Lymph Formation and Flow

Abstract

It is now recognized that the physiological roles of lymphatic vessels and lymphoid tissues may be considered separately. Getti et al ( 1 6), in a recent review, focused on the complicated topic of lymphoid tissues and immune reactions, aspects of the lymphatic system not considered here. An earlier review by Allen (I) discussed lymph formation in some peripheral sites and problems of clinical interest arising from disorders in this mechanism. Witte & Witte (60) reviewed the role lymphatics perform in the regulation of interstitial fluid volume and considered how disorders in this process lead to tissue edema. In the same series of papers, Taylor et al (57) considered in detail how Starling forces are involved in lymph formation and how interstitial fluid enters the lymphatic capillaries. In a symposium held at Bad Biirk­ heim in 1972, the major factors involved in capillary-interstitum-lymphatic ex­ changes were reviewed in considerable detail. The proceedings of this conference (17) give a concise and readable overview of the structures and activities involved in these exchanges and provide excellent bibliographies for the different topics considered. The present review is divided into two parts. The first portion deals with contribu­ tions to lymph formation and lymph flow from studies at the microscopic level of the peripheral lymphatics mainly as found in the thin wing membrane of some bat species. The remaining section reviews the recent contributions implicating lymph formation and flow as a significant basic factor in the fluid exchange between blood and interstitium. Sites in mammals where the initial elements or capillary units of the lymphatic system are available for direct observation and study are few. These initial Iymphat-