Endo 4 jho

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Endo 4 jho

  1. 1. Adrenal. Thyroid. Parathyroid.
  2. 2. Adrenal Glands Paired organs that cap the superior borders of the kidneys Each consists of:  Adrenal cortex (outer) – derived from neural crest ectoderm – does not receive neural innervation so it must be stimulated hormonally - Consists of three zones: zona glomerulosa, zona fasciculata and zona reticularis  Adrenal medulla (inner) – derived from mesoderm – innervated by preganglionic sympathetic nerve fibers
  3. 3. Structure of Adrenal Gland
  4. 4. Functions of Adrenal Cortex Secretes steroid hormones (corticosteroids or corticoids)  Mineralocorticoids – regulate Na+ and K+ balance  Glucocorticoids – regulate the metabolism of glucose and other organic molecules  Sex steroids – weak androgens (dehydroepiandrosterone or DHEA)
  5. 5. Aldosterone Most potent mineralocorticoid Secreted by the zona glomerulosa Stimulate the kidneys to retain NaCl and water while excreting K+ in the urine  These actions help to increase the blood volume and pressure and to regulate blood electrolyte balance
  6. 6. Cortisol Predominant glucocorticoid Secreted by zona fasciculata and perhaps also the zona reticularis Secretion is stimulated by the ACTH from the anterior pituitary gland have effects on metabolism:  Stimulate gluconeogenesis  Inhibit glucose utilization  Promote lipolysis and consequent release of free fatty acids into the blood
  7. 7. Exogenous Glucocorticoids Taken as pills, injections, sprays and topical creams Used medically to suppress the immune response Very useful in treating inflammatory diseases (asthma, rheumatoid arthritis) Side effects:  Hyperglycemia  Decreased glucose tolerance  Decrease synthesis of collagen and other extracellular matrix proteins and increased bone resorption (osteoporosis)
  8. 8. Cushing’s Syndrome Hypersecretion of ACTH (glucocorticoid) Can also result from a tumor of the adrenal cortex Characterized by:  Changes in carbohydrate and protein metabolism  Hyperglycemia  Hypertension  Muscular weakness
  9. 9. Functions of Adrenal Medulla Secrete epinephrine and norepinephrine Effects of catecholamine hormones secreted by the medulla:  Increase cardiac output  Dilate coronary blood vessels  Increase mental alertness  Increase respiratory rate  Elevates metabolic rate Supported by the metabolic actions of E and NE:  Rise in blood glucose (due to stimulation of hepatic glycogenolysis)  Rise in blood fatty acids (due to lipolysis)
  10. 10. Stress and the Adrenal Gland 1936 – Hans Selye discovered that injections of cattle ovary extract into rats: 1. stimulated growth of the adrenal cortex 2. caused the atrophy of the lymphoid tissue of the spleen, lymph nodes and thymus, and 3. produced bleeding peptic ulcers Same things happened when he subjected the rats to cold environment and when he dropped them into water and made them swim until they were exhausted
  11. 11. Stress and the Adrenal Gland Stress – reaction of the organism to stimuli (stressors) which may produce damaging effects Stressors stimulate the pituitary-adrenal axis Under stressful conditions, there is a increased secretion of ACTH therefore there is the increased secretion of glucocorticoids
  12. 12. Stress and the Adrenal Gland There is a nonspecific response of the body to readjust itself following any demand made upon it A rise in the plasma glucocorticoid level results from the demands of the stressors (General Adaptation Syndrome or GAS) 3 stages in response to stress:  Alarm reaction (adrenal glands are activated)  Stage of resistance (readjustment occurs)  Stage of exhaustion (if readjustment is not complete – this leads to sickness and possibly, death)
  13. 13. Thyroid Gland Located just below the larynx Two lobes are positioned on either side of the trachea and are connected anteriorly by a medial mass of the thyroid tissue (isthmus) Largest pure endocrine gland (20-25 grams in wt.)
  14. 14. Thyroid Gland
  15. 15. Thyroid Gland Consists of numerous spherical hollow sacs (thyroid follicles) lined with simple cuboidal epithelium composed of follicular cells (secrete thyroxin) The interior of follicles contain colloid (protein-rich fluid) Also contains parafollicular cells (secrete calcitonin or thyrocalcitonin)
  16. 16. Thyroid Gland
  17. 17. Production and Action of ThyroidHormones Thyroid follicles actively accumulate iodide (I-) from the blood and secrete it into the colloid Iodide will be oxidized to form iodine once it enters the colloid then it will be attached to amino acids (tyrosines) within the polypeptide chain of protein (called thyroglobulin) The attachment of:  One iodine to tyrosine => monoiodotyrosine (MIT)  Two iodines => diiodotyrosine (DIT)
  18. 18. Production and Action of ThyroidHormones Within the colloid, enzymes modify the structure of MIT and DIT and couple them together Tetraiodothyronine (T4) or thyroxine – produced when two DIT molecules that are appropriately modified are coupled together Triiodothyronine (T3) – combination of one MIT with one DIT Upon stimulation of TSH, the cells of the follicle take up a small volume of colloid by pinocytosis, hydrolyze the T3 and T4 from the thyroglobulin, and secrete free hormones into the blood
  19. 19. Production and Action of ThyroidHormones Through the activation of genes, thyroid hormones:  Stimulate protein synthesis  Promote maturation of the nervous system  Increase the rate of cell respiration  Through this, thyroxin elevates the basal metabolic rate (the resting state of calorie expenditure by the body) Calcitonin– works with parathyroid hormones to regulate calcium levels of the blood- Inhibits dissolution of the calcium phosphate crystals of bone and stimulates the excretion of calcium in the urine by the kidneys
  20. 20. Hyperthyroidism Iodine-deficiency (endemic) Goiter– abnormal growth of the thyroid gland– due to the absence of the dietary iodine, the thyroid cannot produce adequate amounts of T4 and T3– the resulting lack of negative feedback inhibition causes hypersecretion of TSH that stimulates abnormality
  21. 21. Hypothyroidism Condition of people who have inadequate secretion of the thyroid hormone People who have hypothyroidism have an abnormally low basal metabolic rate and they experience weight gain and lethargy In adults, it causes:  Myxedema – accumulation of mucoproteins and fluid in subcutaneous connective tissues – symptoms: swelling of the hands, face, feet and tissues around the eyes
  22. 22. Hypothyroidism Can also be caused by insufficient thyrotropin- releasing hormone (TRH) secretion from the hypothalamus, or insufficient secretion of TSH from the anterior pituitary or insufficient iodine in the diet
  23. 23. Parathyroid Glands Small flattened glands that are embedded in the posterior surfaces of the lateral lobes of the thyroid gland
  24. 24. Parathyroid Glands
  25. 25. Parathyroid hormone Only hormone secreted by the parathyroid glands Important in the control of calcium levels of the blood Promotes rise in blood calcium levels by acting on the bones, kidneys and intestine

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