Question

Your human body has two chemical messenger systems: Neurotransmitters and Hormones. 1) Where does each system primarily operate? 2) Which system is slower? 3) Briefly describe how the HPA axis uses three main structures to cause cortisol to be released into the bloodstream. 4) How does the HPA axis prevent itself from constantly releasing cortisol into the bloodstream once the threatening stimulus has gone away?

Answer 1

1) Where does each system primarily operate?

Neurotrasmitters primarily system is the nervous system, they are not used by any other system, though nervous system may signal other tissues with neurotransmitters.

Hormones primarily system is the endocrine system, this system is wide spread across the body in different organs, they signal other tissues through the release of hormones.

2) Which system is slower?

The endocrine (hormones) system is slower. The speed of action in neurotransmitters comes from the electrochemical potential used by neurons, this method travels really fast across the body, while endocrine system has to wait for the hormones to reach the target tissue through vascular system

3) Briefly describe how the HPA axis uses three main structures to cause cortisol to be released into the bloodstream.

This axis uses the Hypothalamus, Pituitary gland and Adrenal glands for this purpose, they function with some feedback events. The hypothalamus produces a hormone called corticotropin-releasing hormone (CRH), this one reaches the pituitary gland and stimulates it to produce adrenocorticotropic hormone (ACTH). This one reaches the adrenal glands and stimulates them to produce cortisol. Cortisol has a negative feedback over hypothalamus and pituitary gland, inhibiting the release of both CRH and ACTH.

4) How does the HPA axis prevent itself from constantly releasing cortisol into the bloodstream once the threatening stimulus has gone away?

Through the negative feedback cycle. Excess of cortisol inhibits the production of more cortisol by inhibiting the production of CRH and ACTH.