PARATHYROID DISORDERS -
(i) Hypoparathyroidism (deficiency of PTH). It causes the lowering of blood calcium level. This increases the excitability of nerves and muscles, causing cramps and convulsions. Sustained contractions of the muscles of larynx, face, hands and feet are produced. This disorder is called parathyroid tetany or hypocalcaemic tetany.
(ii) Hyperparathyroidism (excess of PTH). Excess of PTH draws more calcium from the bones.