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Endocrine System

Endocrine System. Week 8 Dr. Walid Daoud A. Professor. Posterior Pituitary Gland Hormones. ADH and oxytocin are synthesized by hypothalamic neurons and then transported through hypothalamo-hypophyseal tract to be stored in the posterior pituitary galnd until their release.

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Endocrine System

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  1. Endocrine System Week 8 Dr. Walid Daoud A. Professor

  2. Posterior Pituitary Gland Hormones ADH and oxytocin are synthesized by hypothalamic neurons and then transported through hypothalamo-hypophyseal tract to be stored in the posterior pituitary galnd until their release.

  3. Antidiuretic Hormone (ADH) ADH or vasopressin is formed in supraoptic nuclei of hypothalamus. Actions: 1- On kidneys: antidiuretic effects. 2- On blood vessels: pressor effects. 3- On smooth muscles: contraction.

  4. Regulation of ADH secretion 1- ADH secretion is increased by: . Increased osmotic pressure of ECF. . Decreased blood volume (hypovolemia) . Stress: pain, cold, trauma. . Drugs: morphine and nicotine. 2- ADH secretion is decreased by: . Decreased osmotic pressure of ECF. . Ethanol. . Cortisol.

  5. Diabetes insipidus It is caused by deficiency of ADH. -Polyuria. -Polydepsia. -Loss of water-soluble vitamins.

  6. Oxytocin It is formed in paraventricular nuclie of hypothalamus. Actions: 1- Uterine contraction during delivery. 2- Milk letting action. 3- Mild antidiuretic effects.

  7. Thyroid Gland In the neck in front of trachea. 2 lobes connected by isthmus. . Tri-iodothyronine (T3) . Tetra-iodothyronine (T4) . Thyrocalcitonin

  8. Actions of Thyroid Hormones 1-Calorigenic effect: increased metabolic activity in all tissues. 2-Effects secondary to calorigenesis: . On GIT: increased activities. . On metabolism: Increased. . On basal metabolic rate: increased BMR. . On respiration: increased rate and depth. . On CVS: increased flow, COP and HR. . On CNS: Increased reactivity of synapses . On muscles: increased reaction.

  9. Actions of Thyroid Hormones 3-Effects on growth: . Physical growth: increase linear growth in children. . Mental growth: brain development in the first few years of life. . Sexual development: secretion of gonadal hormones and sexual maturation.

  10. Regulation of Thyroid Hormones 1-TRH from hypothalamus increases TSH. 2-TSH from anterior pituitary gland increases synthesis and secretion of thyroid hormones. 3-Cold increases TRH secretion. 4-Emotional stress increases TRH secretion. 5-Feedback inhibition: decreased T3 and T4 cause increased TSH and TRH secretion.

  11. Hypothyroidism In adults: Myxoedema: 1-Low BMR (-40%). 2-Accumulation of fluid containing proteins under skin (myxoedematous tissues). 3-Decreased heart rate and cardiac output. 4-Constipation. 5-Slow mentation and sleepiness. 6-Sterility.

  12. Hypothyroidism Since birth: Cretinism: - Deficiency of thyroid hormone since birth - Delay development. - Distorted bone and muscle growth.- - Dwarf with mental retardation. - Deficient sexual maturation. - Depressed bridge of nose with wide nostril. - Protruding tongue, thick lips. - Protuberant abdomen.

  13. Hyperthyoidisn (Throtoxicosis) Exophthalmic goitre; autoimmune disease, TSH receptor-stimulating antibodies increase T3 and T4 causing exophthalmos - Increased BMR. Warm skin, can not tolerate heat. - Tremors, irritability, insomnia and exaggerated tendon jerk. - Loss of weight in spite of ↑ food intake. - Increased heart rate, COP and diarrhea.

  14. Calcium Homeostasis Functions of calcium: - Mineralization of bone and teeth. - Blood clotting. - Release of neurotransmitters. - Neuromuscular excitability. - Muscle contraction and relaxation. - Hormonal secretion and function.

  15. Calcium Homeostasis Calcium Balance: Absorbed calcium passed to ECF which contain 1 gm of calcium, 50% is deposited daily in bones and absorbed again to pass to ECF, so bones are in a continuous turnover and remodeling. 1% of bone calcium is (exchangeable Ca), providing buffering mechanism to maintain Ca in ECF constant.

  16. Calcium Homeostasis Calcium balance: 10 gms calcium filtered by kidney daily but 98% are reabsorbed in renal tubules and only 175 mg are lost in urine daily equal to the amount absorbed from GIT. Amounts of calcium lost in urine and feces vary depending on body needs. There is less calcium loss in pregnancy, lactation and infancy.

  17. Plasma calcium Normal plasma calcium 9-11 mg/100 ml: 1- 50% ionized 2- 40% protein-bound (bound to albumin) 3- 10% complex diffusible calcium bound to phosphates, bicarbonates and citratesSolubility product: Ca++ x PO4--- = constant Increase in one leads to decrease in other.

  18. Bone cells 1- Osteobalsts: bone-forming cells. 2- Osteocytes. 3- Osteoclasts: bone-eating cells.

  19. Hormones involved in calcium homeostasis

  20. Tetany ↑ neuromuscular excitability due to ↑ ionized Ca causing increased neuronal permeability and clonic contractions of skeletal muscles. Causes of hypocalcemia: - Hypoparathyroidism. - Vitamin D deficiency. - Alkalemia. - Renal failure.

  21. Tetany Latent tetany: Ca level is between 7-9 mg% Spasm in certain parts of the body as carpopedal spasm of the hands muscles. Manifest tetany: Ca level drops below 7 mg%. Spasmodic contractions of hands & feet. May die with asphyxia & cyanosis due to spasmodic contractions of laryngeal and respiratory muscles.

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