Question

You have learnt that a characteristic feature of endocrine system is the presence of feedback loops. By this what is meant if hormone A stimulates gland ‘X’ to secrete hormone B, the production of ‘A’ could be modified when the level of B changes in our blood.

An example is the relation between hormones LH and estrogen (E2). An old woman exhibits the following features. High levels of LH in blood but low levels of E2 in the blood. Another woman exhibits high level of LH in blood and also high level of E2 in the blood. Where is the defect in both these women? Provide suitable diagram to support this answer.

Answer 1

Feedback mechanism:

When the secretion of hormones is under the control of factors or other hormones it is called feedback control.

• Negative feedback: It usually involves attaining homeostasis by maintaining a constant level of hormones in the blood. If there is a high concentration of hormone B in our blood, it will have an inhibitory effect on the secretion of hormone A. Decreased secretion of A will eventually result in a decrease in the production of hormone B.
• Positive feedback: It usually involves production of a response that continues to intensify to achieve the desired effect. The hormone signals the system to produce and release an increased amount of that hormone. If there is a high concentration of hormone B in our blood then it will have a stimulatory effect on the secretion of hormone A. Increased secretion of A will eventually result in increased hormone B production.

Relation between LH and Estrogen (E2):

LH and estrogen production follow negative feedback mechanism:

• Hypothalamus releases gonadotropin releasing hormones which acts on the pituitary.
• Release of FSH and LH from the anterior lobe of the pituitary occurs.
• They stimulate the ovaries to release estrogens.
• Increase in the level of estrogens will inhibit hypothalamus to release the gonadotropin releasing hormones. Also it results in inhibition of release of FSH and LH from the pituitary, thereby normalising the level of estrogens.

Case 1:

Old woman Low level of estrogen (E2) should stimulate the secretion of LH from the anterior pituitary. But the old woman has low levels of estrogen (E2) and high levels of hormone LH. This means that LH is not stimulating the gland, X, to secrete hormone E2. There may be a defect in the glandular receptors of LH.


Case 2:

Younger woman High levels of E2 should have negative feedback control on secretion of LH which can result in decrease in production of E2. But this woman shows a high level of both E2 and LH. This implies some defect in the negative feedback loop. The receptors of the pituitary or hypothalamus might be non-responsive to the negative feedback given by high levels of E2. More amounts of GnRH may have been produced by the hypothalamus causing more LH and thus more E2.