Digestion, Nutrition, AbsorptionAnatomy of the Digestive System 2 groups of organs • Alimentary tract (aka GI tract) – Mouth (or oral cavity): – Pharynx (throat) – Esophagus – Stomach – Small intestine (duodenum, ileum, jejunum) Large intestine and – Anus • Accessory organs – Teeth, tongue, gallbladder, salivary glands, liver and pancreasIngestion: introduction of food into body by mouth Mastication: chewing. breaking down large particles mechanically to facilitates chemical digestion. Secretion: lubricate, liquefy, digest contents – Mucus: secreted along entire digestive tract, lubricates food and lining, coats lining and protects it from mechanical damage, from acid and from digestive enzymes. – Bile: emulsifies fats from liver and gall bladder – Enzymes: chemical digestion (from saliva, stomach, pancreas, small intestine) Digestion: Mechanical (churning) and chemical Absorption: Movement from gi tract into circulation or lymph– diffusion, active transport, symport, exocytosis Elimination: Defecation. Waste products removed from body; feces. Functions of the Digestive System• Mastication: – Mechanical digestion (teeth and tongue) – Chemical digestion • Saliva – Salivary amylase-- breaks down starch (Polysaccharides) into disaccharides– starts chemical digestion. – Anti-bacterial: » Contains lysozymes, Oral Cavity:Histology of the Stomach Gastric pits: openings for gastric glands. Cells of gastric pits • mucus: mucus that protects Parietal: produces hydrochloric acid • Chief: pepsinogen • Endocrine: produces hormonesSecretions of the Stomach Mucus: lubrication of digestive tract Pepsinogen: converted to Pepsin by HCl Breaks down proteins HCl: produced by parietal cells • Helps convert pepsinogen to pepsin • Kills bacteria • Denatures proteins (e.g., salivary amylase) – Stops carbohydrate digestion by inactivating salivary amylaseHydrochloric Acid ProductionSmall Intestine • Site of greatest amount of digestion and absorption of nutrients and water • Divisions – Duodenum- Jejunum- – Ileum-• bile released into duodenum from gall bladder and liver • Villi that contain capillaries and lacteals. • Microvilli: folds of cell membranes of absorptive cells. Site of nutrient (carbohydrates, lipids, and proteins) absorption Small Intestine: Duodenum Cystic duct Duodenum Hepatopancreatic ampulla Gallbladder Bile duct and sphincter Main pancreatic duct and sphincter Pancreas Head of pancreas Common hepatic duct Major duodenal papilla (b) Absorptive cells Lacteal Intestinal crypt Mucosa associated lymphoid tissue Muscularis mucosae Duodenal gland Submucosa Enteroendocrine cells Venule Lymphatic vessel Goblet cell Blood capillaries Vilus Microvilli (brush border)Pancreas Pancreas both endocrine and exocrine • Endocrine: pancreatic islets. Produce insulin and glucagon • Exocrine: acinar cells release digestive enzymes (e.g., trypsinogen) and bicarbonate (HCO3) into duodenum pancreasCarbohydrates Active transport Symport diffusion Carbohydrate absorbed by small intestine as monosacharides: glucose, galactose, and fructose Body converts galactose and fructose to glucose to be used for ATP synthesisLipids • Bile salts surround lipids to form micelles • Lipids absorbed by small intestine as: monoglycerides, glycerols, and fatty acids • Chylomicrons enter blood stream, thru lymph, lactealsAmino Acid Transport Proteins absorbed by small intestine mostly as dipeptides ( two amino acids)Large Intestine • Bacteria produce vitamin K and vitamin B12, which is then absorbed • Water is reabsorbedGlucose, galactose, fructose And glycerolNutrition • Chemicals taken in to body to produce energy, provide building blocks or function in other chemical rxns • Classes – Carbohydrates, lipids, proteins, water: required in large amounts – Vitamins, minerals: required in small amounts • Essential nutrients: must be ingested, cannot be synthesized. Certain amino acids, certain fatty acids, most vitamins, minerals, waterCarbohydrates • Most come from plants • Monosaccharides: include glucose, fructose, galactose • Disaccharides: include sucrose • Polysaccharides (complex): include starch, glycogen, cellulose. Cellulose is indigestibleCarbohydrates: Uses in the Body • Digestion breaks poly- and disaccharides into monosaccharides before absorption • Liver converts monosaccharides into glucose which is then used as an energy source to produce ATP • Excess glucose converted to glycogen and stored in muscles and liver cells • Excess beyond storage is converted to fatLipids Triglycerides (~95% ingested): glycerol + 3 FAs e.g, Linoleic acids: essential fatty acids. Found in fish, seeds, nuts, legumes, grains and green leaves Cholesterol: found in animals, but not in plants; sterol Phospholipids: major components of plasma membranes (e.g. egg yolks) glycerol + phosphate + choline +2 FAsLipids: Uses in the Body • Triglycerides: used to produce ATP – Excess stored in adipose tissue or liver. • Cholesterol: Component of plasma membranes. Can be eaten or manufactured in the body. • Phospholipids: part of plasma membrane and used to construct the myelin sheath.Proteins • Chains of amino acids – Types • Essential: must be obtained in diet His, iso, leu, lys, met, phe, thr, try, val • Nonessential: body can synthesize • Complete proteins: contain all necessary amino acids (meat, fish, poultry, milk, cheese, eggs)Minerals • Inorganics, necessary for normal metabolic functions • Functions: establish resting membrane potentials, generate action potentials, add strength to bones and teeth, buffers, involved in osmotic balance; • Components of hemoglobin, bone, etc. • Obtained from animal and plant sources.Metabolic States (2) • Absorptive state: period immediately after eating when nutrients absorbed through intestinal wall into circulatory and lymphatic systems (for up to 4 hours after each meal) • Insulin released for uptake of Glucose into cells • Postabsorptive state: • After absorptive state • Blood glucose levels maintained by conversion of other molecules to glucose – Glucagon released to break down glycogen to