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Digestion, Absorption, and Transport. Overview Digestive System. Functions: Digestion, Absorption, Elimination Digestion – process of breaking down foods to release nutrients Goal is to break nutrients into absorbable units 2 types of digestions: Mechanical Enzymatic (chemical).
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Overview Digestive System • Functions: Digestion, Absorption, Elimination • Digestion – process of breaking down foods to release nutrients • Goal is to break nutrients into absorbable units • 2 types of digestions: • Mechanical • Enzymatic (chemical)
Overview Digestive System • Absorption – movement of nutrients out of GI tract into blood or lymph • Water soluble nutrients • Fat soluble nutrients • Excretion – elimination of undigested foods (feces)
Digestive Tract • Layers of GI tract organs • Serosa (outermost) • Interface between GI tract and lymph & blood • Muscle Layers • Longitudinal muscles • Circular muscles • Submucosal and Mucosal and layers (innermost) • Nerves, blood and lymph vessels • Cells of the mucosal layer produce secretions
Mouth • Structure – teeth, tongue, salivary glands • Secretions • Saliva • Salivary amylase ….. • Digestion • Mechanical …. • Enzymatic/chemical …. • Swallow tongue pushes food pharynx ……
Esophagus • Structure – 12” tube • UES and LES • Function • Transports food from mouth to stomach • Peristalsis and gravity aid food movement • Secretions -- mucus • Digestion • Mechanical (limited) • Enzymatic/chemical – starch digestion continues
Stomach • Structure – muscular sack that can expand • extra muscle layer to aid in the mechanical digestion of food (pg 73)
Stomach Related Secretions • Gastrin – hormone that stimulates stomach to release secretions • Hydrochloric Acid (HCl) -- unravels proteins, kills bacteria, activates pepsinogen • Pepsinogen – once activated, begins protein digestion • Mucus – secreted by goblet cells, protects stomach, moistens food
Stomach - Digestion • Mechanical • Stomach muscles grind food into a paste called chyme • Enzymatic/chemical • Proteins uncoiled • Protein digestion to polypeptides begins • Starch digestion stops
Small Intestine (SI) • Function – The SI is where: • the majority of digestion to absorbable units occurs • Digestion of carbohydrates, fats, and proteins • Vitamins and minerals do not need digestion • Nutrients are absorbed into either capillaries or lacteals
Small Intestine • Digestion - Mechanical • Peristalsis pushes food through SI • Segmentation mixes chyme with digestive enzymes • Also breaks up food mass into smaller masses • Bile emulsifies fats
Muscular Action of Digestion Segmentation
SI • Absorbed into lacteals (lymph) • Digested fats • Fat soluble vitamins • Cholesterol • Nutrients travel through lymph system to chest area where lymph and blood join • Nutrients enter blood and travel to liver
Preparing Nutrients for Transport • Transport pathways • Bloodstream • Water-soluble nutrients and smaller products of fat digestion • Liver • Lymphatic system • Larger fats and fat-soluble vitamins • Chylomicrons • Bypass liver at first
The Vascular System • Closed system of vessels • Heart pump • Blood • Delivers oxygen and nutrients • Removes carbon dioxide and wastes • Blood flow • Special routing for digestive system • Liver
Large Intestine or Colon • Undigested foods (fiber) enter into colon • Unabsorbed nutrients pass into colon • E.g. calcium, iron, cholesterol trapped in fiber
Colon • Structure • 5-6’ long • Wider diameter than SI • No villi or microvilli • Appendix is a little pouch near beginning of colon • Colon “wraps around” SI