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Adrenal Gland Physiology

Adrenal Gland Physiology

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Adrenal Gland
Comprises an inner medulla and an outer cortex.
Medulla
  • Accounts for approximately 20% of the total adrenal tissue.
  • Is neuroectodermal origin
  • Secretes the catecholamines:
Epinephrine Norepinephrine
Cortex
  • Accounts for the other 80% of the adrenal gland.
  • It is of mesodermal origin.
  • Secretes:
Mineralocorticoids. Glucocorticoids. Androgens.
Cortical Hormones
  • Hormonal secretion is triggered by ACTH stimulation (from anterior lobe of pituitary)
  • Secretes steroid hormones; cholesterol is common precusor.
  • Enzyme availability accounts for differential hormonal production in the cortical layers.
Zona reticularis
  • Primarily produces androgens
Includes DHEA and androstenendione, which are precursor hormones that can be converted to testosterone and estradiol; thus, they are a non-gonadal source of "sex-steroids."
Zona fasciculata
  • Primarily produces glucocorticoids, including cortisol, which has multiple effects throughout the body: increases gluconeogenesis and glycogen storage, suppresses the inflammatory response, and maintains vascular response to catecholamines. Thus, it is secreted in response to mental or physical stressors.
Zona glomerulosa
  • Produces mineralocorticoids
  • Specifically, angiotensin II (which we discuss in renal physiology), drives the production of aldosterone, which increases sodium reabsorption and potassium secretion in the late distal tubules and collecting ducts of the nephron;
Thus, it is secreted in response to decreased extracellular fluid volume to conserve body water.
Clinical Correlations:
Adrenal cortex malfunction has deleterious effects; these effects are predictable based on the source of the deficiency.
Primary adrenocortical insufficiency, aka, Addison's disease
  • The destruction of the adrenal cortex inhibits hormone production.
  • A distinguishing characteristic of this disorder is that ACTH levels are high, which causes hyperpigmentation. In healthy individuals, circulating cortical hormones inhibit secretion of ACTH from the anterior pituitary via negative feedback; in the absence of cortical hormone production, ACTH secretion goes unchecked.
Secondary adrenocortical insufficiency
  • ACTH secretion is insufficient to stimulate conversion of cholesterol for production of the cortical hormones.
Incidentally, aldosterone levels may be normal, because its production does not depend on increased levels of ACTH.
Cushing's Syndrome
  • Refers to collection of signs and symptoms caused by excess cortisol production:
Hypertension, hyperglycemia, muscle wasting, "moon face," and central obesity (fat deposits disproportionally at the core).
  • Excessive cortisol production can be caused by a variety of factors, including glucocorticoid drugs or pituitary tumors (Cushing's disease).
  • Drugs that reduce cortisol secretion can be used to counteract some of these effects.
Tumor pathophysiology

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