Tutoring Biology 12, you cover LH and FSH.  Today, the biology tutor introduces them with reference to the male; the female will be next time.

FSH stands for follicle stimulating hormone.  To my knowledge, males don’t even have follicles; females do.  LH stands for luteinizing hormone; once again, the name refers to a structure found in the female reproductive system, rather than the male.  However, FSH and LH are used by the hypothalamus to control the reproductive function of both sexes. The hypothalamus does not release either LH or FSH; rather, it causes the pituitary to do so.  Negative feedback figures prominently in this control system.

In the male, LH targets the interstitial cells in the testis, causing them to release testosterone.  The hypothalamus monitors the testosterone level in the blood.  In answer to the testosterone level being correct, the hypothalamus relaxes its demand of the pituitary to release LH.  This situation can be referred to as negative feedback:  once the low level of testosterone is corrected, the hypothalamus stops its corrective action. Less LH means less stimulation of the interstitial cells, so they in turn produce less testosterone.   Yet, if the testosterone level falls again, the hypothalamus will once again cause the pituitary to release LH in order to stimulate the interstitial cells once more. So the cycle continues:  low level, corrective action, refreshed level, cease of corrective action, and so on.

FSH targets the seminiferous tubules in the testis, causing them to produce sperm and, at the same time, inhibin.  The blood’s inhibin level is monitored by the hypothalamus for the purpose of negative feedback.  Since the inhibin is produced alongside sperm, the hypothalamus can monitor the inhibin level in order to track the level of sperm production.

For a description of negative feedback, see my post here. For a treatment of the action of LH and FSH in the female, see my next post:)

Source: Mader, Sylvia S. Inquiry into Life, 11th edition. New York: McGraw-Hill, 2006.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.