Q.You have learnt that a characteristic feature of endocrine system is the presence of feed back 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.

The two women show defects at different points of the LH-estrogen feedback loop.

• The old woman (high LH, low E2): her ovary is no longer responding properly to LH stimulation and is not producing adequate estrogen; because low estrogen fails to hold back pituitary LH secretion, LH stays persistently high — a pattern consistent with declining ovarian function with age.
• The second woman (high LH and high E2 together): normally, once estrogen rises it should feed back and restrain further LH release; here LH stays high despite high estrogen, pointing to a failure of the normal feedback control at the hypothalamus-pituitary level rather than a problem with the ovary itself. …

The endocrine system's feedback loops work in a specific direction: hormone A (here, LH from the pituitary) stimulates a gland X (the ovary) to secrete hormone B (estrogen), and the level of B then feeds back to modify further production of A. Under this loop, an abnormal reading tells us where along the chain the fault lies.

In the old woman, LH is high but estrogen (E2) is low. Since LH is present and should be stimulating the ovary, but estrogen output stays low, the defect points to the ovary itself failing to respond to LH stimulation — it is not producing estrogen despite adequate stimulating hormone. Because low estrogen does not exert its usual restraining feedback on the pituitary, LH secretion continues unchecked, which is why LH stays elevated.

In the second woman, both LH and estrogen are high together. Here the ovary is clearly responding and producing estrogen normally, since E2 is elevated. But normally, once estrogen rises sufficiently, it should feed back on the hypothalamus and pituitary to restrain further LH release. Since LH remains high despite high estrogen, the defect in this case lies not in the ovary but in the feedback-sensing machinery at the hypothalamus/pituitary level, which is failing to respond to and be restrained by the elevated estrogen. …