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24 Digestive
Digestive System
| Question | Answer |
|---|---|
| gastrointestinal (GI) tract (alimentary canal) | mouth, most of pharynx, esophagus, stomach, small intestine, and large intestine |
| accessory digestive organs | teeth, tongue, salivary glands, liver, gallbladder, and pancreas |
| digestive process | ingestion, secretion, mixing and propulsion, digestion, absorption, and defecation |
| secretion | water, acid, buffers, and enzymes into lumen from GI tract cells |
| mixing and propulsion | alternating contractions and relaxations of smooth muscle in the walls of the GI tract, known as motility |
| digestion | mechanical digestion churns food; chemical digestion – hydrolysis |
| components of the wall of GI tract | mucosa, submucosa, muscularis, and serosa |
| mucosa's 3 layers | epithelium, lamina propria, and muscularis mucosae |
| lamina propria | connective tissue with blood and lymphatic vessels and mucosa-associated lymphatic tissue (MALT) that contain immune system cells |
| muscularis mucosae | thin layer of smooth muscle making folds to increase surface area |
| submucosa | connective tissue binding mucosa to muscularis; contains many blood and lymphatic vessels; submucosal plexus (neurons) |
| muscularis | voluntary skeletal muscle (mouth, pharynx, esohpagus, and anal sphincter) and involuntary; arranged in circular fibers and outer longitudinal fibers; myenteric plexus |
| enteric nervous system (ENS) | extends from esophagus to anus; myenteric plexus and submucosal plexus; motor neurons, interneurons, and sensory neurons |
| myenteric plexus (plexus of Auerbach) | located between circular and longitudinal smooth muscle layers; controls GI tract motility |
| submucosal plexus (plexus of Meissner) | located within the submucosa; controls secretions |
| ANS influence | parasympathetic stimulation increases secretions and motility by stimulating the ENS; sympathetic stimulation inhibits ENS |
| peritoneum | largest serous membrane in the body; parietal peritoneum, peritoneal cavity, and visceral peritoneum |
| ascites | accumulation of liters of fluid in the peritoneal cavity |
| parietal peritoneum | lines the wall of the abdominopelvic cavity |
| visceral peritoneum | covers some of the organs in the cavity |
| retroperitoneal | kidneys, ascending and descending colons, duodenum, and pancreas (located behind the peritoneum) |
| major peritoneal folds (5) | greater omentum, falciform ligament, lesser omentum, mesentery, and mesocolon |
| greater omentum | the largest peritoneal fold that drapes over the transverse colon and small intestine like a “fatty apron” |
| falciform ligament | attaches the liver to the anterior abdominal wall and diaphragm |
| lesser omentum | suspends the stomach and duodenum from the liver |
| mesentery | binds the jejunum and ileum of the small intestine to the posterior abdominal wall |
| mesocolon | binds the transverse colon and sigmoid colon to the posterior abdominal wall |
| structure of the mouth | cheeks, hard and soft palates, and tongue |
| uvula | a conical muscular process hanging from the soft palate; drawn superiorly during swallowing to prevent food from entering the nasal cavity |
| function of salivary glands | when food enters the mouth, secretion increases to lubricate, dissolve, and begins chemical digestion |
| 3 pairs of salivary glands | parotid, submandibular, and sublingual |
| parotid glands | located between the skin and masseter muscle; secrete saliva via a parotid duct |
| submandibular glands | found in the floor of the mouth; submandibular ducts |
| sublingual glands | Found beneath the tongue; lesser sublingual ducts |
| saliva | 99.5% water and 0.5% solutes;ions, dissolved gases, urea, uric acid, mucus, IgA, lysozyme, and salivary amylase |
| urea and uric acid in saliva | helps remove waste molecules |
| IgA in saliva | prevents attachment of microbes |
| tongue structure | skeletal muscle covered with mucous membrane; attached to the hyoid bone; extrinsic muscles (hyoglossus, genioglossus, and styloglossus); intrinsic muscles; lingual frenulum (fold of mucous membrane on the bottom of the tongue) |
| tongue function | maneuvers food for chewing, shapes mass, and forces food back for swallowing |
| lingual glands | secrete salivary lipase (fats and oils) |
| ankyloglossia | abnormally short or rigid lingual frenulum resulting in an impairment of speech |
| major regions of a tooth (3) | crown, root, and neck |
| layers of a tooth (5) | enamel, dentin, cementum, pulp, and root canals |
| dentitions | sets of teeth |
| deciduous dentitions | primary teeth, milk teeth, or baby teeth; 20 teeth (no molars) |
| permanent dentitions | deciduous teeth replaced somewhere between the ages of 6-12; 32 teeth |
| pharynx | food passes into the oropharynx and laryngopharynx; the muscular contractions in those areas help propel food into the esophagus to the stomach |
| histology of the esophagus | mucosa, submucosa, muscularis, sphincters, and adventitia (attaches to the surroundings) |
| function of the esophagus | secretes mucus and transports food |
| upper esophageal sphincter (UES) | regulates movement into the esophagus |
| lower esophageal sphincter (LES) | regulates movement into the stomach |
| deglutition | swallowing; involving mouth, pharynx, and esophagus |
| 3 stages of deglutition | voluntary, pharyngeal, and esophageal |
| peristalsis | progression of coordinated contractions and relaxations to push a bolus forward; occurs in the esophageal stage |
| pharyngeal stage | when bolus enters the oropharynx it sends impulses to the deglutition center in the medulla; returning impulse tells the uvula to ascend and the epiglottis to close |
| four main regions of the stomach | cardia, fundus, body, and pylorus |
| pylorus (2) | pyloric antrum, connects to the body of the stomach; pyloric canal, connects into the duodenum |
| histology of the stomach | mucosa, submucosa, muscularis, and serosa |
| mucosa of the stomach | gastric glands open into gastric pits; mucous neck cells, parietal cells, chief cells, and G-cells |
| mucous neck cells | secrete mucus |
| parietal cells | produce intrinsic factor (for absorption of B12) and hydrochloric acid |
| chief cells | secrete pepsinogen and gastric lipase |
| G-cells | endocrine cell that secrete gastrin |
| gastrin | stimulates gastric activity |
| muscularis of the stomach | has an additional 3rd inner oblique layer |
| serosa of the stomach | part of the visceral peritoneum |
| rugae | folds of the stomach when it is empty |
| mechanical digestion in the stomach | mixing waves (produces chyme) and gastric emptying (forces 3 mL of chyme into the duodenum) |
| chemical digestion in the stomach | salivary amylase (digestion of starch continues until inactivated by gastric juice), lingual lipase (gastric juice activates it), and HCl (secreted by parietal cells; the proton pumps powered by H+/K+ ATPases) |
| pepsin | secreted by chief cells in its inactive form pepsinogen, becomes active when in contact with HCl; helps breakdown proteins |
| why is pepsin secreted in an inactive form? | it would breakdown the chief cells that produce it; the stomach is protected by a 1-3mm thick alkaline mucus |
| gastric lipase | breaks triglycerides into fatty acids and monoglycerides |
| location of the pancreas | retroperitoneal, lies posterior to the greater curvature of the stomach |
| anatomy of the pancreas | head, body, tail, and two ducts |
| pancreatic duct (duct of Wirsung) | (larger duct) joins the common bile duct from the liver and gallbladder and enters the duodenum at the hepatopancreatic ampulla |
| sphincter of hepatopancreatic ampulla (sphincter of Oddi) | regulates pancreatic juice and bile into the small intestine |
| accessory duct (duct of Santorini) | leads from the pancreas into the duodenum, just above the hepatopancreatic ampulla |
| pancreatic acini | 99% of the epithelial clusters; constitute the exocrine portion; secrete a mix of fluid and digestive enzymes (pancreatic juice) |
| pancreatic islets (islets of Langerhans) | 1% endocrine portion; secrete glucagon, insulin,somatostatin, and pancreatic polypeptide |
| pancreatic juice (5) | neutral pH, somewhat alkaline; sodium bicarbonate, pancreatic amylase, proteolytic enzymes, pancreatic lipase, and deoxy/ribonuclease |
| sodium bicarbonate in pancreatic juice | buffers chyme, stops pepsin from the stomach, and creates the proper pH for enzymes in the small intestine |
| proteolytic enzymes | trypsin activates enzymes |
| liver anatomy | two lobes joined by the falciform ligament, inferior quadrate lobe, and posterior caudate lobe; coronary ligament suspends the liver from the diaphragm |
| ligamentum teres (round ligament) | remnant of the umbilical vein of the fetus |
| histology of the liver | hepatocytes, bile canaliculi, hepatic sinusoids, and Kupffer cells |
| hepatocytes | major functional cells of the liver; secretes bile |
| bile canaliculi | ducts between hepatocytes that collect bile; exit liver as common hepatic duct and joins the cystic duct from the gallbladder to form common bile duct |
| hepatic sinusoids | receives oxygenated blood form hepatic artery and deoxygenated nutrient-rich blood from hepatic portal vein |
| stellate reticuloendothelial (Kupffer) cells | destroy worn-out RBCs, WBCs, and bacteria from the GI tract |
| portal triad | bile duct, hepatic artery, and hepatic vein |
| bile properties | yellow, brownish liquid; pH 7.6-7.8; water bile salts, cholesterol, lecithin, bile pigments and ions |
| bile function | partial excretory product and partial digestive secretion; bile salts play a role in emulsification and providing a large surface area for pancreatic lipase |
| emulsification | breakdown of a large lipid globule into smaller lipid globules |
| liver functions | bile synthesis and secretion; carbohydrate metabolism; lipid metabolism; protein metabolism; processing drugs and hormones; excretion of bilirubin; storage for vitamins; phagocytosis; and activation of Vit-D |
| small intestine regions (3) | duodenum, jejunum, and ileum |
| small intestine histology | mucosa, submucosa, muscularis, and serosa |
| small intestine mucosa | absorptive cells, goblet cells (mucus), intestinal glands (intestinal juice), paneth cells (lysozyme), enteroendocrine cells, and MALT |
| small intestine serosa | completely surrounds the organ except for a major part of the duodenum |
| circular folds (plicae circulares) | ridges of mucosa and submucosa cause chyme to spiral (increased surface area for absorption) |
| villi | finger-like projections of the mucosa; contain an arteriole, venule, blood capillary and lacteal |
| microvilli | projections of apical (free) membrane of absorptive cells; brush border with brush border enzymes |
| intestinal juice | water and mucus; slightly alkaline; 1-2L; provides liquid medium aiding in absorption |
| brush border enzymes | produced by absorptive cells and inserted into plasma membrane by microvilli; carbs, proteins, and nucleic acids |
| mechanical digestion in the small intestine | controlled by myenteric plexus; segmentations, mixing contractions to bring chyme in contact with mucosa; migrating motility complexes (MMC) |
| carbohydrate digestion in the small intestine | pancreatic amylase, α-dextrinase, sucrase, lactase, and maltase break them to monosaccharides which can be absorbed |
| protein digestion in the small intestine | trypsin, chymotrypsin, carboxypeptidase, and elastase from pancreas; completed by aminopeptidase and dipeptidase in brush border |
| lipid digestion in the small intestine | pancreatic lipase and emulsification by bile salts |
| nucleic acid digestion in the small intestine | ribonuclease and deoxyribonuclease in pancreatic juice; nucleosidases and phosphatases in brush border. |
| absorption in the small intestine | occurs by facilitated diffusion into blood (monosaccharides, amino acids, dipeptides, and tripeptides); lipids absorbed by simple diffusion |
| micelles | formed by bile salts and ferry chains of fatty acids and monoglycerides for absorption |
| chylomicrons | formed within a cell it is recreated from triglycerides |
| lacteals | used to transport lipids into blood with a chylomicron protein coat |
| electrolyte absorption | sodium ions reclaimed by active transport along with some other ions |
| vitamin absorption | fat-soluble absorbed by simple diffusion |
| water absorption | 9.3L ingested, 7.0L in GI secretions; occur by osmosis |
| daily volume | 9.3L ingested/secreted, 0.1L excreted,; total absorbed 9.2L |
| large intestine regions (5) | cecum, appendix, colon, rectum, and anal canal |
| ileocecal sphincter | regulates passage of chyme between the small intestine and large intestine |
| colon divisions (4) | ascending, transverse, descending, and sigmoid |
| internal anal sphincter | smooth muscle |
| external anal sphincter | skeletal muscle |
| histology of large intestine | mucosa, submucosa, muscularis, and serosa |
| large intestine mucosa | no circular folds or villi; does have microvilli on absorptive cells |
| large intestine muscularis | longitudinal muscle modified to form teniae coli also forms haustra (pouches, segments seen) |
| mechanical digestion by the large intestine | haustral churning, peristalsis, mass peristalsis (pushes contents toward the rectum) |
| chemical digestion by the large intestine | final stage by bacterial action; ferment carbs; produces some vitamins B and K; mucus but no enzymes |
| phases of digestion (3) | cephalic phase, gastric phase,and intestinal phase |
| cephalic phase | smell, sight, thought or initial taste of food activates neural centers; prepares mouth and stomach for food to be eaten |
| gastric phase | neural regulation by stretch receptors and chemorecptors; hormonal mechanisms (gastrin from G-cells); promotes gastric secretion and motility |
| intestinal phase | begins when food enters small intesting; slows exit of chyme from the stomach |
| cholecystokinin (CCK) | stimulates flow of bile and pancreatic juice; from CCK cells in the small intestinal crypts in response to chyme containing amino acids |
| secretin | stimulates flow of pancreatic juice that is rich in bicarbonate (HCO3-) ions to buffer the acidic chyme; produced by S cells of the small intestinal crypts |
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sibuxiang
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