DON W. FAWCETT / SCIENCE PHOTO LIBRARY DON W. FAWCETT / SCIENCE PHOTO LIBRARY
This illustration shows how the body increases the available surface area in the intestinal tract without increasing the overall size of the organs. A depicts the elongation and convolution of the tubular bowel. B shows the mucosa plication. C shows the formation of the intestinal villi. D shows microvilli on individual cells. Finally, E shows saccharide residues of membrane glycoproteins projecting from the microvilli. The same devices repeat at the subcellular level in the elongation and convolution of the endoplasmic reticulum, and the plication of the inner mitochondrial membranes.
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