VM8054 Veterinary Histology

Note: Amplification of Surface Area

Author: Dr. Thomas Caceci

Consider a hypothetical small intestine with a length of 5 meters and a diameter of 25 mm. This tube, without modification, would have a volume of a little less than a liter. Without any villi the maximum surface area would be approximately the size of a small windowpane.

If an average villus is 1.0 mm long by 0.5 mm in diameter, and if villi are distributed at a uniform 25 per square centimeter, the increase in surface area compared to a simple tube is substantial. With villi present at this density, the available surface area for absorption from that volume would be more on the order of a very large room.

Actually, the villi are not the only (or even the principal) adaptation to increased surface area; the presence of microvilli on the cells and crypts between villi increases the surface area to several acres. The result of increasing surface area is an enormous increase in the efficiency of the absorptive process compared to a simple tube, since the rate at which absorption occurs across a given area is limited. Need more absorption, make more surface. This design solution is found over and over in the "engineering" of living organisms.