Renal Regulation of ECF Volume

Natriuresius: with positive Na balance there is an increase in ECF volume which causes an increase in Na excretion
Effective Circulating Volume: the portion of the ECF that is contained within the vascular system and is effectively perfusing tissue
1. Varies directly with ECF volume, blood pressure and cardiac output
Volume Sensing Systems
1. CARDIOVASCULAR
  1. Baroreceptors
  2. Stretch receptors
  3. Pressure receptors
  4. 5% change in pressure is required to evoke a response
2. Alters (decreases) sympthetic activity and ADH secretion
  1. afferent arteriole constricted by alpha adrenergic receptor
    1. Decreases hydrostatic pressure within glomerular capillary lumen
      1. Decrease in GFR
        Filtered Na is reduced
        Renin secreted
        increased SNS activity drceases excretion of Na to restore ECF
3. JUXTAGLOMERULAR APPARATUS: decrease in pressure causes secretion of renin
4. Atrial myocytes release peptide hormone ATRIAL NATRIURETIC PEPTIDE ANP during volume expansion
  1. Antagonises renin-AII-aldosterone system
    1. Afferent dilation to increase GFR so more Na is filtered
      1. Inhibits renin secretion to reduce aldosterone release
        reduces ADH release
        Inhibits Na reabsorbtion in collecting duct
    2. Raises cGMP levels

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