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Chapter 14

Overview Of Digestion. Chapter 14. The Digestive System and Body Metabolism. 20 Cool Things You Don’t Know About the Digestive System. Pill Cam. Digestive System.

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Chapter 14

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  1. Overview Of Digestion Chapter 14 The Digestive System and Body Metabolism 20 Cool Things You Don’t Know About the Digestive System

  2. Pill Cam

  3. Digestive System • Takes in food, breaks it down into nutrient molecules and absorbs them into the bloodstream, then rids the body of indigestible remains

  4. Anatomy of Digestive System • Alimentary canal – • digests food and absorbs digested fragments through its lining into the blood • GI, tract - continuous hollow tube: mouth, pharynx, esophagus, stomach, small and large intestine • Accessory digestive organs - assist: teeth, tongue, glands

  5. Mouth (Oral Cavity) • Food enters • Mucus membrane-lined cavity • lips, cheeks, hard palate (anterior roof), soft palate (posterior roof) • uvula - fingerlike projection of soft palate

  6. Mouth • Tongue - attached to hyoid bone and styloid processes of skull • papillae containing taste buds on surface • Frenulum - secures tongue and limits its posterior movements • As food enters, it is mixed w/ saliva by tongue and chewed and swallowed Taste

  7. Salivary Glands - 3 pair • Parotid glands - anterior to ears • mumps is inflammation of parotid glands • Submandibular and sublingual glands - empty secretions into mouth through ducts

  8. Saliva • Product of salivary glands, mixture of mucus and serous fluids • mucus moistens and binds food together into a mass (bolus) • serous part contains salivary amylase (enzyme for starch digestion) Polls Everywhere

  9. Teeth • Masticate (chew) • Deciduous (baby or milk) teeth - first set; formed from 6 months to 2 years • Permanent teeth - cause baby teeth to fall out b/t 6 and 12 • 32 permanent teeth • 3rd molars (wisdom teeth) form b/t 17 and 25; sometimes absent or impacted in jawbone and must be surgically removed

  10. Teeth by shape/function • Incisors - chisel-shaped, cutting • Canines - fanglike, tearing/piercing • Premolars (bicuspids) • Molars - broad crowns w/ rounded tips, grinding

  11. Pharynx • Nasopharynx (respiratory), oropharynx (potesterior to oral cavity), and laryngopharynx (continuous w/ esophagus) • Peristalsis: Alternating contraction of muscles propel food into esophagus Peristalsis

  12. Esophagus • Conducts food from pharynx through diaphragm to stomach • 25 cm long

  13. Walls of Alimentary Canal • Mucosa - innermost layer; moist membrane • Submucosa - blood vessels, nerve endings, lymph • Muscularis externa - inner circular, outer longitudinal smooth muscle • Serosa - outermost layer

  14. Stomach Peristalsis • C-shaped, left side, nearly hidden by liver and diaphragm • cardioesophageal sphincter - food enters from esophagus • fundus - expanded part • body – midportion • 3rd oblique layer in muscularis externa to move, churn, mix, and pummel food • chemically breakdown proteins

  15. Stomach • Pylorus - funnel-shaped, terminal • Pyloric sphincter - goes to small intestine • 25 cm long • when full, holds 4 liters of food • empty - collapses into folds (rugae) Rugae on Dog Stomach

  16. Stomach • Mucosa has gastric pits which lead into gastric glands that secrete gastric juice • chief cells - produce protein-digesting enzymes (pepsionogen) • parietal cells - produce HCl • Chyme is produced

  17. Stomach - Food Breakdown • Secretion of gastric juice by sight, smell, and taste of food • presence of food and falling pH stimulate release of hormone gastrin that makes stomach produce enzymes, mucus, & HCl • 2-3 liters gastric juice per day

  18. Stomach: Food Propulsion • Peristalsis in lower half, and contractions squirt 3 ml of chyme into small intestine • takes 4 hrs for stomach to empty • Irritation (food poisoning) may activate vomiting

  19. Small Intestine • Major digestive organ • Muscular tube extending from pyloric sphincter to ileocecal valve • average length: 2 m (6 feet) • Hangs from coils suspended by mesentery • Large intestine encircles and frames it

  20. Small Intestine - 3 subdivisions • Duodenum - curves around head of pancreas • Jejunum - extends from duodenum to ileum • ileum - terminal part that joins large intestine at ileocecal valve

  21. Small Intestine • Chemical digestion begins • Small amount of food processed at a time - controlled by pyloric sphincter • Pancreatic enzymes from pancreatic duct and bile from bile duct enter duodenum

  22. Small Intestine - 3 structures that increase absorption • Microvilli - tiny projections that give fuzzy look (brush border) • Villi - fingerlike projections that give velvety appearance • Circular folds - deep folds of both mucosa and submucosa

  23. Small Intestine: Food Breakdown and Absorption • Takes 3-6 hours • By end, digestion is complete and most absorption has occurred • Microvilli have brush border enzymes to break down sugars and complete protein digestion

  24. Food Breakdown and Absorption • Pancreatic juice digests starch, proteins, fats, and nucleic acids; contains bicarbonate to neutralize chyme • When chyme enters, it stimulates hormones secretin and cholecystokinin to release bile

  25. Food Breakdown and Absorption • Bile is necessary for absorption of fats and fat-soluble vitamins K,D,A • At end, all that remains is water, indigestible food and bacteria which enters large intestine • Food propulsion - peristalsis

  26. Large Intestine • Larger in diameter, shorter in length (1.5 m) • Extends from ileocecal valve to anus • Dries out indigestible food by absorbing water, eliminates residue as feces

  27. Large Intestine Subdivisions • Cecum - saclike, first part • Appendix - wormlike structure hanging from cecum; ideal bacteria location - appendicitis • Colon - ascending, transverse, descending, and sigmoid • Rectum • Anal canal - ends in anus which opens to exterior; has external voluntary sphincter and internal involuntary sphincter

  28. Large Intestine • Lots of goblet cells to produce mucus to act as lubricant to ease passage of feces

  29. Large Intestine: Food Breakdown and Absorption • Residue is there 12-24 hours • Bacteria metabolize nutrients and release gases (methane, hydrogen sulfide) • 500 ml of gas produced each day

  30. Food Breakdown and Absorption • Absorption limited to vitamins, some ions, and most of remaining water • Feces - solid product delivered to rectum; undigested food residue, mucus, bacteria, and some water

  31. Large Intestine: Propulsion and Defecation • Peristalsis and mass movements (long, slow-moving, powerful contractile waves that move over colon 3-4 times daily to push contents toward rectum) • occur after eating; fiber increases strength of contraction

  32. Propulsion and Defecation • When feces in rectum, defecation reflex causes rectum to contract and anal sphincters to relax • Diarrhea - food rushes through before water is absorbed, can result in dehydration and electrolyte imbalance How fast food Travels thorough.

  33. Propulsion and Defecation • Constipation - food residue remains too long and too much water is absorbed; due to lack of fiber, poor bowel habits, or laxative abuse A constipated body

  34. Other Accessory Digestive Organs – Pancreas • Soft, pink, triangular gland extending from spleen to duodenum • produces enzymes that break down food and neutralize acidic chyme from stomach, produces hormones insulin, glucagon

  35. Liver • Liver - largest gland in body; under diaphragm on right • 4 lobes • produces bile which leaves liver through common hepatic duct

  36. Gallbladder • Small, thin-walled green sac in the inferior surface of liver • When digestion is not occurring, bile is stored and concentrated by removal of water • bile stored too long, it crystallizes forming gallstones • Yellow-green, watery solution of bile salts, bile pigments (bilirubin), cholesterol, phospholipids, and electrolytes • bile salts emulsify fats to provide more surface area

  37. Disease: Jaundice • Bile pigments enter bloodstream • Can result from hepatitis (inflammation of liver from viral infection of contaminated water or blood transfusion) or cirrhosis (severe damage from drinking excess alcoholic beverages)

  38. Nutrition and Metabolism • Most foods used as metabolic fuels (transformed into ATP); some nutrients build cellular molecules • Energy value measured in kilocalories (kcal) or Calories (C)

  39. Nutrition • Nutrient - substance in food used to promote normal growth, maintenance and repair • Carbohydrates, lipids, proteins - bulk of food; vitamins, and minerals in minute amounts

  40. . • Water - 60% of volume of food • Most foods are combination of nutrients from 5 food groups (grains, fruits, vegetables, meats, and milk products)

  41. Obesity Rates in the US.

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