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The Digestive System: Overview and Anatomy

This chapter provides an overview of the digestive system and its anatomy. It explores the process of digestion, the organs involved, and the breakdown and absorption of nutrients. Discover interesting facts about the digestive system and the Pill Cam used for diagnosis.

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The Digestive System: Overview and Anatomy

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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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