Hormones of neuro-hypophysis : Neuro-hypophysis does not secrete any hormone itself but stores the hormones which are secreted by hypothalamic neurons. It stores and releases the following hormones, viz. ADH, Oxytocin and coherin.
1. Anti Diuretic Hormone (ADH) or Vasopressin:
- ADH brings about anti-diuretic action and also increases blood pressure.
- It is a regulatory hormone which plays a major role in osmoregulation.
- It increases the permeability of distal convoluted tubule or collecting tubules of uriniferous tubules of kidney.
- Higher ADH levels decrease the urine output and helps for water conservation. It helps in the absorption of water from the ultrafiltrate thus regulates the water balance of body fluids.
- ADH also controls constriction of arterioles and increases blood pressure in kidney which facilitates ultra filtration. Therefore it is also called vasopressin.
- ADH is regulated by increase or decrease of osmotic pressure of blood in a feedback manner.
- The osmotic pressure is detected by osmoreceptors in the hypothalamus.
2. Oxytocin (Birth hormone):
- Oxytocin helps in parturition.
- It is a powerful stimulant of contraction of uterine myometrium at the end of gestation due to which the labour is initiated.
- It also stimulates myoepithelial cells of mammary glands for milk ejection during lactation.
- It also helps in fertilization by powerful contractions of the uterine musculature to drive the sperms upward towards fallopian tubes.
- Oxytocin also excites musculature of gallbladder, ureters, urinary bladder, intestine, etc. for proper functioning of these organs.
3. Coherin : Coherin induces prolonged, rhythmic integrated contractions of the jejunum.
