Anatomy - parathyroid glands

Anatomy - parathyroid glands

1. Anatomy-PARATHYROID GLANDS

2. There are four small parathyroid glands, two embedded in the posterior surface of each lobe of the thyroid gland.

3. They are surrounded by fine connective tissue capsules.

4. The cells forming the glands are spherical in shape and are arranged in columns with channels containing blood between them.

5. FUNCTION OF PARATHYROID GLANDS The parathyroid glands secrete parathyroid hormone (PTH, parathormone ). Secretion is regulated by the blood level of calcium.

6. When this falls, secretion of PTH is increased and vice versa. The main function of PTH is to increase the blood calcium level when it is low.

7. This is achieved by indirectly increasing the amount of calcium absorbed from the small intestine and reabsorbed from the renal tubules.

8. If these sources provide inadequate supplies then PTH stimulates osteoclasts (bone-destroying cells) and resorption of calcium from bones.

9. Parathormone and calcitonin from the thyroid gland act in a complementary manner to maintain blood calcium levels within the normal range.

10. This is needed for: • Muscle contraction • Blood clotting • Nerve impulse transmission.

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