DETERMINANTS OF LYMPH FLOW AND COMPOSITION

Abstract

According to Starling's hypothesis, the rate of fluid movement across capillary walls depends on the balance of hydrostatic (P) and colloid osmotic (Π) forces. Under normal conditions, a small net loss of fluid from the capillaries is compensated for by lymphatic drainage of leaked fluid and solutes from the interstitium. Filtration rate and lymph flow can be increased by raising capillary hydrostatic pressure or by lowering plasma colloid osmotic pressure or by combinations of these procedures. The results of a study described in the chapter show that the increase in lymph flow for a given decrease in transcapillary colloid osmotic pressure difference is 1.4 to 1.8 times as great as that produced by an equivalent increase in hydrostatic pressure. For a given increase in lymph flow, decreasing colloid osmotic pressure produces a larger increase in blood–lymph protein clearance. Both these observations are contrary to expectation based on fluid and protein transport through large pores or channels, with low reflection coefficients for plasma proteins.