Renal & Adrenal Endocrinology — Adrenal & Aldosterone

Adrenal Gland

• Wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule.
• Blood flow:
  • have one of the greatest blood supply rates per gram of tissue of any organ: up to 60 small arteries may enter each gland
  • Artery → Cortex → Medulla → Veins
  • Three arteries:
    • Superior Suprarenal A. (Br. Of Inferior Phrenic)
    • Middle Suprarenal A. (Br. Of Aorta)
    • Inferior Suprarenal A. (Br. Of Renal Artery)
  • One Suprarenal on each side:
    • Rt Suprarenal drains into IVC
    • Lt Suprarenal drains into Lt renal V.or Lt Inferior Phrenic V.

The gland can be divided into:

• Adrenal cortex
  • component of the hypothalamic-pituitary-adrenal (HPA) axis
  • secretes steroid hormones important for the regulation of the long-term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation.
• Adrenal medulla
  • neuroendocrine tissue composed of postganglionic sympathetic (SNS) neurons
  • The sympathomedullary (SAM) pathway involves the stimulation of the medulla by impulses from the hypothalamus via neurons from the thoracic spinal cord.
  • The medulla is stimulated to secrete the catecholamine hormones epinephrine and norepinephrine.

Mineralocorticoids (Aldosterone)

Aldosterone is the key mineralocorticoid hormone, accounting for 95% of mineralocorticoid activity:

• Release is stimulated by:
  • Increased serum K⁺
  • Increased Angiotensin II
    • Hypovolaemia
    • Decreased osmolarity
  • Increased ACTH
  • Decreased serum pH
• Acts to increase sodium and water retention (and removal of potassium), via:
  • Increased expression and activation of Na⁺/K⁺ pumps on the basolateral membrane of DCT and CT cells, causing increased Na⁺ (and water) reabsorption and K⁺ elimination
  • Stimulation of the Na⁺/H⁺ pump in intercalated cells on the DCT
  • upregulates epithelial sodium channels (ENaCs) in the collecting duct and the colon, increasing apical membrane permeability for Na+ and thus absorption.
  • increases Na⁺ (and water) reabsorption in exchange for K⁺ (kidney, gut, salivary, sweat)

Sources:
https://opentextbc.ca/anatomyandphysiology/chapter/17-6-the-adrenal-glands/
https://cnx.org/contents/FPtK1zmh@7.28:kaX2y2XZ@3/The-Adrenal-Glands

JC 2019

Answer by JC