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Digestion and Absorption of Macromolecules

Digestion and Absorption of Macromolecules Authors: Krisha Patel Reviewers: Parker Lieb, Sunawer Aujla Ran (Marissa) Zhang, Shyla Bharadia, Mao Ding Sylvain Coderre* *MD at time of publication Lipids (triglycerides) Gastric lipase breaks down triglycerides into diglycerides and fatty acids (little digestion of triglycerides occur in stomach) Bile, produced by the liver, and pancreatic lipase enter the small intestine through the common bile duct The hydrophobic and hydrophilic properties of bile allow it to effectively bind hydrophobic fats with hydrophilic pancreatic lipases Pancreatic lipases break down triglycerides into monoglycerides, fatty acids, and glycerol as a result of emulsification by bile Monoglycerides and fatty acids are absorbed through bile-stabilized chylomicrons (lipid molecules arranged in spherical form) Triglyceride-rich chylomicrons are transported through the lymphatic system and require the activity of tissue lipoprotein lipase when they arrive at the tissue Triglycerides enter systemic circulation for metabolism, energy source, and fat storage Ingestion of nutrition sources containing macromolecules Carbohydrates (oligosaccharide) Salivary amylases in the mouth break down oligosaccharides and starch into shorter polysaccharides Pancreatic amylases break down polysaccharides into monosaccharides, disaccharides, and oligosaccharides in the stomach Brush border enzymes in small intestinal villi break down disaccharides into Proteins (peptides) Pepsinogen is secreted by the stomach wall Hydrochloric acid activates pepsinogen to pepsin in the stomach Pepsin breaks down protein peptides into oligopeptides and amino acid chains The pancreas generates trypsinogen and other enzymes to be released into the duodenum Trypsinogen undergoes cleavage in the duodenum through the action of duodenal enteropeptidases to form trypsin Intravenous proton pump inhibitors used in upper gastrointestinal bleeds stabilize pepsinogen, and prevent pepsin from breaking down clotting factors (proteins) enabling clotting Maltose Maltase monosaccharides: Sucrose Sucrase Glucose + fructose Lactose Lactase Glucose + galactose Glucose + glucose Conditions affecting the duodenum (e.g., Celiac disease) can lead to lower enteropeptidase levels, resulting in impaired protein digestion Activation of trypsinogen to trypsin within the pancreas, rather than in the duodenum, contributes to autodigestion observed in acute pancreatitis Absorption of glucose and galactose through active transport via SGLT-1 carrier protein in the Jejunum and Ileum Absorption of fructose through facilitative diffusion via transporter GLUT5 in the Jejunum and Ileum Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) break down oligopeptides and amino acid chains into amino acids, dipeptides, and tripeptides in the duodenum Monosaccharides enter systemic circulation for energy use and storage Active Na+ cotransporters facilitate amino acid absorption in the jejunum and ileum PEPT1 enzymes facilitate absorption of dipeptides and tripeptides, which are then immediately cleaved into amino acids in the jejunum and ileum Amino acids enter systemic circulation for building & repairing muscles Legend: Pathophysiology Mechanism Treatment Effect Complications Published May 18, 2023 on www.thecalgaryguide.com