Science World

Pituitary Gland and Hypothalamus

· The pituitary gland and hypothalamus act as a unit, regulating the most of the activity of the other endocrine glands.

Hypothalamus

Nuclei of the hypothalamus

Principles hypothalamic regulatory mechanisms

Function Integrating area

Temperature regulation Anterior hypothalamus - Heat

Posterior hypothalamus - Cold

Neuroendocrine function of,

Catecholamines Dorsal & Posterior hypothalamus

Vasopressin Supraoptic & Paraventricular nuclei

Oxytocin Supraoptic & Paraventricular nuclei

TSH via TRH Paraventricular nuclei & neighboring areas

ACTH via CRH Paraventricular nuclei

FSH & LH via GnRH Preoptic area, other areas

Prolactin via PIH & PRH Arcuate nucleus, other areas

Growth hormone via Somatostatin & GRH Paraventricular & Arcuate areas

Appetite behavior,

Thirst Lateral Superior hypothalamus

Hunger Ventromedial satiety center, Lateral hunger center

Sexual behavior Anterior ventral hypothalamus plus, in the male piriform cortex

Defensive reactions ( fear, rage) Diffuse in limbic system & hypothalamus

Control of various endocrine & activity

rhythms Suprachiasmatic nuclei

Control of posterior pituitary secretion

Vasopressin and Oxytocin

· Are neural hormones
· Are synthesized in the cell bodies of the magnocellular neurons in the supraoptic and the paraventricular nuclei
· Are secreted in response to electrical activity in the endings

Intraneural transport

The precursor molecules are synthesized in the ribosomes of the cell bodies in the neurons
They have their leader sequences removed in the ER, are packed into secretory granules in the Golgi apparatus
They are transported down the axons to the endings in the posterior pituitary
Cleavage of the precursor molecules occurs as they are being transported
The storage granules in the endings contain free vasopressin of oxytocin

Electrical activity of magnocellular neurons

· Oxytocin and Vasopressin secreting neurons generate and conduct action potentials

· Action potential reaching their endings trigger release of hormone from them by Calcium dependent exocytosis

Hormones of Posterior Pituitary

Vasopressin

Oxytocin

Vasopressin / Anti - diuretic Hormone (ADH)

· From the posterior lobe of the pituitary gland

· Sensory nerve cells in the hypothalamus (osmoreceptors) detect changes in osmotic pressure of the blood

· Nerve impulses from the osmoreceptors stimulate the release of ADH

· Increases the permeability of the collecting duct of the kidney, V2 receptors are activated and involved insertion of protein water channels in the luminal membranes of collecting duct cells

· The retention of water by the kidney

· Water enters the hypertonic interstitum of the renal pyramids

· The urine become concentrated and its volume decreases

Oxytocin

Stimulate two target tissues during and after parturition

Uterine smooth muscles : during child births, increased amounts of oxytocin are released in response to increasing distention of sensory stretch receptors in the uterine cervix by the baby’s head; more forceful uterine contractions and grater stretching of the uterine cervix.

Muscle cells of the lactating breast : contraction of the myoepithelial cells around the glandular cells and ducts of the lactating breast to contract , injecting milk