Endocrine physiology of the hypothalamus
Hypothalamic neurons secrete RH-releasing hormones and IRH-inhibiting hormones that inhibit or stimulate anterior pituitary activity.
The hypothalamus is a structure of the midbrain, located around the third ventricle and in the middle of the limbic system, closely related to the pituitary gland through blood vessels and nerves, forming the hypothalamic axis. The target pituitary gland regulates the endocrine functions of the body.
The neurons of the hypothalamus, in addition to the function of transmitting nerve impulses, also have the function of synthesizing and secreting hormones.
Hormones secreted by the hypothalamus follow vascular and neural pathways to store or affect (stimulate or inhibit) pituitary function.
Release and Inhibitory Hormones
The hypothalamic neurons secrete RH (Releasing Hormone) and Inhibiting Releasing Hormone (IRH) inhibitory hormones that inhibit or stimulate anterior pituitary activity.
Release and inhibitory hormones after synthesis from the neuron body, are transferred down the axon to store in the medial convex region. Here, hormones diffuse into the first capillary network and then follow the hypothalamic-pituitary portal system to the anterior pituitary.
Thyrotropin Releasing Hormone (TRH) is a 3-amino acid peptide that stimulates the pituitary gland to secrete TSH (Thyroid Stimulating Hormone).
CRH (Corticotropin-releasing hormone) is a polypeptide consisting of 41 amino acids, which stimulates the pituitary gland to secrete ACTH (Adrenocorticotropic Hormone).
GnRH (Gonadotropin-Releasing Hormone) is a 10-amino acid peptide that stimulates the pituitary gland to secrete FSH (Folicle-Stimulating Hormone) and LH (Luteinizing Hormone).
GRH (Growth Releasing Hormone) is a peptide with 10 amino acids that stimulates the pituitary gland to secrete GH (Growth Hormone).
PIH (Prolactin Inhibitor Hormone) of unknown structure, inhibits the pituitary secretion of Prolactin.
Finally, the IRHs (Somatostatin) are GIH (Growth Inhibitor Hormones) that inhibit the synthesis and release of GH.
These hormones are mainly regulated by negative feedback mechanisms as described above, regulatory signals coming from the pituitary or other endocrine glands.
Neurons of the supraoptic and paraventricular nuclei in the hypothalamus also secrete two hormones, ADH (Antidiuretic hormone or Vasopressin) and Oxytocin, which are synthesized in the cell body and transported along nerve fibres, to storage in the brain. posterior pituitary.
The chemical nature and regulation of secretion of these two hormones will be discussed in the section on posterior pituitary hormones.