Oxytocin and vasopressin are secreted by the posterior pituitary gland.
(i) Oxytocin, is released into the blood when hypothalamic neurons are stimulated by the widening of uterus at the time of delivery or by the sucking of breasts by an infant. It induces contraction of smooth muscles of the uterus during the birth of a young one and myoepithelial cells of mammary glands to cause release of milk during sucking by an infant. Therefore, it is also known as ‘birth hormone’ and or ‘milk-ejecting hormone’.
(ii) Vasopressin, is also called antidiuretic hormone (ADH). It decrease the loss of water in urine by increasing reabsorption of water in distal convoluted tubules, collecting tubules and collecting ducts of kidneys.