Figure 625

Net movements of water across an epithelium are dependent on net solute movements. The active transport of sodium across the cells, into the surrounding interstitial spaces, produces an elevated osmolarity in this region and a decreased osmolarity in the lumen. This leads to the osmotic flow of water across the epithelium in the same direction as the net solute movement. The water diffuses through protein water channels in the membrane and across the tight junctions between the epithelial cells.

Facilitated diffusion

Blood -vessel

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART ONE Basic Cell Functions

I. Basic Cell Functions

6. Movement of Molecules Across Cell Membranes

© The McGraw-Hill Companies, 2001

Essentials of Human Physiology

Essentials of Human Physiology

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