General Physiology: Cell Membrane Transport, Homeostasis, and Blood Physiology

Passive transport

The random molecular movement of substances through intermolecular spaces in the cell membrane or in combination with a carrier protein, from areas of high concentration to areas of low concentration, driven by the kinetic energy of the molecules.

Simple diffusion

The transport of substances either directly through the lipid bilayer or through selective channel proteins of the cell membrane along an electrochemical gradient without requiring metabolic energy.

Facilitated diffusion

A form of carrier-mediated transport in which lipid-insoluble or large particles, such as glucose and amino acids, bind to a specific carrier protein on one side of the membrane, undergo a conformational change, and are released on the other side along their concentration gradient.

Osmosis

The net diffusion of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) across a partially permeable membrane.

Osmotic pressure

The exact amount of hydrostatic pressure required in a concentrated solution to prevent the inward movement of water across a semipermeable membrane, determined by the number of solute particles per unit volume of fluid.