Parathyroid Gland

PARATHYROID GLAND PARATHYROID HORMONE [PTH] Normal level: 1 ngm / ml ESSENTIAL FOR LIFE Two types of cells • Chief cells- secrets PTH • OXYPHIL CELLS

ROLE 1. MAINTAIN normal levels of C a+ in blood 2. Acts on bone and kidney

ACTIONS 1. 2. 3. 4.

Increases plasma calcium and decrease plasma phosphate Causes bone resorption and pumps calcium into ECF Decrease Reabsorption of phosphate from kidneys Promotes conversion of 25 HCC to 1,25 DHCC in kidneys that leads to reabsorption of Ca from intestine 5. Decrease excretion of NH+ and H+

REGULATORY MECHANISMS 1. Decreased S. Calcium level Low levels of serum C a+ ↓ Stimulates Parathyroid gland ↓ Increase PTH production ↓ CA+ mobilization from bones to ECF ↓ Normal Calcium level in blood

2. Increased S. Phosphate level High levels of serum phosphate → stimulates PTH

APPLIED HYPOPARATHYROIDISM Cause Destruction of parathyroid gland Respiratory alkalosis- decreased Ionised calcium level S.Calcium level decrease to 4-8 mg% and S.Phosphate increase to 6-15 mg% Characteristic features Decrease in S.Ca+ levels and increase in Phosphate levels 1. Tetany Increased excitability of nerves, numbness, tingling sensations.

Chvosteks sign : Increased excitability of facial nerves to stimulation Carpopedal spasm : Flexion at the wrist and thumb with hyperextension of fingers Trousseau's sign : Inflation of sphygmomanometer cuff occuldes the blood supply to a limb and causes carpopedal spasm.

HYPERPARATHYROIDISM Increase in serum calcium levels above 12 mg% Decrease in Phosphate- < 2.5 mg% Increase in alkaline phosphatase Cause Malignancy Hyperplasia

Characteristic features 1. Weakness, thirst, polyuria, nausea, vomiting, anorexia 2. Kidney stones 3. Demineralization of bones.

CALCITONIN Lowers the plasma level of serum calcium. ACTIONS

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Inhibitory effect on osteoclastic activity of bones. Decrease calcium permeability of Osteoclasts and osteoblasts Increase in alkaline phosphate synthesis Decrease formation of 1,25 DHCC from kidneys, therefore decreasing serum calcium level Inhibits intestinal absorption of calcium and Phosphate..

VITAMIN D

Converted in body to physiological active hormone 1,25 DHCC 1, 25 DHCC acts on GIT, kidney and bones and increase serum calcium and phosphate level ACTION

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GIT- Increases calcium and phosphate absorption in the intestine. Kidney- Increases calcium reabsorption from DCT BONES- Increases calcium mobilisation from bones to ECF

REGULATION OF 1,25 DHCC Low S. Calcium ↓ Stimulates PTH Decreased S. Phosphate ↓ Increase formation of 1, 25 DHCC

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