Renal Physiology 02

Posted by e-Medical PPT Tuesday, July 17, 2012
Aims & Content of this lecture
To continue providing you with a refresher in renal physiology that later lectures covering renal measurement and pathophysiology will build upon.
The role of antidiuretic hormone (ADH)
The renin-angiotensin-aldosterone system (RAAS)
Role of the kidney in volume regulation
Control of acid-base balance by the kidneys
Final review of how the renal system interacts with the cardiovascular and respiratory systems.

ADH also needed to concentrate urine: how does it work?
Antidiuretic Hormone (ADH)/Arginine Vasopressin (AVP)
Increases permeability of collecting ducts to H2O by inserting H2O channels (Aquaporins).
Helps you make small amount of concentrated urine.
Reabsorption of H2O increase urea conc. in tubule, increasing its recycling effect.
ADH allows rapid, graded control of urine conc. – v. sensitive.
ADH released in response to plasma osmolality and ECF volume – osmoreceptors and baroreceptors.

Renin-angiotensin-aldosterone axis
Principal factor controlling Ang II levels is renin release.
Decreased circulating volume stimulates renin release via:
 Decreased BP (symp effects on JGA).
 Decreased [NaCl] at macula densa (“NaCl sensor”)
 Decreased renal perfusion pressure (“renal” baroreceptor)

Angiotensin II – important actions
Stimulation of aldosterone release from adrenal cortex.
Vasoconstriction of renal and other systemic vessels.
Enhanced tubuloglomerular feedback – makes macula densa more sensitive.
Enhance Na-H exchanger and Na channel function to promote Na reabsorption.
Renal hypertrophy.
Stimulates thirst and ADH release by acting upon hypothalamus..
  

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