Posterior Pituitary Hormones: Functions, Actions, And Regulation

Posterior Pituitary Hormones: Functions, Actions, And Regulation

Name the hormones of posterior pituitary gland. Explain their action and regulation of secretion. (or) Oxytocin.
Answer:

Hormones of posterior pituitary:

• Antidiuretic hormone (ADH)
• Oxytocin.

1. Antidiuretic hormone (ADH):

• Antidiuretic hormone Actions:
  • ADH increases the water reabsorption from distal convoluted tubule and collecting duct.
  • Increases urea absorption from collecting ducts.
  • Promotes Na⁺ reabsorption from the thick ascending limb of loop of Henle.
  • Causes constriction of the arteries in all parts of the body.
  • Causes contraction of smooth muscle and increases peristalsis of GIT and detrusor contraction.
• Antidiuretic hormone Regulation:
  • Stimulants of ADH are.
    • Decrease in the ECF volume.
    • Increase in osmolar concentration in the ECF.

Increase in osmolarity of blood.
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Stimulation of osmoreceptors situated in the hypothalamus near supraoptic and paraventricular nuclei.
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Impulses are send to posterior pituitary
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Causes release of ADH
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ADH causes reabsorption of water from renal tubules.

2. Oxytocin:

• Oxytocin Actions:
• Milk ejection oxytocin stimulates contraction of the myoepithelium lining the duct of mammary
• glands causes milk ejection.
• Stimulates contraction of the smooth muscle of uterus.
• It facilitates the process of labour.
• Facilitates the transport of sperm to the uterus by uterine contraction.
• Causes relaxation of blood vessels producing fall in B.P.
• Thus,
  1. On pregnant uterus.
     • Oxytocin facilitates labour.
  2. On non-pregnant uterus.
     • Facilitates transport of sperms.

Oxytocin Regulation:

1. Milk ejection reflex:

Stimulation of touch receptors present on the mammary glands.
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Impulses via somatic afferent nerve fibers reach paraventricular and supraoptic nuclei of hypothalamus.
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These impulses releases oxytocin.
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Oxytocin causes.

• Contraction of myoepithelial cells.
• Ejection of milk from mammary glands.

2. Action on uterus.

Dilation of cervix.
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Stimulation of receptors on the cervix
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Impulses via somatic afferent nerve fibers reach paraventicular and supraoptic nuclei of hypothalamus
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These impulses releases oxytocin.
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Oxytocin causes contraction of uterus and enhances labor