(BQ) Part 1 book Essentials of anatomy and physiology presents the following contents: Organization and general plan of the body, some basic chemistry, cells, tissues and membranes, the integumentary system, the skeletal system, the muscular system, the nervous system, the senses, the endocrine system.
SEVENTH EDITION 3957_FM_i-001 13/10/14 10:25 AM Page i SEVENTH EDITION ESSENTIALS OF ANATOMY AND PHYSIOLOGY 3957_FM_i-001 13/10/14 10:25 AM Page ii 3957_FM_i-001 13/10/14 10:25 AM Page iii SEVENTH EDITION ESSENTIALS OF ANATOMY AND PHYSIOLOGY VALERIE C SCANLON, PhD College of Mount Saint Vincent Riverdale, New York TINA SANDERS Medical Illustrator Castle Creek, New York Formerly Head Graphic Artist Tompkins Courtland Community College Dryden, New York 3957_FM_i-001 13/10/14 10:25 AM Page iv F A Davis Company 1915 Arch Street Philadelphia, PA 19103 www.fadavis.com Copyright © 2015 by F A Davis Company Copyright © 2011, 2007, 2003, 1999, 1995, and 1991 by F A Davis Company All rights reserved This book is protected by copyright No part of it may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher Printed in the United States of America Last digit indicates print number: 10 Publisher, Nursing: Lisa B Houck Director of Content Development: Darlene D Pedersen Content Project Manager: Echo Gerhart Electronic Project Editor: Katherine Crowley Manager of Design and Illustration: Carolyn O’Brien As new scientific information becomes available through basic and clinical research, recommended treatments and drug therapies undergo changes The author(s) and publisher have done everything possible to make this book accurate, up to date, and in accord with accepted standards at the time of publication The author(s), editors, and publisher are not responsible for errors or omissions or for consequences from application of the book, and make no warranty, expressed or implied, in regard to the contents of the book Any practice described in this book should be applied by the reader in accordance with professional standards of care used in regard to the unique circumstances that may apply in each situation The reader is advised always to check product information (package inserts) for changes and new information regarding dose and contraindications before administering any drug Caution is especially urged when using new or infrequently ordered drugs Library of Congress Cataloging-in-Publication Data Scanlon, Valerie C., 1946- author Essentials of anatomy and physiology / Valerie C Scanlon, Tina Sanders — Seventh edition p ; cm Includes index ISBN 978-0-8036-3957-7 I Sanders, Tina, 1943- author II Title [DNLM: Anatomy Physiological Phenomena QS 4] QP34.5 612—dc23 2014012086 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by F A Davis Company for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the fee of $.25 per copy is paid directly to CCC, 222 Rosewood Drive, Danvers, MA 01923 For those organizations that have been granted a photocopy license by CCC, a separate system of payment has been arranged The fee code for users of the Transactional Reporting Service is: 8036-3957-7/15 + $.25 Proudly sourced and uploaded by [StormRG] Kickass Torrents | TPB | ExtraTorrent | h33t 3957_FM_i-001 13/10/14 10:25 AM Page v To my students, past and present VCS To Brooks, for his encouragement TS 3957_FM_i-001 13/10/14 10:25 AM Page vi 3957_FM_i-001 13/10/14 10:25 AM Page vii PREFACE TO THE SEVENTH EDITION Once again, we extend our gratitude to all of you who have used previous editions of Essentials of Anatomy and Physiology and are considering adopting our seventh edition We are pleased to welcome new readers as well, and we thank you for choosing our book The seventh edition remains focused on presenting basic anatomy and physiology with the clarity of the text complemented and enhanced by superb illustrations The text has been updated in many small ways to remain contemporary These include brief discussions of our microbiota in Chapter (and appropriate later chapters), the oligosaccharides in breast milk in Chapter 2, epigenetics and primary cilia in Chapter 3, connective tissue disorders in Chapter 4, motor units and the muscle hormone irisin in Chapter 7, celiac disease in Chapter 16, human papillomavirus in Chapter 20, and evaluation of fetal DNA in maternal blood for prenatal testing in Chapter 21 Chapter 12 has been revised and now begins with a description of cardiac muscle tissue, pulling together material from previous chapters All of the For Further Thought sections now end with at least one illustration question New ones include the relationship of organ systems in Chapter 1, the hydrogen bonds formed by water molecules in Chapter 2, effects of sunlight on the skin in Chapter 5, a nerve pathway (to be named by the student) in Chapter 8, the hormones of stressful situations in Chapter 10, a time line of immune responses in Chapter 14, hormones of the duodenum in Chapter 16, regulation of body temperature in Chapter 17, and relationships of the reproductive organs to other organ systems in Chapter 20 When the students have labeled the picture and answered the questions, the whole then becomes an integral part of the chapter We hope you will consider assigning these questions, and that students will find them enjoyable and helpful Colleagues, please keep in mind that the Instructor’s Guide contains a full list of these additions in the “New to This Edition” section for each chapter of the textbook, as well as detailed answers to all of the For Further Thought questions As always, your comments and suggestions will be most welcome, and they may be sent to us in care of the publisher: F A Davis Company, 1915 Arch Street, Philadelphia, PA 19103 Valerie C Scanlon Dobbs Ferry, New York Tina Sanders Castle Creek, New York vii 3957_FM_i-001 13/10/14 10:25 AM Page viii 3957_FM_i-001 13/10/14 10:25 AM Page ix TO THE INSTRUCTOR The start of the 21st century has already brought many advances in the science and art of medicine and health care; many of these were made possible by research and discoveries in the basic sciences Teachers of introductory anatomy and physiology may wish to include some of these discoveries yet will want to maintain their emphasis on the normal structure and function of the human body Those are the goals of this textbook: to add a little of the new to the foundation of long-standing knowledge and to make all of this material readily accessible to students with diverse backgrounds and varying levels of educational preparation No prior knowledge of biology or chemistry is assumed, and even fundamental terms are defined thoroughly Essential aspects of anatomy are presented clearly and reinforced with excellent illustrations Essential aspects of physiology are discussed simply yet with accuracy and precision The illustrations complement the text material and foster comprehension on the part of the student As you will see, these are images in which detail is readily apparent and all important parts have been labeled Illustrations of physiology lead the student step-by-step Wherever appropriate, the legends refer students to the text for further description or explanation Each illustration also has a question for the student; the illustration questions in each chapter form an ongoing self-test (The answers are given in Appendix G.) The text has three unifying themes: the relationship between physiology and anatomy, the interrelations among the organ systems, and the relationship of each organ system to homeostasis Although each type of cell, tissue, organ, or organ system is discussed simply and thoroughly in itself, applicable connections are made to other aspects of the body or to the functioning of the body as a whole Our goal is to provide your students with the essentials of anatomy and physiology, and in doing so, to help give them a solid foundation for their future work and an appreciation for the incredible living organism that is the human body The sequence of chapters is a very traditional one Cross-references are used to remind students of what they have learned from previous chapters Nevertheless, the textbook is very flexible, and, following the introductory four chapters, the organ systems may be covered in almost any order, depending on the needs of your course Each chapter is organized from the simple to the more complex, with the anatomy followed by the physiology The Instructor’s Guide presents modifications of the topic sequences that may be used, again depending on the needs of your course Certain more advanced topics may be omitted from each chapter without losing the meaning or flow of the rest of the material, and these are indicated, for each chapter, in the Instructor’s Guide Clinical applications are set apart from the text in boxed inserts These are often aspects of pathophysiology that are related to the normal anatomy or physiology in the text discussion Each box presents one topic and is referenced at the appropriate point in the text This material is intended to be an integral part of the chapter but is set apart for ease of reference and to enable you to include or omit as many of these topics as you wish The use of these boxes also enables students to read the text material without interruption and then to focus on specific aspects of pathophysiology A comprehensive list of the boxes appears inside the book’s front and back covers, and another list at the beginning of each chapter cites the boxes within that chapter Tables are utilized as summaries of structure and function, to present a sequence of events, or additional material that you may choose to include Each table is referenced in the text and is intended to facilitate your teaching and to help your students learn New terms appear in bold type within the text, and all such terms are fully defined in an extensive glossary, with phonetic pronunciations Bold type may also be used for emphasis whenever one of these terms is used again in a later chapter Each chapter begins with a chapter outline and student objectives to prepare the student for the chapter itself New terminology and related clinical terms are also listed, with phonetic pronunciations Each of these terms is fully defined in the glossary, with cross-references back to the chapter in which the term is introduced At the end of each chapter are review questions and a study outline The study outline includes all of the essentials of the chapter in a concise form The review questions may be assigned as homework or used by the students as a review or self-test Following each question is a page reference in parentheses This reference cites the page(s) in the chapter on which the content needed to answer the ix 3957_Ch10_252-281 06/10/14 10:33 AM Page 267 The Endocrine System Hyperglycemia (High blood glucose) Glucagon 267 Liver Liver changes glycogen to glucose and converts amino acids to carbohydrates Liver and skeletal muscles change glucose to glycogen Liver Pancreas Skeletal muscles Insulin Hypoglycemia (Low blood glucose) Cells Cells use glucose for energy production Figure 10–8 Insulin and glucagon and their functions related to the maintenance of the blood glucose level QUESTION: Which hormone enables cells to use glucose for energy production? What is the stimulus for secretion of this hormone? Box 10–3 | DIABETES MELLITUS There are two types of diabetes mellitus: Type is called insulin-dependent diabetes and its onset is usually in childhood (juvenile onset) Type is called non–insulin-dependent diabetes, and its onset is usually later in life (maturity onset) Type diabetes is characterized by destruction of the beta cells of the islets of Langerhans and a complete lack of insulin (see Box Figure 10–A); onset is usually abrupt Destruction of the beta cells is an autoimmune response, perhaps triggered by a virus There may be a genetic predisposition because certain HLA types are found more frequently in type diabetics than in other children (see Box 11–5: White Blood Cell Types: HLA in Chapter 11) Insulin is essential to control type diabetes Research is continuing on the use of immunosuppressant medications to try to preserve some beta cells (if diagnosis is early), and also on the transplantation of stem cells to replace lost beta cells Continued 3957_Ch10_252-281 06/10/14 10:33 AM Page 268 268 The Endocrine System Box 10–3 | DIABETES MELLITUS (Continued) In type diabetes, insulin is produced but cannot exert its effects on cells because of a loss of insulin receptors on cell membranes (see Box Figure 10–A) Onset of type diabetes is usually gradual, and risk factors include a family history of diabetes and being overweight Control may not require insulin, but rather medications that enable insulin to react with the remaining membrane receptors For those with a family history of diabetes, a low-fat diet and regular exercise reduce the risk of developing the disease The commitment to exercise must be lifelong but is well worth the effort, because diabetes is very destructive Without insulin (or its effects) blood glucose level remains high, and glucose is lost in urine Because more water is lost as well, symptoms include greater urinary output (polyuria) and thirst (polydipsia) The long-term effects of hyperglycemia produce distinctive vascular changes The capillary walls thicken, and exchange of gases and nutrients diminishes The most damaging effects are seen in the skin (especially of the feet), the retina (diabetic retinopathy), and the kidneys Poorly controlled diabetes may lead to dry gangrene, blindness, and severe kidney damage Atherosclerosis is common, because faulty triglyceride metabolism is linked to faulty glucose metabolism Diabetics must control their blood pressure and cholesterol levels to prevent heart attacks Neuropathy (damage to nerves) leads to impaired cutaneous sensation and difficulty with fine movements, such as buttoning a shirt It is now possible for diabetics to prevent much of this tissue damage by precise monitoring of the blood glucose level and more frequent administration of insulin Insulin pumps are able to more closely mimic the natural secretion of insulin A very serious potential problem for the type diabetic is ketoacidosis When glucose cannot be used for energy, the body turns to fats and proteins, which are converted by the liver to ketones Ketones are organic acids (acetone, acetoacetic acid) that can be used in cell respiration, but cells are not able to utilize them rapidly so ketones accumulate in the blood Ketones are acids, and lower the pH of the blood as they accumulate The kidneys excrete excess ketones, but in doing so excrete more water as well, which leads to dehydration and worsens the acidosis Without administration of insulin to permit the use of glucose, and IV fluids to restore blood volume to normal, ketoacidosis will progress to coma and death Glucose Insulin Insulin Receptor A Normal B Type C Type Box Figure 10–A (A) Cell membrane in normal state, with insulin receptors and insulin to regulate glucose intake (B) Cell membrane in type diabetes: insulin not present, glucose remains outside cell (C) Cell membrane in type diabetes: without insulin receptors, glucose remains outside cell 3957_Ch10_252-281 06/10/14 10:33 AM Page 269 The Endocrine System Secretion of insulin is stimulated by hyperglycemia, a high blood glucose level This state occurs after eating, especially of meals high in carbohydrates As glucose is absorbed from the small intestine into the blood, insulin is secreted to enable cells to use the glucose for immediate energy At the same time, any excess glucose will be stored in the liver and muscles as glycogen You will also notice in Fig 16–7 the cells called delta cells These produce the hormone somatostatin, which is identical to growth hormone–inhibiting hormone from the hypothalamus Pancreatic somatostatin acts locally to inhibit the secretion of insulin and glucagon, and it seems to slow the absorption of the end products of digestion in the small intestine The hormones of the pancreas are summarized in Table 10–5 ADRENAL GLANDS The two adrenal glands are each located on top of a kidney, which gives them their other name of suprarenal glands Each adrenal gland consists of two parts: an inner adrenal medulla and an outer adrenal cortex The hormones produced by each part have very different functions ADRENAL MEDULLA The cells of the adrenal medulla secrete epinephrine and norepinephrine, which collectively are called catecholamines and are sympathomimetic The secretion of both hormones is stimulated by sympathetic impulses from the hypothalamus, and their functions duplicate and prolong those of the sympathetic division of the autonomic nervous system (mimetic means “to mimic”) Table 10–5 269 Epinephrine and Norepinephrine Epinephrine (adrenalin) and norepinephrine (noradrenalin) are both secreted in stress situations and help prepare the body for “fight or flight.” Norepinephrine is secreted in small amounts, and its most significant function is to cause vasoconstriction in the skin, viscera, and skeletal muscles (that is, throughout the body), which raises blood pressure Epinephrine, secreted in larger amounts, increases the heart rate and force of contraction and stimulates vasoconstriction in skin and viscera and vasodilation in skeletal muscles It also dilates the bronchioles, decreases peristalsis, stimulates the liver to change glycogen to glucose, increases the use of fats for energy, and increases the rate of cell respiration Many of these effects indeed seem to be an echo of sympathetic responses, don’t they? Responding to stress is so important that the body acts redundantly (that is, exceeds what is necessary, or repeats itself) and has both a nervous mechanism and a hormonal mechanism Epinephrine is actually more effective than sympathetic stimulation, however, because the hormone increases energy production and cardiac output to a greater extent The hormones of the adrenal medulla are summarized in Table 10–6, and their functions are shown in Fig 10–9 ADRENAL CORTEX The adrenal cortex secretes three types of steroid hormones: mineralocorticoids, glucocorticoids, and sex hormones The sex hormones, “female” estrogens and “male” androgens (similar to testosterone), are produced in very | HORMONES OF THE PANCREAS HORMONE FUNCTIONS Glucagon (alpha cells) ■ Insulin (beta cells) ■ ■ ■ ■ Somatostatin (delta cells) ■ ■ REGULATION OF SECRETION Increases conversion of glycogen to glucose in the liver Increases the use of excess amino acids and of fats for energy Hypoglycemia Increases glucose transport into cells and the use of glucose for energy production Increases the conversion of excess glucose to glycogen in the liver and muscles Increases amino acid and fatty acid transport into cells, and their use in synthesis reactions Hyperglycemia Decreases secretion of insulin and glucagon Slows absorption of nutrients Rising levels of insulin and glucagon 3957_Ch10_252-281 06/10/14 10:33 AM Page 270 270 The Endocrine System Table 10–6 | HORMONES OF THE ADRENAL MEDULLA HORMONE FUNCTION(S) Norepinephrine ■ Causes vasoconstriction in skin, viscera, and skeletal muscles Sympathetic impulses from the hypothalamus in stress situations Epinephrine ■ Increases heart rate and force of contraction Dilates bronchioles Decreases peristalsis Increases conversion of glycogen to glucose in the liver Causes vasodilation in skeletal muscles Causes vasoconstriction in skin and viscera Increases use of fats for energy Increases the rate of cell respiration Sympathetic impulses from the hypothalamus in stress situations ■ ■ ■ ■ ■ ■ ■ small amounts, and their importance is not known with certainty They may contribute to rapid body growth during early puberty They may also be important in supplying estrogen to women after menopause and to men throughout life (see the “Estrogen” section later in this chapter) The functions of the other adrenal cortical hormones are well known, however Both kinds are secreted during stressful situations, and both are considered vital hormones Aldosterone Aldosterone is the most abundant of the mineralocorticoids, and we will use it as a representative of this group of hormones The target organs of aldosterone are the kidneys, but there are important secondary, or indirect, effects as well Aldosterone increases the reabsorption of sodium and the excretion of potassium by the kidney tubules; this is its direct effect Sodium ions (Na+) are returned to the blood, and potassium ions (K+) are excreted in urine Look at Fig 10–10 as you read the following As Na+ ions are reabsorbed, hydrogen ions (H+) may be excreted in exchange This is one mechanism to prevent the accumulation of excess H+ ions, which would cause acidosis of body fluids Also, as Na+ ions are reabsorbed, negative ions such as chloride (ClϪ) and bicarbonate (HCO3Ϫ) follow the Na+ ions back to the blood, and water follows by osmosis This indirect effect of aldosterone, the reabsorption of water by the kidneys, is very important to maintain normal blood volume and blood pressure In summary, then, aldosterone directly maintains normal blood levels of sodium and potassium, and by doing so secondarily, or indirectly, contributes to the maintenance of normal blood pH, blood volume, and blood pressure REGULATION OF SECRETION A number of factors stimulate the secretion of aldosterone These are a deficiency of sodium, loss of blood or dehydration that lowers blood pressure, or an elevated blood level of potassium Low blood pressure or blood volume activates the renin-angiotensin mechanism of the kidneys This mechanism is discussed in Chapters 13 and 18, so we will say for now that the process culminates in the formation of a chemical called angiotensin II Angiotensin II causes vasoconstriction and stimulates the secretion of aldosterone by the adrenal cortex Aldosterone then increases sodium and water retention by the kidneys to help restore blood volume and blood pressure to normal Cortisol We will use cortisol as a representative of the group of hormones called glucocorticoids because it is responsible for most of the actions of this group (Fig 10–11) Cortisol increases the use of fats and excess amino acids (gluconeogenesis) for energy and decreases the use of glucose This is called the glucose-sparing effect, and it is important because it conserves glucose for use by the brain Cortisol is secreted in any type of physiological stress situation: disease, physical injury, hemorrhage, fear or anger, exercise, and hunger Although most body cells easily use fatty acids and excess amino acids in cell respiration, brain cells not, so they must have glucose By enabling other cells to use the alternative energy sources, cortisol ensures that whatever glucose is present will be available to the brain Cortisol also has an anti-inflammatory effect During inflammation, histamine from damaged tissues and mast cells makes capillaries more permeable, and the 3957_Ch10_252-281 06/10/14 10:33 AM Page 271 The Endocrine System Adrenal medulla Norepinephrine Epinephrine Increases rate and force of contraction Vasoconstriction in skin Dilates bronchioles Vasoconstriction in viscera Decreases peristalsis Increases conversion of glycogen to glucose Vasoconstriction in skeletal muscle Vasodilation in skeletal muscle Increases use of fats for energy Increases cell respiration Figure 10–9 Functions of epinephrine and norepinephrine QUESTION: Do epinephrine and norepinephrine have the same effect on skeletal muscle? Explain your answer 271 3957_Ch10_252-281 06/10/14 10:33 AM Page 272 272 The Endocrine System Adrenal cortex Na+ ions reabsorbed HCO3– ions reabsorbed Aldosterone H2O reabsorbed H+ ions excreted K+ ions excreted Blood volume, blood pressure, and pH are maintained Figure 10–10 Functions of aldosterone Direct and indirect functions are shown QUESTION: What ions does aldosterone have a direct effect on, and what is the effect? lysosomes of damaged cells release their enzymes, which help break down damaged tissue for easier cleanup by macrophages but may also cause destruction of nearby healthy tissue Cortisol blocks the effects of histamine and stabilizes lysosomal membranes, preventing excessive tissue destruction Inflammation is a beneficial process up to a point and is an essential first step if tissue repair is to take place It may, however, become a vicious cycle of damage, inflammation, more damage, more inflammation, and so on—a positive feedback mechanism Recall that any positive feedback mechanism requires an external brake Normal cortisol secretion seems to be the brake for this mechanism, to limit the inflammation process to what is useful for tissue repair, and to prevent excessive tissue destruction Too much cortisol, however, decreases the immune response, leaving the body susceptible to infection and significantly slowing the healing of damaged tissue (see Box 10–4: Disorders of the Adrenal Cortex) The direct stimulus for cortisol secretion is ACTH from the anterior pituitary gland, which in turn is stimulated by corticotropin-releasing hormone (CRH) from the hypothalamus CRH is produced in the physiological stress situations mentioned earlier Although we often think of epinephrine as a hormone important for coping with physiological stress, cortisol is also important The hormones of the adrenal cortex are summarized in Table 10–7 OVARIES The ovaries are located in the pelvic cavity, one on each side of the uterus The hormones produced by the ovaries are the steroids estrogen and progesterone, and the protein inhibin Although their functions are an integral part of Chapters 20 and 21, we will briefly discuss some of them here ESTROGEN Estrogen is secreted by the follicle cells of the ovary; secretion is stimulated by FSH from the anterior pituitary gland Estrogen promotes the maturation of the ovum in the ovarian follicle and stimulates the growth of blood vessels in the endometrium (lining) of the uterus in preparation for a possible fertilized egg The secondary sex characteristics in women also develop in response to estrogen These include growth of the duct system of the mammary glands, growth of the 3957_Ch10_252-281 06/10/14 10:33 AM Page 273 The Endocrine System 273 Adipose tissue Increases use of fats ATP Most tissues ATP Amino acids Adrenal cortex Increases use of excess amino acids Liver Cortisol Glycogen Glucose Conserves glucose Brain Limits inflammation Figure 10–11 Functions of cortisol QUESTION: Which food types will be used for energy by most tissues? Which food type may be stored? Box 10–4 | DISORDERS OF THE ADRENAL CORTEX Addison’s disease is the result of hyposecretion of the adrenal cortical hormones Most cases are idiopathic, that is, of unknown cause; atrophy of the adrenal cortex decreases both cortisol and aldosterone secretion Deficiency of cortisol is characterized by hypoglycemia, decreased gluconeogenesis, and depletion of glycogen in the liver Consequences are muscle weakness and the inability to resist physiological stress Aldosterone deficiency leads to retention of potassium and excretion of sodium and water in urine The result is severe dehydration, low blood volume, and low blood pressure Without treatment, circulatory shock and death will follow Treatment involves administration of hydrocortisone; in high doses this will also compensate for the aldosterone deficiency Continued 3957_Ch10_252-281 06/10/14 10:33 AM Page 274 274 The Endocrine System Box 10–4 | DISORDERS OF THE ADRENAL CORTEX (Continued) Cushing’s syndrome is the result of hypersecretion of the adrenal cortex, primarily cortisol The cause may be a pituitary tumor that increases ACTH secretion or a tumor of the adrenal cortex itself Excessive cortisol promotes fat deposition in the trunk of the body, while the extremities remain thin The skin becomes thin and fragile, and healing after injury is slow The bones also become fragile because osteoporosis is accelerated Also characteristic of this syndrome is the rounded appearance of Table 10–7 | HORMONES OF THE ADRENAL CORTEX HORMONE FUNCTION(S) Aldosterone ■ ■ Cortisol the face Treatment is aimed at removal of the cause of the hypersecretion, whether it be a pituitary or adrenal tumor Cushing’s syndrome may also be seen in people who receive corticosteroids for medical reasons Transplant recipients or people with rheumatoid arthritis or severe asthma who must take corticosteroids may exhibit any of the above symptoms In such cases, the disadvantages of this medication must be weighed against the benefits provided ■ ■ ■ ■ REGULATION OF SECRETION Increases reabsorption of Na+ ions by the kidneys to the blood Increases excretion of K+ ions by the kidneys in urine Low blood Na+ level Low blood volume or blood pressure High blood K+ level Increases use of fats and excess amino acids for energy Decreases use of glucose for energy (except for the brain) Increases conversion of glucose to glycogen in the liver Anti-inflammatory effect: stabilizes lysosomes and blocks the effects of histamine ACTH (anterior pituitary) during physiological stress uterus, and the deposition of fat subcutaneously in the hips and thighs The closure of the epiphyseal discs in long bones is brought about by estrogen, and growth in height stops Estrogen is also believed to lower blood levels of cholesterol and triglycerides For women before the age of menopause this is beneficial in that it decreases the risk of atherosclerosis and coronary artery disease Research suggests that estrogen no longer be considered only a “female” hormone Estrogen seems to have effects on many organs, including the brain, the heart, and blood vessels In the brain, testosterone from the testes or the adrenal cortex can be converted to estrogen, which may be important for memory, especially for older people Estrogen seems to have non-reproductive functions (such as influencing fat storage) in both men and women, although we cannot yet be as specific as we can be with the reproductive functions in women, mentioned previously PROGESTERONE When a mature ovarian follicle releases an ovum, the follicle becomes the corpus luteum and begins to secrete progesterone in addition to estrogen This is stimulated by LH from the anterior pituitary gland Progesterone seems to be necessary for the successful implantation of the very early embryo (5 to days old) in the endometrium It also promotes the storage of glycogen and the further growth of blood vessels in the endometrium, which thus becomes a potential placenta The secretory cells 3957_Ch10_252-281 06/10/14 10:33 AM Page 275 The Endocrine System of the mammary glands also develop under the influence of progesterone Both progesterone and estrogen are secreted by the placenta during pregnancy; these functions are covered in Chapter 21 INHIBIN The corpus luteum secretes another hormone, called inhibin Inhibin helps decrease the secretion of FSH by the anterior pituitary gland, and GnRH by the hypothalamus TESTES The testes are located in the scrotum, a sac of skin between the upper thighs Two hormones, testosterone and inhibin, are secreted by the testes TESTOSTERONE Testosterone is a steroid hormone secreted by the interstitial cells of the testes; the stimulus for secretion is LH from the anterior pituitary gland Testosterone promotes maturation of sperm in the seminiferous tubules of the testes; this process begins at puberty and continues throughout life At puberty, testosterone stimulates development of the male secondary sex characteristics These include growth of all the reproductive organs, growth of facial and body hair, growth of the larynx and deepening of the voice, and growth (protein synthesis) of the skeletal muscles Testosterone also brings about closure of the epiphyses of the long bones INHIBIN The hormone inhibin is secreted by the sustentacular cells of the testes; the stimulus for secretion is increased testosterone The function of inhibin is to decrease the secretion of FSH by the anterior pituitary gland The interaction of inhibin, testosterone, and the anterior pituitary hormones maintains spermatogenesis at a constant rate OTHER HORMONES Melatonin is a hormone produced by the pineal gland, which is located at the back of the third ventricle of the brain The secretion of melatonin is greatest during darkness and decreases when light enters the eye and the retina signals the hypothalamus The retina also produces melatonin, which seems to indicate that the eyes and pineal gland work with the biological clock of the hypothalamus In other mammals, melatonin helps regulate seasonal reproductive cycles For people, melatonin 275 definitely stimulates the onset of sleep and increases its duration Other claims, such as that melatonin strengthens the immune system or prevents aging, are without evidence as yet Some organs produce hormones that have only one or a few target organs For example, skeletal muscle produces irisin, which affects adipocytes, and adipose tissue produces the appetite-suppressing hormone leptin The stomach and duodenum produce hormones that regulate aspects of digestion (pancreas and liver functioning) and appetite The thymus gland produces hormones necessary for the normal functioning of the immune system, and the kidneys produce a hormone that stimulates red blood cell production in the red bone marrow All of these will be discussed in later chapters PROSTAGLANDINS Prostaglandins (PGs) are made by virtually all cells from the phospholipids of their cell membranes They differ from other hormones in that they not circulate in the blood to target organs, but rather exert their effects locally, where they are produced There are many types of prostaglandins, designated by the letters A through I, as in PGA, PGB, and so on Prostaglandins have many functions, and we will list only a few of them here Prostaglandins are known to be involved in inflammation, pain mechanisms, blood clotting, vasoconstriction and vasodilation, contraction of the uterus, reproduction, secretion of digestive glands, and nutrient metabolism Current research is directed at determining the normal functioning of prostaglandins in the hope that many of them may eventually be used clinically One familiar example may illustrate the widespread activity of prostaglandins For minor pain such as a headache, many people take aspirin Aspirin inhibits the synthesis of prostaglandins involved in pain mechanisms and usually relieves the pain Some people, however, such as those with rheumatoid arthritis, may take large amounts of aspirin to diminish pain and inflammation These people may bruise easily because blood clotting has been impaired This, too, is an effect of aspirin, which blocks the synthesis of prostaglandins necessary for blood clotting MECHANISMS OF HORMONE ACTION Exactly how hormones exert their effects on their target organs involves a number of complex processes, which will be presented simply here 3957_Ch10_252-281 06/10/14 10:33 AM Page 276 276 The Endocrine System All hormones are secreted into the blood and circulate throughout the body What determines whether a hormone will affect a particular organ or tissue? That is, what makes a cell a target? A target is determined by the presence of receptors into which the hormone fits A hormone must first bond to a receptor for it on or in the target cell Cells respond to certain hormones and not to others; that is, they are targets or not because of the presence of specific receptors, which are proteins These receptor proteins may be part of the cell membrane or within the cytoplasm or nucleus of the target cells A hormone will affect only those cells that have its specific receptors Liver cells, for example, have cell membrane receptors for insulin, glucagon, growth hormone, and epinephrine; bone cells have receptors for growth hormone, PTH, and calcitonin Cells of the ovaries and testes not have receptors for PTH and calcitonin but have receptors for FSH and LH, which bone cells and liver cells not have Once a hormone has bonded to a receptor on or in its target cell, other reactions will take place (Fig 10–12) THE TWO-MESSENGER MECHANISM— PROTEIN HORMONES The two-messenger mechanism of hormone action involves “messengers” that make something happen, that is, stimulate specific reactions Protein hormones usually bond to receptors of the cell membrane, and the hormone is called the first messenger The hormone–receptor bonding activates the enzyme adenyl cyclase on the inner surface of the cell membrane Adenyl cyclase synthesizes a substance called cyclic adenosine monophosphate (cyclic A B Figure 10–12 Mechanisms of hormone action (A) Two-messenger mechanism of the action of protein hormones (B) Action of steroid hormones See text for description QUESTION: What must a cell have in order to be a target cell for a particular hormone? 3957_Ch10_252-281 06/10/14 10:33 AM Page 277 The Endocrine System 277 AMP or cAMP) from ATP, and cyclic AMP is the second messenger Cyclic AMP activates specific enzymes within the cell, which bring about the cell’s characteristic response to the hormone These responses include a change in the permeability of the cell membrane to a specific substance, an increase in protein synthesis, activation of other enzymes, or the secretion of a cellular product In summary, a cell’s response to a hormone is determined by the enzymes within the cell, that is, the reactions of which the cell is capable These reactions are brought about by the first messenger, the hormone, which stimulates the formation of the second messenger, cyclic AMP Cyclic AMP then activates the cell’s enzymes to elicit a response to the hormone (see Fig 10–12) AGING AND THE ENDOCRINE SYSTEM ACTION OF STEROID HORMONES The hormones of endocrine glands are involved in virtually all aspects of normal body functioning The growth and repair of tissues, the utilization of food to produce energy, responses to stress, the maintenance of the proper levels and pH of body fluids, and the continuance of the human species all depend on hormones Some of these topics will be discussed in later chapters As you might expect, you will be reading about the functions of many of these hormones again and reviewing their important contributions to the maintenance of homeostasis Steroid hormones are soluble in the lipids of the cell membrane and diffuse easily into a target cell Once inside the cell, the steroid hormone combines with a protein receptor in the cytoplasm, and this steroid-protein complex enters the nucleus of the cell Within the nucleus, the steroid-protein complex activates specific genes, which begin the process of protein synthesis The enzymes produced bring about the cell’s characteristic response to the hormone (see Fig 10–12) Most of the endocrine glands decrease their secretions with age, but normal aging usually does not lead to serious hormone deficiencies There are decreases in adrenal cortical hormones, for example, but the levels are usually sufficient to maintain homeostasis of water, electrolytes, and nutrients The decreased secretion of growth hormone leads to a decrease in muscle mass and an increase in fat storage A lower basal metabolic rate is common in elderly people as the thyroid slows its secretion of thyroxine Unless specific pathologies develop, however, the endocrine system usually continues to function adequately in old age SUMMARY STUDY OUTLINE Endocrine glands are ductless glands that secrete hormones into the blood Hormones exert their effects on target organs or tissues Chemistry of Hormones Amines—structural variations of the amino acid tyrosine; thyroxine, epinephrine Proteins—chains of amino acids; peptides are short chains Insulin, GH, and glucagon are proteins; ADH and oxytocin are peptides Steroids—made from cholesterol; cortisol, aldosterone, estrogen, testosterone Regulation of Hormone Secretion Hormones are secreted when there is a need for their effects Each hormone has a specific stimulus for secretion The secretion of most hormones is regulated by negative feedback mechanisms: As the hormone exerts its effects, the stimulus for secretion is reversed, and secretion of the hormone decreases until the stimulus reoccurs Pituitary Gland (Hypophysis)—hangs from hypothalamus by the infundibulum; enclosed by sella turcica of sphenoid bone (see Figs 10–1 and 10–2) Posterior Pituitary (Neurohypophysis)—stores hormones produced by the hypothalamus (Figs 10–2 and 10–3 and Table 10–1) — ADH—increases water reabsorption by the kidneys, decreases sweating, in large amounts causes vasoconstriction Result: decreases urinary output and increases blood volume; increases BP Stimulus: nerve impulses from hypothalamus when body water decreases for any reason 3957_Ch10_252-281 06/10/14 10:33 AM Page 278 278 The Endocrine System — Oxytocin—stimulates contraction of myometrium of uterus during labor and release of milk from mammary glands Stimulus: nerve impulses from hypothalamus as cervix is stretched or as infant sucks on nipple Anterior Pituitary (Adenohypophysis)—secretions are regulated by releasing hormones from the hypothalamus (Fig 10–3 and Table 10–2) — GH—through intermediary molecules, IGFs, GH increases amino acid transport into cells and increases protein synthesis; increases rate of mitosis; increases use of fats for energy (Fig 10–4) Stimulus: GHRH from the hypothalamus — TSH—increases secretion of thyroxine and T3 by the thyroid Stimulus: TRH from the hypothalamus — ACTH—increases secretion of cortisol by the adrenal cortex Stimulus: CRH from the hypothalamus — Prolactin—initiates and maintains milk production by the mammary glands Stimulus: PRH from the hypothalamus — FSH—In women: initiates development of ova in ovarian follicles and secretion of estrogen by follicle cells In men: initiates sperm development in the testes Stimulus: GnRH from the hypothalamus — LH—In women: stimulates ovulation, transforms mature follicle into corpus luteum and stimulates secretion of progesterone In men: stimulates secretion of testosterone by the testes Stimulus: GnRH from the hypothalamus Thyroid Gland—on front and sides of trachea below the larynx (see Figs 10–1 and 10–5 and Table 10–3) — Thyroxine (T4) and T3—(Fig 10–5) produced by thyroid follicles; both hormones contain iodine Increase use of all food types for energy production and increase protein synthesis Necessary for normal physical, mental, and sexual development Stimulus: TSH from the anterior pituitary — Calcitonin—produced by parafollicular cells Decreases reabsorption of calcium from bones and lowers blood calcium level Stimulus: hypercalcemia Parathyroid Glands—four; two on posterior of each lobe of thyroid (see Figs 10–6 and 10–7 and Table 10–4) — PTH—increases reabsorption of calcium and phosphate from bones to the blood; increases absorption of calcium and phosphate by the small intestine; increases reabsorption of calcium and excretion of phosphate by the kidneys, and activates vitamin D Result: raises blood calcium and lowers blood phosphate levels Stimulus: hypocalcemia Inhibitor: hypercalcemia Pancreas—extends from curve of duodenum to the spleen Islets of Langerhans contain alpha cells and beta cells (see Figs 10–1 and 10–8 and Table 10–5) — Glucagon—secreted by alpha cells Stimulates liver to change glycogen to glucose; increases use of fats and amino acids for energy Result: raises blood glucose level Stimulus: hypoglycemia — Insulin—secreted by beta cells Increases use of glucose by cells to produce energy; stimulates liver and muscles to change glucose to glycogen; increases cellular intake of fatty acids and amino acids to use for synthesis of lipids and proteins Result: lowers blood glucose level Stimulus: hyperglycemia — Somatostatin—inhibits secretion of insulin and glucagon Adrenal Glands—one on top of each kidney; each has an inner adrenal medulla and an outer adrenal cortex (see Fig 10–1) Adrenal Medulla—produces catecholamines in stressful situations, preparing the body for “fight or flight” (Table 10–6 and Fig 10–9) — Norepinephrine—stimulates vasoconstriction in skin, viscera, and skeletal muscles and thereby raises blood pressure 3957_Ch10_252-281 06/10/14 10:33 AM Page 279 The Endocrine System — Epinephrine—increases heart rate and force of contraction, causes vasoconstriction in skin and viscera and vasodilation in skeletal muscles; dilates bronchioles; slows peristalsis; causes liver to change glycogen to glucose; increases use of fats for energy; increases rate of cell respiration Stimulus: sympathetic impulses from the hypothalamus Adrenal Cortex—produces mineralocorticoids, glucocorticoids, and very small amounts of sex hormones (function not known with certainty) (Table 10–7) — Aldosterone—(Fig 10–10) increases reabsorption of sodium and excretion of potassium by the kidneys Results: hydrogen ions are excreted in exchange for sodium; chloride and bicarbonate ions and water follow sodium back to the blood; maintains normal blood pH, blood volume, and blood pressure Stimulus: decreased blood sodium or elevated blood potassium; decreased blood volume or blood pressure (activates the renin-angiotensin mechanism of the kidneys) — Cortisol—(Fig 10–11) increases use of fats and amino acids for energy; decreases use of glucose to conserve glucose for the brain; antiinflammatory effect: blocks effects of histamine and stabilizes lysosomes to prevent excessive tissue damage Stimulus: ACTH from the anterior pituitary during physiological stress Ovaries—in pelvic cavity on either side of uterus (see Fig 10–1) — Estrogen—produced by follicle cells Promotes maturation of ovum; stimulates growth of blood vessels in endometrium; stimulates development of secondary sex characteristics: growth of duct system of mammary glands, growth of uterus, fat deposition Promotes closure of epiphyses of long bones; lowers blood levels of cholesterol and triglycerides Stimulus: FSH from anterior pituitary — Progesterone—produced by the corpus luteum Promotes successful implantation of the very early embryo and storage of glycogen and further growth of blood vessels in the endometrium; promotes growth of secretory cells of mammary glands Stimulus: LH from anterior pituitary — Inhibin—inhibits secretion of FSH 279 Testes—in scrotum between the upper thighs (see Fig 10–1) — Testosterone—produced by interstitial cells Promotes maturation of sperm in testes; stimulates development of secondary sex characteristics: growth of reproductive organs, facial and body hair, larynx, skeletal muscles; promotes closure of epiphyses of long bones Stimulus: LH from anterior pituitary — Inhibin—produced by sustentacular cells Inhibits secretion of FSH to maintain a constant rate of sperm production Stimulus: increased testosterone Other Hormones — Melatonin—secreted by the pineal gland during darkness; brings on sleep — Prostaglandins—synthesized by cells from the phospholipids of their cell membranes; exert their effects locally Are involved in inflammation and pain, reproduction, nutrient metabolism, changes in blood vessels, blood clotting Mechanisms of Hormone Action (see Fig 10–12) The target cells for a hormone are those cells with receptors for it Receptors are proteins with which hormones bond or fit; receptors may be part of the cell membrane, or within the cytoplasm or nucleus of the target cell — The two-messenger mechanism: a protein hormone (1st messenger) bonds to a membrane receptor; this reaction stimulates formation of cyclic AMP (2nd messenger) inside the cell; cyclic AMP activates the cell’s enzymes to bring about the cell’s characteristic response to the hormone — Steroid hormones diffuse easily through cell membranes and bond to cytoplasmic receptors The steroid-protein complex enters the nucleus and activates certain genes, which initiate protein synthesis to bring about the cell’s characteristic response to the hormone 3957_Ch10_252-281 06/10/14 10:33 AM Page 280 280 The Endocrine System REVIEW QUESTIONS Use the following to describe a negative feedback mechanism: TSH, TRH, decreased metabolic rate, thyroxine, and T3 (pp 262, 264) Name the two hormones stored in the posterior pituitary gland Where are these hormones produced? State the functions of each of these hormones (pp 256–258) Name the hormones necessary for development of egg cells in the ovaries Name the hormones necessary for development of sperm in the testes (pp 272, 274–275) 10 State what prostaglandins are made from, and state three functions of prostaglandins (p 275) Name the two hormones of the anterior pituitary gland that affect the ovaries or testes, and state their functions (p 261) 11 Name the hormones that promote the growth of the endometrium of the uterus in preparation for a fertilized egg, and state precisely where each hormone is produced (pp 272, 274) Describe the antagonistic effects of PTH and calcitonin on bones and on blood calcium level State the other functions of PTH (p 264) 12 Explain the functions of growth hormone and thyroxine (also T3) as they are related to normal growth (pp 259, 262) Describe the antagonistic effects of insulin and glucagon on the liver and on blood glucose level (pp 266–267) 13 State the direct stimulus for secretion of each of these hormones: (pp 262, 269, 272, 264, 270, 264, 260, 266, 275, 257) Describe how cortisol affects the use of foods for energy Explain the anti-inflammatory effects of cortisol (pp 270, 272) State the effect of aldosterone on the kidneys Describe the results of this effect on the composition of the blood (p 270) a Thyroxine f Calcitonin b Insulin g GH c Cortisol h Glucagon d PTH i Progesterone e Aldosterone j ADH When are epinephrine and norepinephrine secreted? Describe the effects of these hormones (p 269) FOR FURTHER THOUGHT During a soccer game, 12-year-old Alicia got in a tangle with another player, fell hard on her hand, and fractured her radius She is going to be fine, though she will be wearing a cast for a few weeks What hormones will contribute to the repair of the fracture, and how? Darren is 15 years old, tall for his age, but he wants to build more muscle He decides that he will eat only protein foods, because, he says, “Muscle is protein, so protein will make protein, and the more protein, the more muscle.” In part he is correct, and in part incorrect Explain why, name the hormones involved in protein metabolism, and state how each affects protein metabolism Many people love pasta, others love potatoes, and still others love rice Name the hormones involved in carbohydrate metabolism, and, for each, explain its specific function Unfortunately, more than 50% of the calories in many fast-food meals (such as a cheeseburger and fries) come from fat Name the hormones involved in fat metabolism, and for each, explain its specific function You have read about the liver several times in this chapter and often seen its picture as a target organ Many functions of the liver are stimulated by hormones Name as many hormones as you can think of with effects on the liver, and state the function of each 3957_Ch10_252-281 06/10/14 10:33 AM Page 281 The Endocrine System Look at Question Fig 10–A, which depicts hormone feedback mechanisms for body processes Each of these graph lines depicts the secretion of a hormone over time One hormone is regulated by a positive feedback mechanism and the other by a negative feedback mechanism Which is which? Give reasons for your answers Both parts of an adrenal gland contribute to our ability to respond to stressful situations Look at Question Figure 10–B and label the parts indicated The orange arrows represent hormones to target organs To get you started, # is the hypothalamus and corticotropin-releasing hormone to the anterior pituitary gland, and # is an autonomic pathway Once you have the hormones, describe a response of each target organ A Increases B Hormone secretion Decreases Time QUESTION FIGURE 10–A: Hormone feedback mechanisms for body processes Adrenal gland 281 QUESTION FIGURE 10–B: Hormones secreted during stressful situations ...3957_FM_i-0 01 13 /10 /14 10 :25 AM Page i SEVENTH EDITION ESSENTIALS OF ANATOMY AND PHYSIOLOGY 3957_FM_i-0 01 13 /10 /14 10 :25 AM Page ii 3957_FM_i-0 01 13 /10 /14 10 :25 AM Page iii SEVENTH EDITION ESSENTIALS OF. .. Homeostasis, Aging and the Muscular System, Major Muscles of the Body, 15 4 15 6 15 7 15 8 15 8 16 0 16 4 16 4 16 6 xv 3957_FM_i-0 01 13 /10 /14 10 :25 AM Page xvi xvi Contents Chapter THE NERVOUS SYSTEM 18 4 Nervous... 3957_FM_i-0 01 13 /10 /14 10 :25 AM Page viii 3957_FM_i-0 01 13 /10 /14 10 :25 AM Page ix TO THE INSTRUCTOR The start of the 21st century has already brought many advances in the science and art of medicine and