EXCHANGE OF SUBSTANCES THROUGH CAPILLARY WALLS 



A. 



971 



16 



'140 



fig. 2.6. Left: small vessel pressure and flow response to a low-frequency stimulation of the 

 ipsilateral lumbar sympathetic trunk (15 v, 1 stimulation/to sec for 1 min) Aortic pressure (A), 

 small artery pressure (a), small vein pressure (»), and small vein flow (/•') against atmospheric 

 pressure. Numerals on pressure tracings indicate pressure in mm Hg. Numerals on flow tracing 

 represent flow in ml/min. Timer set at 10 sec. Rig/it: same but with high frequency stimulation 

 (15 v, 10 stimulations/sec for 1 min). Symbols same except that F is small artery flow proximal to 

 distal segment. [From Davis & Hamilton (66).] 



fig. 2.7. Effects on resistance and capacitance vessels and net transcapillary fluid shift produced 

 by maximal lumbar vasoconstrictor fiber stimulation at different frequencies. Changes in blood 

 flow reflect effects on resistance vessels (inflow and outflow pressures kept constant). The initial 

 and rapid decreases in volume reflect effects on capacitance vessels and the subsequent slower and 

 continuous decreases in volume (slopes indicated by dashed lines), transcapillary influx of extra- 

 vascular fluid. Reductions in mean hydrostatic capillary pressure calculated in approximate figures. 

 [From Mellander (243).] 3 



nephrine was also constrictor and produced absorption 

 of fluid. Acetylcholine increased blood flow markedly 

 but produced less filtration than small doses of epi- 

 nephrine. Presumably capillary pressure increased 

 very little because pre- and postcapillary resistances 

 were reduced equally. Johnson and Hanson ( 1 68a) 

 have recently applied the isogravimetric technique 



to a study of pre- and postcapillary resistance in the 

 intestine of the dog. In this preparation, the isogravi- 

 metric capillary pressure is only about 65 per cent of 

 the plasma protein osmotic pressure, probably reflect- 

 ing the higher permeability to protein of intestinal 

 capillaries. The postcapillary resistance to blood flow 

 through the intestine was increased markedly when 



