Juxtaglomerular apparatus region of aerent arteriole

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Unformatted text preview: eability to sodium, chloride, urea, and water • Blood in the vasa recta capillaries entering the medulla loses water and gains NaCl and urea progressively as it descends. • When blood flow in the vasa recta capillaries reverses direc*on and ascends from the medulla to the cortex, it progressively gains water and loses NaCl and urea, resul*ng in countercurrent exchange • This anatomical arrangement, combined with the rela*vely low blood flow to the medulla, permits sufficient perfusion for nutri*on without destroying the high osmolality of the medulla •  The main reason is to preserves Hyperosmolarity of the Renal Medulla ADH Regula*on of Water Reabsorp*on •  ADH (an*diure*c hormone) –  inser*on of aquaporins into the plasma membrane of tubule cells •  ↑ permeability of distal tubule and collec*ng duct walls to water •  ↑ H2O reabsorp*on = ↓ urine volume, ↑ urine concentra*on –  Secreted by anterior pituitary in response to s*mula*on of osmoreceptors in hypothalamus •  respond to elevated plasma osmolarity Fig 13.12 Renin ­Angiotensin ­Aldosterone System (RAAS) Cue: Decrease in BP or Vol Juxtaglomerular apparatus (JGA) Releases Renin Cleaves Angiotensinogen (released from Liver) Angiotensin I in presence of ACE (enzyme) Produces Angiotensin II (func*on as hormone) Raises the Blood Pressure by constric*ng Arterioles Subsequent decrease in blood flow to kidney Angiotensin IIS*mulates Adrenal Gland Release of Aldosterone (Acts on Nephron’s distal tubules) Reabsorbs more Na+ and H20 Increases BP and Vol Renin ­Angiotensin ­Aldosterone System •  Juxtaglomerular apparatus –  region of afferent arteriole that comes into contact w/ascending limb of Loop of Henle •  Releases renin (enzyme) into blood in response to ↓blood pressure –  Low Na+ levels contribute to low blood pressure •  Renin converts angiotensinogen (plasma protein)→ angiotensin I •  Angiotensin I converted to angiotensin II (fully ac*vated) by angiotensin conver4ng enzyme in lungs •  Angiotensin II s*mulates aldosterone release from adrenal cortex Aldosterone Influences Na+ and Water Reabsorp*on, K+ Secre*on •  Aldosterone s*mulates Na+ reabsorp*on and K+ secre*on by the distal tubule and upper (cor*cal) collec*ng duct) •  Elevated plasma K+ directly s*mulates adrenal cortex to...
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