Parathyroid Glands
PARATHYROID GLANDS
- Parathyroid gland, 4 in number (a superior pair and an inferior pair) are located on the posterior border of thyroid gland.
- Small endocrine gland.
Shape- Each parathyroid is oval or lentiform in shape.
Size- measuring 6x4x2 mm, and each weighs about 50 mg.
Development:
- The superior parathyroids are also referred to as ‘parathyroids IV’ because they develop from the fourth pharyngeal pouch.
- Inferior parathyroids are also referred to as ‘parathyroids III’ because they develop from the endoderm of third pharyngeal pouch.
SECRETION:
- It secretes hormones called Parathhormone, which controls the calcium & phosphorus metabolism along with thyrocalcitonin.
- It causes resorption of calcium from bones & makes them weak liable to fracture.
Position:
- Superior parathyroids are more consistent in position lying at the middle of posterior border of thyroid gland immediately above the termination of inferior thyroid artery (80%).
- In about 20% cases they lie posterolateral to upper pole of thyroid lobe.
- Inferior parathyroids are more variable in positon. It may lie:
- within thyroid capsule, below inferior thyroid artery
- outside thyroid capsule, above inferior thyroid artery
- within the substance of the lobe near posterior border.
BLOOD SUPPLY:
- Each parathyroid receives blood supply from inferior thyroid artery, and also from the anastomosis b/w superior and inferior thyroid arteries.
VEINS & LYMPHATICS:
- Veins & lymphatics of gland are associated with those of thyroid gland i.e. inferior thyroid & middle thyroid vein.
- Pre & para tracheal group of lymph nodes.
NERVE SUPPLY:
- Vasomotor nerves are derived from middle & superior cervical sympathetic ganglion.
- Parathyroid activity– is controlled by blood calcium levels-low levels-stimulate and high level inhibit the activity of the gland.
APPLIED:
1. Tumors of parathyroid glands- lead to excessive secretion of parathormone- causes increased removal of calcium from bones making them weak & liable to fracture.
Hypercalcaemia and increased urinary excretion of calcium salts lead to formation of stones in urinary tract.
2. Hypoparathyroidism– may occur spontaneously or from accidental removal of glands durind thyroidectomy- results in hypocalcaemia leading to increased neuromuscular irritability causing muscular spasm & convulsions (Tetany).
Exam Question
- Number of parathyroid glands is-4.
- The superior parathyroids are also referred to as ‘parathyroids IV’ because they develop from the fourth pharyngeal pouch.
- Inferior parathyroids are also referred to as ‘parathyroids III’ because they develop from the endoderm of third pharyngeal pouch.
- Each parathyroid receives blood supply from inferior thyroid artery.
Don’t Forget to Solve all the previous Year Question asked on Parathyroid Glands
