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Chapter 45 Hormones and the Endocrine System PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings YOU MUST KNOW • Two ways hormones affect target organs. • The secretion, target, action, and regulation of at least three hormones. • An illustration of both positive and negative feedback in the regulation of homeostasis by hormones. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Body’s Long-Distance Regulators • The endocrine system and the nervous system act individually and together in regulating an animal’s physiology. – The endocrine system of an animal is the sum of all its hormone-secreting cells and tissues. – Endocrine glands are ductless and secrete hormones directly into body fluids. – Hormones are chemical signals that cause a response in target cells. – Positive and negative feedback regulates most endocrine secretion. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Control Pathways and Feedback Loops Pathway Example Low blood glucose Stimulus Receptor protein Pancreas secretes glucagon ( ) Endocrine cell Blood vessel Target effectors Response Pathway Stimulus Example Example Pathway Suckling Hypothalamic neurohormone released in response to Sensory neural and neuron hormonal signals Hypothalamus Sensory neuron Hypothalamus/ posterior pituitary Neurosecretory cell Posterior pituitary secretes oxytocin Blood ( ) vessel Stimulus Neurosecretory cell Hypothalamus secretes prolactinBlood releasing vessel hormone ( ) Liver Glycogen breakdown, glucose release into blood (a) Simple endocrine pathway Target effectors Response Smooth muscle in breast Milk release Anterior pituitary secretes Endocrine prolactin ( ) cell Blood vessel (b) Simple neurohormone pathway Target effectors Response Figure 45.2a–c Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mammary glands Milk production (c) Simple neuroendocrine pathway Mechanisms of Hormone Action • Hormones and other chemical signals bind to target cell receptors, initiating pathways that culminate in specific cell responses. There are basically two mechanisms of hormone action: – Cell Surface Receptors: bind the hormone, and a signal transduction pathway is triggered, eliciting a response to the signal. • Ex: The binding of epinephrine to liver cells causes a cascade that leads to the conversion of glycogen to glucose. – Intracellular Receptors: bound by hormones that are lipidsoluble. The receptor then acts as a transcription factor, causing a change in gene expression. • Ex: Testosterone and estrogen enter the nuclei of target cells, bind the DNA, and stimulate transcription of certain genes. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Varying Degrees of Hormonal Effect • The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress Different receptors different cell responses Epinephrine Epinephrine Epinephrine a receptor b receptor b receptor Glycogen deposits Vessel dilates Vessel constricts (a) Intestinal blood vessel Figure 45.4a–c (b) Skeletal muscle blood vessel Different intracellular proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycogen breaks down and glucose is released from cell (c) Liver cell different cell responses Paracrine Signaling by Local Regulators • In a process called paracrine signaling – Various types of chemical signals elicit responses in nearby target cells • Paracrine signaling involves local regulators – they convey messages between neighboring cells (as opposed to long-distance endocrine signaling by hormones). – These can elicit cell responses more quickly than hormones. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Major Human Endocrine Glands Hypothalamus Pineal gland Pituitary gland Thyroid gland Parathyroid glands Hypothalamus Neurosecretory cells of the hypothalamus Axon Adrenal glands Pancreas Posterior pituitary HORMONE TARGET Anterior pituitary ADH Kidney tubules Ovary (female) Oxytocin Mammary glands, uterine muscles Testis (male) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Relation Between the Hypothalamus and Pituitary Gland • Other hypothalamic cells produce tropic hormones that are secreted into the blood and transported to the anterior pituitary or adenohypophysis 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) HORMONE TARGET Figure 45.8 FSH and LH Testes or ovaries TSH Thyroid Endocrine cells of the anterior pituitary Pituitary hormones (blue dots) ACTH Prolactin MSH Endorphin Adrenal cortex Mammary glands Melanocytes Pain receptors in the brain Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Growth hormone Liver Bones Human Endocrine Glands & Their Hormones Table 45.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human Endocrine Glands & Their Hormones Table 45.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nonpituitary Hormones • Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior • Many nonpituitary hormones regulate various functions in the body and include: – Thyroid hormones – Parathyroid Hormone and Calcitonin – Insulin and Glucagon – Adrenal Hormones – Glucocorticoids, such as cortisol – Mineralocorticoids, such as aldosterone – Sex hormones Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Thyroid Hormones • The thyroid gland consists of two lobes located on the ventral surface of the trachea – Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Negative Feedback Loops Control Thyroid Hormones • The hypothalamus and anterior pituitary control the secretion of thyroid hormones through two negative feedback loops Hypothalamus Anterior pituitary TSH Thyroid Figure 45.9 T3 + Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings T4 Hyperthyroidism • The thyroid hormones play crucial roles in stimulating metabolism and influencing development and maturation Figure 45.10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parathyroid Hormone and Calcitonin: • The maintainence of blood calcium level is one example of how homeostasis is maintained by negative feedback. Thyroid gland releases calcitonin. Calcitonin Reduces Ca2+ uptake in kidneys Stimulates Ca2+ deposition in bones Blood Ca2+ level declines to set point STIMULUS: Rising blood Ca2+ level Homeostasis: Blood Ca2+ level (about 10 mg/100 mL) STIMULUS: Falling blood Ca2+ level Blood Ca2+ level rises to set point Stimulates Ca2+ release from bones Parathyroid gland PTH Increases Ca2+ uptake in intestines Figure 45.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Active vitamin D Stimulates Ca2+ uptake in kidneys Maintenance of Glucose Homeostasis Body cells take up more glucose. Insulin Beta cells of pancreas are stimulated to release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Rising blood glucose level (for instance, after eating a carbohydraterich 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. Figure 45.12 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Liver breaks down glycogen and releases glucose into blood. STIMULUS: Dropping blood glucose level (for instance, after skipping a meal) Alpha cells of pancreas are stimulated to release glucagon into the blood. Glucagon Diabetes Mellitus • Diabetes mellitus, perhaps the best-known endocrine disorder – Is caused by a deficiency of insulin or a decreased response to insulin in target tissues – Is marked by elevated blood glucose levels • Type I diabetes mellitus (insulin-dependent diabetes) – Is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas • Type II diabetes mellitus (non-insulin-dependent diabetes) – Is characterized either by a deficiency of insulin or, more commonly, by reduced responsiveness of target cells due to some change in insulin receptors Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Adrenal Hormones: Response to Stress • The adrenal glands are adjacent to the kidneys and are actually made up of two glands: the adrenal medulla and the adrenal cortex Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stress Hormones from the Adrenal Cortex • Hormones from the adrenal cortex also function in the body’s response to stress and 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 hormones – Are produced in small amounts Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stress and the Adrenal Gland Stress Spinal cord (cross section) Nerve signals Hypothalamus Releasing hormone Nerve cell Anterior pituitary Blood vessel Adrenal medulla secretes epinephrine and norepinephrine. Nerve cell Adrenal cortex secretes mineralocorticoids and glucocorticoids. ACTH Adrenal gland Kidney (a) Short-term stress response Effects of epinephrine and norepinephrine: 1. Glycogen broken down to glucose; increased blood glucose 2. Increased blood pressure 3. Increased breathing rate 4. Increased metabolic rate Figure 45.13a,b 5. Change in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings (b) Long-term stress response Effects of mineralocorticoids: 1. Retention of sodium ions and water by kidneys 2. Increased blood volume and blood pressure Effects of glucocorticoids: 1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose 2. Immune system may be suppressed Gonadal Sex Hormones • The gonads (testes and ovaries) produce most of the body’s sex hormones: androgens, estrogens, and progestins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Melatonin and Biorhythms • The pineal gland, located within the brain secretes melatonin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Invertebrate Regulatory Systems • In insects, molting and development are controlled by three main hormones: Brain 1 Neurosecretory cells in the brain produce brain hormone (BH), which is stored in the corpora cardiaca (singular, corpus cardiacum) until release. Neurosecretory cells Brain hormone (BH) Corpus cardiacum Corpus allatum Low JH Prothoracic gland Ecdysone Juvenile hormone (JH) 2 BH signals its main target organ, the prothoracic gland, to produce the hormone ecdysone. 3 Ecdysone secretion from the prothoracic gland is episodic, with each release stimulating a molt. EARLY LARVA Figure 45.15 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LATER LARVA PUPA 4 Juvenile hormone (JH), secreted by the corpora allata, determines the result of the molt. At relatively high concentrations of JH, ecdysone-stimulated molting produces another larval stage. JH suppresses metamorphosis. But when levels of JH fall below a certain concentration, a pupa forms at the next ecdysone-induced molt. The adult insect emerges from the pupa. ADULT