Adrenocorticotropic hormone (ACTH)

Definition

Adrenocorticotropic hormone (ACTH) is a peptide hormone produced by the anterior pituitary gland that stimulates the adrenal cortex to release cortisol, a key hormone in the body's stress response. It plays a central role in the hypothalamic-pituitary-adrenal (HPA) axis, which regulates various physiological processes related to stress and metabolism, making it crucial for maintaining homeostasis during stressful situations.

5 Must Know Facts For Your Next Test

1. ACTH is secreted in response to stress signals received by the hypothalamus, which produces corticotropin-releasing hormone (CRH).
2. Elevated levels of ACTH lead to increased production of cortisol from the adrenal glands, which helps the body respond to stress by mobilizing energy resources.
3. The release of ACTH follows a circadian rhythm, with higher levels typically present in the early morning and lower levels at night.
4. Chronic stress can result in prolonged high levels of ACTH and cortisol, which can have negative effects on health, including immune suppression and increased risk for various diseases.
5. Dysregulation of ACTH secretion can be linked to conditions such as Cushing's disease, where excess cortisol is produced due to an ACTH-secreting tumor.

Review Questions

• How does ACTH function within the HPA axis during a physiological stress response?
  • ACTH plays a crucial role in the HPA axis by being released from the anterior pituitary gland in response to corticotropin-releasing hormone (CRH) from the hypothalamus. This release is triggered by stress signals and prompts the adrenal cortex to secrete cortisol. Cortisol then acts to mobilize energy and regulate other bodily functions to help cope with stress, illustrating how ACTH mediates the physiological adaptations required during stressful situations.
• Discuss the implications of chronic stress on ACTH secretion and its potential health effects.
  • Chronic stress leads to sustained high levels of ACTH secretion, which results in prolonged production of cortisol from the adrenal glands. This persistent elevation can cause various health issues, including immune system suppression, increased risk of metabolic disorders, and mood disturbances. Understanding this relationship highlights the importance of managing stress effectively to prevent adverse health consequences linked to dysregulated ACTH levels.
• Evaluate the role of ACTH in the feedback mechanisms of the HPA axis and how this influences overall homeostasis.
  • ACTH is integral to the feedback mechanisms of the HPA axis, as it not only stimulates cortisol release but is also regulated by feedback from cortisol levels themselves. When cortisol levels are adequate or elevated, they inhibit further secretion of CRH from the hypothalamus and ACTH from the pituitary gland. This feedback loop is essential for maintaining homeostasis; it ensures that cortisol levels do not become excessively high, which could lead to detrimental health effects. Disruption in this feedback mechanism can result in disorders like Cushing's disease or adrenal insufficiency.

Related terms

Cortisol: A steroid hormone released by the adrenal cortex in response to ACTH, playing a vital role in regulating metabolism, immune response, and stress.

Hypothalamus: A brain region that secretes corticotropin-releasing hormone (CRH), which stimulates the release of ACTH from the anterior pituitary gland.

HPA Axis: The hypothalamic-pituitary-adrenal axis is a complex set of interactions between the hypothalamus, pituitary gland, and adrenal glands that controls stress responses and various bodily functions.