and Coordination Chapter 17, contain different organs. The male reproductive sys- tem consists of the testes, other glands, and various ducts that The nervous system, discussed in Chapter 8, consists of the conduct semen to and through the penis. The female repro- brain, spinal cord, and associated nerves. The nerves conduct ductive system consists of the ovaries, uterine tubes, uterus, nerve impulses from the sense organs to the brain and spinal vagina, and external genitalia. Both systems produce sex cells, cord. They also conduct nerve impulses from the brain and but in addition, the female system receives the sex cells of the spinal cord to the muscles and glands. male and also nourishes and protects the fetus until the time The sense organs, discussed in Chapter 9, provide us with of birth. Development before birth and the process of birth information about the outside environment. This informa- are discussed in Chapter 18 Part I Human Organization

Mader: Understanding Human Anatomy & Physiology, Fifth Edition I. Human Organization 1. Organization of the Body © The McGraw−Hill Companies, 2004 1.4 Organ Systems The organs of the body work together in systems. Today, cer￾tain diseased organs can be replaced by organ transplanta￾tion, during which a healthy organ is received from a donor. In the future, tissue engineering may provide organs for trans￾plant, as discussed in the Medical Focus on page 9. The reference figures in Appendix A can serve as an aid to learning the 11 organ systems and their placement. The type of illustration that will be used at the end of each of the organ system chapters is introduced on page 13. In this chapter, the illustration demonstrates the general functions of the body’s organ systems. The corresponding illustrations in the organ system chapters will show how a particular organ system in￾teracts with all the other systems. In this text, the organ sys￾tems of the body have been divided into four categories, as discussed next. Support, Movement, and Protection The integumentary system, discussed in Chapter 5, includes the skin and accessory organs, such as the hair, nails, sweat glands, and sebaceous glands. The skin protects underlying tissues, helps regulate body temperature, contains sense or￾gans, and even synthesizes certain chemicals that affect the rest of the body. The skeletal system and the muscular system give the body support and are involved in the ability of the body and its parts to move. The skeletal system, discussed in Chapter 6, consists of the bones of the skeleton and associated cartilage, as well as the ligaments that bind these structures together. The skeleton protects body parts. For example, the skull forms a protective encasement for the brain, as does the rib cage for the heart and lungs. Some bones produce blood cells, and all bones are a storage area for calcium and phosphorus salts. The skeleton as a whole serves as a place of attachment for the muscles. Contraction of skeletal muscles, discussed in Chapter 7, accounts for our ability to move voluntarily and to respond to outside stimuli. These muscles also maintain posture and are responsible for the production of body heat. Cardiac mus￾cle and smooth muscle are called involuntary muscles because they contract automatically. Cardiac muscle makes up the heart, and smooth muscle is found within the walls of inter￾nal organs. Integration and Coordination The nervous system, discussed in Chapter 8, consists of the brain, spinal cord, and associated nerves. The nerves conduct nerve impulses from the sense organs to the brain and spinal cord. They also conduct nerve impulses from the brain and spinal cord to the muscles and glands. The sense organs, discussed in Chapter 9, provide us with information about the outside environment. This informa￾tion is then processed by the brain and spinal cord, and the individual responds to environmental stimuli through the muscular system. The endocrine system, discussed in Chapter 10, consists of the hormonal glands that secrete chemicals that serve as messengers between body parts. Both the nervous and en￾docrine systems help maintain a relatively constant internal environment by coordinating and regulating the functions of the body’s other systems. The nervous system acts quickly but has a short-lived effect; the endocrine system acts more slowly but has a more sustained effect on body parts. The endocrine system also helps maintain the proper functioning of the male and female reproductive organs. Maintenance of the Body The internal environment of the body is the blood within the blood vessels and the tissue fluid that surrounds the cells. Five systems add substances to and/or remove substances from the blood: the cardiovascular, lymphatic, respiratory, digestive, and urinary systems. The cardiovascular system, discussed in Chapter 12, con￾sists of the heart and the blood vessels that carry blood through the body. Blood transports nutrients and oxygen to the cells, and removes waste molecules to be excreted from the body. Blood also contains cells produced by the lym￾phatic system, discussed in Chapter 13. The lymphatic system protects the body from disease. The respiratory system, discussed in Chapter 14, consists of the lungs and the tubes that take air to and from the lungs. The respiratory system brings oxygen into the lungs and takes carbon dioxide out of the lungs. The digestive system (see Fig. 1.1), discussed in Chapter 15, consists of the mouth, esophagus, stomach, small intes￾tine, and large intestine (colon), along with the accessory or￾gans: teeth, tongue, salivary glands, liver, gallbladder, and pancreas. This system receives food and digests it into nutri￾ent molecules, which can enter the cells of the body. The urinary system, discussed in Chapter 16, contains the kidneys and the urinary bladder. This system rids the body of nitrogenous wastes and helps regulate the fluid level and chemical content of the blood. Reproduction and Development The male and female reproductive systems, discussed in Chapter 17, contain different organs. The male reproductive sys￾tem consists of the testes, other glands, and various ducts that conduct semen to and through the penis. The female repro￾ductive system consists of the ovaries, uterine tubes, uterus, vagina, and external genitalia. Both systems produce sex cells, but in addition, the female system receives the sex cells of the male and also nourishes and protects the fetus until the time of birth. Development before birth and the process of birth are discussed in Chapter 18. 8 Part I Human Organization

Mader: Understanding ② The McG ysiology, Fifth Edition What's New Organs for transplant Transplantation of a human kidney, heart, liver, pancreas, lung, make some bioartificial organs-hybrids created from a comb and other organs is now possible due to two major break nation of living cells and biodegradable polymers. Presently, lab- throughs. First, solutions have been developed that preserve grown hybrid tissues are on the market. For example, a product donor organs for several hours. This made it possible for one composed of skin cells growing on a polymer is used to tem- young boy to undergo surgery for 16 hours, during which time he porarily cover the wounds of burn patients. Similarly, damaged received five different organs. Second, rejection of transplanted cartilage can be replaced with a hybrid tissue produced after organs is now prevented by immunosuppressive drugs; therefore, chondrocytes are harvested from a patient. Another connective organs can be donated by unrelated individuals, living or dead. tissue product made from fibroblasts and collagen is available to Even so, rejection is less likely to happen if the donors tissues help heal deep wounds without scarring. Soon to come are a host match" those of the recipient-that is, their cell surface mole. of other products, including replacement corneas, heart valves, cules should be similar to one another. Living individuals can de bladder valves, and breast tissue. nate one kidney, a portion of their liver, and certainly bone m. The ultimate goal of tissue engineering is to produce fully row, which quickly regenerates functioning transplant organs in the laboratory. After nine years, After death, it is still possible to give the "gift of life"to some. Harvard Medical School team headed by Anthony Atala has one else-over 25 organs and tissues from the same person can be duced a working urinary bladder. After testing the bladder in lab- used for transplants at that time. A liver transplant, for example, oratory animals, the harvard group is ready to test it in humans can save the life of a child born with biliary atresia, a congenital de- whose own bladders have been damaged by accident or disease, fect in which the bile ducts do not form. Dr Thomas Starzl, a pio- or will not function properly due to a congenital birth defect. An- neer in this field, reports a 90% chance of complete rehabilitation other group of scientists has been able to grow arterial blood ves- among children who survive a liver transplant. (He has also tried sels in the laboratory. Tissue engineers are hopeful that they will inimal-to-human liver transplants, but so far, these have not been one day produce more complex organs such as a liver or kidney. successful. )So many heart recipients are now alive and healthy that they have formed basketball and softball teams, demon- strating the normalcy of their lives after surgery. One problem persists: The number of Americans waiting for organs now stands at over 80,000 and is get- ng larger by the day. Although it is possible for people to ignify their willingness to donate organs at the time of their death, only a small percentage do so. Organ and tis- sue donors need only sign a donor card and carry it at all times. In many states, the back of the drivers license acts s a donor card. Age is no drawback, but the donor should have been in good health prior to death. Organ and tissue donation does not interfere with funeral arrangements, and most religions do not object to the do. nation. Family members should know ahead of time about the desire to become a donor because they will be asked to sign permission papers at the time of death. Especially because so many Americans are waiting for organs and a chance for a normal life, researchers trying to develop organs in the laboratory. Just a few years ago, scientists believed that transplant organs had to come from humans or other animals. Now, however, Figure 1A Laboratory-produced bladder. This urinary bladder was tissue engineering is demonstrating that it is possible to made in the laboratory by tissue engineering. Chapter 1 Organization of the Body9

Mader: Understanding Human Anatomy & Physiology, Fifth Edition I. Human Organization 1. Organization of the Body © The McGraw−Hill Companies, 2004 Chapter 1 Organization of the Body 9 Transplantation of a human kidney, heart, liver, pancreas, lung, and other organs is now possible due to two major break￾throughs. First, solutions have been developed that preserve donor organs for several hours. This made it possible for one young boy to undergo surgery for 16 hours, during which time he received five different organs. Second, rejection of transplanted organs is now prevented by immunosuppressive drugs; therefore, organs can be donated by unrelated individuals, living or dead. Even so, rejection is less likely to happen if the donor’s tissues “match” those of the recipient—that is, their cell surface mole￾cules should be similar to one another. Living individuals can do￾nate one kidney, a portion of their liver, and certainly bone mar￾row, which quickly regenerates. After death, it is still possible to give the “gift of life” to some￾one else—over 25 organs and tissues from the same person can be used for transplants at that time. A liver transplant, for example, can save the life of a child born with biliary atresia, a congenital de￾fect in which the bile ducts do not form. Dr. Thomas Starzl, a pio￾neer in this field, reports a 90% chance of complete rehabilitation among children who survive a liver transplant. (He has also tried animal-to-human liver transplants, but so far, these have not been successful.) So many heart recipients are now alive and healthy that they have formed basketball and softball teams, demon￾strating the normalcy of their lives after surgery. One problem persists: The number of Americans waiting for organs now stands at over 80,000 and is get￾ting larger by the day. Although it is possible for people to signify their willingness to donate organs at the time of their death, only a small percentage do so. Organ and tis￾sue donors need only sign a donor card and carry it at all times. In many states, the back of the driver’s license acts as a donor card. Age is no drawback, but the donor should have been in good health prior to death.Organ and tissue donation does not interfere with funeral arrangements, and most religions do not object to the do￾nation. Family members should know ahead of time about the desire to become a donor because they will be asked to sign permission papers at the time of death. Especially because so many Americans are waiting for organs and a chance for a normal life, researchers are trying to develop organs in the laboratory. Just a few years ago, scientists believed that transplant organs had to come from humans or other animals. Now, however, tissue engineering is demonstrating that it is possible to make some bioartificial organs—hybrids created from a combi￾nation of living cells and biodegradable polymers. Presently, lab￾grown hybrid tissues are on the market. For example, a product composed of skin cells growing on a polymer is used to tem￾porarily cover the wounds of burn patients. Similarly, damaged cartilage can be replaced with a hybrid tissue produced after chondrocytes are harvested from a patient. Another connective tissue product made from fibroblasts and collagen is available to help heal deep wounds without scarring. Soon to come are a host of other products, including replacement corneas, heart valves, bladder valves, and breast tissue. The ultimate goal of tissue engineering is to produce fully functioning transplant organs in the laboratory. After nine years, a Harvard Medical School team headed by Anthony Atala has pro￾duced a working urinary bladder. After testing the bladder in lab￾oratory animals, the Harvard group is ready to test it in humans whose own bladders have been damaged by accident or disease, or will not function properly due to a congenital birth defect. An￾other group of scientists has been able to grow arterial blood ves￾sels in the laboratory. Tissue engineers are hopeful that they will one day produce more complex organs such as a liver or kidney. Organs for Transplant Figure 1A Laboratory-produced bladder. This urinary bladder was made in the laboratory by tissue engineering

Mader: Understanding ② The McG ysiology, Fifth Edition 5 Homeostasis Igure 1.7 Negative feedback. In each example, a sensor detects an intemal environmental change and signals a regulatory Homeostasis is the relative constancy of the bodys internal center. The center activates an effector, which reverses this environment. Because of homeostasis, even though exter- change. a. The general pattern b. A mechanical example al conditions may change dramatically, internal condi C A human example. tions stay within a narrow range. For example, regardless of how cold or hot it gets, the temperature of the body stay environmental chang round37°C(97°to99°F). No matter how acidic your meal, the ph of your blood is usually about 7. 4, and even if you eat a candy bar, the amount of sugar in your blood is just about O.1%. It is important to realize that internal conditions are not inhibits absolutely constant; they tend to fluctuate above and below a particular value. Therefore, the internal state of the body is often described as one of dynamic equilibrium. If internal reversal regulatory conditions change to any great degree, illness results. This makes the study of homeo Negative Feedback negative feedback is the primary homeostatic mechanism room is cool (66F) e, or set poin homeostatic mechanism has three components: a sensor, a egulatory center, and an effector(Fig. 1.7a). The sensor de- tects a change in the internal environment; the regulatory cen- turns off hemostat ter activates the effector; the effector reverses the change and set point=68°F brings conditions back to normal again. Now, the sensor is no longer activated oom is warm(70F) A home heating system illustrates how a negative feedback mechanism works(Fig. 1.7b). You set the thermostat at, say, 68 F. This is the set point. The thermostat contains a ther- mometer, a sensor that detects when the room temperature falls below the set point. The thermostat is also the regula tory center; it turns the furnace on. The furnace plays the blood essure falls role of the effector. The heat given off by the furnace raises the temperature of the room to 70 F. Now, the furnace turns Notice that a negative feedback mechanism prevents change inhibits the same direction: the does not get tivates the blood ressure nses center in brain Human Example: Regulation of blood Pressure Negative feedback mechanisms in the body function similarly to the mechanical model. For example, when blood pressure reversal falls, sensory receptors signal a regulatory center in the brain walls constrict (Fig. 1.7c). This center sends out nerve impulses to the arterial walls so that they constrict. Once the blood pressure rises, the system is inactivated 10 Part I Human Organization

Mader: Understanding Human Anatomy & Physiology, Fifth Edition I. Human Organization 1. Organization of the Body © The McGraw−Hill Companies, 2004 1.5 Homeostasis Homeostasis is the relative constancy of the body’s internal environment. Because of homeostasis, even though exter￾nal conditions may change dramatically, internal condi￾tions stay within a narrow range. For example, regardless of how cold or hot it gets, the temperature of the body stays around 37°C (97° to 99°F). No matter how acidic your meal, the pH of your blood is usually about 7.4, and even if you eat a candy bar, the amount of sugar in your blood is just about 0.1%. It is important to realize that internal conditions are not absolutely constant; they tend to fluctuate above and below a particular value. Therefore, the internal state of the body is often described as one of dynamic equilibrium. If internal conditions change to any great degree, illness results. This makes the study of homeostatic mechanisms medically important. Negative Feedback Negative feedback is the primary homeostatic mechanism that keeps a variable close to a particular value, or set point. A homeostatic mechanism has three components: a sensor, a regulatory center, and an effector (Fig. 1.7a). The sensor de￾tects a change in the internal environment; the regulatory cen￾ter activates the effector; the effector reverses the change and brings conditions back to normal again. Now, the sensor is no longer activated. Mechanical Example A home heating system illustrates how a negative feedback mechanism works (Fig. 1.7b). You set the thermostat at, say, 68°F. This is the set point. The thermostat contains a ther￾mometer, a sensor that detects when the room temperature falls below the set point. The thermostat is also the regula￾tory center; it turns the furnace on. The furnace plays the role of the effector. The heat given off by the furnace raises the temperature of the room to 70°F. Now, the furnace turns off. Notice that a negative feedback mechanism prevents change in the same direction; the room does not get warmer and warmer because warmth inactivates the system. Human Example: Regulation of Blood Pressure Negative feedback mechanisms in the body function similarly to the mechanical model. For example, when blood pressure falls, sensory receptors signal a regulatory center in the brain (Fig. 1.7c). This center sends out nerve impulses to the arterial walls so that they constrict. Once the blood pressure rises, the system is inactivated. 10 Part I Human Organization sensory receptors (in aortic and carotid sinuses) reversal inhibits arterial walls constrict regulatory center in brain blood pressure rises blood pressure falls reversal reversal environmental change sensor b. a. c. effector regulatory center room is cool (66˚F) furnace thermostat set point = 68˚F furnace turns on furnace turns off inhibits room is warm (70˚F) Figure 1.7 Negative feedback. In each example, a sensor detects an internal environmental change and signals a regulatory center. The center activates an effector, which reverses this change. a. The general pattern. b. A mechanical example. c. A human example

Mader: Understanding ② The McG Human Anatomy ysiology, Fifth Edition Figure 1. 8 Homeostasis and body temperature regulation. Negative feedback mechanisms control body temperature so that it remains relatively stable at 37 C. These mechanisms return the temperature to normal when it fluctuates above and below this set point. Brain signals dermal ody heat is lost to rises above normal 37c(9869) Body temperature Body temperature drops below normal. rises toward normal Hypothalamic set point lood vessels unstrict and sweat glands Body heat is to remain inactive dy heat. uscles to contract involuntarily Positive Feedback The thermostat for body temperature is located in a part of Positive feedback is a mechanism that brings about an ever the brain called the hypothalamus. When the body temper- greater change in the same direction. A positive feedback ature falls below normal, the regulatory center directs(via mechanism can be harmful, as when a fever causes metabolic nerve impulses) the blood vessels of the skin to constrict changes that push the fever still higher. Death occurs at a body (Fig. 1.8). This conserves heat. If body temperature falls even temperature of 45 C because cellular proteins denature at this ower,the regulatory center sends nerve impulses to the temperature and metabolism stops skeletal muscles, and shivering occurs. Shivering generates Still, positive feedback loops such as those involved in heat, and gradually body temperature rises to 37C. When blood clotting, the stomachs digestion of protein, and child- the temperature rises to normal, the regulatory center is birth assist the body in completing a process that has a def nactivated nite cutoff When the body temperature is higher than normal, the Consider that when a woman is giving birth, the head of regulatory center directs the blood vessels of the skin to dilate. the baby begins to press against the cervix, stimulating sensory This allows more blood to flow near the surface of the body, receptors there. When nerve impulses reach the brain, the brain where heat can be lost to the environment. In addition, the causes the pituitary gland to secrete the hormone oxytocin nervous system activates the sweat glands, and the evapora- Oxytocin travels in the blood and causes the uterus to contract tion of sweat helps lower body temperature. Gradually, body As labor continues, the cervix is ever more stimulated, and uterine contractions become ever stronger until birth occurs Chapter1 Organization of the Body11

Mader: Understanding Human Anatomy & Physiology, Fifth Edition I. Human Organization 1. Organization of the Body © The McGraw−Hill Companies, 2004 Human Example: Regulation of Body Temperature The thermostat for body temperature is located in a part of the brain called the hypothalamus. When the body temper￾ature falls below normal, the regulatory center directs (via nerve impulses) the blood vessels of the skin to constrict (Fig.1.8). This conserves heat. If body temperature falls even lower, the regulatory center sends nerve impulses to the skeletal muscles, and shivering occurs. Shivering generates heat, and gradually body temperature rises to 37°C. When the temperature rises to normal, the regulatory center is inactivated. When the body temperature is higher than normal, the regulatory center directs the blood vessels of the skin to dilate. This allows more blood to flow near the surface of the body, where heat can be lost to the environment. In addition, the nervous system activates the sweat glands, and the evapora￾tion of sweat helps lower body temperature. Gradually, body temperature decreases to 37°C. Positive Feedback Positive feedback is a mechanism that brings about an ever greater change in the same direction. A positive feedback mechanism can be harmful, as when a fever causes metabolic changes that push the fever still higher. Death occurs at a body temperature of 45°C because cellular proteins denature at this temperature and metabolism stops. Still, positive feedback loops such as those involved in blood clotting, the stomach’s digestion of protein, and child￾birth assist the body in completing a process that has a defi- nite cutoff point. Consider that when a woman is giving birth, the head of the baby begins to press against the cervix, stimulating sensory receptors there. When nerve impulses reach the brain, the brain causes the pituitary gland to secrete the hormone oxytocin. Oxytocin travels in the blood and causes the uterus to contract. As labor continues, the cervix is ever more stimulated, and uterine contractions become ever stronger until birth occurs. Chapter 1 Organization of the Body 11 Normal body temperature 37°C (98.6°F) Body temperature rises above normal. Brain signals dermal blood vessels to dilate and sweat glands to secrete. Body heat is lost to its surroundings. Body temperature drops toward normal. Body temperature drops below normal. Brain signals dermal blood vessels to constrict and sweat glands to remain inactive. If body temperature continues to drop, nervous system signals muscles to contract involuntarily (shivering). Body heat is conserved. Body temperature rises toward normal. Muscle activity generates body heat. Hypothalamic set point hypothalamus Figure 1.8 Homeostasis and body temperature regulation. Negative feedback mechanisms control body temperature so that it remains relatively stable at 37°C. These mechanisms return the temperature to normal when it fluctuates above and below this set point