The Anterior Lobe - essential facts (iii)

The anterior lobe secretes six neurohormones.

1. ACTH - Adrenocorticotropic Hormone (Adrenocorticotropin)
2. TSH - Thyroid Stimulating Hormone (Thyrotropin)
3. GH - Growth Hormone
4. Prolactin
5. FSH - Follicle Stimulating Hormone
6. LH - Luteinising Hormone

Additional Information

ACTH - Adrenocorticotropic Hormone (Adrenocorticotropin)

• peptide (39 amino acids).
• secretion is regulated by corticotropin-releasing hormone (CRH) from the hypothalamus which is released during physiological stress e.g. pain, trauma, hypovolaemia.
• CRH releases ACTH and ß-endorphin.
• ACTH stimulates the synthesis and secretion of glucocorticoids (cortisol) by adrenal cortex.
• cortisol is the major regulator of adaptive responses to stress e.g. maintenance of blood glucose levels, conservation of fluid, cardiovascular and behavioural changes.

TSH - Thyroid Stimulating Hormone (Thyrotropin)

• glycoprotein.
• secretion and synthesis of TSH is regulated by thyrotropin-releasing hormone (TRH) from the hypothalamus when circulating levels of thyroid hormones are low or by cold exposure.
• TSH stimulates synthesis and release of thyroid hormones thyroxine (T₄) and triiodothyronine (T₃).
• T₄ and T₃ stimulate cell metabolism and increase heat production.

GH - Growth Hormone

• polypeptide (191 amino acids); half-life 20 minutes.
• secretion and synthesis of GH is regulated by two hormones secreted by the hypothalamus :
  • growth hormone-releasing hormone (GRH)
  • somatostatin which is inhibitory.
• GH has growth promoting effects (stimulates protein synthesis) in many somatic tissues.

Prolactin

• polypeptide (198 amino acids); half-life 30 - 50 minutes.
• secretion and synthesis of prolactin is regulated by prolactin inhibiting hormone (PIH), and oestrogen (stimulatory) during pregnancy. Suckling also stimulates prolactin release.
• stimulates milk production during lactation.
• inhibits LH and FSH production causing cessation of menstrual periods.

FSH - Follicle Stimulating Hormone

• secretion and synthesis of FSH is regulated by gonadotropin-releasing hormone (GnRH)
• FSH stimulates growth and secretion of ovarian follicles in females and the production of sperm in males

LH - Luteinising Hormone

• In females
  • a surge of LH (and FSH to a lesser degree) in the middle of the menstrual cycle triggers ovulation and the conversion of ovarian follicles into corpus luteum.
• n males
  • LH (or ICSH - Interstitial cell stimulating hormone) acts on Leydig cells in the testes and stimulates the synthesis and secretion of male sex hormones (testosterone).