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Endocrine System

Endocrine System. Anatomy & Physiology Chapter 16. Endocrine vs. Nervous System. See Table 16-1. Classification of hormones by chemical structure. Steroid hormones. Derived from cholesterol Lipid-soluble Pass through plasma membranes easily. Nonsteroid hormones.

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Endocrine System

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  1. Endocrine System Anatomy & Physiology Chapter 16

  2. Endocrine vs. Nervous System • See Table 16-1

  3. Classification of hormones by chemical structure

  4. Steroid hormones • Derived from cholesterol • Lipid-soluble • Pass through plasma membranes easily

  5. Nonsteroid hormones • Synthesized primarily from amino acids • Protein hormones: long chains of amino acids ex: insulin, PTH • Glycoproteins: protein hormones with a carbohydrate group attached ex: FSH, LH • Peptide hormones: short chain of amino acids ex: oxytocin, ADH • Amino acid derivatives: derived from a single amino acid • Amine hormones: derived from tyrosine ex:epinephrine • Iodine added to tyrosine ex: thyroid hormones

  6. General Principles of Hormone Action • Bind to a specific receptor on cell by “lock-and-key” mechanism • Some hormones are attached to plasma proteins in bloodstream • Since blood carries hormones most everywhere lots more produced than makes it to its target

  7. Mechanism of steroid hormone action (Mobile-receptor hypothesis) • Attach to soluble plasma proteins in blood • Receptors usually found within the cell • Regulate cells by regulating production of certain critical proteins • Amount of steroid hormone present determines magnitude of target cell’s response • Response to steroid hormones often slow

  8. Mechanisms of Nonsteroid Hormones • Second messenger mechanism: also called fixed-membrane-receptor hypothesis • Nuclear receptor mechanism

  9. Second messenger mechanism • Binds to receptors on target cell’s plasma membrane • Then second messenger within cell triggers appropriate cellular changes • Most use cAMP as second messenger • Operates more quickly than steroid mechanism

  10. Nuclear receptor mechanism • Small iodinated amino acids (T3 & T4) • Enter target cell & bind to receptors associated with DNA which triggers transcription of mRNA

  11. Regulation of hormone secretion • Usually part of a negative feedback loop and is called endocrine reflexes • Endocrine cells often sensitive to changes produced by its target cells • May be regulated by hormone produced by another gland, esp pituitary gland • May be influenced by nervous system input

  12. Prostaglandins • Lipid molecules • Tissue hormones: secretion produced in tissues & diffuse short distance only to other cells in same tissue • Tissues known to secrete prostaglandins: kidneys, lungs, iris, brain, thymus

  13. Vocabulary Words • Hormone • Synergism • Permissiveness • Antagonism • Tropic hormones • Sex hormones • Anabolic hormones

  14. Pituitary Gland

  15. Pituitary gland (Hypophysis) • Lies within sella turcica of skull • Connected to the hypothalamus by a stalk, infundibulum • Consists of 2 different glands • Adenohypohysis or anterior pituitary • Neurohypophysis or posterior pituitary

  16. Anterior Pituitary • Two parts • pars anterior: major part • pars intermedia • 5 types of secretions • Somatrophs-secrete GH • Corticotrophs-secrete ACTH • Thyrotrophs: secrete TSH • Lactotrophs: secrete prolactin • Gondatrophs: secrete LH and FSH

  17. Growth Hormone (GH) • Promotes protein anabolism thus promotes growth of bones, muscles • Promotes lipid mobilization & catabolism • Indirectly inhibits glucose metabolism • Indirectly increases blood glucose levels

  18. Prolactin (PRL) • During pregnancy promotes breast development • After birth stimulates mammary gland to begin milk secretion

  19. Tropic hormones • Have stimulating effect on other endocrine glands • Thyroid stimulating hormone: TSH • Adrenocorticotropic hormone: ACTH • Follicle stimulating hormone: FSH • Luteinizing hormone: LH

  20. TSH • Maintains growth & development of thyroid gland & causes it to secrete its hormones

  21. ACTH • Promotes & maintains normal growth of cortex of adrenal gland & stimulates it to secrete some of its hormones

  22. Gonadotropins • Stimulate growth & development of gonads • FSH: stimulates follicles (with ovum) to maturity, also stimulates follicle to secrete estrogen; in male: stimulates development of seminiferous tubules • LH: stimulates formation of corpus luteum; in males: stimulates interstitial cells in testes to develop & secrete testosterone

  23. Control of secretion of anterior pituitary • Hypophyseal portal system: complex of small blood vessels between hypothalamus & anterior pituitary • Hypothalamus secretes releasing hormones through this system • During times of stress cerebral cortex can send impulses to hypothalamus to secrete releasing hormones thus mind-body link

  24. Posterior pituitary • Storage & release site for: • ADH (antidiuretic hormone) • Oxytocin • Hormones are not made within the pituitary but within the supraoptic or paraventricular nuclei of hypothalamus • Release of these hormones thus controlled by nervous stimulation

  25. Antidiuretic hormone • Prevents formation of a large volume of urine • Release triggered by osmoreceptors near supraoptic nucleus

  26. Oxytocin • Stimulates contraction of uterine muslces • Causes ejection of milk from breasts • Regulated by a positive feedback mechanism

  27. Pineal gland • Located on dorsal surface of brain’s diencephalon • Member of both nervous system & endocrine system • Produces melatonin, functions to support biological clock

  28. Thyroid gland • In neck, on anterior & lateral surface of trachea just below the larynx • Composed of structural units called follicles • Hormones: • Thyroid hormones • Calcitonin

  29. Thyroid hormones • T3: principal thyroid hormone • T4: most abundant, precursor of T3 • Thyroid gland stores thyroid hormone as thyroglobulins • Regulate metabolic rate of all cells

  30. Calcitonin • Produced by parafollicular cells of thyroid • Influences processing of calcium by bone cells by decreasing blood calcium levels • Antagonist to parathyroid hormone

  31. Parathyroid gland • 4-5 of them embedded on posterior surface of thryoid’s lateral lobes • Hormone: PTH (parathryroid hormone)

  32. PTH • Antagonist to calcitonin • Acts on bones & kidneys to increase blood calcium • Bones: calcium & phosphate released from bones • Kidneys: calcium reabsorbed, phosphate secreted, activates Vitamin D in kidney which permits Ca to be absorbed in intestine

  33. Adrenal glands • On top of kidneys • Adrenal cortex: outer part • Zona glomerulosa: mineralocorticoids • Zona fasiculata: glucocorticoids • Zona reticularis: gonadocorticoids • Adrenal medulla: inner portion

  34. Mineralocorticoids • Aldosterone: important mineralocorticoid • Primary function is maintenance of sodium homeostasis by increasing sodium reabsorption in kidneys • Increase water retention & promotes loss of potassium • Secretion controlled by renin-angiotensin & blood potassium concentration

  35. Glucocorticoids • Cortisol most significant • Affect every cell in body • Protein mobilizing, lipid catabolism as energy source, secretion increase in times of stress, essential for maintaining normal blood pressure, decrease in number of WBCs

  36. Gonadocorticoids • Secretes small amounts of male hormones • Released from zona fasiculata & zona glomerulosa • Influences appearance of pubic & axillary hair

  37. Adrenal medulla • Composed of neurosecretory tissue • Produce epinephrine & norepinephrine • Prolong & enhance effects of sympathetic stimulation (fight or flight response)

  38. Pancreas • Endocrine portion: pancreatic islets (or islets of Langerhans) • Alpha cells: secrete glucagon • Beta cells: secrete insulin • Delta cells: secrete somatostatin • Pancreatic polypeptide cells: secrete pancreatic polypeptide

  39. Glucagon • Increase blood glucose levels by stimulating conversion of glycogen to glucose in liver cells • Also stimulates gluconeogenesis in liver • Hyperglycemic effect

  40. Insulin • Promotes movement of glucose, amino acids, fatty acids into tissue cells • Lowers blood glucose

  41. Somatostatin • Regulates other endocrine cells of pancreatic islets by inhibiting secretion

  42. Gonads • Primary sex organs • Males: testes • Females: ovaries

  43. Testes • Interstitial cells within testes produce testosterone • Responsible for growth & maintenance of male sexual characteristics & for sperm production

  44. Ovaries • Estrogens: secreted by follicles, promote development & maintenance of female sexual characteristics, breast development, menstrual cycle • Progesterone: secreted by corpus luteum, maintains lining of uterus necessary for pregnancy

  45. Placenta • Produces human chorionic gonadotropin (hCG), serves as a signal to maintain uterine lining for pregnancy • Temporary endocrine gland

  46. Thymus • Atrophies at puberty • Produces thymosin & thymopoietin • Stimulate production of T cells

  47. Gastric & Intestinal Mucosa • Secretin: reduce acid secretion, triggers pancreas to produce bicarbonate • CCK: trigger pancreas to release digestive enzymes, gall bladder contraction • Ghrelin: stimulates hypothalamus to boost appetite

  48. Heart • Atrial natriuretic hormone (ANH): promotes loss of sodium in urine thus it opposes increase in blood volume or blood pressure • Antagonistic to ADH & aldosterone

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