Veterinary Physiology-III

GENERAL INFORMATION

• The hypothalamus is located adjacent to the third ventricle in the forebrain and is connected by the hypophyseal stalk to the pituitary gland (hypophysis cerebri) immediately inferior to it.
• The hypothalamus receives input from various regions of brain, sensory signals from visceral organs and retina. Hypothalamus controls autonomic nervous system, regulates body temperature, thirst, hunger, sexual behaviour and defense reactions like fear and rage.
• Hypothalamus forms the critical link between the nervous system and the endocrine system. The hypothalamus regulates both autonomic nervous activity and several aspects of endocrine function. The latter role is fulfilled through its links with the pituitary gland, which secretes a wide range of hormones.
• Hypothalamus - monitors the state of the body’s internal environment by analyzing negative feedback (eg. various concentrations of chemicals in the blood) and regulates the pituitary gland.
• Secretory neurons in the arcuate, paraventricular, supra optic nuclei and preoptic area of hypothalamus synthesize and secrete seven neurohormones called hypophysiotropins otherwise known as hypothalamus‑releasing hormones/fac­tors (RH or RF) and hypothalamus inhibitory hormones or factors (IH or IF). These hypothalamic hormones pass via the hypophyseal portal system to pituitary gland and regulate the release of all the six hormones of the adenohypophysis. Regulation of the anterior pituitary secretions is mediated by the reciprocal actions of RH or IH of the hypothalamus and the concentrations of hormones of the pituitary gland
• The releasing hormones of hypothamus include
  • Growth Hormone‑Releasing Hormone (GHRH/ GRH): Increases the release of GH
  • Thyroid Stimulating Hormone–Releasing Hormone (TRH): Increases the release of TSH
  • Corticotropin‑ Releasing Hormone (CRH): Increases the release of ACTH
  • Gonadotropic ‑ Releasing Hormone ( GnRH/LHRH): Increases release of FSH and LH
  • Prolactin-Releasing Hormone (PRH): increases release of prolactin
• The inhibitory hormones of hypothamus include
  • Somatostatin (SRIF/ GHIH): Inhibits the release of GH.
  • Prolactin Release Inhibitory Hormone (PIH-Dopamine): Inhibits the prolactin secretion
• The hormones released by the neurohypophysis – Oxytocin and ADH, are actually formed in the paraventricular and supaoptic nuclei of hypothalamus. They then travel via nerve fibres to the neurohypophysis for storage until release.