Chapter 3.3, Problem 3AYLO

Summary Introduction

To discuss:

Simple diffusion, factors that determine its speed, and examples of its physiological and clinical relevance.                             

Introduction:

Cells are regarded as the simplest unit (structural and functional) of life. Cellular membrane, nucleus, and cytoplasm are the three major components of a cell. Cellular membrane, which surrounds the entire cell, is composed of phospholipids and proteins. By defining the cell’s boundary, the plasma membrane controls the intake of substances into the cell and releases substances out of the cell. This selectively permeable membrane is a phospholipid bilayer with proteins inserted in it. It acts as both wall and gateway between the extracellular fluid and the cytoplasm. Both passive mechanisms (diffusion, filtration, and osmosis) and active transports are involved in the transport of a few molecules across the cell membrane. It permits the passage of some substances (wastes and nutrients), while hindering the passage of other substances (phosphates and proteins).