Digestion and Absorption

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Topic 6.1 Digestion and Absorption of IB Biology Chapter 6 Human Physiology

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Digestion and Absorption
1 Peristalsis
1.1 contraction of circular and longitudanal small intestine muscles to mix food and enzymes
1.2 gut muscles
1.2.1 smooth
1.2.2 short cells
1.2.3 continuous moderate force with periods of vigorous contraction
1.3 circular muscles prevent food from going back
1.4 longitudanal muscles push the food along the gut
1.5 unconsciously performed
1.6 away from mouth
1.7 one wave down esophagus
2 Pancreatic juice
2.1 pancreas secrets enzymes into lumen of small intestine
2.2 pancreas contains 2 types of gland tissue
2.3 small groups of cells secret glucagon and insulin; rest secret digestive enzymes
2.4 enteric nervous system = mediation of hormones synthesized and stomach secretions
2.5 ducts = small group of cells clustered around tubes into which enzymes are secreted
2.6 sythesized on ribosomes in rER
2.7 processed by Golgi apparatus and secreted by exocytosis
2.8 ducts merge into pancreatic duct; 1L of pancreatic juice secreted to lumen per day
2.9 enzymes
2.9.1 amylase for starch
2.9.2 lipase for trigylcerides and phospholipids
2.9.3 protease for proteins and peptides
3 Digestion in the small intestine
3.1 enzymes digest macromolecules in food to monomers
3.2 hydrolysis reactions
3.2.1 starch to maltose by amylase
3.2.2 triglycerides to fatty acids and glycerol or fatty acids and monoglycerides by lipase
3.2.3 phospholipids to fatty acids, gycerol and phosphate by phospholipase
3.3 proteins and polypeptides to shorter peptides by protease
3.4 wall of small intestines produce enzymes to digest more
3.4.1 DNA and RNA to nucleotides by nucleases
3.4.2 maltose to glucose by maltase
3.4.3 lactose to glucose and galactose by lactase
3.4.4 sucrose to glucose and fructose by sucrase
3.4.5 dipeptides to amino acids by dipeptidases
3.4.6 peptide to dipeptide by exopeptidases
3.5 most immobilized enzymes in plasma membrane of epithelium cells; some in intestinal juice
3.6 takes hours due to length
3.7 some not synthesized eg. cellulose
4 Villi and the surface area for digestion
4.1 increases epithelium surface area for increased rate of absorption
4.2 absorption = taking substances into cells and blood
4.3 in small intestine (7m long; 25-30mm wide)
4.4 folds on inner surface for increased surface area
4.5 villi = small finger like projections of mucosa lining inner wall of intestine
4.6 villus 0.5-1.5 mm long (40/sq mm)
4.7 increase surface area 10x
5 Absorption by villi
5.1 absorbs monomer, vitamins and mineral ions
5.1.1 glucose, fructose, galactose, other monosaccharides
5.1.2 all 20 amino acids
5.1.3 fatty acids, monoglycerides, glycerol
5.1.4 bases from digestion of nucleotides
5.1.5 calcium, potassium, sodium
5.1.6 ascorbic acid (Vit C)
5.2 epithelium cover: barrier for harmful substances; permeable to allow useful nutrients to enter
5.3 harmful substances that enter removed from blood, detoxified by liver
5.4 bacteria removed by phagocytic cells
5.5 useless substances in urine
6 Methods of absorption
6.1 nutrients small intestine lumen --> capillaries/lacteals in villi
6.2 absorbed through plasma membrane of epithelium cells
6.3 detailed example of triglycerides and glucose in textbook
6.4 plasma membrane surface area increased by microvilli
6.5 nutrients exit through plasma membrane facing inward towards capillaries/lacteals
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