Question

Describe the function of the HPG axis and its role in regulation.

a. What exactly, is the HPG axis?

b. How does it regulate hormone release in males? In females?

c. How do the hormones regulated by the HPG axis influence spermatogenesis and oogenesis?

d. How long does it take to establish a balance of hormone regulation in males? In Females? Why?

Answer 1

a. the relationship between hypothalamus and pituitary gland is called hypothalamo-hypophyseal relationship/ HPG axis.hormones secreted by hypothalamus are transported to anterior pituitary and posterior pituitary.but the mode of transport of these hormones are different.

hormones from hypothalamus are transported to anterior pituitary through hypothalamo-hypophysealportal blood vessels . but , the hormones from hypothalamus to posterior pituitary are transported by nerve fibres of hypothalamo-hypophyseal tract.

RELEASING AND INHIBITORY HORMONES SECRETED BY HYPOTHALAMUS

1. GROWTH HORMONE RELEASING HORMONE(GHRH) : stimulates the release of growth hormone

2.GROWTH HORMONE RELEASING PEPTIDE(GHRP): stimulates the release of GHRH and growth hormone

3.GROWTH HORMONE INHIBITORY HORMONE(GHIH)OR SOMATOSTATIN:inhibits the release of growth hormone

4.THYROTROPIC RELEASING HORMONE(TRH):stimulates release of thyroid stimulating hormone

5. corticotropin releasing hormone(CRH): stimulates release of adrenocorticotropin

6.GONADOTROPIN RELEASING HORMONE(GnRH): stimulates release of gonadotropins

7. PROLACTIN INHIBITORY HORMONE(PIH): inhibits prolactin secretion

b. hypothlamus stimulates gonadotropin releasing hormone ieFSH and LH

FSH: FOLLICLE STIMULATING HORMONE

IN MALES : FSH acts along with testosterone and accelerates the process of spermiogenesis

females

i causes the development of graafian follicle from primordial follicle

ii stimulates the theca cells of graafian follicles and cause secretion of estrogen

iii promotes the aromatase activity in granulosa cells , resulting in conversion of androgen to estrogen

LH: LUTEINIZING HORMONE

in males LH known as interstitial cell stimulating hormone because it stimulates interstitial cells of leydig in testis.

in females:

i causes maturation of vesicular follicle into graafian follicle

ii induces synthesis of androgen from theca cells of growing follicles

iii is responsible for ovulation

iv is necessary for formation of corpus luteum

v activates the secretory functions of corpus luteum.

c. LH stimulates the leydig cells for the secretion of androgens which in turn stimulates the process of spermatogenesis.

FSH stimulates the sertoli cells for spermiogenesis.

the LH surge induces rupture of graafian follicle and release of an ovum.