Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 23 Chemical Control of the Animal Body: The Endocrine System Lectures by Gregory Ahearn University of North Florida Copyright © 2009 Pearson Education, Inc.. 23.1 How Do Animal Cells Communicate? Cells communicate by releasing chemical messenger molecules that affect other cells, either nearby or far away. • A messenger molecule alters the physiology of a cell by binding to receptors, which are specialized proteins located on the surface of the cell. • When a messenger molecule binds to a receptor, the recipient cell responds in a way that is determined by the messenger, the receptor, and the type of cell. Copyright © 2009 Pearson Education Inc. 23.1 How Do Animal Cells Communicate? Responses to messenger molecules can be varied. • • • • Muscle contraction Electrical activity of nerve cells Secretion of milk in women Active transport of salt by kidney cells Copyright © 2009 Pearson Education Inc. 23.1 How Do Animal Cells Communicate? Almost all animals have two large, specialized organ systems in which chemical communication is especially important. • The endocrine system • The nervous system The endocrine system is an integrated group of secretory structures, called glands, that regulate growth, development, metabolism, and reproduction. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Hormones are chemical messengers, secreted by specialized cells of endocrine glands, that initiate changes in other cells. • Hormones travel from the tissues where they are synthesized to target cells via the blood. • Hormones only have an effect in target cells of specific organs or tissues where appropriate receptors for the hormones are present. • Each cell, therefore, can respond to some hormones but not to others. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Hormone release, distribution, and reception Endocrine cells release hormone The hormone enters the blood and is carried throughout the body The hormone leaves the capillaries and diffuses to all tissues through the extracellular fluid (extracellular fluid) capillary biceps The hormone affects cells bearing receptors to which the hormone can bind uterus The hormone cannot affect cells that only bear receptors to which the hormone cannot bind Fig. 23-1 Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Many different molecules serve as hormones. • There are three classes of hormones: • Peptide hormones: chains of amino acids • Amino acid-derived hormones: modified amino acids • Steroid hormones: synthesized from cholesterol Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Hormones act by binding to receptors in or on target cells. • Hormone receptors can be on the plasma membrane or within the nucleus of target cells. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Some hormones bind to receptors on the surfaces of target cells. • Peptide and amino acid-derived hormones cannot penetrate plasma membranes to initiate a series of reactions in the target cell. • Instead, they bind to receptors on the target cell’s plasma membrane. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Peptide and amino-acid based hormones • Step 1: Hormone–receptor binding stimulates production of a second messenger molecule in the cell. • Step 2: The second messenger transfers the signal from the first messenger—the hormone—to other molecules within the cell. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Peptide and amino acid-derived hormones (continued) • Step 3: The second messenger, such as adenosine monophosphate (cyclic AMP), initiates a chain of biochemical reactions. • Step 4: The target cell synthesizes or secretes substances. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Actions of peptide and amino acid–derived hormones on target cells peptide or amino acid-derived hormone (1st messenger) The hormone binds to a receptor on the plasma membrane of a target cell Hormone–receptor binding activates an enzyme that catalyzes the synthesis of a second messenge such as cyclic AMP (cytoplasm) cyclic AMPsynthesizing enzyme ATP (extracellular fluid) receptor active enzyme cyclic AMP (2nd messenger) product The activated enzymes catalyze specific reactions plasma membrane inactive enzyme reactant The second messenger activates other enzymes Copyright © 2009 Pearson Education Inc. nuclear envelope (nucleus) Fig. 23-2 23.2 How Do Animal Hormones Work? PLAY Animation—Peptide Hormones Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Some hormones bind to receptors inside target cells. • Steroid hormones are lipid soluble, so they pass through plasma membranes and initiate a series of reactions inside cells. • Step 1: Once inside, these hormones bind to receptors inside target cells. • Step 2: These receptors are either in the nucleus or move into the nucleus after binding to the hormone. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Steroid hormones (continued) • Step 3: The hormone–receptor complex binds to the DNA of the promoter region of specific genes. • Step 4: Transcription of mRNA is stimulated. • Step 5: The mRNA travels to the cytoplasm and directs protein synthesis. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Steroid hormone action on target cells steroid hormone (extracellular fluid) The hormone binds to a receptor in the nucleus or to a receptor in the cytoplasm that carries it into the nucleus The hormone–receptor complex binds to DNA and causes RNA polymerase to bind to a nearby promoter site for a specific gene A steroid hormone diffuses through the plasma membrane DNA plasma membrane hormone receptor ribosome RNA polymerase The mRNA leaves the nucleus, then attaches to a ribosome and directs the synthesis of a specific protein product mRNA RNA polymerase catalyzes the transcription of DNA into messenger RNA (mRNA) gene new protein nuclear envelope (cytoplasm) (nucleus) Fig. 23-3 Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? PLAY Animation—Steroid Hormones Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Hormone release is regulated by feedback mechanisms. • The release of most hormones is controlled by negative feedback. • This is a response to a change that tends to counteract the change and to restore the system to its original condition. • Excessive perspiration is followed by pituitary release of antidiuretic hormone, which causes your kidneys to reabsorb water to restore your blood volume. Copyright © 2009 Pearson Education Inc. 23.2 How Do Animal Hormones Work? Hormone release is regulated by feedback mechanisms (continued). • In a few cases, hormone release is controlled by positive feedback, in which the response to a change enhances the change. • During birth, the baby’s pressure on the mother’s cervix causes her brain to release oxytocin, which stimulates contractions of the uterus, pushing the baby harder against the cervix. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? What are the major endocrine glands and organs? • • • • • The hypothalamus–pituitary complex The thyroid gland The pancreas The sex organs The adrenal glands Copyright © 2009 Pearson Education Inc. Hypothalamus ADH, oxytocin, and regulatory hormones for the anterior pituitary Pineal gland melatonin Pituitary gland anterior pituitary: Parathyroid glands (on the posterior surface of the thyroid gland) parathyroid hormone ACTH, TSH, GH, PRL, FSH, LH posterior pituitary: oxytocin and ADH Thyroid gland thyroxine, calcitonin Heart atrial natriuretic peptide Thymus gland thymosins Kidneys erythropoietin Digestive tract several hormones (see Chapter 21) Adrenal glands (one on each kidney) medulla: epinephrine, norepinephrine cortex: Fat leptin glucocorticoids (cortisol), mineralocorticoids (aldosterone), testosterone Gonads testes (male): Pancreas islet cells insulin, glucagon androgens, especially testosterone ovaries (female): testis estrogens, progesterone ovary Copyright © 2009 Pearson Education Inc. Fig. 23-4 Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Hormones of the hypothalamus and pituitary gland regulate many functions throughout the body. • The hypothalamus and pituitary gland coordinate the action of many key hormonal system. • The hypothalamus is a part of the brain that contains clusters of specialized nerve cells, called neurosecretory cells. • Neurosecretory cells synthesize peptide hormones, store them, and release them when stimulated. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Hormones of the hypothalamus and pituitary gland regulate many functions throughout the body (continued). • The pituitary gland is a pea-sized gland that dangles from the hypothalamus by a stalk. • It consists of two parts: the anterior pituitary and the posterior pituitary. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The hypothalamus/pituitary system hypothalamus Neurosecretory cells of the hypothalamus produce oxytocin and ADH Neurosecretory cells of the hypothalamus produce releasing and inhibiting hormones Releasing or inhibiting hormones (green circles) are secreted into capillaries feeding the anterior lobe of the pituitary Oxytocin and ADH (blue triangles are secreted into the blood via capillaries in the posterior pituitary blood flow pituitary (anterior lobe) endocrine cell pituitary (posterior lobe) capillary bed capillary bed Endocrine cells of the anterior pituitary secrete hormones (red squares) in response to releasing hormones blood flow Fig. 23-5 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? PLAY Animation—Hypothalamic Control of the Pituitary Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The anterior pituitary is a true endocrine gland, composed of several types of hormone-secreting cells enmeshed in a network of capillaries. The posterior pituitary, however, develops as an outgrowth of the hypothalamus. • It consists of a capillary bed and the endings of neurosecretory cells whose cell bodies are in the hypothalamus. The hypothalamus controls the release of hormones from both parts of the pituitary. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Hormones from the hypothalamus control release in the anterior pituitary. • Neurosecretory cells of the hypothalamus produce nine different hormones that regulate the release of hormones from the anterior pituitary. • These hormones travel between the two structures by way of a capillary bed. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The anterior pituitary produces and releases several hormones. • Four of these regulate hormone production in other endocrine glands. • Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) stimulate production of sperm and eggs. • Thyroid-stimulating hormone (TSH) stimulates the thyroid to release its hormones. • Adrenocorticotropic hormone (ACTH) stimulates the release of hormone from the adrenal cortex. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The anterior pituitary produces and releases several hormones (continued). • The remaining hormones do not act on other endocrine glands. • Prolactin stimulates development of mammary glands during pregnancy. • Growth hormone (GH) regulates body growth by increasing protein synthesis; too little results in dwarfism, too much in gigantism. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The posterior pituitary releases hormones synthesized in the hypothalamus. • Hormones of the posterior pituitary: • Antidiuretic hormone (ADH) helps prevent dehydration by increasing water uptake by the kidney before it is lost in urine. • Oxytocin triggers “milk letdown” in nursing mothers by causing the contraction of muscles around the mammary glands to expel milk to the infant during breast-feeding. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Hormones and breastfeeding Neurosecretory cells of the hypothalamus release oxytocin from endings in the posterior pituitary hypothalamus Oxytocin is carried in the blood to the breast Receptors send nerve impulses to the hypothalamus Suckling stimulates sensory receptors in the breast posterior pituitary Oxytocin binds to receptors on milk gland muscles, causing milk to be squeezed out milk gland muscle cells duct milk-producing cells nipple clusters of milk glands Fig. 23-7 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The thyroid and parathyroid glands influence metabolism and calcium levels. • Lying at the front of the neck, the thyroid gland produces two major hormones: thyroxine and calcitonin. • The parathyroid gland consists of two pairs of small disks of endocrine cells, one pair on each side of the back of the thyroid gland; these cells release parathyroid hormone. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The thyroid and parathyroid glands larynx thyroid gland esophagus parathyroid glands trachea Fig. 23-8 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Parathyroid hormone and calcitonin regulate calcium metabolism. • The proper concentration of calcium is essential to nerve and muscle function. • Parathyroid hormone and calcitonin work together to maintain nearly constant calcium levels in the blood and body fluids. • The skeleton and kidneys are the major body structures that help regulate blood calcium concentrations. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Thyroxine influences energy metabolism. • Thyroxine increases metabolism and breaks down glucose, providing more energy; it also regulates body temperature. • In juvenile animals, thyroxine helps regulate growth by stimulating both metabolic rate and nervous system development. • Undersecretion of thyroxine early in life can cause cretinism, a condition characterized by mental retardation and dwarfism. • Too much thyroxine in vertebrates speeds up development. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Thyroxine release is controlled by the hypothalamus. • The release of thyroxine is under control of the hypothalamus by negative feedback. • Thyroid-stimulating hormone (TSH) from the anterior pituitary stimulates the thyroid to release thyroxine; high thyroxine concentrations in the blood inhibit TSH release from the anterior pituitary. • Iodine in the diet is necessary for thyroxine synthesis; deficiency leads to an enlarged thyroid, called a goiter. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Goiter Fig. 23-9 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The pancreas has both digestive and endocrine functions. • The pancreas produces both digestive secretions and hormones. • The pancreas produces bicarbonate and a number of enzymes that are released into the small intestine, promoting food digestion. • The endocrine portion of the pancreas consists of clusters of cells called islet cells. • Each islet cell produces one of two hormones: insulin or glucagon. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Insulin and glucagon work in opposition to regulate carbohydrate and fat metabolism: insulin reduces blood glucose concentration, and glucagon increases it. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The pancreas controls blood glucose levels. Blood glucose is increased Glucagon stimulates cells to burn fat instead of glucose; the liver converts glycogen to glucose Eating raises blood glucose high blood glucose High blood glucose stimulates insulin release and inhibits glucagon release pancreas glucagon Insulin stimulates glucose uptake by body cells; the liver converts glucose to glycogen Low blood glucose stimulates glucagon release and inhibits insulin release Exercise, fasting also reduce blood glucose low blood glucose insulin liver muscle Blood glucose is reduced Fig. 23-10 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? If blood glucose rises after you have eaten: • Step 1: insulin is released by the pancreas. • Step 2: insulin causes body cells to take up glucose. • Step 3: in body cells, glucose is either metabolized for energy or is converted to fat or glycogen. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? If blood glucose level drops by skipping a meal: • Step 1: insulin secretion is inhibited; glucagon secretion is stimulated. • Step 2: glucagon activates an enzyme in the liver that breaks down glycogen, releasing glucose into the blood. • Step 3: glucagon also promotes lipid breakdown, which releases fatty acids that can be metabolized for energy. • Step 4: these effects increase blood glucose levels, which inhibits glucagon secretion. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Diabetes results from malfunctions of the insulin control system. • Defects in insulin synthesis or release by the pancreas—or in the ability of target cells to respond to insulin in the blood—result in diabetes mellitus. • Diabetes mellitus is a condition in which blood glucose levels are high and fluctuate wildly with sugar intake. • Severe diabetes causes fat deposits to accumulate in blood vessels, increasing blood pressure and heart disease. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Diabetes results from malfunctions of the insulin control system (continued). • Diabetes is a major cause of heart attacks. • Fat deposits in small blood vessels in the kidneys and the retina of the eye may cause kidney failure and blindness, respectively. • Insulin replacement therapy improves glucose and lipid metabolism, and it improves the health of diabetics. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The sex organs produce both gametes and sex hormones. • The testes secrete several male sex hormones, all steroids, of which the most important is testosterone. • The ovaries secrete two types of steroid hormones: estrogen and progesterone. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Sex hormone levels increase during puberty. • Puberty begins when the hypothalamus starts to secrete increasing amounts of hormones that stimulate the anterior pituitary to secrete more lutenizing hormone (LH) and folliclestimulating hormone (FSH) into the blood. • LH and FSH stimulate target cells in the testes or ovaries to produce higher levels of sex hormones. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Sex hormone levels increase during puberty (continued). • In females, estrogen released by the ovaries stimulates the growth of breasts and the maturation of the female reproductive system, including the production of mature egg cells. • Progesterone prepares the reproductive tract to receive and nourish the fertilized egg, and is also secreted by the ovaries during pregnancy. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Sex hormone levels increase during puberty (continued). • In males, testosterone, secreted by the testes, promotes sperm cell production and stimulates the development of male secondary sexual attributes. • These attributes include the growth of body and facial hair, the development of a large larynx, which lowers the voice, and increased muscle growth. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The adrenal glands secrete hormones that regulate metabolism and responses to stress. • The adrenal glands consist of two very different parts: the adrenal cortex and the adrenal medulla. • The cortex secretes two major types of steroid hormones called glucocorticoids and mineralocorticoids. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The adrenal glands The adrenal medulla secretes epinephrine and norepinephrine The adrenal cortex secretes glucocorticoids, mineralocorticoids, and testosterone kidney Fig. 23-11 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Glucocorticoids help control glucose metabolism. • Their release is stimulated by adrenocorticotropic hormone (ACTH) from the anterior pituitary. • ACTH release is stimulated by hormones produced by the hypothalamus in response to stimuli, such as trauma, infection, or exposure to temperature extremes. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Glucocorticoids help control glucose metabolism. • Glucocorticoids raise glucose levels in the blood. • Glucocorticoids reduce inflammation. • Excess glucocorticoids cause Cushing’s syndrome, which is characterized by weight gain, fragile skin, weakening of the bones, excessive hair growth, and increased thirst and urination. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Cushing’s syndrome in an elderly horse Fig. 23-12 Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Mineralocorticoid hormones regulate the mineral (salt) content of the blood. • The most important mineralocorticoid is aldosterone, which helps control sodium concentrations. • Sodium ions are the most abundant positive ions in the blood and extracellular fluid. • If blood sodium falls, the adrenal cortex releases aldosterone, which causes the kidneys and sweat glands to retain sodium. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The hormones of the adrenal medulla prepare the body for stress and exercise. • The adrenal medulla is located in the center of each adrenal gland. • It produces two hormones: epinephrine and norepinephrine (also called adrenaline and noradrenaline, respectively). • These hormones prepare the body for emergency action by increasing heart and respiratory rates, increasing blood pressure, causing blood glucose to rise, and directing blood flow away from the digestive tract and toward the brain and muscles. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Hormones are also produced by the pineal gland, thymus, kidneys, digestive tract, heart, and fat cells. • The pineal gland is located between the two hemispheres of the brain, just above and behind the hypothalamus. • The pineal gland produces the hormone melatonin. • The pineal gland may suppress the onset of puberty. • It may also play a role in sleep–wake cycles and can reduce jet lag during long-distance travel. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The thymus is located in the chest cavity behind the breastbone. • The thymus produces the hormone thymosin, which stimulates the reproduction and development of the T blood cells, which in turn play crucial roles in the immune response. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The kidney secretes erythropoietin when the blood is not transporting enough oxygen. • Erythropoietin stimulates the bone marrow to produce more oxygen-carrying red blood cells. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? The heart release the hormone, atrial natriuretic peptide (ANP), which inhibits the release of ADH and aldosterone, and increases the excretion of sodium. • This hormone is released in response to increased blood volume; ANP helps lower blood volume. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Fat cells release the hormone leptin. • Mice genetically engineered to lack the gene for leptin became obese, and leptin injections caused them to lose weight. • Trials of leptin as a human weight-loss aid have not been encouraging. • Many people with high levels of leptin seem to be relatively insensitive to it. • Leptin also stimulates the growth of new capillaries and speeds wound healing. Copyright © 2009 Pearson Education Inc. 23.3 What Are The Structures And Functions Of The Mammalian Endocrine System? Leptin helps regulate body fat. Fig. 23-13 Copyright © 2009 Pearson Education Inc.