Adrenal gland

In mammals, the adrenal glands (also known as suprarenal glands or colloquially as kidney hats) are the triangle-shaped endocrine glands that sit atop the kidneys; their name indicates that position (ad, "near" or "at" + renes, "kidneys"). They are chiefly responsible for regulating the stress response through the synthesis of corticosteroids and catecholamines, including cortisol and adrenalin.

Adrenal cortex

Situated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.

Related Topics:
Mineralocorticoid - Glucocorticoid - Aldosterone - Cortisol - Androgen

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The cortex can be divided into three distinct layers of tissue based on cell type and function:

Related Topics:
Tissue - Cell

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• zona glomerulosa - mineralocorticoid production, primarily aldosterone
• zona fasciculata - glucocorticoid production, mainly cortisol (roughly 95%)
• zona reticularis - androgen production, including testosterone

All the adrenocortical hormones are synthesised from cholesterol. Cholesterol is transported into the inner mitochondrial membrane by Steroidogenic Acute Regulatory Protein (StAR), where it is converted into pregnenolone by the enzyme CYP11A. Accordingly, production of hormones in all three layers of the adrenal cortex is limited by the transportation of cholesterol into the mitochondria and by its conversion there into pregnenolone.

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Pregnenolone can then be either dehydrogenated to progesterone or hydroxylated to 17-alpha-hydroxypregnenolone. The steps up to this point occur in many steroid-producing tissues. Subsequent steps, however, only occur in the adrenal cortex.

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• Progesterone ->(hydroxylation at C21)-> Deoxycorticosterone ->(two further hydroxylations)-> Aldosterone
• Progesterone -> (hydroxylation at C17)-> 17-alpha-hydroxyprogesterone ->(hydroxylation)-> Deoxycortisol ->(hydroxylation)-> Cortisol

Zona glomerulosa

In response to increased potassium levels or decreased blood flow to the kidneys, cells of the zona glomerulosa secrete the mineralocorticoid aldosterone into the blood as part of the renin-angiotensin system. Aldosterone regulates the body's concentration of electrolytes, primarily sodium and potassium, by acting on the distal convoluted tubule of kidney nephrons to:

Related Topics:
Potassium - Aldosterone - Renin-angiotensin system - Electrolyte - Sodium - Distal convoluted tubule - Nephron

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• increase potassium excretion
• increase sodium reabsorption
• increase water reabsorption through osmosis

Zona fasciculata

Cortical cells responsible for the production of glucocorticoids are the primary effectors of adrenocorticotropic hormone (ACTH). The hypothalamus secretes corticotropin-releasing hormone which stimulates the anterior pituitary gland to release ACTH; another hypothalamic hormone, arginine vasopressin (AVP) augments ACTH secretion, with the two together stimulating larger release than ACTH in isolation. ACTH acts on the adrenal cortex to stimulate the release of glucocorticoids. This three-organ endocrine system is commonly called the hypothalamic-pituitary-adrenal axis.

Related Topics:
Adrenocorticotropic hormone - Hypothalamus - Corticotropin-releasing hormone - Anterior pituitary gland - Arginine vasopressin - Hypothalamic-pituitary-adrenal axis

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The primary glucocorticoid released by the adrenal gland is cortisol. Upon binding to its target, cortisol enhances metabolism in several ways:

Related Topics:
Cortisol - Metabolism

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• stimulating the release of amino acids from the body
• stimulating lipolysis, the breakdown of fat
• stimulating gluconeogenesis, the production of glucose from newly-released amino acids and lipids
• conserving glucose by inhibiting uptake into muscle and fat cells

Zona reticularis

Cells of the zona reticularis provide a secondary source of androgens such as testosterone, dihydrotestosterone (DHT), androstenedione, and dehydroepiandrosterone (DHEA). These enhance muscle mass, stimulate cell growth, and aid in the development of the secondary sexual characteristics.

Related Topics:
Testosterone - Dihydrotestosterone - Androstenedione - Dehydroepiandrosterone - Muscle - Cell growth - Secondary sexual characteristics

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