Hormones in Reproduction
Gonadotropin-Releasing Hormone (GnRH)
Gonadotropin-Releasing Hormone is produced by the hypothalamus. The target organ of GnRH is the anterior pituitary gland (APG). In females, GnRH stimulates the release of stimulating hormone (FSH) and luteinizing hormone (LH) from the APG. The release of FSH and LH initiates puberty and sustains female reproductive cycles. However, the release of the hormone is pulsatile. In males, FSH and LH are released from the APG through the work of GnRH initiating puberty.
Follicle-Stimulating Hormone (FSH)
Follicle-stimulating hormone (FSH) is produced by the anterior pituitary gland (APG). FSH stimulates the ovaries in females and testes in males to produce another hormone. In Females FSH does the following:
- Stimulates the final maturation of follicle.
- Stimulates growth and maturation of Graafian follicles before ovulation takes place.
In males FSH stimulates the release of testosterone in the Leydig cells of the testes.
Luteinizing Hormone (LH)
LH is another hormone produced by the Anterior Pituitary Gland that in return stimulates the ovaries in females and testes in males. In males luteinizing hormone stimulates the Leydig cells of the testes to secrete and release testosterone. In females LH does the following:
- Stimulates final maturation of follicle.
- Causes ovulation by the surging LH levels 14 days before the next menstrual period.
- Stimulates the alteration of Graafian follicles to corpus luteum. Corpus luteum continues to secrete estrogen and progesterone for about 12 days if no fertilization occurs. If the ovum is not fertilized, placenta gradually takes over this function.
The hormone estrogen is both produced in male and female body. In the early stages of menstrual cycle estrogen is produced by the ovaries. In the latter part of menstrual cycle, when the Graafian follicle is transformed into corpus luteum, estrogen is produced by the corpus luteum. During pregnancy the placenta is responsible for releasing this hormone. In males, it is formed in small quantities from testosterone in Sertoli cells of testes. Also, other tissues such as the liver, produces estrogen in small quantities in males.
The target organs of estrogen in females are the internal and external reproductive organs and the breast. In males, estrogen plays a vital role for normal sperm formation in the testes. The actions of estrogen in females are:
- Development and maturation of the reproductive organs at puberty.
- Stimulates the endometrium before ovulation.
- Initiates fat deposition at the breasts during puberty.
- Induces the growth of ductal and glandular tissues of the breasts.
- Stimulates the growth of long bones but causes the closure of epiphyses, thus, restricting mature height.
- Promotes uterine and breast tissue growth during pregnancy.
- Inhibits active breast milk production during pregnancy.
- Relaxes pelvic ligaments during pregnancy.