Control and Co-ordination — BIOLOGY STD 12 Science — Question

I. Somatotropic Hormone (STH) or Growth Hormone (GH):

1. The secretion of GH is under dual control of hypothalamus through GHRF (Growth hormone releasing factor) and GHIF (Growth hormone inhibiting factor).
2. The GH brings about general growth of the body.
3. The principal actions of GH Eire promotion of linear growth in the skeleton, increase in the size of the muscles and connective tissue.
4. GH enhances the protein synthesis. The lipolysis in adipose tissue to release more fatty acids is also stimulated by GH.
5. The growth of bones by absorption of calcium takes place due to GH.

II. Thyroid Stimulating Hormone (TSH) or Thyrotropin:

1. TSH is regulated by TRF (Thyrotropin releasing factor) from hypothalamus’
2. For inhibition there is a negative feedback between thyroxine level in the blood and secretion of TSH.
3. TSH stimulates thyroid glands to increase uptake of iodine for synthesis of thyroxine. It brings breakdown of colloid to release thyroxine.

III. Adrenocorticotropic Hormone (ACTH) Corticotropin :

1. ACTH stimulates growth of adrenal cortex Eind stimulates it to secrete glucocorticoids Eind mineralocorticoids.
2. The regulation of ACTH secretion is under the control of hypothalamic CRF (Corticotropin releasing factor) and the negative feedback mechanism between plasma level of cortisol and ACTH.

IV. Prolactin (PRL) or Luteotropic hormone (LTH):
1. Secretion of prolactin is under duad control by hypothalamus by two factors such as PRF (Prolactin releasing factor) and PIF (Prolactin inhibiting factor) of hypothalamus.2. Prolactin performs many functions therefore it has many terms as follows :

• Development of mammary glands (Mammo tropin).
• Milk secretion by mammary glands (Lactogenic hormone).
• Maintenance of corpus luteum so that- it keeps on secreting progesterone during pregnancy (Luteotropin).

3. It may be inhibiting the chances of pregnancy during lactation period.V. Gonadotropic Hormones (GTH) or Gonadotropins:
1. There are two types of gonadotropins, viz. FSH and LH or ICSH.2. The secretions of gonadotropin are regulated by gonadotropin releasing factor (GHRF) of hypothalamus.(3) They are regulated by negative feedback by sex hormones such as testosterone and estrogen.
(a) Follicle Stimulating Hormone (FSH):

• FSH in female stimulates development of Graafian follicles. It helps in the formation of ovum by stimulating oogenesis.
• It also stimulates ovarian follicular cells for secretion of female sex hormones, estrogen.
• Under influence of estrogen, development of secondary sexual characters occurs in female.
• In males, FSH stimulates germinal epithelium of seminiferous tubules for spermatogenesis and helps in the production and maturation of sperms.
• Deficiency of FSH leads to infertility in both the sexes.

(b) Luteinizing hormone (LH) in females and Interstitial cell stimulating hormone (ICSH) in males:

• LH brings about ovulation, i.e. rupture and release of ovum from the mature Graafian follicle. The empty Graafian follicle is transformed into corpus luteum.
• Corpus luteum is a secondary endocrine source which secretes gestational hormone progesterone. Progesterone is a pregnancy stabilizing hormone.
• In males, ICSH stimulates interstitial cells of Leydig which in turn secretes male sex hormone, the testosterone.
• Testosterone develops secondary sexual characters in males.
• High level of progesterone in female signals negative feedback, to pituitary to stop secretion of LH.
• In males, high level of testosterone in blood gives negative feedback signal to Inhibit the secretion of FSH.