Physiology of Finfish and Shellfish (2+1)

5.3.3. Hypothalamus, pituitary and each of the glands they control

5.2.3. Hypothalamus, pituitary and each of the glands they control

1. Somatotrophs (STH cells) or growth hormone (GH): These hormones are secreted by somatotroph cells and are mainly found in pars distalis and are released under the influence of hypothalamic Growth Hormone Releasing Hormone (GHRH) or inhibited by hypothalamic Somatostatin. These hormones increase growth rate and basal metabolic rate of fish body. Growth is retarded in a hypophysectomised (Hypophysectomy or hypophysis is the removal of the pituitary gland) fish and injection of GH in such a fish causes increase in length. It is believed that increase in length of teleosts by GH is caused by increasing appetite and protein synthesis and by stimulating synthesis and release of insulin.
2. Prolactin (PRL): Prolactin (PRL), also known as 'Luteotropic' hormone (LTH). It is released by lactotroph cells under the influence of multiple hypothalamic Prolactin Releasing Factors (PRH). These cells secrete prolactin hormone which is involved in osmoregulation and influences movement of water and sodium through gills, kidney and urinary bladder or it is concerned with the regulation of the level of sodium in blood plasma. This hormone is also believed to influence lipid metabolism and storage of fat. Thyroxine level of serum is reduced by prolactin. A prolactin releasing inhibiting hormone (PIH) is reported to control the secretion of prolactin in fishes.
3. Melanocyte-Stimulating Hormone (MSH): This influences the pigments of the skin i.e., darkening of skin in fishes. (Hormones of Pars intermedia- 2 hormones Melanophore Dispersing Hormone (MDH) and Melanophore Concentrating Hormone (MCH) are secreted in this region. These influences the pigments of the skin i.e., darkening of skin in fishes).
4. Thyrotrophs or Thyroid Stimulating Hormones (TSH): It is released by the thyrotroph cell of adenohypophysis under influence of hypothalamic Thyrotropin Releasing Hormone (TRH) . It stimulates the thyroid gland to secrete thyroxine. TSH is in turn controlled by thyroxine. It also controls overall metabolic process of the body.
5. Gonadotrophs (FSH and LH cells): There are two 'Gonadotropins' and are released by the gonadotroph cell. The gonadotrophic hormones of the pituitary gland appear to be regulated by the gonadotrophic releasing hormone (GnRH) identified in different locations of the teleostean brain. Besides, a gonadotrophic inhibiting hormone (GIH) is also present in the brain of teleosts. LH and FSH from the anterior pituitary stimulate the gonads (ovaries and testes). Follicle cell stimulating hormone controls development of follicles in fishes and sperm formation. Leutinizing hormone (also referred to as 'Lutropin' or 'LH' or in males, 'Interstitial Cell Stimulating Hormone' (ICSH) controls ovulation and spermatogenesis. Both released under influence of Gonadotropin Releasing Hormone (GnRH).
6. Corticotrophs or Adrenal Corticotrophic Hormone (ACTH): It is released by corticotroph cells under influence of hypothalamic Corticotropin Releasing Hormone (CRH). It controls secretion of adrenal gland. Some investigators have found that the adrenocorticotropic hormone (ACTH) is also under the control of hypothalamus and a corticotrophin releasing factor (CRF) is present in the extracts of telencephelon ( The anterior portion of the forebrain).