Compare and contrast renal and hepatic blood flow and its regulation
Another fundamental physiology topic that required candidates to understand, and
synthesize knowledge from multiple areas. Generally well done with some very good
answers. A tabular format worked well. Candidates were expected to mention values for
renal and hepatic flow (total flow, % of cardiac output and oxygen consumption), basic
anatomical comparisons, distribution (e.g. renal cortex 95% , renal medulla 5%,), two
capillary beds (glomerular and peritubular) for renal, and hepatic triad and sinusoids for the
liver, function (filtration for renal blood flow and metabolic activity for hepatic) and
regulatory mechanisms for each (e.g. myogenic, autonomic, metabolic and humoral for
both and tubuloglomerular feedback for renal).
These college comments are commendably detailed, and they were used to compose the answer included here, as they are helpfully prescriptive about the format and content. With the local renal section in advanced stages of decomposition, the author had no original thoughts about the kidney, and referred extensively to Judith Askew's excellent answer.
| Domain | Hepatic circulation | Renal circulation |
| Anatomy of blood supply | Portal vein (70%) Hepatic artery (30%) |
Renal arteries (100%) |
| Blood flow (ml/min) | total = 1500 ml/min | total = 1100 ml/min |
| Blood flow (% of CO) |
25% of cardiac output | 20% of cardiac output |
| Venous drainage | Hepatic veins | Renal veins |
| Oxygen consumption | 6ml O2/100g/min | 2ml O2/100g/min |
| Blood flow distribution | Arterial and portal venous blood mix in hepatic sinusoids | 95% of flow goes to the renal cortex, 5% to medulla |
| Capillary beds | Hepatic sinusoids (large diameter low-pressure capillaries with discontinuous endothelium) | Glomerular capillary bed; peritubular capillary bed |
| Function | Metabolic activity Blood storage reservoir |
Filtration Clearance of waste substances |
| Regulatory mechanisms | Portal venous flow regulation:
Hepatic arterial flow regulation:
|
Local arterial autoregulation:
Systemic autoregulation:
Extrarenal factors affecting flow:
|
Eipel, Christian, Kerstin Abshagen, and Brigitte Vollmar. "Regulation of hepatic blood flow: the hepatic arterial buffer response revisited." World journal of gastroenterology: WJG 16.48 (2010): 6046.
Abshagen, K., et al. "Anatomy and physiology of the hepatic circulation." PanVascular Medicine (2015): 3607-3629.
Greenway, C. V., and R. D. Stark. "Hepatic vascular bed." Physiological reviews 51.1 (1971): 23-65.
Dancygier, Henryk. "Hepatic Circulation." Clinical Hepatology. Springer, Berlin, Heidelberg, 2010. 55-
Wilkinson, Grant R., and David G. Shand. "A physiological approach to hepatic drug clearance." Clinical Pharmacology & Therapeutics 18.4 (1975): 377-390.