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BIOL 103
Peter T Boag

Biology 103 Readings Page 899 – Ruminants - Herbivores do not have cellulase to digest cellulose - Rely on microbes living within their digestive tracts to digest the cellulose - Microbes break down the cellulose into monosaccharides that can be absorbed along with other by-produce of digestion - Ruminants have complex stomachs consisting of several chambers, beginning with three outpouchings of the lower esophagus collectively referred to the forestomach - Forestomach composed of rumen, reticulum, and omasum - Rumen and reticulum contain microbes - Omasum absorbs some of the water and salts released from the chewed and partially digested food - Tough, partially digested food (the cud) is occasionally regurgitated, rechewed, and swallowed again - Partially digested food, microbes, and the by-products of microbinal digestion reach the true stomach, the abomasum - Abomasum contains the acid and proteolytic enzymes typical of other vertebrate stomachs - After the abomasum, materials pass intestine to complete digestion and absorption - Some microbes remain in the rumen and quickly multiply to replenish their population Page 899-900 – Absorption - Mostly occurs in the small intestine - Digestion products get absorbed across the epithelial cells and enter the blood - Vitamins and minerals are absorbed too - Water is absorbed by osmosis - Infoldings and specializations along the small intestine help it carry out absorption and digestion - Villi: finger-like projections extending from the liminal surface into the lumen of the small intestine; they aid digestion and absorption - Microvilli: small projections in the surface membranes of epithelial cells in the small intestine - Brush Border: the combination of villi and microvilli in the small intestine, which increase the surface area about 600-fold over that of flat-surfaced tube having the same length and diameter - Likelihood of ingested food particle encountering a digestive enzyme and being absorbed across the epithelium is very high; therefore, digestion and absorption proceed rapidly - Lacteal: a vessel in the centre of each intestinal villus; lipids are absorbed by the lacteals, which eventually empty into circulatory system - Fat absorbed in the small intestine exists as bulky protein-bound particles that cannot enter capillaries – too large - Absorbed fat enters larger, wider lacteals, that are part of lymphatic system - Materials absorbed by lacteals empty into the circulatory system - Other nutrients are absorbed directly into the capillaries then veins - Three major parts of small intestine: duodenum, jejunum, and ileum Figure 6.12 – Osmosis - Osmosis may promote cell shrinkage in cells lacking a cell wall - A hypertonic medium causes the plasma membrane to pull away from the cell wall in cells with a rigid cell wall - Hypotonic medium causes only a minor amount of expansion - Animal cells: o Initial cells are in isotonic solution  placed in hypotonic solution  cells swell, may undergo osmotic lysis – water is taken into cell o Initial cells are in isotonic solution  placed in hypertonic solution  cells shrink (crenation) – water exits the cell - Plant cells: o Initial cells in isotonic solution  placed in hypotonic solution  cell wall prevents major expansions, small amount of water may enter o Initial cells in isotonic solution  placed in hypertonic solution  volume inside plasma membrane shrinks, membrane pulls away from the cel
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