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chapter 18: Endocrine System

by: Aja

chapter 18: Endocrine System

Marketplace > Edison State College, Naples FL > > chapter 18 Endocrine System
Edison State College, Naples FL
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This 6 page Class Notes was uploaded by Aja on Saturday January 16, 2016. The Class Notes belongs to at Edison State College, Naples FL taught by in Fall 2015. Since its upload, it has received 17 views.

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Date Created: 01/16/16
Chapter 18: Endocrine System The Nervous and Endocrine systems act together The Nervous system acts through nerve impulses (action potentials) conducted along axons of neurons. At synapses, nerve impulses trigger the release of neurotransmitters. The endocrine system controls body activities by releasing hormones. A hormone: molecule that is released in one part of the body that regulates the activity of cells in other parts of the body. Hormones enter interstitial fluid, then the bloodstream. The circulating blood delivers hormones to cells. Neurotransmitters and hormones exert their effects. Binding to receptors on or in their “target” cells. Mediators act as BOTH neurotransmitters and hormones. Endocrine System: Endocrine glands Exocrine glands Exocrine glands: secret their products into ducts, which carry the secretions into body cavities, lumen of organs, or outer surfaces of the body • sudoriferous ( sweat) • sebaceous ( oil) • mucous • digestive glands Endocrine glands: secrete their products into the interstitial fluid • surrounding the secretory cells rather than into ducts • hormones diffuse into blood capillaries • blood carries them to target cells throughout the body • examples: 1. pituitary glands 2. thyroid glands 3. parathyroid glands 4. adrenal glands 5. pineal glands A given hormone travels throughout the body in the blood, it affects only specific target cells. Hormones influence their target cells by chemical binding to specific protein receptors. Only the target cells for a given hormone have receptors that bind and recognize that hormone. Down- regulation: hormone is present in excess, the number of target cell receptors may decrease • target cell is less sensitive to a hormone Up-regulation: when a hormone is deficient, the number of receptors may increase • target cell is more sensitive to a hormone Circulating hormones are distant from the target cell, pass from interstitial fluid to the bloodstream while local hormones are either paracrine (act on neighboring cells) or autocrine (same cell that secreted itself). Local hormones are inactivated quickly while circulating hormones linger longer in the bloodstream while they exert their effects for a few mins before they are inactivated by the liver and exerted by the kidneys. There are two types: 1 lipid soluble hormones • steroid- derived from cholesterol • thyroid • gas nitric oxide ( NO) 6. water soluble hormones • amine hormones: epinephrine and norepinephrine and dopamine • peptide: antidiuretic hormone • protein: thyroid stimulating/human growth hormone and insulin There are different ways hormones transport in the blood: 1 lipid soluble • bound to transport proteins and go “inside” target cell 7. water soluble • circulate in the blood plasma in a “free form”, stay outside target cell ( not attached to other molecules) The response to a hormone depends on both the hormone and the target cell. A hormone first announces its arrival to a target cell by binding to its specific receptors. 1 lipid soluble hormones • located inside the target cells 8. water soluble hormones • part of the plasma membrane of target cells ( knock on door but don't enter) • the first messenger ( hormone) causes the production of a second messenger inside of the target cell, which is told what to do from the first messenger ( hormone) Hormones that bind to plasma membrane can induce their effects at very low concentrations because they initiate a chain reaction. Each step multiplies the initial effect. Hormones have certain interactions with each other. The responsiveness of a target cell to a hormone depends on the hormone concentration, the abundance of there target cells hormone receptors, and influxes exerted by other hormones. There are two types of effects: 1 synergistic effect- the effect of two hormones acting together is greater or more extensive than the effect of each hormone acting alone 9. antagonistic effect- one hormone opposes the actions of another hormone Release of most hormones occur in short bursts. When stimulated, a gland will release its hormones in more frequent bursts. Increasing the concentration of the hormone in the blood. Hormone secretion is regulated by signals from the nervous system, chemical changes in the blood, and other hormones. The Pituitary Gland : • secretes several hormones that control other endocrine glands • has a master—-the hypothalamus. • the major link between the nervous and endocrine systems • pea shaped structure that measures 0.5 in in diameter • two anatomically and functionally separate portions • attaches to the hypothalamus by a stalk- the infundibulum There are two parts of the pituitary gland: 1 Anterior pituitary • adenohypophysis • 75% of total weight of gland • the pars distills • the pars tubercles 10.Posterior pituitary • neurohypophysis The anterior pituitary secretes hormones that regulate a wide rang of bodily activities, from growth to reproduction. It releases hormones that are stimulated by releasing hormones. It also is suppressed by inhibiting hormones from the hypothalamus. There are 5 types of Anterior Pituitary cells: 1 Somatotrophs: • Human growth hormone (hGH) or somatotropin 11.Thyrotrophs: • Thyroid stimulating hormone ( TSH) 12.Gonadotrophs: • stimulate secretion of estrogens and progesterone 13.Lactotrophs: • Prolactin (PRL)- initates milk production in the mammary glands 14.Corticotrophs: • stimulates the adrenal cortex The posterior pituitary does NOT synthesize hormones but does store and release two hormones: 1 Oxytocin- during and after delivery of a baby, oxytocin affects the mothers uterus and breasts 15.Antidiuretic hormone(ADH) - substance that decreases urine production and causes the kidneys to return more water to the blood, which decreases urine volume The Thyroid gland: • butterfly shaped and inferior to the larynx • right/left lateral lobes are connected by an isthmus, anteriorly to the trachea • highly vascularized • main cell——follicular cell There are two hormones known as thyroid hormones : Thyroxine (T4) and Triiodothyronine (T3) They have a few main functions: • They increase basal metabolic rate by stimulating the use of cellular oxygen to product ATP • stimulate protein synthesis/ increase lipolysis and increase the use of glucose and fatty acids for ATP production • using human growth hormone ( hGH) and insulin, they accelerate body growth ( nervous and skeletal systems) • stimulate synthesis of sodium-potassium pumps, which use ATP to eject sodium ions ( NA) from the cytosol to the ECF As cells produce/ use more ATP, more heat is given up. Therefore body temperature rises. There are parafollicular cells ( C Cells) that lie between the follicles and produce calcitonin—-which helps regulate calcium homeostasis. The thyroid gland is the only endocrine gland hat stores its secretary product in large quantities. On the posterior surface of the lateral lobes are small, round masses of tissue, one superior and one inferior parathyroid gland are attached to each lateral thyroid lobe. There are two kinds of epithelial cells: 1 chief(principal) cells- produce parathyroid hormone ( PTH) 16.oxyphi cell ( function not known) Parathyroid hormone has plenty of important functions: • a major regulator of the levels of calcium (Ca), magnesium (Mg2+) and phosphate ( HP042-) ions in the blood. • increase the number and activity of osteoclasts • elevated bone resorption • slows the rate at which Ca2+ and Mg are lost from blood into the urine The paired adrenal glands lie superior to each kidney in the retroperitoneal space and are in the shape of a flattened pyramid. There are two distinct regions: 1 adrenal cortex- peripherally located • produces steroid hormones that are essential for life 17.adrenal medulla- small and centrally located • produces norepinephrine, epinephrine, and a small amount of dopamine The adrenal cortex is divided into 3 zones: 1 outer zone ( zona glomerulosa) • secretes mineralocorticoids like aldosterone - regulates homeostasis of two mineral ions like sodium ions (Na) and potassium ions (K) - helps adjust blood pressure and blood volume 18.middle zone ( zona fasciculata) • secretes glucocorticoids like cortisol/cortisone - regulate metabolism and resistance to stress 19.inner zone (zona reticularis) • synthesize small amounts of weak androgens The Glucocorticoids (cortisol) have certain functions: 1 protein breakdown • increase the rate of protein breakdown mainly in muscle fibers 20.glucose formation • liver cells may convert lactic acid to glucose, which neurons and other cells can use for ATP production 21.lipolysis • breakdown of triglycerides and release from adipose tissue into the blood 22.resistance to stress • glucose supplied by the liver cells provides tissues with a ready source of ATP 23.anti-inflammartory effects • inhibit white blood cells that participate in inflammatory responses 24.depression of immune responses The adrenal medulla produces the hormone-producing cells called chromaffin cells. Adrenaline and noradrenaline are produced. They increase heart rate and force of contraction , which in turn increases the output of the heart which increase blood pressure. They also increase blood flow to the heart, liver, skeletal muscles, and adipose tissue while dilating airways to the lungs and increasing blood levels of glucose and fatty acids. Pancreatic Islets (Islets of Langerhans): A flattened organ that is arranged in clusters called acini, which are scattered among the endocrine tissue in the pancreas. There are different cell types in the pancreatic islets: 1 Alpha or A cells: • secrete glucagon and raise blood glucose level 25.Beta or B cells: • secrete insulin and lowers blood pressure 26.Delta or D cells: • secrete somatostatin and inhibit both insulin and glucagon release 27.F cells: • secrete pancreatic polypeptide and inhibits somatostatin secretion,gallbladder contraction, and secretion of digestive enzymes by the pancreas The ovaries produce two estrogens ( estradiol and estrone) and progesterone. They also have a few functions: • regulate the menstrual cycle, maintain pregnancy, and prepare the mammary glands for lactation • promote enlargement of the breasts • widening of the hips at puberty • produce relaxin, which increases the flexibility of the pubic symphysis during pregnancy • helps dilate the uterine cervix during labor and delivery The testes produce testosterone, which has its own functions: • stimulates descent of the testes before birth • regulates production of sperm • stimulates the development of beard growth and deepening of the voice The pineal gland is a small endocrine gland that is attached to the roof of the third ventricle of the brain at the midline, also part of the epithalamus. It is covered by a capsule formed by the pia mater. The gland consists of masses of neuralgia and secretory cells called the pinealocytes and secretes melatonin, which is controlled by the hypothalamus and is the setting of the boys biological clock. As more melatonin is liberated during dark than in light, this hormone is thought to promote sleepiness. The thymus is located behind the sternum and between the lungs. It produces the hormones Thymosin and Thymopoietin, which promote the maturation of T cells ( type of white blood cell that destroys microbes and foreign substances) and may retard the aging process.


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