The Digestive System Digestive System Digestion Mechanical & chemical breakdown of food into a form that can be used by cells Mechanical breaks large pieces into smaller pieces Chemical breaks food into simpler chemicals. Ex. Carbohydrates broken into glucose, proteins into amino acids Digestive Processes Ingestion taking in food Digestion mechanical & chemical breakdown Deglutition swallowing Propulsion movement of food thru system Absorption nutrients & water move into surrounding cells Defecation removal of ingestible waste 1
Digestive System 2 main divisions Alimentary canal(gi tract) continuous coiled hollow tube from mouth to anus Accessory digestive organs release secretions into GI tract Organs of the Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anal canal Accessory Organs Salivary glands Liver Gallbladder Pancreas 2
ACCESSORY ORGANS Salivary glands Secrete saliva, which contains enzymes that initiate breakdown of carbohydrates ALIMENTARY CANAL Mouth Mechanical breakdown of food; begins chemical digestion of carbohydrates Pharynx Connects mouth with esophagus Esophagus Peristalsis pushes food to stomach Liver Produces bile, which emulsifies fat Gallbladder Stores bile and introduces it into small intestine Pancreas Produces and secretes pancreatic juice, containing digestive enzymes and bicarbonate ions, into small intestine Stomach Secretes acid and enzymes; mixes food with secretions to begin enzymatic digestion of proteins Small intestine Mixes food with bile and pancreatic juice; final enzymatic breakdown of food molecules; main site of nutrient absorption Large intestine Absorbs water and electrolytes to form feces Rectum Regulates elimination of feces Anus Characteristics of GI tract Muscular tube ~ 8 meters long (~26 ft) Peristalsis wavelike motion of muscular contractions that propel food forward 4 layers Mucosa membrane Inner epithelial layer surrounding lumen Villi present tiny folds or projections that absorb nutrients Submucosa layer Loose CT containing glands, nerves & blood vessels Nourishes surrounding cells Transports nutrients to blood stream Muscular layers Inner layer of circular smooth muscles; movement of food Outer layer of longitudinal smooth muscles; movement of food Serosa membrane Outer visceral peritoneum that secretes serous fluid that lubricate layer Movements of the AI Tract Segmentation movement in the S.I. that aids in mixing Peristalsis contractions that move food down the A.I. tract 3
Mouth (Oral Cavity) Lips (labia) protect anterior opening Cheeks some taste buds; muscles for chewing Teeth mastication; mechanical digestion Salivary glands chemical digestion Hard palate forms anterior roof Soft palate forms posterior roof Uvula fleshy projection of the soft palate; prevents food from entering nasal cavity Tongue attached by the lingual frenulum; contains papillae which houses taste buds; mixes food Vestibule space between lips, teeth & gums Tonsils lymphatic tissues Mouth (Oral Cavity) Teeth Hardest structure in body Mastication Primary teeth (20) baby teeth Secondary teeth (~ 32) some lack wisdom teeth Incisors cut Cuspid/canine grasp & tear Molars grind 4
Salivary Glands Secretes saliva which moistens food Mucosa cells secrete mucus that binds food (bolus) Serous cells produce amylase that digest starches Solvent for taste buds Keeps ph of mouth about 6.5-7.5 3 salivary glands Parotid gland- largest Submandibular gland Sublingual gland Lipase - fats Sucrase - sugars Pharynx Connects nasal & oral cavities Passage way for food & air Nasopharynx not part of digestive system Oropharynx posterior to oral cavity Laryngopharynx connects to esophagus Epiglottis prevents food entering larynx Esophagus Passageway for food only; no digestion Runs from pharynx to stomach thru diaphragm Esophageal hiatus point where esophagus passes thru diaphragm Esophageal sphincter(cardiac sphincter) controls opening into stomach prevents regurgitation Food propelled forward by peristalsis Mucosa cells moisten & lubricate 5
Stomach Anatomy Left side of abdominal cavity Avg. capacity ~ 1 liter ph ~ 2 Food enters at the esophageal sphincter Regions of the stomach Cardiac region near heart & esophageal sphincter Fundus upper curved area; contains air Body region center Pylorus funnel-shaped terminal end of stomach Stomach Anatomy Pyloric sphincter controls movement of food to small intestine Rugae internal folds of the mucosa lining of the stomach External regions Lesser curvature Greater curvature Slide 14.17 6
Stomach Functions Storage tank for food Site of mechanical breakdown 3 layers of muscles mix food circular, longitudinal & oblique Chemical breakdown of protein begins Delivers chyme (processed food; semiliquid state) to the small intestine Only absorption in stomach is alcohol, some H 2 O & some drugs Mucosa of the Stomach Lined w/gastric pits leading to gastric glands Gastrin hormone that regulates secretion of gastric glands Mucous neck cells produce a sticky alkaline mucus that lines stomach walls Gastric glands secrete gastric juice Chief cells produce protein-digesting enzymes (pepsinogens) Parietal cells produce hydrochloric acid (HCl) & intrinsic factor needed for B 12 absorption Goblet cells produce mucus Structure of the Stomach Mucosa 7
Small Intestine ~18-20 ft. (5-6m) Receives chyme from stomach Receives secretions from liver, gallbladder & pancreas Site of nutrient absorption into the blood Extends from pyloric sphincter to ileocecal valve Mesentery peritoneal membrane stabilizing intestines; supports blood vessels & nerves to S.I. Greater omentum peritoneal membrane draped from stomach over intestines Omentum Subdivisions of Small Intestine Duodenum Attached to stomach at pyloric sphincter Shortest part Pancreatic & bile ducts empty here Jejunum Attaches to duodenum Thicker & more vascular Ileum Extends from jejunum to large intestine Longest section 8
Structures Involved in Absorption of Nutrients Villi - fingerlike projections lining mucosa surface area for absorption Columnar epithelia Blood capillaries present Lacteals - specialized lymphatic capillaries Plicae circulares circular folds of mucosa Microvilli smaller projections on villi to absorption 9
Small Intestinal Movements The small intestine carries on mixing movements that include: Peristalsis pushing movements that propel chyme Segmentation ring-like contractions that can move chyme back and forth Large Intestine ~ 1.5 m long (~4.5-5 ft) Larger diameter than S.I. Absorbs water & electrolytes little or no digestion ileocecal sphincter - controls movement of chyme from S.I. to L.I. Cecum beginning of L.I. Appendix hangs down from cecum; lymphatic tissues Colon into 4 areas; segmented pockets called HAUSTRA Ascending colon right side of body; turns left at hepatic flexure Transverse colon horizontal; turns down at splenic flexure Descending colon left side of body; turns toward pelvis to form Sigmoid colon S-shaped curve Teniae coli longitudinal muscles on surface of colon Rectum last section of L.I. Anus opening controlled by internal & external sphincters Functions of the Large Intestine Absorption of water & electrolytes Eliminates indigestible food as feces No digestion of food Goblet cells produce mucus to act as a lubricant 10
Accessory Digestive Organs Pancreas Liver Gall bladder Salivary glands Pancreas Mixed gland both endocrine & exocrine Pancreatic duct merges w/common bile duct & secretions are released into duodenum Alkaline fluid introduced with enzymes neutralizes acidic chyme 2 types of cells Acinar cells bulk of pancreas; produce pancreatic juices Islet cells produce hormone insulin 11
Pancreatic Enzymes Pancreatic amylase splits starch or glycogen Pancreatic lipase breaks down triglycerides; fats Trypsin & chymotrypsin digest proteins Nucleases digest nucleic acids Bicarbonate ions make pancreatic juice alkaline Liver Largest organ in body Right upper quadrant of the body, under diaphragm 4 lobes suspended from the diaphragm & abdominal wall by the falciform ligament Connected to the gall bladder via the hepatic duct Produces glycogen from glucose Converts glycogen to glucose Synthesizes cholesterol 12
Inferior vena cava Coronary ligament Falciform ligament Right lobe (a) Gallbladder Right lobe Left lobe Round ligament Gallbladder Inferior vena cava (b) Quadrate lobe Left lobe Cystic duct Hepatic duct Hepatic artery Hepatic portal vein Bile duct Caudate lobe Liver Breaks down red blood cells Filters & detoxifies blood Stores iron, vitamin A, D & glycogen Produces bile Bile consist of the following Bile salts Bile pigments (Bilirubin & biliverin) Cholesterol Phospholipids Gall Bladder Sac beneath liver that stores concentrated bile Cystic duct carries bile from liver to gall bladder Common bile ducts secretes bile into the duodenum in the presence of fatty food Hepatopancreatic sphincter controls release Emulsification when bile salts break fat globules into smaller pieces Gallstones form when cholesterol solidifies & can cause blockages 13
Processes of the Digestive System Chemical Digestion Enzymes break down food molecules into their building blocks Each major food group uses different enzymes Carbohydrates are broken to simple sugars Proteins are broken to amino acids Fats are broken to fatty acids and glycerol 14