PHGY 210 Lecture : PHGY 210 Lecture 24 Digestion.doc
16 Mar 2012
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Document Summary
In an earthworm there is the simplest form of a git it stretches linearly along the body and connects the external environment. The lumen is the central cavity that links the external environments at both ends. Throughout evolution, there has been growth and differentiation of the digestive tract. The tubular nature and the communication with the external environment have been maintained. We also have a lumen that is an extension of the external environment. Growth: from the mouth, through the stomach to small intestine, large intestine to the anus the git tract is about 4. 5m long. As well, the surface area of the lining of the lumen has grown through folds such that the internal structure is 600x that of the outer surface of the tube. The total surface area of the lining of the cavity is 200-250m2. This is important to maintain maximal transport across the membrane.
