Question

Discuss the 3 ways that hormones are regulated and give an example of each.

Answer 1

The three ways how the secretion of hormones is regulated are-

1. Negative feedback- This is the most fundamental control mechanism. Changes induced by a hormone in the target tissue are monitored and they cause reverse inhibition of hormone. For example, a decrease in postprandial glucose inhibits insulin secretion or reaching adequate plasma concentrations of cortisol and corticosterone inhibits the secretion of adrenocorticotropic hormone from adenohypophysis. Similar principle is used for modulation of thyroid hormones production – hypothalamic TRH (thyrotropin-releasing hormone) stimulates the secretion of TSH (thyroid-stimulating hormone) from the pituitary gland, which stimulates cells of the thyroid gland to produce thyroxine and triiodothyronine. These hormones then cause feedback inhibition of the secretion of TSH and TRH.

Here the control variable is often one that is self regulated. This prevents hormone hypersecretion because when target level of control variables is reached down to maintanence level.

2. Positive feedback- A special control mechanisms which leads to cyclic changes, each potentiates the next until it reaches the level leading to a qualitative change in control system. Here the control variable does not inhibit the production of the hormone, but rather leads to further potentiation.

Example is ovulation, during which luteinizing hormone synthesized in gonadotropes in in adenohypophysis stimulates estrogen production in the ovaries. They again stimulate the production of luteinizing hormone until the critical concentration is reached, which leads to rupture of the follicle and release oocyte.

3. Cyclic changes- This can be due to change in sleep, changing of the seasons of the year and our development and aging. These changes are usually based on the activity of central nervous system pathways that change over time of day, cycle sleep and throughout the year.

Example- secretion of growth hormone which reaches its peak during the early stages of sleep, but as sleep progresses it returns again to maintanence level.