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Chapter 45

Chapter 45. Hormones and the Endocrine System. Overview: The Body’s Long-Distance Regulators. Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

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Chapter 45

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  1. Chapter 45 Hormones and theEndocrine System

  2. Overview: The Body’s Long-Distance Regulators • Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body • Hormones reach all parts of the body, but only target cells are equipped to respond

  3. Concept 45.1: The endocrine system and the nervous system act individually and together in regulating an animal’s physiology • Animals have two systems of internal communication and regulation: the nervous system and the endocrine system

  4. The nervous system conveys high-speed electrical signals along specialized cells called neurons • The endocrine system secretes hormones that coordinate slower but longer-acting responses

  5. Overlap Between Endocrine and Nervous Regulation • The endocrine and nervous systems function together in maintaining homeostasis, development, and reproduction • Specialized nerve cells known as neurosecretory cells release neurohormones into the blood • Both endocrine hormones and neurohormones function as long-distance regulators of many physiological processes

  6. Control Pathways and Feedback Loops • There are three types of hormonal control pathways: simple endocrine, simple neurohormone, and simple neuroendocrine • A common feature is a feedback loop connecting the response to the initial stimulus • Negative feedback regulates many hormonal pathways involved in homeostasis

  7. LE 45-2a Example Pathway Low blood glucose Stimulus Receptor protein Pancreas secretes glucagon ( ) Endocrine cell Blood vessel Target effectors Liver Glycogen breakdown, glucose release into blood Response Simple endocrine pathway

  8. LE 45-2b Pathway Example Stimulus Suckling Sensory neuron Hypothalamus/ posterior pituitary Neurosecretory cell Posterior pituitary secretes oxytocin ( ) Blood vessel Target effectors Smooth muscle in breast Milk release Response Simple neurohormone pathway

  9. LE 45-2c Example Pathway Stimulus Hypothalamic neurohormone released in response to neural and hormonal signals Sensory neuron Hypothalamus Neurosecretory cell Hypothalamus secretes prolactin- releasing hormone ( ) Blood vessel Anterior pituitary secretes prolactin ( ) Endocrine cell Blood vessel Target effectors Mammary glands Milk production Response Simple neuroendocrine pathway

  10. Concept 45.2: Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses • Hormones convey information via the bloodstream to target cells throughout the body • Three major classes of molecules function as hormones in vertebrates: • Proteins and peptides • Amines derived from amino acids • Steroids

  11. Signaling by any of these hormones involves three key events: • Reception • Signal transduction • Response

  12. Cell-Surface Receptors for Water-Soluble Hormones SECRETORY CELL SECRETORY CELL • The receptors for most water-soluble hormones are embedded in the plasma membrane, projecting outward from the cell surface Hormone molecule Hormone molecule VIA BLOOD VIA BLOOD Signal receptor TARGET CELL TARGET CELL Signal transduction pathway Signal receptor OR Cytoplasmic response DNA Signal transduction and response mRNA DNA NUCLEUS Nuclear response Synthesis of specific proteins NUCLEUS Receptor in plasma membrane Receptor in cell nucleus Animation: Water-Soluble Hormone

  13. different cell responses Different receptors • The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress Epinephrine Epinephrine Epinephrine  receptor  receptor a receptor Glycogen deposits Vessel dilates Glycogen breaks down and glucose is released from cell Vessel constricts Skeletal muscle blood vessel Liver cell Intestinal blood vessel Different intracellular proteins different cell responses

  14. Intracellular Receptors for Lipid-Soluble Hormones • Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus • Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes Animation: Lipid-Soluble Hormone

  15. Concept 45.3: The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system • The hypothalamus and the pituitary gland control much of the endocrine system

  16. LE 45-6 Hypothalamus Pineal gland Pituitary gland Thyroid gland Parathyroid glands Adrenal glands Pancreas Ovary (female) Testis (male)

  17. Relation Between the Hypothalamus and Pituitary Gland • The hypothalamus, a region of the lower brain, contains neurosecretory cells • The posterior pituitary, or neurohypophysis, is an extension of the hypothalamus • Hormonal secretions from neurosecretory cells are stored in or regulate the pituitary gland

  18. LE 45-7 Hypothalamus Neurosecretory cells of the hypothalamus Axon Posterior pituitary Anterior pituitary ADH Oxytocin HORMONE Mammary glands, uterine muscles Kidney tubules TARGET

  19. Other hypothalamic cells produce tropic hormones, hormones that regulate endocrine organs • Tropic hormones are secreted into the blood and transported to the anterior pituitary • The tropic hormones of the hypothalamus control release of hormones from the anterior pituitary

  20. LE 45-8 Tropic Effects Only FSH, follicle-stimulating hormone LH, luteinizing hormone TSH, thyroid-stimulating hormone ACTH, adrenocorticotropic hormone Neurosecretory cells of the hypothalamus Nontropic Effects Only Prolactin MSH, melanocyte-stimulating hormone Endorphin Portal vessels Nontropic and Tropic Effects Growth hormone Hypothalamic releasing hormones (red dots) Endocrine cells of the anterior pituitary Pituitary hormones (blue dots) FSH and LH MSH Endorphin Growth hormone HORMONE TSH ACTH Prolactin Melanocytes Thyroid Adrenal cortex Mammary glands Pain receptors in the brain Bones TARGET Testes or ovaries Liver

  21. Posterior Pituitary Hormones • The two hormones released from the posterior pituitary act directly on nonendocrine tissues • Oxytocin induces uterine contractions and milk ejection • Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys

  22. Anterior Pituitary Hormones • The anterior pituitary produces both tropic and nontropic hormones

  23. Tropic Hormones • The four strictly tropic hormones are • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) • Thyroid-stimulating hormone (TSH) • Adrenocorticotropic hormone (ACTH) • Each tropic hormone acts on its target endocrine tissue to stimulate release of hormone(s) with direct metabolic or developmental effects

  24. Nontropic Hormones • Nontropic hormones produced by the anterior pituitary: • Prolactin • Melanocyte-stimulating hormone (MSH) • -endorphin

  25. Growth Hormone • Growth hormone (GH) has tropic and nontropic actions • It promotes growth directly and has diverse metabolic effects • It stimulates production of growth factors

  26. Parathyroid Hormone and Calcitonin: Control of Blood Calcium • Two antagonistic hormones, parathyroid hormone (PTH) and calcitonin, play the major role in calcium (Ca2+) homeostasis in mammals

  27. LE 45-11 Calcitonin Thyroid gland releases calcitonin. Reduces Ca2+ uptake in kidneys Stimulates Ca2+ deposition in bones STIMULUS: Rising blood Ca2+ level Blood Ca2+ level declines to set point Homoeostasis: Blood Ca2+ level (about 10 mg/100 mL) STIMULUS: Falling blood Ca2+ level Blood Ca2+ level rises to set point Parathyroid gland Stimulates Ca2+ release from bones PTH Increases Ca2+ uptake in intestines Stimulates Ca2+ uptake in kidneys Active vitamin D

  28. Insulin and Glucagon: Control of Blood Glucose • The pancreas secretes insulin and glucagon, antagonistic hormones that help maintain glucose homeostasis • Glucagon is produced by alpha cells • Insulin is produced by beta cells

  29. LE 45-12 Body cells take up more glucose. Insulin Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Rising blood glucose level (for instance, after eating a carbohydrate- rich meal) Blood glucose level declines to set point; stimulus for insulin release diminishes. Homeostasis: Blood glucose level (about 90 mg/100 mL) Blood glucose level rises to set point; stimulus for glucagon release diminishes. STIMULUS: Dropping blood glucose level (for instance, after skipping a meal) Alpha cells of pancreas release glucagon into the blood. Liver breaks down glycogen and releases glucose into the blood. Glucagon

  30. Target Tissues for Insulin and Glucagon • Insulin reduces blood glucose levels by • Promoting the cellular uptake of glucose • Slowing glycogen breakdown in the liver • Promoting fat storage

  31. Glucagon increases blood glucose levels by • Stimulating conversion of glycogen to glucose in the liver • Stimulating breakdown of fat and protein into glucose

  32. Diabetes Mellitus • Diabetes mellitus is perhaps the best-known endocrine disorder • It is caused by a deficiency of insulin or a decreased response to insulin in target tissues • It is marked by elevated blood glucose levels

  33. Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells • Type II diabetes mellitus (non-insulin-dependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors

  34. Adrenal Hormones: Response to Stress • The adrenal glands are adjacent to the kidneys • Each adrenal gland actually consists of two glands: the adrenal medulla and adrenal cortex

  35. Catecholamines from the Adrenal Medulla • The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) • These hormones are members of a class of compounds called catecholamines • They are secreted in response to stress-activated impulses from the nervous system • They mediate various fight-or-flight responses

  36. Stress Hormones from the Adrenal Cortex • Hormones from the adrenal cortex also function in response to stress • They fall into three classes of steroid hormones: • Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system • Mineralocorticoids, such as aldosterone, affect salt and water balance • Sex hormonesare produced in small amounts

  37. LE 45-13 Stress Nerve signals Spinal cord (cross section) Hypothalamus Releasing hormone Nerve cell Anterior pituitary Blood vessel ACTH Nerve cell ACTH Adrenal gland Kidney Long-term stress response Short-term stress response Effects of glucocorticoids: Effects of epinephrine and norepinephrine: Effects of mineralocorticoids: 1. Glycogen broken down to glucose; increased blood glucose 1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose 1. Retention of sodium ions and water by kidneys 2. Increased blood pressure 3. Increased breathing rate 2. Increased blood volume and blood pressure 4. Increased metabolic rate 2. Immune system may be suppressed 5. Change in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity

  38. Gonadal Sex Hormones • The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins

  39. The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system • Testosterone causes increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks

  40. Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics • In mammals, progestins, which include progesterone, are primarily involved in preparing and maintaining the uterus

  41. Melatonin and Biorhythms • The pineal gland, located in the brain, secretes melatonin

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