DIGESTIVE SYSTEM 2.docx

DIGESTIVE SYSTEM 2 Esophagus Between pharynx/stomach, 25cm long, in mediastinum (posterior to trachea, anterior to vertebrae, parallel to thoracic descending aorta). Passes through esophagul hiatus * (opening) of diaphragm, ends in stomach, food from pharynx to stomach. 4 tunics in wall > mucosa, submucosa, muscularis, adventitia. Muscular tunic > outer longitudinal layer, inner circular layer, skeletal muscle in superior esophagus and smooth in inferior. Upper esophageal sphincter + lower esophageal sphincter > regulate mvmnt of materials in/out of esophagus. Mucosal lining > moist stratified squamous ET Mucous glands in submucosal layer > thick lubricating mucous, passes through ducts to surface of esophageal mucosa. Stomach Gastroesophageal opening > opening from esophagus into stomach (cardiac opening) Lower esophageal sphincter > surrounds cardiac opening. Fundus > part of stomach superior to cardiac opening Body > largest part of stomach w/ greater/lesser curvatures Pyloric Part > body narrows, funnel shaped Pyloric Antrum > wider part of funnel towards body of stomach Pyloric Canal > narrow part of funnel Pyloric Orifice > opens pyloric canal into small intestine Pyloric Sphincter > surrounds pyloric orifice, thick ring of smooth muscle, regulates movement of gastric contents into small intestine. Hypertrophic pyloric stenosis > defect of stomach in infants, pyloric sphincter is thickened, interferes with normal stomach emptying. Histology of the Stomach Serosa > outer layer of stomach, outer simple squamous layer, inner CT layer Muscularis > 3 layers: outer longitudinal layer, middle circular layer, inner oblique layer Submucosa + mucosa > deep to muscular layer, thrown into folds called RUGAE* when stomach is empty which allow these layers to stretch as stomach volume increases. Lined w/ simple columnar ET, forms gastric pits* (openings for gastric glands*) Epithelial cells in stomach are 5 types > Surface Mucous Cells > on surface/lining gastric pit, protect stomach wall from being damaged by acid/enzymes. Produce alkaline mucous on their surface to neutralize acid, cells connected by tight junctions (creates additional barrier), rapidly replaced when damaged. Mucous neck cells > produce mucus, near opening of glands Parietal cells > produce HCl and intrinsic factor (for vit. B12 absorption), in deeper parts of glands, pH 1.5-3.5 Chief cells > produce pepsinogen (inactive), converted to pepsin by HCl for protein digestion, in deeper parts of glands Endocrine cells > produce regulatory hormones/paracrine factors, in deeper parts of glands, release histamine and Gastrin (stimulates acid secretion by parietal cells) Gastric Secretions Cephalic Phase > stimuli act on centers within medulla oblongata to influence gastric secretions. Taste, smell of food, stimulation of tactile receptors during chewing/swallowing, pleasant thoughts of food. AP’s sent from medulla oblongata along parasympathetic neurons within Vagus nerves to stomach. In stomach wall, preganglionic neurons stimulate postganglionic neurons in the ENS (primarily cholinergic), stimulate cells of stomach mucosa. Releases Ach, increases secretory activity of parietal/chief cells, stimulates secretion of gastrin and histamine from endocrine cells. Gastrin circulates to parietal cells, stimulates additional HCl and pepsinogen secretion. Stimulates eneterochromaffin cells to release histamine, stimulates parietal cells to secrete HCl. Histamine stimulates gastric gland secretory activity. Ach, histamine and gastrin secretes more HCL than any of them separately. Histamine has greatest stimulatory effect** drugs that block histamine lower acid levels. Gastric Phase > produces greatest volume of gastric secretions. Presence of food in stomach, distension of stomach/presence of amino acids and peptides are primary stimuli. Distension of stomach wall stimulates mechanoreceptors, they generate AP’s to initiate reflexes involving CNS and ENS, reflexes cause Ach release and cascade of events to increase secretion. Presence of partially digested proteins, alcohol, caffeine also stimulate gastrin secretion. When stomach pH is below 2, increased gastric secretion produced by distension of stomach is blocked, limits secretion of gastric juice. Intestinal Phase > inhibits gastric secretions. Controlled by entrance of acidic chime into duodenum of small intestine, activated neural/hormonal mechanisms. When pH of chime entering duodenum is less than 2 or when it contains lipid digestion products, gastric secretions are inhibited. Secretin > hormone released in response to acidic solutions in duodenum, inhibits parietal/chief cells Cholecystokinin > hormone that inhibits gastric secretions, released by fatty acids, lipids, protein digestion products in duodenum/proximal jejunum. Under nervous control > enterogastric reflex > local reflex/one integrated w/ medulla oblongata to reduce gastric secretion. Activated by: distention of duodenal wall, presence of irritating substances, reduced pH, hyper/hypotonic solutions in duodenum. Small Intestine Duodenum> curves with abdominal cavity, head of pancreas lies in its arc, down the descending part are 2 mounds: major duodenal papilla + minor duodenal papilla where ducts from liver/pancreas open. Surface allows for better digestion/absorption of food, mucosa+submucosa have Circular Folds*, projections of mucosa form villi* each covered by simple columnar ET and has blood capillary network/lymphatic capillary network called LACTEAL*. Cytoplasmic extensions called Microvilli* (increase SA). All microvilli form > Brush Border* (contains brush border enzymes – final breakdown of food molecules) Mucosa = simple columnar ET with 4 cell types: Absorptive cells > w/ microvilli that produce digestive enzymes and absorb digested food Goblet cells > produce protective mucus Granular cells > protect intestinal epithelium from bacteria Endocrine cells > produce regulatory hormones. Epithelial cells produced in Intestinal Glands* (neutralize acidic chime) at base of villi, absorptive+goblet cover villi then shed from its tip, granular+endocrine remain at bottom of glands. Submucosa contains coiled, tubular mucous glands (duodenal glands*), open at base of intestinal glands. Jejunum/Ileum Gradual decrease in diameter of small intestine, thickness of wall, number of circular folds, # of villi, intraperitoneal, mobile Peyer patches > lymphatic nodules in mucosa/submucosa of ileum, inntiate immune responses against foreign microorganisms. Iliocecal Junction > where ileum connects to large intestine Ileocecal sphincter > ring of smooth muscle Iliocecal valve > one way valve, allows intestinal contents to move from ileum into large intestine only. Liver Anatomy – Right upper quadrant of abdomen, inferior surface of diaphragm Right/Left lobes separated by CT septum (falciform ligament) Caudate Lobe and Quadrate Lobe (minor lobes) Porta > inferior surface of liver where vessels, ducts, nerves enter/exit liver Hepatic portal vein/Hepatic Artery, small hepatic nerve plexus enter here, lymphatic vessels, hepatic ducts from r/l lobes exit here. Hepatic ducts > transport bile from liver, R/L combine to form Common Hepatic Duct * Cystic Duct > from gallbladder joins common hepatic duct to form = Common Bile Duct, which joins pancreatic duct at the Hepatopancreatic Ampulla** (where pancreatic/hepatic ducts come together) Hepatopancreatic Ampulla > empties into duodenum at major duodenal papilla Smooth muscle sphincter surrounds bile duct where it enters hepatopancreatic ampulla. Gallbladder > small sac on inferior surface of liver that stores bile. Bile flows from gallbladder through cystic duct into common bile duct, or back up cystic duct into gallbladder. DIAGRAM ** 1) Hepatic ducts carry bile from liver lobes, combine to form hepatic duct * 2) Common hepatic duct combines with cystic duct from gallbladder to form common bile duct 3) Common bile duct and pancreatic duct combine to form hepatopancreatic ampulla 4) Hepatopancreatic ampulla empties bile/pancreatic secretions into duodenum at major duodenal papilla 5) Accessory pancreatic duct empties pancreatic secretions into duodenum at minor duodenal papilla Liver Functions Metabolism Receiv