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BIO270H1 (61)
Lecture

Digestion.docx

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Department
Biology
Course
BIO270H1
Professor
Chris Garside
Semester
Fall

Description
Lecture 10 Digestion Functions of Digestive system: - Absorption - Secretion - Motility (movement along tract) We eat for: - Nutrients - Energy Assimilation: conversion of nutrients into fluid/solid body substance by digestion and absorption Ingestion: gain access to environmental chemicals (usually through GI tract) Egestion: Elimination of undigested food Diet: - Must meet metabolic demands (dependent on growth rate, body size activity, stress) - Imbalances are buffered by fuel storage depots - Net energy: energy available to animals through assimilation - Specific dynamic Action: energy reflected in increase of metabolic rate. Vitamins: - Unrelated molecules with diverse functions - Enzyme cofactors Fat-Soluble: DAKE - Toxic in large doses - D/K synthesized internally Water Soluble: BC - Excess gpoes into urine - Most mammals (except us and guinea pigs) get vitamin C from bacteria in GI tract Coprophagy: eat pheces for lost nutrients Scurvy: no vitamin C Minerals: - Metallic protein structure - Calcium, phosphorous, iron - Copper and zinc (enters interstitial by carriers) Calcium: - Enters through voltage insensitive calcium channel - Exported into blood with CaATPase - Accelerated by calbidin protein and controlled by vitamin D Phosphorus: - Imported inorganically - Transported with sodium co-transporter Iron: - Fe2+ form - Nonspecific divalent metal transporter - Co-transported with H+ - Can be directly absorbed if in Heme form Amino Acids: - 20 overall - 8 essential (depending on species) - Deficit causes developmental defects - Protein quality: animals have better quality because plant lack some essential aa, eat diversity of plants for best results Fatty Acids: - Make acetyl coA - Need omega-3 (linolenic from fish) and omega-6 (linoleic from seeds) Digestive Enzymes - Lipases: break triglycerides and phospholipids into fatty acids - Proteases: break proteins into short polypeptides - Amylases: break polysaccharides into oligosaccharides - Nucleases: break DNA into nucleotides ** Lactase: age reduced production Protein Carrier Transportation: - Polar - Down concentration gradient by facilitated diffusion or GluT proteins (glucose transporter ) - Against concentration gradient by active transport: sodium-depenmdent cotranspoter Vesicle Transportation - Pinocytosis: nutrients in solution - Phagocytosis: some nutrients - Exocytosis Carbohydrate Breakdown o Polysaccharides: glycogen, starch, cellulose o Disaccharides: lactose, sucrose, maltose o Monosaccharides: glucose, fructose, galactose (absorbed by enterocytes in small intestine epithelial) Carbohydrate Absorption: - Active transport (SGLT-1) Sodium glucose transporter - Facilitated Dffution (GluT) High level: - No ATP hydrolysis - Also, GluT2 goes into apical - Save energy - Na+Glucose transporter Monitors concentration of Glucose Protein Breakdown: - Transported by amino acid sodium cotransporter - Some proteins are carried intact by transcytosis (colostrum for immunoprotection) Lipids: - Complicated breakdown because of hydrophobicity - Cross membrane freely - Bile: emulsifies into micelles  Micelles are accessible to pancreatic lipase Transport: - Short Chain: polar enough to go through blood - Triglycerides in lymph as chylomicrose o Taken up by peripheral tissue and repackaged in liver o Processed by lipoprotein lipase (glycerol and fatty acids) Chylomicron: appoproteins on membranes. Ampipathic. Hydrophobic core and hydrophilic exterior. Digestive System: Two-way gut: - Diverticula: more surface area (spinges, cniderians, flatworms) One-way gut: - GI tract - Gastrointestinal - Specialized regions o Mouth pharynx and esophagus in charge of mechanical breakdown o
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