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Transcript
ENDOCRINE SYSTEM The Endocrine System reg. growth, dev., reprod., adjusts metabolism. ductless system; secretions in interstitial fluid or blood compare with exocrine (sweat glands, gastric glands) Hormones – chemical messengers responsible for regulations/adjustments ENDO/NEUROENDO Cell Signaling – cell communication neurotransmitters hormones (through blood) local regulators (diffuses through interstitial fluids and acts on nearby cells) AUTO/PARA local regulators cont’d… autocrine regulation : acts on cells that produce hormone paracrine regulation: nearby cells Includes: histamine, growth factors, Nitric oxide (dilates blood vessels) and prostaglandins (affects cAMP levels; stimulate/inhibit smooth muscle contractions; reduce/raise blood pressure; induce labour) pheromones (prod. By exocrine glands; communication between animals of same species – mating, territory, alarm) neurohormones (secreted by neuroendocrine cells that are linked with nervous system and endocrine system) Hormones Classes 1. fatty acid derivatives - prostaglandins, juvenile hormones of insects steroids - molting hormone of insects, cortisol, testosterone, progesterone, estrogen amino acid derivatives - simplest hormones; T3 and T4 from tyrosine and iodide; epinephrine and norepinephrine from tyrosine; Melatonin from trytophan peptides or proteins largest group; oxytocin ADH, glucagons, secretin, ACTH, calcitonin, insulin, Growth hormone, TSH and gonadotropic hormones RESPONSE TO HORMONES A)Matching receptor? If yes B) Molecules/genes affected after binding Ie. Response to insulin Ie Different response to insulin between muscle/adipose tissue Regulation-hormone secretion Negative feedback typical regulation restores homeostasis ie. Low calcium levels stimulate parathyroid gland to release parathyroid hormone which raises calcium levels and shuts off parathyroid secretions. Positive feedback secretion of hormone promotes further secretion ie. Oxytocin secretion stimulates more oxytocin secretion Mechanism of Hormone Action Hormones only have effects when they hit target cells Receptor up and down regulation too much insulinreceptor down regulation; low concentrations of hormones can create more receptors in “up” regulation Peptide Hormones bind to cell surface receptors in 2 ways: a) G protein-linked receptors (G = use of GTP) to intiate signal transduction (convert extracellular signal to intracellular) b) Enzyme-linked receptors – not linked to G proteins (most are receptor tyrosine kinases) - bind signal molecules known as growth factors (insulin, nerve growth factor) - activated receptor converts amino acid tyrosine into cell proteins SIGNAL TRANSDUCTION INVOLVES MANY RELAY MOLECULES AND AMPLIFICATION (prod. dramatic response ie adrenalin) hormone does not enter cell; relays info to secondary mess. - secondary messenger signals effector mol. that carry out action (cAMP is a common secondary messenger that is catalyzed by adenylyl cyclase – it activates protein kinases – and inactivated by phosphodiesterases (conv. kinase activity (phosphorylation) on proteins alters its activity which therefore leads to altered function (ie change in metabolism) Phospholipids and Ca2+ can also function as secondary messengers (inositol triphosphate – IP3 – opens calcium channels in ER that releases calcium in cytosol to regulate muscle contractions, neural signaling microtubule disassembly, blood clotting, activation of some enzymes) 3. Steroid, fatty acid hormones (and thyroid hormones) enter cells (hydrophobic) -pass plasma mem. - bind receptors in cytoplasm or nucleus forming receptor-hormone complexbinds DNA turning genes on or off (activating/inactivating transcription.) generally slow but long lasting (steroid effects such as testosterone) Antagonistic Hormones – counteract each other Insulin and Glucagon Calcitonin and Parathyroid hormone Atrial natriuretic peptide (ANP) and aldosterone Islets of Langerhans Secrete insulin Stim. cells to take up glucose/lowers blood glucose levels Secrete glucagon Raises blood glucose conc. Diabetes mellitus Results in decreased use of glucose Nervous and endocrine regulation Integrated in the hypothalamus, which regulates the pituitary gland Oxytocin and ADH Produced by the hypothalamus Released by the posterior lobe of the pituitary Hypothalamus Secretes Releasing hormones Inhibiting hormones These regulate the hormone output of the anterior lobe of the pituitary Anterior lobe of the pituitary Secretes the growth hormone, prolactin Several tropic hormones that stimulate other endocrine glands Growth hormone (GH) Anabolic hormone that stimulates body growth Stimulates the liver to produce insulin-like growth factors (IGFs), which promote skeletal and tissue growth Credit: © Mediscan/Visuals Unlimited Acromegaly, also called acromegalia, is a long-term problem in which bones of the face, jaw, arms, and legs get larger. It occurs in middle-aged patients and is caused by too much growth hormone. It is treated by x-rays to shrink the pituitary, or part of the pituitary gland is removed. The most common cause is a somatotropin-secreting pituitary adenoma. 206401 Thyroid gland Secretes Thyroxine Triiodothyronine Stimulate the rate of metabolism Regulation of thyroid secretion Depends mainly on a negative feedback system Anterior pituitary gland Thyroid gland Thyroid hyposecretion Childhood cretinism Adult myxedema Thyroid hypersecretion Most common cause is Grave’s disease Goiter associated with both hyposecretion and hypersecretion Parathyroid glands Secrete PTH Regulates calcium level in the blood Stimulates calcium release from bones Calcitonin, secreted by the thyroid, acts antagonistically to PTH Credit: © Mediscan/Visuals Unlimited Rickets is a condition caused by a deficiency of vitamin D, especially in infancy and childhood, with disturbance of normal ossification. The disease is marked by bending and distortion of the bones under muscular action, by the formation of nodular enlargements on the ends and sides of the bones, by delayed closure of the fontanels, pain in the muscles, and sweating of the head. Vitamin D and sunlight together with an adequate diet are curative, provided that the parathyroid glands are functional. 206184 Addison’s or Cushings? Test? Dexamethosone test – drug inhibitis pituitary sec. of ACTH for high cortisol Synthetic ACTH injection for low cortisol Addison’s low cortisol Cushing’s high cortisol STRESS RESPONSE Adrenal glands Secrete hormones that help the body cope with stress Adrenal medulla secretes Epinephrine Norepinephrine Adrenal cortex secretes Mineralocorticoids (ie aldosterone) Glucocorticoids (ie cortisol) Adrenal gland REPRODUCTIVE HORMONES Estrogen inc. due to stimulation from FSH and LH Estrogen has endo/auto and paracrine functions Stimulates cells to prod. More estrogen (pos. feedback) Estrogen inhibits (at low conc.) hypothalamus Neg. Feedback Estrogen stim.(at higher conc) Hypo/ Ant.Pituitary Pos. Feedback Estrogen/Progesterone inhibit hypo and ant. Pituitary Without fertilization corpus luteum degenerates and estrogen/progesterone levels fall