The HPA axis is an important component of the vertebrate stress response. What d

Question

The HPA axis is an important component of the vertebrate stress response. What does HPA stand for? Explain the chain of events that leads to elevated blood glucose involving the HPA axis. This response pathway is also an excellent example of a negative feedback loop. Explain what is meant by a negative feedback loop and how does the HPA axis exemplify this? What other pair of hormones regulate blood glucose levels by antagonistic control? How (not just in which direction) do each of these hormones regulate blood glucose?

Explanation / Answer

HPA stands for hypothamic pituitary adrenal.

HPA axis is central stress response system .HPA is responsible for neurorndocribe adaptation of stress response .This response is characterised by release of CRH or CRF( corticotropin releasing hormone) by hypothamic release . ACTH IS released When CRH binds to CRH receptors on anterior pituitary gland .

ACTH binds to receptors on adrenal cortex and release cortisol. Cortisol is released untill the effect of stressor is controlled.

Increased production of cortisol during stress result in increased availability of glucose in order to facilitate fighting or fleeing .resulting in elevated production of glucose. So by this blood glucose levels rise.

At a certain blood concentration of cortisol this protection is ostensibly achieved and cortisol exerts negative feedback to hypothalamic release of CRH and ACTH release of pituitary gland. And then the hameostatis is returned.

Insulin and glucogen are two pair of antagonistic hormones that control blood glucose levels.

Glucogen is hyperglycemic and insulin is hypoglycemic hormone. Glucogen rise blood glucose levels by breakdown of glucogen into glucose,synthesis of glucose from lactic acid.

Insulin lowers blood glucose levels by enhancing membrane transport of glucose into most body cells , it inhabits the breakdown of glucogen into glucose. Inhabits conversion of amino acids and fats to glucose. So by this way they maintain blood glucose levels working antagonistic to each other.

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