1. The Microcirculation & Lymphatic System

2. Structure of the Microcirculation Capillary System Metarterioles Precapillary sphincter Large “preferential channels” Small “true capillaries”

3. Structure of the Microcirculation Venule Arteriole Preferential Channel Metarteriole Precapillary Sphincter True Arterioles

4. Structure of the Microcirculation Basement Membrane (Collagen Type I) Vesicular Channel? Endothelial Cell Intercellular Cleft Plasmalemmal Vesicles (1 Endothelial Cell Thick)

5. Transport Mechanisms Diffusion Intercellular Clefts Plasmalemmal Vesicles “Tight Junctions” (brain) Open Junctions (liver) Fenestra (kidney)

6. Capillary Vasomotion Intermittent flow regulated by precapillary sphincters. Controlled by O 2 concentration.

7. Diffusion through Capillary Membrane Lipid soluable – through endothelial cell membrane. Water soluable – through intercellular pores Size Dependent

8. Diffusion through Capillary Membrane This figure illustrates that the permeability of substances through capillary membrane decreases roughly with the logarithm of size.