Digestive System

Digestive System Ex 38

Overview • Alimentary Canal • hollow tube from mouth to anus • outside of the body • covered with mucous membrane • Accessory Digestive Organs • teeth, tongue, gallbladder, salivary glands, liver, and pancreas

Oral Cavity • Tongue and Teeth

Oral Cavity • Teeth • incisors, canines, premolars, molars

Oral Cavity • Salivary Glands • secrete saliva • contains enzymes for digestion • contains mucous for formation of the bolus • Parotid Gland • serous • enzymes • Sublingual Gland • mucous • Submandibular Gland • mixed • demilune

Oral Cavity

Lumen Overview • Serosa • supports, protects, allows viscera to move without friction • epithelium, connective tissue • Muscularis Externa • contractions cause peristalsis • myenteric plexus • outer longitudinal, inner circular • Submucosa • area for nutrition and protection • carries blood vessels, submucosal plexus, lymph nodules • Mucosa • secretes digestive enzymes & mucous, barrier for bacteria, absorption of food • epithelium, lamina propria, muscularis mucousae

Lumen Overview • Serosa • protects, allows viscera to move without friction • epithelium, connective tissue • Muscularis Externa • contractions cause peristalsis • myenteric plexus • outer longitudinal, inner circular • Submucosa • area for nutrition and protection • carries blood vessels, submucosal plexus, lymph nodules • Mucosa • secretes digestive enzymes & mucous, barrier for bacteria, absorption of food • epithelium, lamina propria, muscularis mucousae

Esophagus • Esophagus • transports food bolus from oropharynx to the stomach via peristaltic action • Body of the esophagus • Sphincters • upper esophageal sphincter • lower esophageal sphincter • defects in sphincter tone can cause disease: GERD and Hiatal Hernia

Esophagus • Lower Esophageal Sphincter • Made up not only of a muscular band but also forces of the surrounding diaphragm contribute to the lower esophageal tone. • Defects in tone can cause disease • GERD • Hiatal hernia

Esophagus • Mucosa • nonkeratinized stratified squamous epithelium • Submucosa • esophageal glands, submucosal plexus, blood vessels • Muscularis Externa • upper 1/3 voluntary striated smooth muscle • middle 1/3 mixed • lower 1/3 involuntary smooth muscle • myenteric plexus • Adventitia • no serosa

Stomach • Responsible for initial digestion of food • mechanical breakdown through contractions of musculature • secretion of enzymes (namely pepsin) • Parts of the Stomach • lesser curvature • lesser omentum • greater curvature • greater omentum • fundus • cardia • body • antrum or pylorus • pyloric sphincter

Stomach • Responsible for initial digestion of food • Parts of the Stomach • lesser curvature • lesser omentum • greater curvature • greater omentum • fundus • cardia • body • antrum or pylorus • pyloric sphincter • angulus • rugae • increases surface area for absorbtion

Stomach • Mucosa • simple columnar epithelium • gastric pits leading to gastric glands • mucous neck cells, parietal cells (HCL), chief cells (pesinogen) • Submucosa • usual glands, submucosal plexus, blood vessels • Muscularis Externa • inner oblique, middle circular, outer longitudinal • myenteric plexus • Serosa

Gastric Glands • Gastric Pit • mucous neck cell • thick, alkaline mucous • parietal cell • HCl, intrinsic factor • chief cell • pepsinogen, gastric lipase • G cell • gastrin

Intestine Overview • Small Intestine • pyloric sphincter to ileocecal valve • breaks down food so molecules can be absorbed • duodenum • jejunum • ileum • Large Intestine • fluid absorbtion • some vitamin production • cecum • ascending colon • transverse colon • descending colon • sigmoid colon • rectum

Small Intestine • Duodenum • full chemical mixture for food digestion • bile and pancreatic enzymes enter here • major and minor papillae (spincter of Oddi) • mostly retroperitoneal • most absorption occurs here • Bulb • C-Loop

Small Intestine • Jejunum • plicae circularis • free of mesenteric fat

Small Intestine • Ileum • no plicae • mesenteric fat partially attached • important for iron absorbtion

Small Intestine • Mucosa • simple columnar epithelium folded into villi • microvilli on luminal cell surface • crypts of Lieberkuhn • Submucosa • duodenal glands (brunner) • Peyer’s Patches (lymphoid tissue in ileum) • Muscularis Externa • inner circular • outer longitudinal • myenteric plexus • Serosa

Small Intestine

Small Intestine • Mucosa • simple columnar epithelium folded into villi • microvilli on luminal cell surface • crypts of Lieberkuhn • Submucosa • duodenal glands (brunner) • Peyer’s Patches (lymphoid tissue in ileum) • Muscularis Externa • inner circular • outer longitudinal • myenteric plexus • Serosa

Small Intestine

Small Intestine • Mucosa • simple columnar epithelium folded into villi • microvilli on luminal cell surface • crypts of Lieberkuhn • Submucosa • submucosal plexus • duodenal glands (brunner) • Peyer’s Patches (lymphoid tissue in ileum) • Muscularis Externa • inner circular • outer longitudinal • myenteric plexus • Serosa

Large Intestine • ileocecal valve • Gateway to the cecum • cecum • ascending colon • hepatic flexure • transverse colon • splenic flexure • descending colon • sigmoid colon • rectum • anus

Large Intestine • Ileum • Cecum • Appendix • contains a small lumen, when it is unable to clear debris it becomes infected

Large Intestine • Tinea Coli • outer longitudinal layer is reduced to 3 bands that run longitudinally along the colon • Haustra • bulging walls of the colon due to lack of longitudinal muscular support.

Large Intestine • Mucosa • simple columnar epithelium • no villi or microvilli • crypts of Lieberkuhn • goblet cells • Submucosa • usual glands, submucosal plexus, blood vessels • Muscularis Externa • inner circular • outer longitudinal in three bands called tinea coli • myenteric plexus • Serosa

Large Intestine • Rectum • storage are for stool • has 3 valves • controls flow of stool/gas

Large Intestine • anus • stratified squamous epithelium • internal/external anal sphincters

Liver • Main Functions • produces bile • acts as a soap to aid digestion of fat • stores sugar • as glycogen • processes chemicals and toxins • most of the venous return from the digestive system passes through the liver

Liver • Anatomy • Lobes • right • left • caudate • quadrate • Falciform Ligament • divides R and L lobes • suspends liver from diaphragm and ant abd wall • gallbladder

Liver

Liver • Anatomy • hepatic artery • branches off celiac trunk

Liver • Anatomy • Portal Vein • most of the venous return from the digestive system

Liver • Anatomy • Hepatic Vein • returns venous blood to IVC

Liver: Histology • Venous Flow Through Liver • Portal Vein • blood coming in from intestines • Sinusoids • channels between rows of hepatic cells • Central Vein • sinusoids empty into this structure • blood returns to hepatic vein • Bile Canaliculi • bile produced by hepatocytes travel to bile ducts • Portal Triad • portal vein is accompanied by a bile duct and a branch of the hepatic artery

Pancreas • Anatomy • snuggled in the C-loop of the duodenum • head • body • tail

Pancreas • functions • produces insulin for control of blood glucose • islets of langerhans • released into bloodstream • produces digestive enzymes • acinar cells • released into duodenum through pancreatic ducts • main (Wirsung) • accessory (Santorini)

Pancreas Histology • functions • lobular structure much like a salivary gland • acini lined with acinar cells • contain zymogen granules that contain digestive enzymes • islets of Langerhans • produce insulin

Pancreas Histology • Pancreatic ducts • secretes bicarb • neutralizes stomach acid

Liver and Pancreas • Bile ducts • R/L hepatic, common hepatic, cystic, common bile duct • the common bile duct and the pancreatic duct usually join just before emptying into the duodenum

Digestive System