Peritubular Capillary Circulation
In normal man approximately 120 ml/min are filtered, but only 1 ml/min is excreted as urine. Thus over 99 percent must be reabsorbed, removed from the kidney and returned to the systemic circulation. There has been considerable recent interest in the role played by the peritubular environment, especially as it is influenced by renal haemodynamics, in the control of net reabsorption of salt and water from the proximal tubule. The concept that has evolved reflects the possibility that changes in colloid osmotic pressure and hydrostatic pressure in tubular capillaries can influence proximal tubular reabsorption. Peritubular capillary pressure is among the lowest in the body: for example, Wunderlich and Schnermann (1969) and Falchuk and Berliner ( 1971) applied a new, remarkably sensitive pressure measuring device to assess peritubular capillary pressure in the rat kidney, and found a pressure of 65 i 0-5 mmHg, about 20-25 per cent of the value in typical systemic capillaries. Simila