Unit 1.5 - Epithelial Transport, Osmolarity, and Tonicity

Epitlelial Transport

The movement of substances across apical and basolateral membranes.

Requires different transporters to transport substances from the lumen into the cell and from the cell to the extracellular compartments.

Absorption = lumen to ECF.

Secretion = ECF to lumen.

Apical Membrane

the surface of the lining that faces the lumen of an organ.

Basolateral Membrane

the surface of the lining that faces the extracellular fluid.

Paracellular Transport

Transport through junctions between adjacent cells.

A type of epithelial transport.

Transcellular Transport

Transport through both the apical and basolateral membrane with the help of carrier proteins or transcytosis.

A type of epithelial transport.

Transcytosis

A combination of endocytosis, vesicular transport, and exocytosis.

Molarity

The amount of the solute / the amount of volume of the mixture.

Osmoles

1 mole of Na = 1 osmole of Na

1 mole of dissolved CaCl₂ = 3 osmoles of CaCl₂

osmole / L = osmolarity

osmole / kg H₂O = osmolality (preffered, it is independent of temperature)

Tonicity

The effect of a solution on the cellular volume.

Have to consider the ability of the solute to cross the cell membrane.