Micromanipulation of pressure in terminal lymphatics in the mesentery.

The terminal lymphatics are a network of highly previous vessels that are distributed in a loose association with the blood capillary bed, in particular along with the collecting venules. The base-line pressure in these lymphatics is close to atmospheric, but after they converge to form valved collecting channels PL is increased with a pressure differential of 1-2 cmH20 built up across each valve. This increment in lymphatic pressure is clearly related to the presence of one-way valves, the contractile activity of the collecting channels, and the comparative impermeability of these channels. The pressure differential required to draw fluid from the interstitium into the lymphatics would appear to reside in the vasomotor activity of the collecting channels, although the data do not rule out changes in Pt coincident with net capillary filtration or absorption.