Abnormalities of parathyroid gland :
1. Due to hyposecretion : Secretion of the PTH in lesser amount that the normal results in :
(a) Decrease of calcium of blood which causes cramps and convulsions.
(b) It also causes parathyroid tetani which is characterised by sustained contraction of muscles of face, larynx, limbs etc.
2. Due to hypersecretion : Secretion of the hormone in excess amount results in abnormal increase in the amount of calcium in blood. The increased calcium levels may results in easy fractures of bones.