Question

Describe how each of these two factors differently influence the secretory rate of FSH and LH:

1. Testosterone:

2. FSH:

Answer 1

Ans: Reproductive system consists of two main organs i.e. ovary and testis which regulate the different hormones related to reproduction and sexual activities.

Hypothalamus pituitary gonadal axis: It consists of three major endocrine glands i.e., Hypothalamus, pituitary gland and gonadal glands. Hypothalamus pituitary gonadal axis plays a very essential role in development, growth, reproduction and aging of individuals. This HPG axis controls the various organ systems in our body such as the reproductive system and immune system.

Gonadotropin releasing hormone secretion is stimulated by GnRH expressing neurons which is located in the brain and causes the production of GnRH from the hypothalamus.Gonadotropin releasing hormone: Gonadotropin hormones is peptide hormone produced and secreted by the anterior pituitary gland, which enhances the secretion of sex hormone by acting on the gonads ie, testis in males and ovaries in females. There are two main gonadotropin releasing hormones which directly act on testis and ovaries are luteinizing hormones (LH) and Follicle stimulating hormone (FSH).

These two hormones Play essential role in regulating and interacting with gonads.

In male, the HPG axis causes the secretion of FSH and LH from the hypothalamus and anterior pituitary and which act on sertoli cells. Sertoli cell is a type of sustentacular cell located in seminiferous tubules of testicles. Then these sertoli cells secrete the androgen binding protein which increases the binding of testosterone. And the another hormone LH binds to the interstitial cell, which leads to secretion of testosterone. Testosterone is necessary during spermatogenesis and inhibition of hypothalamus. Inhibin is secreted from the sertoli cell to inhibit the secretion from hypothalamus.

In females, HPG axis secrete the FSH and LH from hypothalamus and anterior pituitary, which act on the ovaries to produce estrogen and inhibit and regulate the uterine cycle and ovarian cycle. By positive feedback mechanism the FSH, LH and estrogen, the maturation of follicles occurs inside the ovary and prepares the uterus for ovulation and implantation. After the maturation, the egg is released from the ovary and follicles become empty. These empty follicular sacs release progesterone hormone, which inhibits the hypothalamus in turn the positive feedback mechanism of estrogen and LH is stopped. If egg and sperm are fertilized, then secretion of progesterone takes place by placenta and mother is not ovulated again. If fertilization does not occur, gradually the progesterone level decreases and again activation of positive feedback mechanism of estrogen and LH from hypothalamus. FSH and LH also control the menstrual cycle or uterine cycle and causes the proliferative phase, in which preparing for ovulation, secretory phase in which ovulation occurs and shedding of endometrial blood vessels or menstruation in which conception does not occur. By the negative feedback mechanism, estrogen blocks the secretion of GnRH from hypothalamus. And the activin which is produced by peripheral tissue causes the secretion of GnRH are inhibited by inhibin and follistatin.

HPG axis, regulates the puberty in both males and females, also controls the secondary sexual characteristic in both. During puberty HPG axis is activated then it is present throughout the life in male, but in females it is deregulated. After some time the hormone secretion becomes low due to the lack of primary oocyte and leads to menopause in females.