Anatomy - parathyroid glands

1. Anatomy-PARATHYROID
GLANDS

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

4. They are surrounded by fine connective
tissue capsules.

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

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

7. 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.

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

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

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

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

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