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 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 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 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 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 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 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 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.) 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 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) 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 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 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 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 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 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 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 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) 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. 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 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 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 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 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