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PHSL233 lecture 01.doc

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Kirk Hamilton

PHSL233 Lecture 01 Epithelia overview and signal transduction Epithelia is a sheet of cells that line body cavities surfaces which can separate 2 different environments. They come as sheets and there are different types, respiratory and follapian tubes have cillia on them, on the digestive system there are microvilli which allows absorption. So they take on different types depending on their job. Simple are just one layer of epithelia cells, they can be squamous, cuboidal or columnar. More than one layer is referred to as being stratified, and transitional. Epithelia cells have 4 main functions, protection such as epidermis which is a type of epithelia cell that is called skin, they help with our outer protection with the environment. There are number of modified epithelia cells that allow us to sense things such as organs in ear and nose. They also have a secretatory and absorption function, also they can excrete. Excretion is getting ride of waste products whereas secretion is movement of fluid from internal to external environment. This is a cross section of the kidney tubule, you can see the lumen of tubule and surrounding it is epithelia cells. One end of the epithelia cell is facing the lumen while other side is associated with the basement membrane. The surface of the epithelia cell that is facing the lumen is called apical surface, while the other surface attaching to the basement membrane is the basolateral surface or membrane. These 2 surfaces have different property, such as different lipid and protein populations on these surfaces so giving them a different function. Epithelia are specialised for movement of ions and molecules and allow to set up this polarity or concentration difference between the 2 sides. This shows a gastrointestinal system, where glucose is eaten and need to be absorbed. On the left shows the apical surface of the gastrointestinal epithelia with microvilli, also there are sodium-glucose co-transporters (SGLT) which transports a Na ion down it's concentration gradient into the epithelia cell and at the same time a glucose molecule is transported into the epithelia cell, a symporter effect (same direction). Then the glucose is transported on the basolateral surface of epithelia into
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