QS Study

Control of Hormone Secretion

A hormone is a chemical substance that is secreted into the internal body fluid by one cell or group of cells and exerts a physiological control effect on other cells of the body. It affects our body’s functions, from growth and sexual development and mood to how well we sleep, how we manage stress, and how our body breaks down food.

Two control systems –

(A) Feed hack control of hormone secretion:

(i) Negative feedback mechanism: Most endocrine glands are under negative feedback control that acts to maintain homeostasis, i.e., prevents deviation from an ideal value.

  • The endocrine gland has a natural tendency to over secrete its hormone.
  • So, the hormone exerts more and more control effect on the target organ.
  • Target organ then performs its function.
  • As much function occurs, organ exerts a signal which causes a negative effect on the gland to decrease the rate of secretion.

(ii) Positive feedback mechanism:

In a few instances, positive feedback occurs when the biological activity of the hormone causes additional secretion of the hormone. Positive feedback systems are much less common although they do exist. e.g., LH surge occurs due to the stimulatory effect of estrogen, on the anterior pituitary gland before ovulation. The secretion LH acts on ovaries to stimulate additional secretion of estrogen which in turn causes more secretion of LH.

(iii) A cyclical variation occurs in hormone release:

Periodic variation in hormone release are influenced by seasonal changes, various stages at development and aging, the diurnal (daily) cycle or sleep.

e.g., Secretion of growth hormone is markedly increased during the early period of sleep but is reduced during the later stage of sleep.

(B) Direct control and regulation of secretion of hormone: In a few instances, conc. of a certain substance in blood directly controls the hormone secretion.

e.g., Insulin from β cell of the pancreas is promoted by increased blood glucose level.

Glucagon from α cell is promoted by decreased blood glucose level.

An important factor to be controlled usually not the secretory rate of the hormone itself but the degree of activity of the target organ.