foreign antigens to T cells and receptors on the surface of the T cell TCR are

Foreign antigens to t cells and receptors on the

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foreign antigens to T cells, and receptors on the surface of the T cell (TCR) are uniquely suited to recognition of proteins of this type. MHC are highly variable between individuals, and therefore the T cells from the host recognize the foreign MHC with a very high frequency leading to powerful immune responses that cause rejection of transplanted tissue. Identical twins and cloned tissue are MHC matched, and are therefore not subject to T cell mediated rejection. 2.) a.) Insects Insects require oxygen to live, and produce carbon dioxide as a waste product, just as we do. To say insects breathe, though, might be a stretch. They don't have lungs, nor do they transport oxygen through their circulatory systems. Instead, insects use a series of tubes called a tracheal system to perform gas exchange throughout the body. Gas exchange, is accomplished mostly by simple diffusion through the cell walls. Air enters the spiracles, and moves through the tracheal system. Each tracheal tube ends in a moist tracheole, a specialized cell for exchanging gases with another cell in the body. When air reaches the tracheole, oxygen dissolves into the tracheole liquid. Through simple diffusion, oxygen then moves to the living cell and carbon dioxide enters the tracheal tube. Carbon dioxide, a metabolic waste, exits the body through the spiracles. b.) Fish In fish, respiration takes place in their gills. Gills can collect dissolved oxygen from the water and release carbon dioxide. Gills are much more complex than just a slit in the cheek of a fish. Gills are comprised of gill arches with hundreds of gill filaments extending from them. Each filament is lined with rows of lamellae, and the gas exchange takes place as water flows through them. The frills and flaps increase the surface area to allow more gas exchange to take place, just as the alveoli do in the lungs. Fish utilize a countercurrent exchange pathway (except for cartilaginous fish), which means that their arteries are arranged so that blood flows in the opposite direction of water movement against the gills. By having their respiration pathway in this orientation, maximum gas exchange can take place. If the blood and the water were moving in the same direction, the blood would always be next to the same bit of water which would soon be depleted of oxygen. By setting up a countercurrent pathway, the blood is always passing water that still has oxygen. This allows the
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  • Fall '17
  • Randy Smith
  • inflammatory disease

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