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Chapter 15 - The Digestive System

Chapter 15 - The Digestive System Irregular tube; open at both ends, called “ Alimentary canal ” or “ Gastrointestinal (GI) Tract ” 29 feet long (adults) - 9 meters Food & other substances that enter tube are not really inside body

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Chapter 15 - The Digestive System

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  1. Chapter 15 - The Digestive System • Irregular tube; open at both ends, called “Alimentary canal” or “Gastrointestinal (GI) Tract” • 29 feet long (adults) - 9 meters • Food & other substances that enter tube are not really inside body • Passageway of food: broken down (digested) and absorbed thru walls < entering body - cells • Both - Mechanical & Chemical Digestion

  2. Break Down of Food • Teeth- first physical breakdown • Stomach-churning of food (physical) • Mouth- first chemical breakdown (salvia) • Digestive enzymes throughout GI tract • Digestion - Process where large food particles reduced to absorbable molecules • Absorption - Process of small molecules passing thru digestive system walls into body

  3. Key Organs of the GI Tract • Know Main & Accessory organs, Table 16-2; page 476 • Small Intestine : Duodenum, Jejunum, & Ileum • Large Intestines (elimination > feces): • Cecum, Colon: Ascending, Transverse, Descending, Sigmoid

  4. Wall of Digestive Tract - • Mouth to anus • Four layers of tissue; surrounding the hollow space within the tube “lumen” • May vary in structure in different organs • Mucosa or mucous membrane - tough in esophagus, delicate, for absorption or secretion in rest of tract • Submucosa - connective tissue, blood vessels & nerves

  5. Muscularis - 2 layers, responsible for wavelike, rhythmic contractions (peristalsis), moves contents, assists in mixing & mechanical breakdown • Serosa - outermost covering, composed of visceral peritoneum • Mesentery - double folded peritoneal tissue, anchors loops of digestive tract to posterior wall of abdominal cavity

  6. Mouth - • Oral cavity - hollow chamber (roof, a floor, & walls) • Entrance of food; digestion begins immediately • Mucous membranes > mucus, protects against digestive juices & lubricates food passage • This mucous protects & lubricates • Hard palate - bony structure, front portion • Soft palate - posterior, chiefly muscles • Uvula - cone-shaped process hanging down from soft palate. W/ help of soft pal., prevents food or liquid from entering nasal cavity

  7. Floor of the mouth - • Tongue - skeletal muscular structure, covered w/ mucous membrane • Anchored to bones in skull > hyoid bone • Frenulum- thin membrane; attaches tongue to floor of mouth • Tongue-tied: too short • Papillae: small elevations on surface • Vallate type - largest, inverted V-shaped row of about 10-12 mushroomlike elevations - tastebuds

  8. Teeth - • Four major types - • Incisors - (sharp/cutting) • Canines - cuspids (pierce/tear) • Premolars - bicuspids & Molars - tricuspids (grinding/crush) • Mastication > chewing of food • Forms a bolus > ready for swallowing • By age 2 - full set 20 teeth (cut 1st - 2 yrs.) • By age 17 to 24 - 32 permanent teeth (cut 1st - 6 yrs.)

  9. Typical Tooth - • Three main parts - • Crown - visible, covered w/ enamel (hardest tissue in body) • Neck - narrow portion surrounds by gum tissue (gingiva) • Root - fitted into socket in upper or lower jaw, lined by fibrous, periodontal membrane • Inside Structure - Enamel on outside, Dentin, Pulp cavity (blood vessels & nerves) moving inward

  10. Salivary Glands - • 3 Pairs - ducts drain saliva into oral cavity, secretes about 1 liter/day • Parotid - in front of each ear (mumps - tender) • Submandibular - ducts by fernullum • Sublingual - ducts into floor of mouth • Saliva contents - salivary amylase (begins CHO digestion), mucus (moistens food)

  11. Pharynx - • Behind nasal cavity & mouth • Tubelike structure made of muscles, lined w/ mucous membrane • Part of respiratory & digestive systems • Esophagus - • Passage for food to stomach • Tube-like structure, 10 inches long • Mucous lined • GERD - often caused by hiatal hernia

  12. Stomach - • Upper part of abdominal cavity, under diaphragm • Pouch for food, hollow, expands (can push up on diaphragm > discomfort) • Lower esophageal sphincter (LES) or cardiac sphincter - rings of muscle tissue at end of esophagus - keeps food from reentering the esophagus when the stomach contracts

  13. Chyme - semi-solid mixture, produced by contraction of stomach muscles that mixes food w/ gastric juices • Stomach contractions - • Created by 3 layers of muscles, run lengthwise, around, obliquely • Makes stomach one of strongest organs > peristalsis • Breaks food into tiny particles

  14. Mucous membranes line stomach - contains gastric glands > secrete gastric juice & hydrochloric acid • When empty, wrinkled folds - rugae • Three divisions of stomach - • Fundus, body, pylorus • Pyloric sphincter - holds food in stomach, empties contents slowly into small intestine

  15. Ulcer - carterlike wound or sore in membrane of stomach • 1 in 10 persons suffer in USA • Helicobacter pylori bacterium (H. pylori) • Small Intestines - • Portion of digestion tract that extends from the pylorus to the ileocecal valve • 12- 20 feet in length, coiled, convoluted, and occupies most of the abdominal cavity • Intestinal glands - secrete digestive juices • Smooth muscle wall - contracts > peristalsis

  16. Plicea - circular folds covered w/ villi, increases surface area > absorption • In or on the villi - • Blood capillaries - absorb CHO & protein end products (glucose & amino acids) • Lacteal - lymphatic vessel - absorb lipids • Microvilli - brushlike border, > surface more • Chemical digestion - most occurs in 1st subdivision of duodenum • Minor & major duodenal papillae - ducts where pancreatic enzymes & bile enter small intestine

  17. Liver - • Large organ, fills R upper abdominal cavity • Exocrine gland - secretes bile into ducts • Hepatic - means liver • Bile - essential for breaking up or emulsification of fats • CCK (cholecystokinin) - hormone secretion triggered by lipids in chyme > makes gallbladder contract & release bile • Drains from common bile duct into duodenum • Gallbladder - concentrates & stores bile

  18. Pancreas - • C-shaped, exocrine gland that lies behind the stomach & duodenum • Pancreatic juice - most important digestive juice - contains enzymes for all 3 food groups • Sodium bicarbonate (alkaline substance) - neutralizes hydrochloric acid • Enters small intestine thru same duct as bile • Islets of Langerhans - hormones produced • Pancreatitis - inflammation (blockage, CF)

  19. Large Intestine - • Begins with the ending of the ileum at the ileocecal valve - called the cecum • Approximately 5 feet in length, much larger in diameter than small intestine • Contents - not called chyme • Function - reabsorb water & salts • Material acted on by bacteria > more nutrients from cellulose & other fibers • Synthesis Vit. K needed for blood clotting, • Production of some B-complex vit.

  20. Not as well suited for absorption as small intestine - no villi • Normal passage of material thru large intestine - 3 to 5 days • Subdivisions - flow in GI Tract one-way • Cecum - pouchlike area • Ascending colon - right side of body • Bends at hepatic or right colic flexure • Transverse colon - extends across front • Bends at splenic or left colic flexure • Descending colon - left side abdomen

  21. Sigmond colon - S-shaped segment, terminates in rectum • Anal canal - terminal end of rectum, ends at external opening - anus • Inner anal sphincter - involuntary, smooth muscle, keeps anus closed except during defecation • Outer anal sphincter - striated, voluntary muscle

  22. Appendix - • Vermiform appendix - “worm-shaped”, tubular structure, blind tube • No important digestive fnc. - digest cellulose • Appendicitis - inflammation • Peritoneum - • Large, moist, slippery sheet of serous membrane • Peritoneal space - small space between parietal & visceral layers - surfaces slide freely • Retroperitoneal - organs outside peritoneum • Extensions of peritoneum-mesentary, greater omentum - both assist in anchoring abd. contents

  23. Digestion -Chemical & mechanical breakdown • CHO - amylase in mouth, slight effect • amylase from pancreas - into small intestine • Absorption of simple sugars (glucose) • Proteins - stomach (HCL/pepsinogen> pepsin) • Finished in small intestine by pancreatic (trypsin) & peptidases in intestinal juice • Amino acids - basic protein units

  24. Fats - in small intestine • Bile emulsification of fats > pancreatic lipase > fatty acids & glycerol • Key digestive juices & enzymes • * page 410 Table 15-2 • Absorption - taking food, breaking it down in form for utilization of body • Just as important as digestion

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