Hypothalami-pituitary function

• The pituitary gland, also known as the hypophysis, lies in a little bone cavity called the pituitary fossa
• The pituitary gland is attached to the hypothalamus of the brain and is nicknamed the 'master gland'
• The pituitary gland secretes at least nine hormones that control metabolism, growth, development, reproduction, lactation, and water intake
• The pituitary gland is made of two lobes:

  • Anterior lobe (adenohypophysis) of non-neuronal origin
  • Posterior lobe (neurohypophysis) is an extension of the hypothalamus
• The posterior lobe (neurohypophysis) is made of nerve endings from specific hypothalamic neurons and glial-like cells called pituitocytes with no secretory function
• The nerve terminals in the posterior lobe release two small peptides: Oxytocin and Vasopressin (ADH)
• Oxytocin is important during and after parturition (child delivery and breastfeeding)
• Vasopressin (ADH) plays a crucial role in controlling the water content of the body
• Vasopressin (ADH) stimulates water reabsorption in the kidneys via V2 receptors and causes vasoconstriction via V1 receptors
• Vasopressin (ADH) is used therapeutically for diabetes insipidus and nocturnal enuresis, as a vasoconstrictor, and in conditions like septic shock
• Oxytocin stimulates contraction of the uterus during labor, milk ejection from mammary glands, and induces constriction of umbilical vessels
• Oxytocin is used therapeutically to stimulate contraction during delivery, assist breastfeeding, reduce postpartum bleeding, and in late therapeutic abortion
• The anterior lobe (adenohypophysis) of the pituitary gland contains at least five different types of glandular cells that secrete at least 7 hormones
• The anterior lobe secretes hormones like TSH, ACTH, LH, FSH, PRL, GH, and a-MSH that regulate various functions in the body
• Hypothalamic factors like TRH, GnRH, GHRH, GHIH, and Dopamine control the release of hormones from the pituitary gland
• GHRH stimulates the release and synthesis of growth hormone (GH) while GHIH inhibits the release of GH
• GH controls growth, tissue regeneration, protein synthesis, and metabolic effects in the body
• Alterations in GH production can lead to conditions like pituitary dwarfism, acromegaly, or giantism
• Treatment for GH-related disorders includes recombinant GH therapy and somatostatin analogues
• Acromegaly in adults and giantism in children are rare conditions caused by hypersecretion of GH
• ACTH stimulates the growth of adrenal cortex and the secretion of glucocorticoids
• The hypothalamic releasing factors are regulated by neuronal impulses, have pulsatile secretion, and are relatively small peptides
• The hypothalamic releasing factors include TRH, GnRH, GHRH, GHIH, and Dopamine, each controlling the release of specific hormones from the pituitary gland
• The pituitary gland plays a crucial role in the endocrine system by regulating various bodily functions through the secretion of hormones
• ACTH, a 39 amino acid peptide synthesized from a long precursor, stimulates the growth of adreno-cortical cells and synthesis of glucocorticosteroids
• CRH, a 41 amino acid peptide, stimulates the release of ACTH from corticotroph cells
• ACTH secretion has a daily rhythm driven by CRH, with the highest peak in the early morning
• Stress modulates ACTH secretion in the hypothalamo-pituitary-adrenal axis
• Cortisol levels feed back ACTH secretion, with a minimum production of ACTH in the middle of the night and a peak in the early morning
• Dopamine, secreted in pulses, strongly inhibits PRL secretion from the pituitary in the hypothalamo-pituitary control of lactation
• Prolactin (PRL) has similarities with GH, is secreted in pulses, and is strongly stimulated by suckling
• Main action of prolactin includes growth during puberty and pregnancy in mammary glands, and inhibition of gonadotropin release
• Hyperprolactinemia symptoms include galactorrhea, oligomenorrhea, amenorrhea, infertility, impotence, and gynecomastia
• TRH, a tripeptide, activates TSH from the pituitary in the hypothalamo-pituitary-thyroid axis
• GnRH, a decapeptide, stimulates the release of LH and FSH from gonadotroph cells in the hypothalamo-pituitary-gonadal axis
• Alterations in gonadotropin production can lead to precocious puberty
• Excessive secretion of pituitary hormones can lead to various pathologies, such as hypothyroidism, Cushing's disease, acromegaly, gigantism, and more
• Absence of growth hormone secretion can cause growth retardation and dwarfism
• Oxytocin can reduce pain during labor and is released by the posterior pituitary
• Prolactin can reduce fertility if oversecreted and stimulate milk ejection by contracting the mammary gland