lec 25.docx

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University of California - Irvine
Biological Sciences
Peter A.Bowler

e109 12/3/12 lec 25 Carbohydrates break down into monosaccharides -Glucose polymers: starch (in plants) and glycogen (in animals like humans) -Amylase: the enzyme found in the saliva and in the small intestine; break down glucose polymers into disaccharides -Disaccharides include maltose, sucrose, and lactose +maltase enzyme converts maltose to 2 glucose (monosaccharides) + sucrose enzyme converts sucrose to 1 glucose + 1 fructose (monosaccharides) +lactase (in milk) enzyme converts lactose to 1 glucose + 1 galactose (monosaccharides) -Cellulose: another glucose polymer that humans cannnot digested (fiber); in plant cell walls Absorption of Amino acids -Absorption of peptides (amino acids, dipeptides, tripeptides +Di and Tripeptides cotransport with H+ +Amino acids contransport with Na+ +Small peptides are carried intact across the cell by transcytosis Hepatic Portal system Fig 21-18 -Once the products of absorption are taken into the blood, the blood goes throw the hepatic portal system and reaches the liver (portal system) +only the absorbed products of carbohydrate and protein digestion +can detoxify the absorbed nutrients coming in from the digestive tract through the portal system and sends the blood through the hepatic vein to the heart -this is for the products of protein and carbohydrate production Fat digestion and absorption 1. Bile salts from the liver coats the fat droplets causes emulsion 2. Pancreatic lipase and colipase break down fats into monoglycerides and fatty acids stored in micelles. 3. Monglycerides and fatty acids move out of micelles and enter cells by diffusion 4. Cholesterol has a transporter and is transported into the cells 5. Absorbed fats combine with cholesterol and proteins in the intestinal cells to form chylomicrons (cholesterol + triglycerides + protein = chylomicrons) 6. Chylomicrons are removed by the lymphatic system (lacteals). One way flow to circulation system and then to heart (don’t first go to liver like with proteins and carbohydrates digestion). Large intestine -Large intestine absorbs water; full of bacteria (~500-1000 species) +water will only be absorbed if the osmolarity in the large intestine is LOWER than the osmolarity of the surroundings -Larger diameter but shorter than small intestine Clicker question:A“fecal transplant cure” is the introduction of feces from a donor into the large intestine to repopulate the large intestine with the “right” kind of bacteria +Clostridium difficule flourishes in the gut when other bacteria are killed during treatment with antibiotics (you’ve been introduced to Clostridium tetani and Clostridium botulinum) +500-1000 species of bacteria normally live in the large intestine Control of food intake by the brain Fig 22.1 Hypothalamic feeding center (in the brain): tonically active group of cells that generate appetite (to eat) Hypothalamic satiety center (in the brain): negatively inhibits the hypothalamic feeding center and indicates that your body is full (not to eat) -Leptin secretion
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