Download Digestion and Absorption of Nutrients: A Focus on Carbohydrates, Proteins, and Fats - Prof and more Study notes Biology in PDF only on Docsity! 19 March Digestion of Food Digestion of complex structures โ polysaccharides, proteins, and triglycerides Absorption of small molecules โ monosaccharides, amino acids, and monoglycerides/free fatty acids/glycerol Digestion of Carbohydrates Glucose polymers (starch, glycogen) digest to disaccharides (maltose, sucrose, lactose) โ uses amylase Maltose + maltase โ 2 glucose Sucrose + sucrase โ 1 glucose + 1 fructose Lactose + lactase โ 1 glucose + 1 galactose Digestion of Fat Triglyceride + lipase, colipase โ monoglyceride + free fatty acids Digestion of Proteins Endopeptidase digests internal peptide bonds Exopeptidase digests terminal peptide bonds to release amino acids Aminopeptidase + H2O breaks off amino acid @ H2N end Carboxypeptidase + H2O breaks off amino acid @ COOH end Absorption of Sugars Secondary active transport Facilitated diffusion Glucose enters the cell with Na+ on the SGLT symporter and exists on GLUT2 Fructose enters on GLUT5 and exits on GLUT2 Absorption of Amino Acids/Peptides Di- and tripeptides cotransport with H+ Amino acids costransport with Na+ Small peptides are carried intact across the cell by transcytosis Objectives Understand digestion of polysaccharides and proteins Understand what is involved with digestion of lipids Regulation of digestion: motility and phases Understand secretions involved in digestion Understand how digestion in small intestine affects stomach Figure 15.6 Chemical absorption and digestion Lumen Complex compounds Enzymes added to digest Epithelial wall Enzymes secreted Degradation smaller compounds Transporters to absorb simple compounds Via nerve plexus in wall of gut (local neural reflex/local stimuli modulated by autonomic nerves) Hormonal Via GI hormones (local reflex/local stimuli modulated by autonomic nerves) Behavioral and CNS reflex central Nerve plexuses in wall for local regulation Feedback regulation using hormones Figure 15.6 Regulation of Gastric Secretions 3 phases Cephalic phase โ sight, smell, taste, touch of food Gastric phase โ presence of food in stomach (digestion and peptides) Intestinal phase โ entrance of chyme into duodenum/distention Figure 15.14 Regulation of Gastric Secretions Cephalic phase Medulla oblongata โ Action potential (AP) โ vagus nerve โ stomach โ parietal chiefs and chief cells โ โ secretions Enteroendocrine cells โ โ gastrin โ parietal cells and chief cells โ โ secretions Gastric phase Distention of stomach โ mechanoreceptors โ AP โ enteric reflexes (stomach) โ โ secretions stomach Peptides in stomach - โ HCl Alcohol/caffeine - โ gastrin Intestinal phase Chyme โ neural and hormonal mechanism pH < 2.0 โ secretin โ inhibits secretion, gastrin (stomach) pH and duodenal wall extention โ enterogastric reflex โ inhibits gastric secretions FA/lipids โ gastric inhibitory peptide and cholecystokinin โ inhibits gastric secretions
