Lecture38&39 - LECTURES 38 39 30 Nov 02 Dec 2009(P...

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-1- LECTURES 38 & 39. 30 Nov & 02 Dec 2009 (P. J. Hollenbeck) BIOL 231 The Cell Biology of Epithelia Reading: Chap. 20: pp. 696-98; 700-707 Probs: 98-100; Exam IV’05, #7 I. Epithelia organize metazoans (A) Analogous to membranes? (1) Epithelial cells form continuous sheets that are the boundary between the inside of a metazoan organism and the outside world. It is analogous to the plasma membrane of the cell forming a boundary between the cytoplasm and the extracellular milieu. (2) Epithelial sheets have most of the boundary properties that we have already described for cell membranes. They are: continuous; selectively permeable; asymmetric; respond to external signals; mediate interactions. (3) Two primary features of epithelial cells that make these properties possible: >SPECIALIZED CELL-CELL JUNCTIONS >SPECIFIC MEMBRANE PROTEINS, PRECISELY LOCATED (B) Continuous with outside world (a 50¢ anatomy lesson) 22 (1) A cell deep within your body: takes up O and releases CO ; takes up nutrients such as glucose and amino acids; releases waste products such as urea. But unlike a single-celled organism swimming in a pond, a cell in our body exchanges material NOT with the outside world, but with the connective tissue space and extracellular fluid that surround it. This in turn exchanges material with the blood. The blood in turn exchanges material with the outside world via specialized interfaces formed by sheets of epithelial cells. Examples: the lung for gases; the kidney for urea; the GI tract for glucose and amino acids. Here is the cave painting that I made in lecture:
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-2- St = stomach L = liver P = pancreas K = kidney (2) All of the epithelial cells in your body form a CONTINUOUS SHEET. This is pretty obvious for skin and GI tract - they are continuous with each other at the mouth and the anus. It is less obvious for epithelia that form glands and organs, such as the liver, kidney, pancreas, etc. But if you could shrink to the size of a bb (or a bit smaller) you could roll along the surface of your skin, through your GI or urogenital tract, and deep into the epithelial tubes and chambers of these organs without breaching any boundaries. Epithelia form a truly continuous layer of cells, even when our anatomy “internalizes” some of the outside world by deep and complex infoldings of cell sheets. Here is my sketch of this idea: (C) Specialized vs common properties
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This note was uploaded on 12/18/2009 for the course BIOL 101 taught by Professor Wormer during the Fall '08 term at Purdue.

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Lecture38&39 - LECTURES 38 39 30 Nov 02 Dec 2009(P...

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