These are small glands which are present in neck very close to the thyroid gland. There are as such 4 glands in our body.The main functions of these glands is to maintain calcium level in the bloods by working on the bones and kidneys.
Parathyroid tumours are very rare. It can occur as an isolated tumour of parathyroid gland like a adenoma(benign) or malignant(cancerous). In patients with renal failure all fours glands can over function and become larger in size(hyperplasia).