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The Endocrine System

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The Endocrine System Chapter 9 Intro to Endocrine System Endocrine works with nervous system to control body (homeostasis). Endocrine acts slower than nervous though. Endocrine system uses hormones – chemical messengers (transported through bloodstream). Endocrine System & Hormone Function Endocrine organs are very small compared to other organs in the body. THE CHEMISTRY OF HORMONES: Hormones are chemical substances that regulate the metabolic activity of other cells in the body. Amino Acid-based hormones vs. Steroids AA-based: proteins, peptides, and amines Steroids: cholesterol; sex hormones (gonads) & hormones in adrenal cortex Prostaglandins: lipids in cell membrane Endocrine System & Hormone Function MECHANISMS OF HORMONE ACTION: Target cells/organs – responds to hormones Must have specific protein receptors on cell membrane where hormone can attach Hormones act to increase or decrease the rate of normal metabolic activities within the cell. Endocrine System & Hormone Function MECHANISMS OF HORMONE ACTION: What happens when the hormone binds to the cell membrane? 1. Changes in plasma membrane permeability or electrical state. 2. Synthesis of proteins or certain regulatory molecules (enzymes) in the cell. 3. Activation or inactivation of enzymes. 4. Stimulation of mitosis (cell division). Endocrine System & Hormone Function 2 Main Mechanisms for Hormone Action: Steroid Hormone Action 1. Steroid hormones diffuse across plasma membrane (lipid-soluble). 2. Steroid hormones enter nucleus. 3. Steroid hormones bind to specific receptor protein. 4. Hormone-receptor complex binds to DNA. 5. Activates transcription & translation (makes protein). Endocrine System & Hormone Function Nonsteroid Hormone Action: 1. Hormone binds to membrane receptor (cannot go through membrane on its own). 2. Starts a series of reactions that activate enzyme. 3. Enzyme catalyzes rxn to make a 2nd messenger molecule. 4. 2nd messenger molecule oversees other intracellular changes. Endocrine System & Hormone Function CONTROL OF HORMONE RELEASE: Negative Feedback Mechanisms – hormone secretion is triggered by some stimulus, and when hormone levels reach a certain level, hormone release is inhibited. Endocrine System & Hormone Function 3 Categories for Endocrine Gland Stimuli: 1) HORMONAL – most common; Hypothalamus secretes hormones that stimulate the anterior pituitary gland to secrete hormones that stimulate other endocrine glands to secrete hormones. Hierarchal control system with the hypothalamus in control Endocrine System & Hormone Function 3 Categories for Ex. Decrease blood Ca Endocrine Gland release of PTH to Stimuli: increase Ca 2) HUMORAL – Increase Ca release monitoring levels of of calcitonin to various substances in decrease Ca body fluids such as blood Changing blood level concentrations release hormone Endocrine System & Hormone Function 3 Categories for Endocrine Gland Stimuli: 3) NEURAL – Nerve fibers stimulate hormone secretion Ex. Sympathetic NS stimulates adrenal medulla cells to secrete catecholamines (epinephrine and norepinephrine) during times of stress Major Endocrine Organs - 10 Organs can be endocrine only (anterior pituitary, thyroid, adrenals, & parathyroids) OR Endocrine & Exocrine (pancreas & gonads) Endocrine glands are ductless (hormones release into blood or lymph) Exocrine glands have ducts to release to body surface or cavities – Ex sweat glands Major Endocrine Organs Hypothalamus Pituitary gland Thyroid gland Parathyroid glands Adrenal gland Pineal gland Thymus gland Pancreas Gonads – Ovaries and Testes Pituitary Gland About the size of a grape Hangs from inferior surface of hypothalamus Surrounded by “turk’s saddle” of sphenoid bone 2 Lobes: Anterior pituitary (glandular tissue) & Posterior pituitary (nervous tissue) Tropic hormones – stimulate target organs, which are also endocrine glands, to secrete their hormones (HORMONAL) Pituitary Gland Hormones ANTERIOR PITUITARY: All are proteins, act through 2nd messenger system, and regulated by hormonal stimuli Growth Hormone (GH) - stimulates growth of bones and muscles; metabolism; regulated by hypothalamus releasing and inhibiting hormones Prolactin (PRL) – stimulates milk production targets human breasts; regulated by hypothalamic hormones Follicle-stimulating hormone (FSH) – stimulates production of ova & sperm; regulated by hypothalamic hormones Pituitary Gland Hormones ANTERIOR PITUITARY: Luteinizing hormone (LH) – stimulates ovulation of egg and causes ruptured follicle to become corpus luteum produce progesterone and some estrogen; in men (also interstitial cell-stimulating hormone (ICSH)) stimulates interstitial cells of testes to produce testosterone; regulated by hypothalamic hormones Thyrotropic hormone (TSH) – Thyroid-stimulating hormone – stimulates thyroid; regulated by thyroxine in blood and hypothalamic hormones Adrenocorticotropic hormone (ACTH) – stimulates adrenal cortex to secrete glucocorticoids; regulated by glucocorticoids and hypothalamic hormones Pituitary Gland Hormones POSTERIOR PITUITARY: Storage area Oxytocin – made by hypothalamus; released during childbirth to increase contractions, released during sex, released when breast-feeding; oxytocin drugs are used to induce labor; oxytocics are used to stop postpartum bleeding and stimulate milk ejection reflex Pituitary Gland Hormones POSTERIOR PITUITARY: Antidiuretic hormone (ADH) – produced by hypothalamus; inhibits urine production causes kidneys to reabsorb more water urine volume decreases & blood volume increases; can increase blood pressure (vasopressin) Drinking alcohol and caffeine inhibits ADH urinate more Homeostatic Imbalance Too much or too little GROWTH HORMONE: Hyposecretion pituitary dwarfism Hypersecretion pituitary gigantism If hypersecretion after long-bone growth has ended acromegaly (malformed facial features) READ pg. 286 Closer Look box Homeostatic Imbalance Too little (hyposecretion) of FSH or LH sterility in males & females Drugs that promote fertility stimulate gonadotropic hormones (multiple births may occur) Hyposecretion of ADH excessive urine (DIABETES INSIPIDUS) Pituitary-Hypothalamus Relationship Anterior pituitary gland is sometimes called the “master endocrine gland” However the hypothalamus produces releasing & inhibiting hormones (sent into the portal circulation) Hypothalamus makes OXYTOCIN & ANTIDIURETIC HORMONE (sent to posterior pituitary for storage by the axons of neurosecretory cells) Thyroid Gland Located at base of throat, inferior to Adam’s apple 2 lobes joined by a central mass called the isthmus Follicles inside thyroid gland store colloidal material hormones Thyroid hormone – major metabolic hormone; made in follicles; Thyroxine (T4) and Triiodothyroxine (T3) Thyroid Gland T4 is major hormone secreted by thyroid follicles T3 is formed at target tissues by converting T4 Thyroid hormone – controls rate of glucose burning into energy; every cell is targeted; controls growth and development in reproductive & nervous systems; regulated by TSH Thyroid Gland Calcitonin – decreases blood calcium levels calcium is deposited into bones; it does opposite of parathyroid hormone; made by C cells in connective tissue between follicles; released when blood calcium is too high; calcitonin production decreases in elderly; regulated by calcium in blood Homeostatic Imbalance Goiters – enlargement of thyroid gland caused by deficient amount of iodine in diet; TSH keeps calling for thyroxine and thyroid gland tries to put it out (enlarges); not common in US (salt has iodine in it) Cretinism – occurs in early childhood as a result of hyposecretion of thyroxine lack of TH stimulation (dwarfism) Myxedema – hypothyroidism in adults; physical and mental sluggishness, puffiness in face, fatigue, poor muscle tone, low body temp. Treat with oral thyroxine Parathyroid Glands Found on posterior surface of thyroid gland Normally 2 glands per lobe = 4 (but 8 have been reported before) Parathyroid hormone (PTH) – regulates blood calcium levels; low blood Ca2+ release PTH stimulates osteoclasts to break down bone and release calcium; regulated by calcium in blood **PTH is hypercalcemic hormone & Calcitonin is hypocalcemic hormone Homeostatic Imbalance Hypoparathyroidsim: Blood calcium is too low neurons become overactive TETANY (uncontrollable spasms) Severe hyperparathyroidism massive bone destruction bones are fragile Adrenal Glands 2 bean-shaped glands that curve over kidneys Parts are medulla region & adrenal cortex Adrenal Cortex Hormones Produces corticosteroids mineralcorticoids, glucocorticoids, and sex hormones MINERALCORTICOIDS: Aldosterone – regulate mineral content of blood; mainly Na & K; Blood levels of aldosterone rises kidney tubules keep Na and allow K to leave in the urine keeps water in body; regulated by changes in bv or bp & K/Na levels in blood RENIN – enzyme that kidneys release when bp drops that causes aldosterone to be released retains Na in blood retains water bv increases bp increases Adrenal Cortex Hormones GLUCOCORTICOIDS: Cortisone & Cortisol – promote normal cell metabolism; help resist long-term stressors (increase blood glucose); Glucocorticoids are high in blood fats & proteins broken down for glucose (hyperglycemic hormones); they also decrease edema (inflammation) and inhibit prostoglandins (cause pain) Given to patients to suppress inflammation Regulated by blood levels of ACTH (released when ACTH is high)
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