Capillary Diffusion, Osmotic Pressure, and Starling’s Law

Abstract

Abstract In order to function, cells are required to move materials in and out of their cytoplasm via their cell membranes. Diffusion is the movement of particles from an area of higher concentration to lower concentration, whereas osmosis is movement of fluid across a semi-permeable membrane. The exchange of gases between the alveoli and the blood occurs by simple diffusion, i.e., oxygen diffusing from the alveoli into the blood and carbon dioxide from the blood. Starling forces (hydrostatic pressure and osmotic pressure) govern the passive exchange of water between the capillary microcirculation and the interstitial fluid. This chapter describes the various degrees of interaction of these forces that govern the movement of fluid and gases in the human body.