The blood calcium level is lowered by the deficiency of
a)	Parathormone	b)	Thyroxine	c)	Calcitonin	d)	Both (a) and (b)

(a)

The chief cells of the parathyroid secrete parathormone. Its deficiency causes the lowering of blood calcium level. This increases the excitability of nerves and muscles causing cramps and convolutions. This caused parathyroid tetany characterised by sustained contractions of muscles of larynx, face, hands and feet.