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Hormones by Posterior Pituitary

Posterior pituitary gland releases 2 hormones
1. Antidiuretic Hormone (ADH), or arginine vasopressin (AVP)
2. Oxytocin

Production of Antidiuretic Hormone
Both the hormones are produced in hypothalamic nuclei
Antidiuretic hormone is produced in SON of hypothalamus
- Supraoptic nucleus ADH + 1/6 oxytocin
- Paraventricular Oxytocin + 1/6 ADH
Both hormones are polypeptides containing 9 aminoacids

Both are transported along the  hypothalamo--hypophyseal tract in  combination with carrier protein called 'neurophysin', to the nerve enpodings in the posterior pituitary gland where they are stored.

Functions & Control of ADH
ADH increases water reabsorption by the distal tubules & collecting ducts of the kidneys leading to reduction in the osmotic pressure of the blood
Control of ADH release :
dehydration - osmolality of plasma increases - osmoreceptors in the hypothalamus - ADH secretion is increased - water reabsorption in the kidneys is increased to combat dehydration
- When blood volume is decreased the  mechanoreceptors in the great arteries (aorta and carotids) and right atrium are stimulated which in turn increases ADH secretion and release
- Decreased blood pressure due to decreased blood volume increases the ADH
- increasing age causes increased ADH
- Pain, emotional stress and physical trauma increase ADH       
- Drugs e.g. morphine, barbiturates and nicotine increase ADH

ADH secretion decreases in
Alcohol consumption

Symptoms of deficiency of ADH
Lack of ADH : leads to Diabetes insipidus
Signs and Symptoms
Polyurea - 20 L/day
Decrease in the specific gravity of urine
Increase in plasma osmolality

Increase in ADH : Schwartz-Bartter Syndrome - occurs after surgery of ademoma of pituitary, ectopic kidney, bronchial carcinoma
Signs and Symptoms
Mental confusion
death due to vetnricular fibrillation

Production of Oxytocin
Produced mainly in the paraventricular nucleus of the hypothalamus

Functions and Control of Oxytocin
Action : contraction of the smooth muscles of the uterus - enances labour
Contraction of mammary gland myoepithelial cells of the alveoli and the ducts - ejection of milk as a reflex in lactating women
In men increases ejaculation

Oxytocin is concerned with releasing or ejection of milk, while prolactin is concerned with synthesis and production of milk.

Factors increasing oxytocin release
Stimulation  of nipple
visual or auditory stimuli from the baby
Distension of uterus and stretching of cervix during delivery
Psychological and emotional factors e.g. fear, anxiety and pain

Factors decreasing oxytocin secretion
Hormones : progesterone - decreases uterine sensitivity to oxytocin
                    estrogen - increases uterine sensitivityto oxytocin

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