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Anatomy & Physiology

Parathyroid Gland

They are tiny little things, with most people having 4, some 5-6. They are found pretty much clinging to the back of the thyroid gland. Their claim to fame is the production of PTH – parathyroid hormone, which is released on a negative feedback loop, based on the level of blood calcium.

Parathyroid Hormone

It plays a major part in calcium homeostasis, working with calcitonin and vitamin D. It’s main actions are below:

On bone:

  • Stimulates osteoclast resorption - releasing calcium from bone.
  • Inhibits the osteoclasts doing else anything constructive with bone.

On kidney

  • Acts on renal tubular epithelium to cause calcium reabsorption
  • Makes it make some kind of mega good Vitamin D.

Vitamin D

Also known as Calcitriol. Produced in the skin with sunlight, and from dietary sources in the liver. But it is refined by the action of PTH in the kidney to be really good. Acts on bone with PTH, and also increases calcium absorption in the intestine.

Clinical Conditions


Quite common (0.1% of population). Seemingly less common in exams though. Presents through symptoms of hypercalcaemia:

  • Renal stones – due to hypercalciuria
  • Muscle weakness
  • Thirst and polyuria
  • Anorexia
  • Constipation

Usual cause (80%) is a benign adenoma, which is treated by removal of all parathyroid glands, and of any other suspected adenoma.


  • Presents with hypocalcaemia
  • Tetany (skeletal muscle spasm)
  • Convulsions
  • Paraesthesiae
  • Psychiatric problems

Most commonly caused by surgical removal of the thyroid, or autoimmune attack.

Hyperphosphataemia is another cause of low calcium – be alert for it, a side effect of chronic renal failure.