11 C-Endocrine Glands - Endocrine Glands-C Lecturer: Dr. R....

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Endocrine Glands-C Lecturer: Dr. R. Ahangari University of Central Florida, Orlando Human Physiology by S.I. Fox and human anatomy by Marieb & Mallat
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Parathyroid gland The parathyroid glands are four pea-sized glands located on the thyroid gland in the neck. The parathyroid glands regulate serum calcium and phosphorus levels through the secretion of parathyroid hormone (PTH), which raises serum calcium levels while lowering the serum phosphorus concentration. The regulation of PTH secretion occurs through a negative feedback loop in which calcium-sensing receptors on the membranes of parathyroid cells trigger decreased PTH production as serum calcium concentrations rise. www.pamf.org/health/healthinfo/index.cfm?sect. .. www.parathyroid.com/parathyroid.htm
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Parathyroid hormone (PTH) is synthesized and secreted by the chief cells of the parathyroid glands. PTH is the major hormone for the regulation of serum [Ca2+] www.bu.edu/histology/p/15001ooa.htm
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Secretion of PTH Is controlled by serum [Ca2+] through negative feedback. Decreased serum [Ca2+] increases PTH secretion. Mild decreases in serum [Mg2+] stimulates PTH secretion Severe decreases in serum [Mg2+] inhibits PTH secretion and produce symptoms of hypoparathyroidism (e.g., hypocalcemia). The second messenger for PTH secretion is cAMP.
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Actions of PTH PTH increases serum [Ca2+] and decreases serum [phosphate]. The 2 nd messenger for PTH actions on its target cells is cAMP. 1- PTH increases bone resorption -This brings both Ca2+ and phosphate from bone minerals to ECF. -Alone, this effect on bone would not increase serum ionized [Ca2+] because phosphate complexes Ca2+. - Resorption of the organic matrix of the bone is reflected in increased hydroxyproline excretion.
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Actions of PTH (continued) 2- PTH inhibits renal phosphate resorption in the proximal tubules, and therefore, increases phosphate excretion (phosphaturic effect). As a result, the phosphate resorbed from bone is excreted in the urine, allowing
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11 C-Endocrine Glands - Endocrine Glands-C Lecturer: Dr. R....

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