Chapter 45 Hormones And The Endocrine System PDF

Chapter 45 Hormones and the Endocrine System 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 have re...

Chapter 45 Hormones and the Endocrine System 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 have receptors for that hormone The nervous system is a network of specialized cells— neurons—that transmit signals along dedicated pathways The nervous and endocrine systems often overlap in function Intercellular Communication Communication between animal cells through secreted signals can be classified by two criteria: The type of secreting cell The route taken by the signal in reaching its target Endocrine signaling Synapse Neuron Blood vessel RESPONSE RESPONSE (a) Endocrine signaling (d) Synaptic signaling Neurosecretory cell RESPONSE Blood vessel RESPONSE (b) Paracrine signaling (e) Neuroendocrine signaling RESPONSE Endocrine signaling maintains homeostasis, mediates responses to (c) Autocrine signaling stimuli, and regulates growth and development Paracrine and Autocrine Signaling Synapse Neuron Blood vessel RESPONSE RESPONSE (a) Endocrine signaling (d) Synaptic signaling Neurosecretory cell RESPONSE Blood vessel RESPONSE (b) Paracrine signaling (e) Neuroendocrine signaling Local regulators are molecules that act over short distances, reaching target cells solely by RESPONSE diffusion Paracrine and autocrine signaling play roles in (c) Autocrine signaling processes such as blood pressure regulation, nervous system function, and reproduction Local regulators that mediate such signaling include the prostaglandins that function in the immune system and Synaptic and Neuroendocrine Signaling Synapse Neuron Blood vessel RESPONSE RESPONSE (a) Endocrine signaling (d) Synaptic signaling Neurosecretory cell RESPONSE Blood vessel RESPONSE (b) Paracrine signaling (e) Neuroendocrine signaling In synaptic signaling, neurons form specialized junctions with target cells, called synapses RESPONSE At synapses, secreted molecules called neurotransmitters diffuse short distances and (c) Autocrine signaling bind to receptors on target cells In neuroendocrine signaling, specialized neurosecretory cells secrete neurohormones that  Members of some animal species may communicate with pheromones, chemicals that are released into the environment Pheromones serve many functions, including marking trails leading to food, defining territories, warning of predators, and attracting potential mates Signaling by Pheromones Classes of Local Regulators Local regulators such as the prostaglandins are modified fatty acids Others are polypeptides, and some are gases Nitric oxide (NO) is a gas that functions in the body as both a local regulator and a neurotransmitter When the level of oxygen in blood falls, NO activates an enzyme that results in vasodilation, increasing blood flow to tissues Classes of Hormones Hormones fall into three major classes: polypeptides, steroids, and amines Polypeptides and most amines are water-soluble Steroid hormones and other largely nonpolar hormones are lipid-soluble Water-soluble (hydrophilic) Lipid-soluble (hydrophobic) Polypeptides Steroids 0.8 nm Insulin Cortisol Amines Epinephrine Thyroxine  (a) Water-soluble hormone; (b) Lipid-soluble hormone; receptor in plasma receptor in nucleus or membrane cytoplasm SECRETORY SECRETORY CELL CELL Water- Lipid- soluble soluble hormone hormone Hormone Pathways Blood vessel Blood vessel Transport Receptor protein protein TARGET CELL TARGET OR Receptor CELL protein (in nucleus or cytoplasm) Cytoplasmic Gene response regulation Cytoplasmic response Gene regulation NUCLEUS NUCLEUS  EXTRACELLULAR FLUID The hormone Hormone (epinephrine) epinephrine (or Adenylyl G protein cyclase adrenaline) regulates many organs in response to stressful situations Epinephrine binds to GTP receptors on the plasma membrane of G protein-coupled ATP liver cells receptor This triggers the cAMP Second messenger release of messenger molecules that activate Inhibition of enzymes and result in glycogen synthesis Protein the release of glucose kinase A into the bloodstream Promotion of glycogen breakdown CYTOPLASM  Hormone EXTRACELLULAR (estradiol) FLUID Estradiol receptor Plasma membrane In female birds and frogs, estradiol, a form of estrogen, Hormone-receptor binds to a cytoplasmic complex receptor in liver cells NUCLEUS The estradiol-bound receptor activates CYTOPLASM transcription of genes needed to produce DNA egg yolk Vitellogenin mRNA for vitellogenin Endocrine Tissues and Organs Endocrine cells are often grouped in ductless organs called endocrine glands In contrast, exocrine glands, such as salivary glands, have ducts to carry secreted substances onto body surfaces or into body cavities Like…. Salivary Lacrimal Sebaceous Mammary Mucus Ceruminous Thyroid gland Pineal gland Hypothalamus Pituitary gland Parathyroid glands Adrenal glands Ovaries (in females) Testes (in males) Pancreas  Simple endocrine pathway Example: secretin signaling – STIMULUS Low pH in duodenum Endocrine S cells of duodenum cell Hormone Secretin ( ) Negative feedback Circulation throughout body Target Pancreatic cells cells RESPONSE Bicarbonate release  Simple neuroendocrine pathway Example: oxytocin signaling + STIMULUS Suckling Neurosecretory cell Hypothalamus Posterior Hormone Oxytocin ( ) pituitary Positive feedback Blood vessel Circulation throughout body Target Smooth muscle in cells mammary glands RESPONSE Milk release Vertebrates The hypothalamus coordinates endocrine signaling It receives information from nerves throughout the body and initiates appropriate neuroendocrine signals At the base of the hypothalamus is the pituitary gland, composed of the posterior pituitary and anterior pituitary  Hypothalamus The posterior pituitary Neurosecretory stores and cells of the secretes hypothalamus hormones that Neurohormone Axons are made in the hypothalamus Posterior by pituitary neurosecretory Anterior pituitary cells HORMONE ADH Oxytocin TARGET Kidney tubules Mammary glands, uterine muscles The anterior Neurosecretory cells pituitary makes of the hypothalamus and releases hormones under regulation of the Hypothalamic Portal vessels hypothalamus releasing and inhibiting hormones HORMONE Endocrine cells of Posterior pituitary the anterior pituitary Anterior pituitary TARGET hormones FSH and LH TSH ACTH Prolactin MSH GH Testes or Thyroid Adrenal Mammary Melanocytes Liver, bones, ovaries cortex glands other tissues EXAMPLES  1 Thyroid hormone STIMULUS levels drop. Neurosecretory In humans and cell in the hypothalamus other mammals, – 2 Neurosecretory TRH thyroid hormone cells secrete TRH () Negative feedback into the blood, which carries it to the regulates many anterior pituitary. functions – 3 TRH causes the anterior pituitary to If thyroid hormone secrete TSH (also known as thyrotropin▲). TSH Anterior pituitary level drops in the Circulation blood, the throughout body via blood hypothalamus secretes Thyroid gland 4 TSH stimulates endocrine cells in the thyrotropin- thyroid gland to secrete thyroid hormone (T3 and T4). releasing hormone Thyroid hormone (TRH), causing the anterior pituitary to Circulation throughout secrete thyroid- body via blood 5 Thyroid hormone levels increase in the stimulating RESPONSE blood and body tissues. hormone (TSH) 6 Thyroid hormone blocks TRH release and TSH release preventing TSH stimulates overproduction of thyroid hormone.  Disorders of Thyroid Function and Regulation Disruption of thyroid hormone production and regulation can result in serious disorders Thyroid hormone is the only iodine-containing molecule synthesized in the body With low levels of thyroid hormone, due to insufficient iodine, the pituitary continues to secrete TSH This causes the thyroid to enlarge, resulting in a goiter  Hormonal Regulation of Growth Growth hormone (GH) is secreted by the anterior pituitary gland The liver is a major target and responds to GH by releasing insulin-like growth factors (IGFs) These stimulate bone and cartilage growth An excess of GH can cause gigantism, while a lack of GH can cause dwarfism Parathyroid Hormone and Vitamin D: Control of Blood Calcium Homeostatic regulation of calcium (Ca2+) in the blood is vital In mammals, parathyroid hormone (PTH) is released by the parathyroid glands when Ca2+ levels fall below a set point Calcitonin (produced by the thyroid) decreases the level of blood Ca2+  NORMAL BLOOD Ca2+ LEVEL (about 10 mg/100 mL) Blood Ca2+ level rises. Blood Ca2+ level falls. Active vitamin D increases Ca2+. PTH stimulates Ca2+ uptake and promotes activation of vitamin D. PTH stimulates Parathyroid Ca2+ release. glands PTH release PTH. Adrenal Hormones: Response to Stress The adrenal glands are located atop the kidneys Each adrenal gland consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion)  (a) Stress response and the adrenal medulla (b) Stress response and the adrenal cortex Stress Hypothalamus Nerve Spinal cord impulses (cross section) Releasing hormone Neuron Anterior pituitary Circulation throughout Short term body Long term Adrenal Neuron ACTH medulla via blood Adrenal Adrenal gland cortex Kidney  The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline) They coordinate a set of physiological responses that comprise the “fight-or-flight” response They… Trigger the release of glucose and fatty acids into the blood Increase oxygen delivery to body cells Direct blood toward heart, brain, and skeletal muscles and away from skin, digestive system, and kidneys The Role of the Adrenal Medulla Multiple Responses to a Single Hormone The same hormone may have different effects on target cells that have Different receptors for the hormone Different signal transduction pathways For example, the hormone epinephrine has multiple effects that form the basis of the “fight-or-flight” response  (a) Liver cell (b) Smooth muscle cell in (c) Smooth muscle cell in wall of blood vessel that wall of blood vessel supplies skeletal muscle that supplies intestines Epinephrine’s Epinephrine Epinephrine Epinephrine Multiple Effects β receptor β receptor α receptor Glycogen deposits Glucose Glycogen breaks down and Cell relaxes. Cell contracts. glucose is released from cell. Blood glucose level Blood vessel dilates, Blood vessel constricts, increases. increasing flow to decreasing flow to skeletal muscle. intestines. Same receptors but different Different receptors intracellular proteins The Role of the Adrenal Cortex The adrenal cortex becomes active under stressful conditions including low blood sugar, decreased blood volume and pressure, and shock A series of hormonal signals lead to production and secretion of a family of steroids called corticosteroids Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system Mineralocorticoids, such as aldosterone, affect salt and water balance  Sex Hormones The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progesterone All three sex hormones are found in both males and females, but in different proportions The testes primarily synthesize androgens, mainly testosterone, which promote development of male reproductive structures Testosterone is responsible for male secondary sex characteristics Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system They are also responsible for development of female secondary sex characteristics In mammals, progesterone is primarily involved in preparing and maintaining the uterus Hormones and Biological Rhythms The pineal gland, located in the brain, secretes melatonin Primary functions of melatonin appear to relate to biological rhythms