EFFECTIVE SOLUTES
& WATER TRANSPORT

LEARNING OBJECTIVES

• Explain osmosis
• Contrast osmolarity and tonicity
• Explain how effective solutes regulate
fluid compartments of the body.

GENERAL CONCEPTS

1. The two fluid compartments of the body, intracellular
fluid (ICF) and extracellular fluid (ECF), are in osmotic
balance.
2. Water moves by facilitated diffusion through
aquaporin channels across most cell membranes. This
process is called osmosis.
3. Non-permeable solutes are called effective solutes.
Cellular volume is critically dependent on the steady state
of effective solutes and water across the cell membrane
in exchange with the extracellular fluid compartment (ECF).
4. Cells shrink in hypertonic ECF conditions. Cells swell in
Hypotonic ECF conditions.