Parathyroid

PTH (Parathyroid Hormone) A polypeptide synthesized and secreted by p.glands Primary function 1. To maintain ECC of Ca ion for optimal cellular and neuromuscular function. Plasma conc. of Ca ion regulates the secretion of PTH. > When Ca conc. is low, PTH secretion is stimulated along with uptake of amino acids, nucleic acid and protein synthesis, and cytoplasmic growth of the gland. > When ionized Ca is high, the same functions are suppressed. 2. PTH helps to maintain plasma Ca about 10mg/100ml by: a. Regulating Ca absorption for the GIT b. Deposition and mobilization of Ca via bone c. Elimination of Ca Hypocalcemia Hypocalcemia can be caused by lack of PTH (Hypoparathyroidism) or lack of response to PTH by target tissue (Pseudohypoparathyroidism) Manifestations 1. Muscle spasm, tetany 2. Paresthesia of extremities 3. Hair Loss 4. Brittle fingernails 5. Cataracts 6. Vascular spasm 7. Enamel hypoplasia 8. Hypodontia 9. Emotional disturbances 10.Highly resistant form of oral candidiasis Hypercalcemia Hyperparathyroidism – Hypercalcemia Ca mobilized from bone is deposited soft tissues (heart, bronchi, kidneys, stomach) Manifestations of Hypercalcemia (Hyperparathyroidism)

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Aches and pains in bones and joints Renal calculi Muscle weakness GI disturbances Inflamed gingival tissue, excessive tooth mobility, recurrent gingival tumors The most prominent effect is to promote mobilization of Ca in bone. This involves a 2 stage process 1. When serum Ca ↓, immediate release of Ca from readily exchangeable portion of bone (due to enzyme modification) 2. Osteoclastic resorption of bone. These 2 phases increase the level of cAMP. Vit D is required for PTH to produce its max effect. Vit D is needed for PTH to increase intestinal absorption of Ca and phosphate PTH is also needed for a. Renal tubular resorption of Ca and excretion of phosphate to decrease elimination of Ca in saliva, swear, and milk.

Ca metabolism is controlled by: 1. PTH 2. Vit D 3. Calcitonin If serum Ca ↓ (Hypocalcemia) PTH ↑ Ct ↓ Bone resorption ↑ Vit D (active form) ↑ intestinal absorption of Ca Renal excretion of Ca ↓ Renal excretion of PO4 ↓ Causing serum Ca ↑ Hypercalcemia Serum Ca ↑ PTH ↓ Ct ↑ Bone resorption ↓ Vit D – ↓ intestinal absorption of Ca

Bone resorption ↓ Renal excretion of Ca and urinary PO ↑ Causing ↓ in serum Ca