Adrenal Physiology

Related Subjects: |Adrenal Physiology |Addisons Disease |Phaeochromocytoma |Adrenal Adenomas |Adrenal Cancer |Cushing Syndrome |Cushing Disease |Congenital Adrenal hyperplasia |Primary hyperaldosteronism (Conn's syndrome) |ACTH |McCune Albright syndrome

Aide memoir - GFR for Glomerulosa (Mineralocorticoids = aldosterone), Fasiculata (cortisol), Reticularis (androgens)

About

• Composed of medulla 10% and cortex 90%
• Also called suprarenal and are found above the kidneys
• Arterial supply from renal arteries
• Venous drainage to IVC on the right and Renal vein on left
• Involved in blood pressure control and steroid production

Diagram

Adrenal Cortex Structuire

• Glomerulosa: Mineralocorticoid aldosterone - Na uptake and K release
• Fasiculata (Cortisol) : affect carbohydrate, lipid and protein metabolism
• Reticularis (androgens) : weak until converted peripherally into testosterone and dihydrotestosterone

Biochemistry

• All steroids hormones are formed from cholesterol
• Cholesterol is released from lipids by cholesterol esterase (+ ACTH and + AgII)
• Cholesterol converted to pregnenolone in mitochondria. Then modified to either glucorticoid, mineralocorticoid or androgen.

Control

• Corticotropin-releasing factor (CRF) from the hypothalamus stimulates ACTH secretion from the pituitary
• This in turn stimulates cortisol and androgen production by the adrenal cortex

Cortex

• Cortisol is produced by the zona fasciculata of the adrenal cortex
• Cortisol secretion is pulsatile every hour with a peak in the morning
• Levels are highest in the morning so replacement tries to mimic this
• Cortisol is excreted as urinary free cortisol and 17-oxogenic steroids.
• Adrenal hypofunction best stimulated with a short synthetic ACTH test
• Adrenal hyperfunction is best inhibited with Dexamethasone suppression test

Function

• Aldosterone is produced and released by the zona glomerulosa by the effect of the RAA system
• Cortisol is produced and released by the zona fasciculata by the effect of ACTH
• Androgens are produced and released by the zona reticularis by androgen stimulating hormone (still being determined)

Adrenal Medulla

• Adrenaline
• Noradrenaline
• Dopamine

Adrenal Receptors

• Alpha-1 (Agonist = phenylephrine)
  • Vasoconstriction
  • Relaxation of GI smooth muscle
  • Salivary secretion
  • Hepatic glycogenolysis
• Alpha-2 (Agonist = clonidine)
  • Mainly presynaptic: inhibition of transmitter release (inc NA, Ach from autonomic nerves)
  • Inhibits insulin
  • Platelet aggregation
• Beta-1 (Agonist = dobutamine)
  • Mainly located in the heart
  • Increased heart rate + force
• Beta-2 (Agonist = salbutamol(Albuterol))
  • Vasodilation and Bronchodilation
  • Relaxation of GI smooth muscle