Adrenocorticotropic Hormone (ACTH)

Definition

Adrenocorticotropic hormone (ACTH) is a peptide hormone produced by the anterior pituitary gland that stimulates the adrenal cortex to release glucocorticoids, primarily cortisol. This hormone plays a crucial role in the stress response and regulates various physiological processes such as metabolism, immune response, and blood pressure by promoting the production of cortisol in response to stressors.

5 Must Know Facts For Your Next Test

1. ACTH is secreted in response to corticotropin-releasing hormone (CRH) released from the hypothalamus, forming part of the hypothalamic-pituitary-adrenal (HPA) axis.
2. Elevated levels of ACTH are often seen in conditions like Cushing's disease, which is characterized by excessive cortisol production.
3. In addition to stimulating cortisol release, ACTH can also promote the production of adrenal androgens and aldosterone to some extent.
4. The secretion of ACTH follows a diurnal rhythm, peaking in the early morning and reaching its lowest levels at night.
5. Stressful stimuli such as physical injury or emotional stress can lead to increased ACTH secretion, resulting in higher cortisol levels to help manage the body's response to stress.

Review Questions

• How does ACTH function within the hypothalamic-pituitary-adrenal axis to regulate stress responses?
  • ACTH plays a pivotal role in the hypothalamic-pituitary-adrenal (HPA) axis by mediating the body's response to stress. When faced with stressors, the hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the anterior pituitary to secrete ACTH. This hormone then acts on the adrenal cortex to promote cortisol release, which helps mobilize energy reserves, modulate immune functions, and maintain homeostasis during stressful situations.
• Discuss how negative feedback mechanisms involving ACTH and cortisol contribute to homeostasis in the body.
  • Negative feedback mechanisms are critical for maintaining hormonal balance and homeostasis within the body. When cortisol levels rise due to ACTH stimulation, elevated cortisol levels signal both the hypothalamus and anterior pituitary to decrease CRH and ACTH secretion respectively. This feedback loop prevents excessive cortisol production and ensures that energy resources are managed effectively during periods of stress while minimizing potential harmful effects of prolonged high cortisol levels.
• Evaluate the impact of abnormal ACTH levels on health and how they relate to various endocrine disorders.
  • Abnormal ACTH levels can significantly impact health, leading to conditions such as Cushing's disease or Addison's disease. Elevated ACTH is typically associated with excess cortisol production, resulting in symptoms like weight gain, hypertension, and weakened immune function. Conversely, low ACTH levels can indicate adrenal insufficiency or secondary adrenal failure due to insufficient stimulation from the pituitary gland. Understanding these relationships is essential for diagnosing endocrine disorders and managing patient care effectively.

Related terms

Cortisol: A steroid hormone produced by the adrenal cortex that helps regulate metabolism, immune responses, and blood pressure, playing a key role in the body's response to stress.

Hypothalamus: A region of the brain that controls the pituitary gland and regulates various bodily functions, including temperature, hunger, thirst, sleep, and hormonal output.

Negative Feedback: A regulatory mechanism in which an increase in a product or output inhibits its own production or release, helping maintain homeostasis within the endocrine system.