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Body’s Long Distance Regulators Chapter 45 Hormones & the Endocrine System Types of Secreted Signaling Molecules • Animals use chemical signals (hormones) to communicate with each other and between the different cells of the body • Hormones (to excite) reach all parts of the body – target cells respond Insect metamorphosis is regulated by hormones • Secreted chemical signals include – Hormones – Local regulators – Neurotransmitters – Neurohormones – Pheromones Figure 45.1 Two systems regulate communication • The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, p , development, p , energy gy metabolism, growth, and behavior • The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells Nervous System •Sensory system •Sends impulses •Impulse passed through neuron parts of body neuron….parts •Fast ..within seconds Endocrine system •Chemical system •Produces hormones •Hormone diffuse in blood •Regulate growth growth, reproduction, metabolism & behavior •Slow…days or months 1 Fig. 45-13-3 Brain Neurosecretory cells Corpus cardiacum PTTH • Invertebrate regulatory systems also involve endocrine and nervous system interactions • Diverse hormones – Regulate different aspects of homeostasis in invertebrates Corpus allatum Low JH Prothoracic gland Ecdysone Juvenile hormone (JH) EARLY LARVA LATER LARVA PUPA ADULT Molting and development are controlled by different hormones • Brain hormone: release of ecdysone • Ecdysone: molting, adult characteristics • Juvenile hormone: retention of larval characteristics • Endocrine & Nervous system function together • Ex. Epinephrine – hormone & neurotransmitter • Neurosecretory cells – nerve cells that secrete hormones • Ecdysone promotes molting (in the presence of juvenile hormone) and development (in the absence of juvenile hormone) of adult characteristics • Endocrine system consists of hormone secreting cells Fig. 45-2a Local Regulators Blood vessel Response (a) Endocrine signaling Response (b) Paracrine signaling Response • Local regulators are chemical signals that travel over short distances by diffusion • Local regulators help regulate blood pressure, nervous system function, and reproduction • Local regulators are divided into two types – Paracrine signals act on cells near the secreting cell – Autocrine signals act on the secreting cell itself (c) Autocrine signaling 2 Fig. 45-2b Synapse Neuron • In paracrine signaling nonhormonal chemicals called local regulators have various functions and include – Cytokines (Immune responses) – Growth G th factors f t ( ti l t cellll di (stimulate division) i i ) – Nitric oxide (vasodilation) – Prostaglandins: modified fatty acids, cause aggregation of platelets before blood clotting, promotes fever and inflammation Response (d) Synaptic signaling Neurosecretory cell Blood vessel Response (e) Neuroendocrine signaling Signaling by Pheromones Synaptic and Neuroendocrine Signaling • Neurons (nerve cells) contact target cells at synapses • At synapses, neurons often secrete chemical signals g called neurotransmitters that diffuse a short distance to bind to receptors on the target cell • Neurotransmitters play a role in sensation, memory, cognition, and movement • Neurohormones are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream • Pheromones are chemical signals that are released l d ffrom th the b body d and d used d tto communicate with other individuals in the species • Pheromones mark trails to food sources, warn of predators, and attract potential mates Fig. 45-3 Water-soluble Lipid-soluble • Three major classes of hormones in vertebrates – Proteins and peptides: GH, ADH, ACTH, Insulin & Glucagon – Amines derived from amino acids: Melatonin,, Epinephrine, Norepinephrine, T3, &T4 – Steroids: Sex hormones, Glucocorticoids & Mineralocorticoids 0.8 nm Polypeptide: Insulin Steroid: Cortisol Amine: Epinephrine Amine: Thyroxine 3 Fig. 45-5-2 Fat-soluble hormone Watersoluble hormone • Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines)) do not • The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells Transport protein Signal receptor TARGET CELL OR Cytoplasmic response Signal receptor Gene regulation Cytoplasmic response (a) NUCLEUS Gene regulation (b) Cellular Response Pathways • Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors • Lipid-soluble p hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells • Signaling by any of these molecules involves three key events – Reception – Signal transduction – Response Fig. 45-6-2 Epinephrine Adenylyl cyclase G protein • Binding of a hormone to its receptor – Initiates a signal transduction pathway – leading to specific responses in the cytoplasm –g gene expression, p synthesis y of enzymes y or proteins….. G protein-coupled receptor GTP ATP cAMP Inhibition of glycogen synthesis Animation: WaterWater-Soluble Hormone Second messenger Protein kinase A Promotion of glycogen breakdown 4 Fig. 45-7-1 Fig. 45-7-2 Hormone (estradiol) Estradiol (estrogen) receptor Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Plasma membrane Hormone-receptor complex Hormone-receptor complex DNA Vitellogenin mRNA for vitellogenin Figure 45.4 Pathway of Lipid Soluble Hormones Major endocrine glands: Hypothalamus Pineal gland Pituitary gland • The response to a lipid-soluble hormone is usually a change in gene expression • Steroids, thyroid hormones, and the hormonal form of vitamin D enter target g 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 Thyroid gland Parathyroid glands (behind thyroid) Adrenal glands (atop kidneys) Organs containing endocrine cells: Thymus Heart Liver Stomach Pancreas Kidneys Ovaries (female) Small intestine Testes (male) Animation: LipidLipid-Soluble Hormone Figure 45.14 Cerebrum Pineal gland Thalamus Hypothalamus Cerebellum Pituitary gland Spinal cord • Hypothalamus : Master switchboard controls endocrine system – sends either hormonal or electrical messages to the pituitary Hypothalamus • Pituitary gland: Master gland regulates secretion of endocrine glands Posterior pituitary Anterior pituitary 5 Table 45-1b Table 45.1a • The posterior pituitary stores and secretes hormones that are made in the hypothalamus • The anterior pituitary makes and releases hormones under regulation of the hypothalamus Table 45-1c Table 45.1b Fig. 45-11 Pathway – Example Stimulus Low pH in duodenum S cells of duodenum secrete secretin ( ) Endocrine cell Blood vessel Target cells Response Pancreas Bicarbonate release Simple Hormone Pathways • Hormones released from an endocrine cell, travel through the bloodstream, and interact with the receptor or a target cell to cause a physiological response • For example, the release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin • This causes target cells in the pancreas, a gland behind the stomach, to raise the pH in the duodenum 6 Figure 45.12 Example Pathway Stimulus Feedback Regulation Suckling Sensory neuron • A negative feedback loop inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity • Positive feedback reinforces a stimulus to produce an even greater response • For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin Positive fe eedback Hypothalamus/ posterior pituitary Neurosecretory cell Neurohormone Blood vessel Target cells Posterior pituitary secretes the neurohormone oxytocin ( ). Smooth muscle in breasts Response Milk release Figure 45.15 Hypothalamus Posterior Pituitary Hormones Neurosecretory cells of the hypothalamus Neurohormone • ADH and Oxytocin are released by posterior pituitary – Act directly on nonendocrine tissues Axons Posterior pituitary • Oxytocin O t i Anterior pituitary – Induces uterine & mammary gland contractions and milk ejection • Antidiuretic hormone (ADH) HORMONE ADH Oxytocin TARGET Kidney tubules Mammary glands, uterine muscles – Enhances water reabsorption in the kidneys Figure 45.16 Tropic effects only: FSH LH TSH ACTH Neurosecretory cells of the hypothalamus Nontropic effects only: Prolactin MSH Anterior Pituitary Hormomes • The anterior pituitary Nontropic and tropic effects: GH Hypothalamic releasing and inhibiting hormones Portal vessels – Is a true-endocrine gland – Produces tropic and nontropic hormones E d Endocrine i cells ll of the anterior pituitary Pituitary hormones Posterior pituitary HORMONE FSH and LH TSH ACTH Prolactin TARGET Testes or ovaries Thyroid Adrenal cortex Mammary glands MSH GH Melanocytes Liver, bones, other tissues 7 Figure 45.17a Pathway Example Cold Stimulus Figure 45.17b To hypothalamus Neurosecretory cell Hypothalamus secretes thyrotropin-releasing hormone (TRH ). Releasing hormone Blood vessel Neg gative feedback Sensory neuron Hypothalamus Pathway Anterior pituitary Tropic hormone Endocrine cell Example Anterior pituitary secretes thyroid-stimulating hormone (TSH, also known as thyrotropin ). Thyroid gland secretes thyroid hormone (T3 and T4 ). Hormone Anterior pituitary Tropic hormone Anterior pituitary secretes thyroid-stimulating hormone (TSH, also known as thyrotropin ). Target cells Response Hormone Cascade Pathway • A hormone can stimulate the release of a series of other hormones, which activates a nonendocrine target cell; this is called a hormone cascade pathway • The release of thyroid hormone results from a hormone cascade pathway involving the hypothalamus, anterior pituitary, and thyroid gland A tropic hormone regulates the function of endocrine cells or glands Four Tropic Hormones by Anteroir Pituitary 1. Follicle-stimulating hormone (FSH): stimulates development of eggs & sperm 2. Luteinizing hormone (LH): stimulates hormone production in ovaries and testes 2. Thyroid stimulating hormone (TSH): stimulates the release of T3 & T4 – controls metabolism. 3. Adrenocorticoptropic hormone (ACTH): long term response to stress Body tissues Increased cellular metabolism • Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones from the hypothalamus • For example, the production of thyrotropin releasing hormone (TRH) in the hypothalamus stimulates secretion of the thyroid stimulating hormone (TSH) from the anterior pituitary • TSH then stimulates release of thyroid hormone by the thyroid gland Nontropic Hormones by Anterior Pituitary • The nontropic hormones produced by the anterior pituitary include • Target nonendocrine cells – Prolactin: stimulates lactation – Melanocyte-stimulating hormone (MSH): skin pigmentation, fat metabolism – -endorphin: inhibits sensation of pain 8 Non Pituitary hormones: Thyroid hormone Growth Hormone (GH) • The thyroid gland • Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic actions • Promotes growth directly and has diverse metabolic effects • Stimulates the production of growth factors by other tissues • Low levels results in dwarfism, high levels results in gigantism, overproduction of GH causes acromegaly – two lobes located on the ventral surface of the trachea – Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4) Thyroid Hormone • The thyroid hormones – stimulates metabolism – influences development and maturation • Hyperthyroidism, excessive secretion of thyroid hormones,, causes high g body y temperature, p , weight g loss, irritability, and high blood pressure • Graves’ disease is a form of hyperthyroidism in humans • Hypothyroidism: Thyroid deficiency results in Cretinism-retards skeletal muscle growth and mental development. • Graves disease, a form of hyperthyroidism caused by autoimmunity, is typified by protruding eyes • Thyroid y hormone refers to a p pair of hormones – Triiodothyronin (T3), with three iodine atoms – Thyroxine (T4) with four iodine atoms • Insufficient dietary iodine leads to an enlarged thyroid gland, called a goiter Figure 45.19 Specialized role of Thyroxine in resorption of the tadpole’s tail as the frog develops into an adult (a) ((b)) • Two antagonistic hormones regulate the homeostasis of calcium (Ca2+) in the blood of mammals – Parathyroid y hormone ((PTH)) is released by y the parathyroid glands – Calcitonin is released by the thyroid gland Tadpole Adult frog 9 Fig. 45-20-1 Fig. 45-20-2 Active vitamin D Increases Ca2+ uptake in intestines Stimulates Ca2+ uptake in kidneys PTH PTH Parathyroid P th id gland l d (behind thyroid) STIMULUS: Falling blood Ca2+ level Parathyroid P th id gland l d (behind thyroid) Stimulates Ca2+ release from bones STIMULUS: Falling blood Ca2+ level Blood Ca2+ level rises. Homeostasis: Blood Ca2+ level (about 10 mg/100 mL) Homeostasis: Blood Ca2+ level (about 10 mg/100 mL) Parathyroid and Low blood calcium Calcitonin and High blood calcium • PTH, secreted by the parathyroid glands…..increases Ca2+ levels Ca2+from – Release bones, – Stimulates the Kidneys to activate vitamin D D, which promotes uptake of Ca2+ …raises Ca2+ levels • Calcitonin, secreted by the thyroid gland…..lower Ca2+ levels – Stimulates Ca2+ deposition p in the bones – secretion of Ca2+ by the kidneys Figure 45.13a-2 Figure 45.13a-1 Insulin Beta cells of pancreas release insulin into the blood. STIMULUS STIMULUS: Blood glucose level rises (for instance, after eating a carbohydrate-rich meal). Homeostasis: Blood glucose level (70–110 mg/100 mL) Insulin Body cells take up more glucose. Blood glucose level declines. Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Blood glucose level rises (for instance, after eating a carbohydrate-rich meal). Homeostasis: Blood glucose level (70–110 mg/100 mL) 10 Figure 45.13b-2 Figure 45.13b-1 Homeostasis: Blood glucose level (70–110 mg/100 mL) Homeostasis: Blood glucose level (70–110 mg/100 mL) STIMULUS: Blood glucose level falls (for instance, after skipping a meal). Alpha cells of pancreas release glucagon into the blood. Glucagon STIMULUS: Blood glucose level falls (for instance, after skipping a meal). Blood glucose level rises. Liver breaks down glycogen and releases glucose into the blood. Alpha cells of pancreas release glucagon into the blood. Glucagon Insulin and Glucagon: Control of Blood Glucose Target tissues for Insulin and Glucagon • Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis • The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin • Insulin reduces blood glucose levels by – Promoting the cellular uptake of glucose – Slowing glycogen breakdown in the liver – Promoting fat storage • Glucagon increases blood glucose levels by – Stimulating conversion of glycogen to glucose in the liver – Stimulating breakdown of fat and protein into glucose Diabetes Mellitus • Endocrine disorder – deficiency of insulin or a decreased response to insulin in target tissues – elevated blood g glucose levels • Type I diabetes mellitus (insulin-dependent diabetes) – Is an autoimmune disorder – the immune system destroys the beta cells of the pancreas • Type II diabetes mellitus (non-insulin-dependent diabetes) – either by a deficiency of insulin – or by reduced responsiveness of target cells due to some change in insulin receptors 11 Fig. 45-21a Adrenal Hormones: Response to Stress Stress • The adrenal glands – adjacent to the kidneys – made up of two glands: the adrenal medulla (inside) and the adrenal cortex (outside) Spinal cord Nerve signals Releasing hormone Nerve cell Hypothalamus Anterior pituitary Blood vessel ACTH Adrenal medulla Adrenal cortex Adrenal gland Kidney Figure 45.21a (a) Short-term stress response and the adrenal medulla Stress Adrenal Medulla • Secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) in response to stress • fight-or-flight responses • Increase glucose levels levels, High blood pressure pressure…. • These hormones are members of a class of compounds called catecholamines • They are secreted in response to stress-activated impulses from the nervous system One hormone, different effects Fig. 45-8-2 Same receptors but different intracellular proteins (not shown) Different receptors Epinephrine Epinephrine Epinephrine receptor receptor receptor Glycogen deposits Glycogen breaks down and glucose is released. (a) Liver cell Vessel dilates. (b) Skeletal muscle blood vessel Vessel constricts. (c) Intestinal blood vessel Spinal cord (cross section) Nerve signals Hypothalamus Nerve cell Adrenal medulla secretes epinephrine and norepinephrine. Effects of epinephrine and norepinephrine: • Glycogen broken down to glucose; increased blood glucose • Increased blood pressure • Increased breathing rate • Increased metabolic rate • Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity Nerve cell Adrenal gland Kidney Effects of Hormone Epinephrine and norepinephrine • Mediating the body’s response to short-term stress • Triggers the release of glucose and fatty acids into blood • Increased I d oxygen delivery d li tto b body d cells ll • Directs the blood toward heart, brain, and skeletal muscles and way from skin, digestive system and kidneys • Epinephrine binds to liver cells and activate enzymes that result in the release of glucose into the bloodstream 12 Figure 45.21a (a) Short-term stress response and the adrenal medulla Stress Spinal cord (cross section) Nerve signals Hypothalamus Nerve cell Adrenal medulla p p secretes epinephrine and norepinephrine. Effects of epinephrine and norepinephrine: • Glycogen broken down to glucose; increased blood glucose Increased blood pressure Increased breathing rate Increased metabolic rate Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity Nerve cell Hormones of the Adrenal Cortex respond to long term stress • Glucocorticoids, such as cortisol – Increase in glucose levels, – suppresses immune system • Mineralocorticoids, Mineralocorticoids Ex. Ex aldosterone Adrenal gland Kidney • • • • Gonadal Hormones – Retention of salt & water....increases blood pressure • Adrenal cortex also produces small amounts of Sex hormones Testes • The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins • All three sex hormones are found in both males and females, but in different amounts • Synthesize androgens, Ex. testosterone – stimulate the development and maintenance of the male reproductive system – Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks Figure 45.22 Ovaries • Estrogens, Ex. estradiol RESULTS Appearance of Genitalia No surgery Embryonic gonad removed XY (male) Male Female XX (female) Female Female Chromosome Set – maintenance of the female reproductive system – development of female secondary sex characteristics • Progesterone – preparing and maintaining the uterus • Synthesis of the sex hormones is controlled by FSH and LH from the anterior pituitary 13 Endocrine Disruptors • Between 1938 and 1971 some pregnant women at risk for complications were prescribed a synthetic estrogen called diethylstilbestrol (DES) g of women treated with DES are at • Daughters higher risk for reproductive abnormalities, including miscarriage, structural changes, and cervical and vaginal cancers • DES is an endocrine disruptor, interrupts the function of estrogen Melatonin and Biorhythms • The pineal gland, located within the brain – Secretes melatonin You should now be able to: 1. • Release of melatonin 2. – Is controlled by light/dark cycles • The primary functions of melatonin – Appear to be related to biological rhythms associated with reproduction 3. 4. 4 5. 6. 7. Distinguish between the following pairs of terms: hormones and local regulators, paracrine and autocrine signals Describe the evidence that steroid hormones have intracellular receptors, while water-soluble hormones have cell-surface receptors Explain how the antagonistic hormones insulin and glucagon regulate carbohydrate metabolism Distinguish between type 1 and type 2 diabetes Explain how the hypothalamus and the pituitary glands interact and how they coordinate the endocrine system Explain the role of tropic hormones in coordinating endocrine signaling throughout the body List and describe the functions of hormones released by the following: anterior and posterior pituitary lobes, thyroid glands, parathyroid glands, adrenal medulla, adrenal cortex, gonads, pineal gland 14