Maintaining the Body's Chemistry:
Dialysis in the Kidneys

Authors: Rachel Casiday and Regina Frey

Key Concepts: Semipermeable mebranes; polarity; diffusion and concentration gradients; dynamic equilibrium.

Blood contains particles of many different sizes and types, including cells, proteins, dissolved ions, and organic waste products. It is the job of the kidneys to remove the harmful particles from the blood and regulate the blood's ionic concentrations, while keeping the essential particles in the blood. The kidneys meet these challenges through a remarkably elegant system. The kidneys use specialized membrane channels and concentration gradients to control the passage of particles between the tubules (specialized components of the kidney that ultimately lead to the ureter for excretion), and the circulating blood. In describing the process by which the kidneys filter blood, the tutorial emphasizes the importance of hydrophilic and hydrophobic properties, concentration gradients and diffusion, and membrane structure. The tutorial then describes artificial dialysis using a cellulose membrane, and shows how the same underlying chemical principles are at work in both natural and artificial kidneys. This tutorial is one of four blood-chemistry tutorials available for General Chemistry from Washington University in St. Louis.

At Washington University in St. Louis, this tutorial accompanies a second-semester experiment in which students learn about biological and artificial membranes, concentration gradients and diffusion across a semipermeable membrane, and the solubility properties of hydrophobic, hydrophilic, and amphipathic molecules. In the experiment, students use a semipermeable cellulose membrane (similar to the membranes used in artificial kidneys) to separate chlorophyll from the proteins to which it is attached in plant cells, study the time-course change in a pH gradient, and examine the effect of detergent on oil-water miscibility.

Click here to view the tutorial.