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THE DIGESTIVE SYSTEM OF
VERTEBRATES
TOPIC: Digestion by endogenous
enzymes,
& absorption of end products
Figure 8.1. Haworth projections of cellulose, xylan, pectin (Van Soest 1982), and chitin (Fruton & Simmonds 1958). The linkage in pectic acid is alpha-1,4. Haworth formulae are misleading in that xylan and pectin appear to have a conformation similar to cellulose, while they actually differ. Pectin, like starch, cannot exist in a linear conformation and must form kinks or coils. However, the axial position of carbon 4 in galacturonic acid results in a different configuration, as compared to starch. (From CD Chapter 8)
Table 8.1. (From CD Chapter 8)
(From Stevens & Hume 1995)
Table 8.2. (From CD Chapter 8)
(From Stevens & Hume 1995)
Table 8.3. (From CD Chapter 8)
(From Stevens & Hume 1995)
Table 8.4. Digestion of the principal dietary carbohydrates by the endogenous enzymes of vertebrates (Modified from Stevens & Hume 1995.) (From CD Chapter 8)
Figure 8.2. The structure of starch. Hydrolysis catalyzed by pancreatic amylase occurs at the alpha-1,4-linkage, and the products of hydrolysis are straight-chain oligosaccharides. Further hydrolysis is catalyzed by the maltases and isomaltase of the brush border of intestinal epithelial cells (Davenport 1982). (From CD Chapter 8)
Table 8.5. (From CD Chapter 8)
All data on adult specimens are expressed in µmoles substrate/minute per gram (wet weight) of mucosa. (modified from Vonk & Western 1984)
Table 8.6a. (From CD Chapter 8)
Enzymatic activity is designated as + (present), trace or 0 (absent). Results in brackets indicate use of and alternate substrate. All data from adult specimens. * suckling animals. (from Vonk & Western 1984)
Table 8.6b. (From CD Chapter 8)
Enzymatic activity is designated as + (present), trace or 0 (absent). Results in brackets indicate use of and alternate substrate. All data from adult specimens. (from Vonk and Western 1984, plus perissodactyla data from Roberts 1975)
Table 8.7. Digestion of the principle dietary lipids by endogenous enzymes of vertebrates (Modified from Stevens & Hume 1995.) (From CD Chapter 8)
Table 8.8. Digestion of proteins and nucleic acids by the endogenous enzymes of vertebrates (Modified from Stevens & Hume 1995.) (From CD Chapter 8)
Table 8.9. (From CD Chapter 8)
Enzyme activities expressed as the equivalent amount of bovine trypsin (casein or BAEE) or chymotrypsin (BTEE) under the same conditions. a measurements of enzyme activity in the pyloric cecal tissue may account for the lower values, b frogs were fed, c frogs fasted at 5 C, * group C: 0-20 µg RNase per gram of pancreatic tissue. (from Vonk & Western 1984)
Table 8.10. (From CD Chapter 8)
Enzyme activities expressed as the equivalent amount of bovine trypsin (casein or BAEE) or chymotrypsin (BTEE) under the same conditions. *A: 200-1,200 g RNase per gram pancreatic tissue; B: 20-100 g per gram pancreatic tissue; C: 0-20 µg RNase per gram pancreatic tissue. (from Vonk & Western 1984)
Figure 8.3. Absorption of monosaccharides, amino acids, and B-vitamins (Stevens 2001.) (From CD Chapter 8)
Figure 8.4. Relative rates of sugar and amino acid absorption in carnivorous, omnivorous, and herbivorous vertebrates on either their natural diet or one of similar nutrient composition. The ordinate is the ratio of the uptake capacity for D-glucose/ L-proline for the midgut or total intestine. Ratios appeared to be independent of body weight; therefore horizontal lines depict average values. Note that this ratio is highest for herbivores and lowest for carnivores in all classes. Glucose uptake showed a greater variation (herbivores > omnivores > carnivores) than proline. (From Karasov & Diamond 1988.) (From CD Chapter 8)
Table 8.11. (From CD Chapter 8)
0, no absorption or transfer; + to +++, degrees of absorption or transfer. (from Brambell 1970)
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