Lesson 29 - Digestion

29: digestion Monday, April 15, 2024 1:47 PM how you fuel your body 1. 2. 3. 4. ingestion digestion absorption elimination feeding strategies • filter feeding: ○ straining small food from surroundings • substrate feeding: ○ live in or on food • fluid feeding: ○ suck fluid with nutrients from living host • bulk feeding: ○ eat relatively large pieces of food extracellular digestion happens in compartments • gastrovascular cavity ○ digestion and distribution of nutrients in the same place ○ single location for ingestion and excretion • alimentary canal ○ complete digestive tract ○ organized into compartments for digestion, storage, and absorption human digestion: the oral cavity • ingestion, initial digestion or carbohydrates • chewing → mechanical digestion • saliva → chemical digestion ○ enzyme amylase hydrolyzes starch and glycogen ○ protects mouth against abrasions, neutralizes acid, contains antimicrobial agents • food moves down through pharynx and esophagus • saliva → chemical digestion ○ enzyme amylase hydrolyzes starch and glycogen ○ protects mouth against abrasions, neutralizes acid, contains antimicrobial agents • food moves down through pharynx and esophagus human digestion: the stomach • storage and digestion of proteins • gastric juices → chemical digestion ○ HCl denatures proteins ○ pepsin breaks peptide bonds of proteins ○ pH of ~2 • stomach churns to aid digestion ○ nutrient-rich broth called chyme • why the stomach doesn't digest itself ○ gastric juices are inactive until released into the lumen ○ mucus from gastric glands protects stomach lining ○ new layer of epithelial cells every 3 days ○ gastric juices restricted to stomach by sphincters human digestion: small intestines • • • • digestion and absorption of nutrients small in diameter (> 6 m long) duodenum → digestion completed digestive juices from: ○ pancreas: alkaline, neutralizes stomach acid; digestion of all compound classes ○ liver: makes bile to digest lipids ○ gallbladder: stores bile • jejunum and ileum → absorption ○ villi and microvilli increase surface area ○ water recovery ○ amino acids and sugars transported across the epithelium via passive or active transport ○ to liver via hepatic portal vein for regulation, conversion, and removal of toxins ○ to heart for circulation • jejunum and ileum → digestion of fat ○ bile salts break fat into small droplets ○ enzymes reduce droplets to fatty acids and monoglycerides ○ fatty acids and monoglycerides diffuse into epithelium, form chylomicron ○ to heart for circulation • jejunum and ileum → digestion of fat ○ bile salts break fat into small droplets ○ enzymes reduce droplets to fatty acids and monoglycerides ○ fatty acids and monoglycerides diffuse into epithelium, form chylomicron ○ chylomicron transported through lymphatic system human digestion: large intestines • colon → completes water resorption ○ houses bacteria that aid in digestion and gut health ○ 12-14 hours for transit • cecum → fermentation ○ small in humans • rectum → storage of feces • anus → elimination chemical digestion in humans homeostasis: regulating glucose digestion differs with diet • different combinations of teeth for different food sources • different sizes and lengths of alimentary canal components to process different food differences in digestive tract • carnivores ○ expandable stomachs for large meals ○ relatively short alimentary canal • herbivores ○ relatively long alimentary canal ○ bacterial or protist symbionts to break down cellulose ○ symbionts often housed in specialized structures the human gut microbiome • diverse bacterial community in the intestines • mutualistic relationship ○ ferment dietary fiber into short-chain fatty acids the human gut microbiome • diverse bacterial community in the intestines • mutualistic relationship ○ ferment dietary fiber into short-chain fatty acids ○ synthesize vitamins B & K ○ metabolize bile ○ aids immune system • varies with age, diet, and geography