Capillary Filtration Demonstration

The controls

• There are six controls located below the graphic to manipulate various properties that affect the glomerular filtration rate:
• [Protein] – Changes the protein concentration
• P Art – Changes the arteriole pressure
• Raff – Changes the afferent arteriole resistance
• Permeability – Changes the permeability of the membrane
• Reff – Changes the efferent arteriole resistance
• P PC – Changes the peritubular capillary pressure

• Below each graph, there are check box items that control whether a particular graph line should be visible or not. The label next to each checkbox is color-coordinated with the graph line that it represents.
• The controls for manipulating the axes for the graphs lie in the bottom-center
• Set Capillary Length – Sets the length of the capillary (x-axis) for which the calculations are made. The length must be a positive integer.
• Set Y-Axis – Rescales the Y-axis for either the pressure graph, or either of the two axes on the GFR graph. Axes are chosen by means of the radio buttons located next to the “Set Y-Axis” button. These values must be positive numbers (notice it is not constrained to be an integer).

The displays

There are three displays to be noticed: the graphic at the top of the module and the two graphs located in the center of the module. The graphic on the top will respond to any changes in the upper controls, except the protein concentration slider. At the start, the values are set to normal values. As you manipulate the values, the graphic will change color that corresponds to the intensity of the change, and that intensity can be qualitatively represented by the color meter on the top-right of the graph.

As the values are changed in the upper control panel, the renal blood flow and total GFR will be displayed along with the color changes in the graphic.

The graph located on the left-hand side of the screen shows how changes in variables will affect the hydrostatic pressure and oncotic pressure. The pressure gradient graph is just the difference between the values of the hydrostatic and oncotic pressures.

The graph located on the right-hand side of the screen shows how changes in variables will affect the instantaneous GFR and total GFR. The instantaneous GFR graph shows how much filtrate is leaving at any given position along the capillary, while the total GFR graph shows how much total filtrate has left the capillary at any given point along the capillary. The total GFR graph can be thought of as the integral of the instantaneous GFR graph.

As the capillary length is adjusted, the total GFR is also changed in the graphic.