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In this article we will discuss about:- 1. Origin of Hypothalamus 2. Location and Structure of Hypothalamus 3. Hormones.
Origin of Hypothalamus:
Hypothalamus develops from the ectoderm of the embryo.
Location and Structure of Hypothalamus:
It lies below or inferior to the thalamus. It provides the anatomical connection between the nervous and endocrine systems. This connection is through the hypophysis (pituitary gland).
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The hypothalamus is connected to the anterior lobe of pituitary gland by hypophysial portal veins, however, it is connected to the posterior lobe of pituitary gland mainly by axons of neurosecretory cells. The hormones of the hypothalamus influence the functioning of the pituitary gland. The hypothalamus is often called the control centre or ‘supreme commander’ of endocrine regulation.
Hormones of Hypothalamus:
Cells in the hypothalamus synthesize at least nine different hormones. The neurosecretory cells (neurons) of hypothalamus secrete hormones called neurohormones (= releasing factors) which are summarised below.
(i) Adrenocorticotropic Releasing hormone (ARH) or Corticotropin Releasing Hormone:
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It stimulates the anterior lobe of the pituitary gland to secrete its adrenocorticotropic hormone (ACTH).
(ii) Thyrotropin Releasing Hormone (TRH):
It stimulates the anterior lobe of the pituitary gland to secrete its thyroid stimulating hormone (TSH) or thyrotropin.
(iii) Growth Hormone-Releasing Hormone (GHRH):
It stimulates the anterior lobe of the pituitary gland to release its growth hormone (GH) or somatotrophin.
(iv) Growth Hormone-Inhibitory Hormone (GHIH):
This hormone is also called somatostatin (SS). It inhibits the secretion of growth hormone from the anterior lobe of the pituitary gland.
(v) Gonadotropin Releasing Hormone (GnRH):
It stimulates the anterior lobe of the pituitary gland to secrete two gonadotropic hormones: (follicle stimulating hormone (FSH) and luteinizing hormone (LH)).
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(vi) Prolactin Releasing hormone (PRH):
It stimulates the anterior lobe of the pituitary gland to secrete its prolactin.
(vii) Prolactin Inhibitory Hormone (PIH):
It inhibits the secretion of prolactin from the anterior lobe of pituitary gland.
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(viii) MSH Releasing Hormone (MSHRH):
It stimulates the intermediate lobe of the pituitary gland to secrete its melanocyte stimulating hormone (MSH).
(ix) MSH Inhibitory Hormone (MSHIH):
It inhibits the secretion of melanocyte stimulating hormone from the intermediate lobe of the pituitary gland.
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Target Cells:
Neurohormones act on the cells of the pituitary gland.
