Adrenocorticotropic Hormone
Adrenocorticotropic Hormone
Adrenocorticotropic hormone (ACTH), also known as corticotropin, is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It plays a crucial role in the hypothalamic-pituitary-adrenal axis, stimulating the adrenal cortex to secrete glucocorticoids, primarily cortisol.
Structure[edit | edit source]
ACTH is a peptide hormone consisting of 39 amino acids. The sequence of ACTH is highly conserved across species, reflecting its essential role in stress response and metabolism. The first 13 amino acids of ACTH are identical to the sequence of α-melanocyte-stimulating hormone (α-MSH), which explains some of the overlapping functions of these hormones.
Function[edit | edit source]
The primary function of ACTH is to regulate the levels of the steroid hormone cortisol, which is released from the adrenal cortex. Cortisol is vital for maintaining homeostasis, influencing metabolism, immune response, and stress response. ACTH binds to the melanocortin receptor 2 (MC2R) on the adrenal cortex, triggering a cascade of reactions that lead to the synthesis and release of cortisol.
Regulation[edit | edit source]
ACTH secretion is regulated by the hypothalamus through the release of corticotropin-releasing hormone (CRH). CRH is released in response to stress and low blood cortisol levels. ACTH secretion follows a circadian rhythm, with levels peaking in the early morning and declining throughout the day.
Clinical Significance[edit | edit source]
Abnormal levels of ACTH can lead to various disorders. Excessive production of ACTH can cause Cushing's syndrome, characterized by high levels of cortisol, leading to symptoms such as weight gain, hypertension, and glucose intolerance. Conversely, insufficient ACTH production can result in Addison's disease, characterized by low cortisol levels, leading to fatigue, weight loss, and hypotension.
Diagnostic Use[edit | edit source]
ACTH levels can be measured in the blood to help diagnose adrenal and pituitary disorders. The ACTH stimulation test is used to assess adrenal gland function by measuring cortisol response to synthetic ACTH.
Also see[edit | edit source]
- Corticotropin-releasing hormone
- Cushing's syndrome
- Addison's disease
- Hypothalamic-pituitary-adrenal axis
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