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Adrenocorticotropic Hormone (ACTH)

Adrenocorticotropic Hormone (ACTH)

Author: Aaron Mullally
Description:

- know what gland secretes ACTH

- know what the cells are that produce ACTH

- know what the target organ for ACTH is

- know what the effects of ACTH are

- know how ACTH secretion is regulated

This packet covers the basics of ACTH

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Tutorial

ACTH Overview

ACTH is synthesized and secreted by corticotropes of the anterior pituitary gland. The target tissue for this hormone is the adrenal cortex. To really understand this concept focus on the name of the hormone: adren/o = adrenal gland; cortico = cortex (cortex = outer covering); -tropic = trophic hormone.

ACTH exerts its effects primarily on the zona fasiculata and zona reticularis of the adrenal cortex.In the zona fasiculata ACTH stimulates the synthesis and secretion of the glucocorticoid cortisol. Cortisol is nicknamed the stress hormone and is also the negative feedback mechanism that lowers the secretion of ACTH from the pituitary. In the zona reticularis ACTH is needed to start the utilization of cholesterol for steroid hormone synthesis. Without ACTH the zona reticularis is unable to synthesize androgens (sex steroids).

Exogenous and endogenous stress (external and internal sources of stress) disrupt the body's ability to maintain homeostasis. When we go through stress we initiall utilize catecholamines (NE & epi) to counteract the stressful stimulus through the fight or flight respons. The catecholamines however cause some major physiologic changes to the body, especially in how we utilize substrates (fuels) for energy. We must compensate for this by utilizing cortisol to counteract the effects of the catecholamines. So when we are stressed the hypothalamus will secrete corticotropin-releasing hormone (CRH) into the portal system and stimulate the corticotropes of the hypothalamus to secrete ACTH. Once cortisol levels rise in the blood, the hypothalamus will slowly stop secreting CRH which will cause a drop in ACTH.

Source: Mind of Aaron

ACTH

Source: Self made

ACTH

Source: Self made