ENDOCRINE STSYTEM PT 3
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What is the process of control of thyroid hormone secretion?
1. Low blood levels of T3 & T4 or low metabolic rate stimulate the hypothalamus to secrete TRH(thyrotropin releasing)
2. TRH flows through hypophyseal portal veins to anterior pituitary, where it stimulates secretion of TSH(thyroid-stimulating)
- 3. TSH stimulates T3 and T4 synthesis and secretion by the thyroid follicles
- 4. The thyroid follicles release T3 and T4 into the blood until the metabolic rate returns to normal
5. An elevated level of T3 inhibits release of TRH and TSH(negative feedback inhibition)
What is the parathyroid gland?
round masses of tissue, partially embedded in the posterior surface of the lateral lobes of the thyroid gland
- 4 parathyroid glands...
Explain PTH(Parathyroid hormone)
major regulator of the levels of calcium, magnesium and phosphate ions in the blood. Stimulates osteoclasts activity. acts on kidneys during urine formation from blood decreasing calcium and magnesium; urinary loss while increasing phosphate. promote formation of hormone: calcitrol(vit D)-increases rate of calcium, magnesium and phosphate absorption from food within gastrointestinal tract into blood.
Roles of calcitonin, PTH and calcitrol in homeostasis of blood calcium level
1. A higher than normal level of calcium in blood stimulates parafollicullar cells to release more calcitonin
2. Calcitonin inhibits the activity of osteoclasts decreases blood calcium level
3. A lower than normal level of calcium in blood stimulate chief cells of parathyroid
4. PTH promotes osteoclasts which release camlcium in blood slows loss of calcium in urine, raising blood level of calcium
5. PTH stimulates kidneys to synthesize calcitrol
6. Calcitrol stimulates increased absorption of calcium from foods in gastrointestinal tract, help increase calcium level
What are the adrenal glands?
One of each lies superior to each kidney. Each gland has adrenal cortex (80%-90% of gland) and adrenal medulla.
What are the 3 zones of the adrenal cortex?
Mineralocorticoids/Aldosterone-Affect mineral homeostasis;Sodium(secrete from urine into blood) and Potassium(excretion into urine help adjust blood pressure in blood volume).
Gluicocorticoids/Cortisol-Affect glucose homeostasis
Explain excretion of Mineralocorticoids/Aldesterone
1. Renin-angiotensin-aldesterone pathway is activated by stimuli that include dehydration sodium deficiency on hemorrhage. Decrease blood volume and blood pressure.
2.Decreased blood pressure stimulates the kidneys to secrete the enzyme renin into the blood.
- 3. renin converts angiotensinogen(a plasma protein produced by the liver in angiotensin I)
- 4. As blood rich in angiotensin I flows through the lings, another enzyme(ACE) converts inactive angiotensin I into active hormone angiotensin II
5. Angiotensin II stimulates contraction of smooth muscle in the walls of arterioles help raise blood pressure to normal
6. As angiotensin II flows through adrenal glands, the adrenal cortex is stimulated to secrete aldosterone
7. Blood with increased level of aldosterone circulates to kidneys where sodium & H20 from urine to blood flows. Increase potassium into urine.
8. As more h20 returns to blood(less lost in urine) blood volume increases. Arterioles constrict, blood pressure increases to normal.
Explain Glucocorticoids/Cortisol zone
Regulates metabolism and resistance to stress include cortisol(95% of activity), hydrocortisone, and corticosterone.
-Control of glucocorticoid secretion is by a typical negative feedback system.
1. low blood levels mainly cortisol stimulate neurosecretory cells in hypothalamus to secrete corticotropin releasing hormone(CRH)
2. CRH travels through infindibulum to the anterior pituitary, promotes release of ACTH corticotropin from anterior pituitary
3. ACTH flows in blood to adrenal cortex stimulates glucocorticoid secretion
4. As the level of glucocorticoid rises, it exerts negative feedback inhibition both on anterior pituitary to reduce release of CRH
List Glucocorticoids effects
- -Protein breakdown
- -Glucose formation
- -Breakdown of triglycerides
- -resistance to stress
- -anti-inflammatory effects
- -Depression of immune responses
Explain inner zone of adrenal cortex: Androgens
Stimulated mostly by ACTH
Males-androgen testosterone is released in greater quantity after puberty.
Females-adrenal adrogen contribute to libido converted to estrogens(feminizing sex steroids/ sex drive) by other body tissues. After menopause, when ovarian secretion of estrogen ceases all female estrogens come from conversion of adrenal androgens. Adrenal androgens stimulate growth of hair under arms and pubic.
What is the Adrenal Medulla?
the inner region of the adrenal gland
- -modified by sympathetic ganglion of autonomic nervous system.
- -synthesizes two hormones: epinephrine and norepinephrine that contributes to to fight or flight.
- Fight or flight: Increased heart rate, blood pressure and blood levels of glucose. Airways of lungs dilate.
Describe the Pancreas
-both endocrine and exocrine gland located in curve of duodenum(first part of small intestine)
Acini-99% of pancreas,clusters of exocrine cells that produce digestive enzymes which flow into gastrointestinal tract through a network of ducts
Pancreatic Islets-are scattered among acini. clusters of endocrine tissue
Explain Regulation of glucagon and insulin secretion
- Alpha cells-secrete hormone glucagon(raise blood sugar)
- Beta cells-secrete insulin(lowers sugar)
- BOTH LOCATED ON PANCREATIC ISLETS
- Principle Actions: increase blood glucose level when it falls below normal
- 1. low blood glucose level(hypoglycemia) stimulates secretion of glucagon from alpha cells of pancreatic islets
2. Glucagon acts on liver cells to accelerate the breakdown of glycogen into glucose and formation of glucose from lactic acid and certain amino acids
3.Liver releases glucose into blood more rapidly and blood glucose level rises
4. If blood glucose continues to rise high blood glucose level(hyper) inhibits release of glucagon by alpha cells(negative feedback)
5. High blood glucose stimulates secretion of insulin by beta cells of pancreatic islets
6. Insulin acts on body cells to increase uptake of glucose accelerate synthesis of glycogen from glucose increase protein synthesis and increase fatty acid synthesis. Brings glucose into cells.
7. As glucose enters and is utilized by cells, blood glucose level falls
8. If blood glucose level drops below normal, low blood glucose inhibits release of insulin by beta cells(negative feedback) and stimulates release of glucagon
What are the gonads of both sexes
Organs that produce
- Males- Females
- Gamete-sperm gamete-oocyte
- testes Ovaries
- testes-produce and secrete testosterone primary androgen or male sex hormone,
- regulate production of sperm and stimulate development and maintenaance of masculine secondary sex such as beard and deepening of voice; also produce inhibin
- Ovaries-produce female hormone estrogen and progesterone, regulate reproductive cycle, maintain pregnancy and prepare mammary glands for lactation
- Promote puberty, inhibin/fsh, during pregnancy ovaries and placenta produce relaxin(increase flexibility of pubic symphysis and helps dilate cervix during labor)
What is the pineal gland
small endocrine gland attached to roof of 3rd ventricle of brain at midline; consists of secretory cells and supportive neuroglia
What is melatonin
Secreted by pineal gland appears to contribute to the setting of the body's biological clock controlled by hypothalamus
What is the Thymus
behind sternum between lungs produces thymosine, thymic humoral factor, and thymopoietin hormone all promote the maturation of T-cells(wjite blood cell that destroys microbes and foreign substances) may retard the aging process
What are Eicosanoids
Water soluable hormone
- Prostaglandins and leukotrienes are found in all body cells except red blood cells, where they respond to chemical or mechanical stimuli
- -synthesized by clipping a 20-carbon fatty acid called arachidonic acid from membrane phospholipid molecules
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