Posterior Pituitary/ Neurohypophysis

Human Physiology

Lesson 37 : Hypothalamus, Pitutary & Thyroid

Posterior pituitary/ neurohypophysis

Two hormones, ADH & oxytocin are produced in hypothalamus (para ventricular nucleus & supra optic nucleus) but are stored & released from posterior pituitary.

ADH(Anti Diuretic Hormone/Vasopressin): It has 9 amino acids chain length with a molecular weight of about 1000 Dalton. Out put of ADH is related to degree of hydration of body and osmoreceptors are located in SON & PVN. Excess hydration of body or water in blood inhibits ADH release resulting in less water resorption from glomerular filtrate in kidneys. ADH acts on distal convoluted tubules & collecting duct of kidneys to increase water re-absorption by increasing the size of pores/ channels. Deficiency of ADH leads to a disease called diabetes insipidus where large volume of dilute urine is discharged.

Oxytocin: Oxytocin causes contraction in smooth muscles of uterus & myoepithelial cell of mammary gland. It also stimulates gravid uterus at the end of term to cause contraction & induce labor. It is released as a result of stimulus from suckling / milking / neuro-endocrine mode. On release it causes contraction of myoepithelial cells of mammary glands and hence complete removal of milk from mammary glands occurs.


Pineal secrets many hormones or neuro-peptides but the most important and identified is melatonin. During the darkness, melatonin secretion increases so involution of gonads occurs. As the day light decreases melatonin level increases and at midnight serum melatonin level is highest. It has also been proposed that biological clock of body is controlled by pineal gland. This regulation occurs through optic nerve of eyes, which modulates pineal gland to the environmental signals.

Pineal gland contains many biologically active substances 5-Hydroxy Tryptamine, serotonin, Dopamine. Norepinephrine, GnRH, TRH, GHIF and vasotocin. These mediate anti-gonadotropic effect of pineal gland. Melatonin is found in highest concentration and is synthesized from tryptophan. So the functions of melatonin and other peptides of Pineal can be summarized as:

  1. Inhibition of gonadotrophins.
  2. Regulator of biological clock
  3. Melatonin has role in sleep regulation.

It is a unique gland that accumulates I2 (iodine) and incorporates it into hormone.
Histological picture shows presence of numerous follicles containing colloid produced by follicular cells. Colloid is gelatinous amber colored material majority of which is thyroglobulin – a complex protein of stored thyroxine. Tri-iodothyronine (T3) and Thyroxine (T4) are two active thyroid hormones found in blood and both perform same physiological functions. To maintain the optimum synthesis of thyroxin, I2 requirement is about 215 mg/day. Out of this dietary intake is about 150 mg while 65 mg is recycled. Function of T 4:

  1. Stimulates O2 utilization and heat production by every cell of the body.
  2. Utilization of carbohydrates.
  3. Protein catabolism.
  4. Excretion of nitrogen.
  5. Oxidation of fat (loss of weight)
  6. Improves Heart Rate & blood flow.
Deficiency of T4 causes lethargies & mental weakness.
Last modified: Tuesday, 10 April 2012, 12:57 PM