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Renal Circulation: Blood Supply, Measurement, and Autoregulation

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  1. RENAL CIRCULATION

  2. Specific learning objectives • Blood supply to the kidney • Special features of renal circulation • Measurement of renal blood flow

  3. Blood supply of Kidney Renal Blood vessels

  4. Blood supply of Kidney

  5. Special features • Renal blood flow is about 1200 ml per minute(300ml/100gm) representing 25 per cent of cardiac output. • The arterio-venous difference in blood oxygen content is low in renal blood vessels (19ml% – 17.5ml%) • Oxygen consumption very high (6ml/100g/min)

  6. Special features • (A-V)O2 difference does not change in spite of alteration of blood flow. • Cortical blood flow is more than medulla • Portal system • High capillary hydrostatic pressure (45mmHg) • Three types of capillaries

  7. Measurement • Direct method • Electromagnetic flowmeter, Doppler method • Indirect method - Fick’s principle

  8. Measurement • Applying the Fick principle • Renal plasma flow can be measured by infusing para-aminohippuric acid (PAH) and determining its urine and plasma concentrations PAH clearance

  9. Measurement • Concentration of PAH in urine (UPAH): 14 mg/mL • Urine flow : 0.9 mL/min • Concentration of PAH in plasma (PPAH): 0.02 mg/mL •   =630 mL/min

  10. Autoregulation Blood flow is maintained at a constant level despite the change in the systemic pressure range between 80-180 mm Hg

  11. Features of Autoregulation • It is a characteristic feature of cortical and outer medullary renal blood flow • Renal autoregulation is present in denervated and in isolated, perfused kidneys • But is prevented by the administration of drugs that paralyze vascular smooth muscle. • Autoregulation is absent below 80 and above 180 mm Hg of renal perfusion pressure

  12. Autoregulation • Myogenic theory • Tubuloglomerular feedback mechanism • Metabolic mechanism – NO, prostagladins, adenosine • Neural regulation • Hormonal regulation

  13. Tubuloglomerular Feedback Stimulate Macula Densa (chemoreceptor)

  14. Summary

  15. References • Comprehensive Textbook of Medical physiology (Vol 2, 1stedition) G K Pal • Text book of medical physiology (Vol 2, 6thedition) A K Jain • Essentials of medical physiology (6thedition) K Sembulingam and PremaSembulingam

  16. Thank you

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