cortisol is secreted by the adrenal gland

Cortisol: A Hormone Secreted by the Adrenal Gland

The adrenal gland plays a crucial role in regulating various bodily functions, including stress response and metabolism. One of its key hormones is cortisol, which is secreted by the adrenal gland in response to adrenocorticotropic hormone (ACTH) produced by the pituitary gland.

Feedback Inhibition and Circadian Rhythm

The secretion of cortisol is closely regulated by ACTH, with plasma cortisol levels parallel to those of ACTH. This feedback inhibition ensures that cortisol production remains within a narrow range, preventing excessive or deficient levels in the body. Additionally, the hypothalamic-pituitary-adrenal (HPA) axis responds to stress stimuli, leading to increased cortisol secretion.

Adrenal Androgens: A Key Role

Dehydroepiandrosterone (DHEA), its sulfate ester DHEA-S, and androstenedione are the most abundantly produced steroids by the adrenal cortex. These hormones have minimal intrinsic androgenic activity but are converted in tissues to more potent male sex hormones such as testosterone and dihydrotestosterone.

Biosynthesis of Cortisol

Synthesis of cortisol begins with cholesterol, which is stored as cholesterol-esters in lipid droplets within adrenocortical cells. Low-density lipoprotein (LDL) accounts for about 80% of cholesterol delivered to the adrenal gland, while synthesis within the gland from acetate also occurs.

Regulation by ACTH and the Hypothalamus

ACTH is regulated by the hypothalamus and central nervous system (CNS) via neurotransmitters, corticotropin-releasing hormone (CRH), and arginine vasopressine (AVP). Excess or deficiency of this hormone can alter the structure and function of adrenal zones.

Adrenal Cortex Layers

The adrenal cortex is arranged as three major layers or zones: zona fasciculata, zona reticularis, and zona glomerulosa. The zona fasciculata produces cortisol and androgens, while the zona reticularis also produces glucocorticoids and androgens. The zona glomerulosa produces mineralocorticoids such as aldosterone.

Medulla: Production of Epinephrine and Norepinephrine

The medulla is responsible for producing epinephrine (adrenaline) and norepinephrine (noradrenaline), which play crucial roles in the body's response to stress.

In conclusion, cortisol is a hormone secreted by the adrenal gland that plays a vital role in regulating various bodily functions. Its secretion is closely regulated by ACTH and the hypothalamus, ensuring that plasma cortisol levels remain within a narrow range. Understanding the biosynthesis, regulation, and function of cortisol is essential for appreciating its importance in human physiology.

Cortisol is secreted by the adrenal gland