Anatomy GI part 1

Functions of the digestive tract

Ingestion; secretion of enzymes/acid/mucus; mixing & propulsion; digestion; absorption; defecation.

Four concentric layers of the GI wall

Mucosa (epithelium + lamina propria + muscularis mucosae); submucosa (dense CT + Meissner's plexus); muscularis externa (inner circular + outer longitudinal mm. + Auerbach's plexus); serosa/adventitia.

Mucosal epithelium of the oral cavity/esophagus

Non-keratinized stratified squamous.

Mucosal epithelium of the stomach

Simple columnar mucus-secreting.

Mucosal epithelium of the small intestine

Simple columnar with microvilli (villi + crypts).

GERD defect

Incompetent lower esophageal sphincter allows reflux; hiatal hernia displaces LES into thorax, further weakening it.

Metaplastic change in Barrett's Esophagus

Squamous → intestinal-type columnar epithelium with goblet cells; predisposes to dysplasia → adenocarcinoma.

Neural plexus lost in achalasia

Loss of myenteric (Auerbach) plexus; 'bird's beak' narrowing at GE junction on barium swallow.

Infantile hypertrophic pyloric stenosis presentation

2-8 weeks of age; palpable 'olive'-shaped mass in right upper quadrant.

Gastric cell destroyed in pernicious anemia

Parietal cells; intrinsic factor loss → vitamin B₁₂ malabsorption → megaloblastic anemia.

Features of WDHA syndrome in VIPoma

Watery diarrhea; hypokalemia; achlorhydria.

Typical obstructive cause of appendicitis in adults

Fecalith.

Typical obstructive cause of appendicitis in children

Lymphoid hyperplasia.

McBurney's point

1/3 from ASIS to umbilicus.

Mucosa of the digestive tract

Inner lining: epithelium + lamina propria + muscularis mucosae.

Epithelium in the GI tract

Lining cell layer facing lumen (varies: squamous or columnar).

Lamina propria

Loose CT beneath epithelium with vessels, immune cells, glands.

Muscularis mucosae

Thin smooth-muscle layer that mobilizes the mucosa for secretion/absorption.

Submucosa

Dense irregular CT with blood/lymphatics, exocrine glands (in select regions), Meissner's plexus.

Muscularis externa

Inner circular & outer longitudinal smooth-muscle layers for segmentation and peristalsis; contains Auerbach's plexus.

Serosa covering intraperitoneal organs

Visceral peritoneum—mesothelium + areolar CT.

Adventitia

Connective-tissue covering of retroperitoneal GI segments.

Functions of the Oral Cavity

Sensory analysis; mechanical processing; lubrication; limited digestion.

Structures of a Tooth

Enamel; dentin; pulp; cementum.

Types of Tongue Papillae

Filiform; fungiform; circumvallate; foliate.

Salivary Glands and their secretions

Parotid (serous), submandibular (mixed), sublingual (mucous).

Bolus

Chewed food mixed with saliva.

Pharynx in digestion

Common passage for air and food; propels bolus to esophagus.

Upper Esophageal Sphincter

Skeletal-muscle ring at pharynx-esophagus junction.

Lower Esophageal Sphincter

Muscle that prevents reflux of stomach contents into the esophagus.

Lower Esophageal Sphincter

Smooth-muscle barrier to prevent reflux at GE junction.

Rugae

Gastric mucosal folds allowing distension.

Regions of the Stomach

Cardia; fundus; body; pylorus.

Gastric pits

Invaginations of surface epithelium leading into glands.

Chief cells

Secrete pepsinogen.

Parietal cells

Secrete HCl and intrinsic factor.

Mucous neck cells

Cells in gastric glands that secrete protective mucus.

Enteroendocrine cells

Cells that secrete GI hormones (gastrin, CCK, etc.).

Gastrin

Stimulates acid secretion, mucosal growth, motility.

G cells

Located in pylorus and duodenum; secrete gastrin.

Histamine in the stomach

From ECL cells; binds H₂ receptors to increase acid.

Enterochromaffin-like (ECL) cells

Cells that secrete histamine.

Somatostatin in the gut

Inhibits release of gastrin, CCK, secretin, GIP, etc.

D cells

Somatostatin-secreting cells in pylorus & pancreas.

Pepsinogen

Inactive precursor to pepsin.

Intrinsic factor

Glycoprotein for B₁₂ absorption in terminal ileum.

Chyme

Semi-liquid mixture of food and gastric secretions.

Gastric Inhibitory Peptide (GIP)

Decreases gastric acid secretion; increases insulin release.

Secretin

Increases pancreatic/biliary HCO₃⁻; decreases gastric acid.

Cholecystokinin (CCK)

Decreases gastric emptying; increases pancreatic enzymes & gallbladder contraction.

Motilin

Stimulates MMC fasting-state peristalsis and pepsin release.

Crypts of Lieberkühn

Intestinal glands secreting alkaline mucus and housing stem cells.

Brunner's glands

Duodenal submucosal glands secreting alkaline mucus.

Peyer's patches

Aggregated lymphoid nodules in the ileum.

Plicae circulares

Permanent mucosal folds in small intestine for absorption.

Villi

Finger-like projections of mucosa to increase surface area.

Microvilli

Brush border extensions on enterocytes.

Enterocytes

Absorptive columnar cells on villi.

Goblet cells

Mucus-secreting cells; increase distally in GI tract.

Paneth cells

Crypt base cells that secrete antimicrobial defensins.

Stem cells in the GI tract

Crypt base cells renewing the epithelium.

Peristalsis

Coordinated waves of muscle contraction propelling contents.

Segmentation

Mixing contractions by circular muscle rings.

Migrating Motor Complex (MMC)

Fasting-state cyclic peristaltic waves clearing debris.

Ileocecal valve reflex

Gastroileal reflex relaxes valve to move chyme into cecum.

Teniae coli

Three longitudinal smooth-muscle bands on colon forming haustra.

Haustra

Sacculations of the colon formed by teniae coli.

Appendix histologically

Lymphoid-rich blind pouch off the cecum.

Rectal columns

Longitudinal mucosal folds in the rectum.

Anal sinuses

Mucus-secreting depressions in the anal canal.

Internal anal sphincter

Smooth-muscle ring under involuntary control.

External anal sphincter

Skeletal-muscle ring under voluntary control.

Portal triad

Not defined in the notes.

Portal triad

Portal vein, hepatic artery, bile duct in liver.

Hepatic lobule

Hexagonal liver unit centered on a central vein.

Hepatocytes

Main parenchymal liver cells.

Sinusoids

Fenestrated capillaries between hepatocyte plates.

Kupffer cells

Liver macrophages lining sinusoids.

Stellate (Ito) cells

Vitamin A-storing perisinusoidal cells.

Bile canaliculi

Small ducts between hepatocytes carrying bile.

Common bile duct

Duct conveying bile to the duodenum.

Cystic duct

Connects gallbladder to common bile duct.

Gallbladder mucosa

Simple columnar with microvilli; no muscularis mucosa.

Rokitansky-Aschoff sinuses

Outpouchings of gallbladder mucosa.

Muscularis externa (GB)

Thick smooth-muscle layer that contracts the gallbladder.

Pancreatic acini

Serous clusters secreting digestive enzymes.

Centroacinar cells

Ductal cells in acini that secrete bicarbonate-rich fluid.

Islets of Langerhans

Endocrine clusters secreting insulin, glucagon, somatostatin.

Intercalated ducts

Smallest pancreatic ducts draining acini.

Intralobular ducts

Ducts within pancreatic lobules.

Interlobular ducts

Larger ducts between lobules leading to main duct.

Sphincter of Oddi

Smooth-muscle valve controlling bile/pancreatic juice flow.

Superior mesenteric artery

Midgut: duodenum (past bile duct) to proximal 2/3 transverse colon.

Inferior mesenteric artery

Hindgut: distal 1/3 transverse colon to anal canal.

Celiac trunk

Foregut: lower esophagus to proximal duodenum.

Hepatic portal vein

Vessel draining GI tract blood into the liver.

Brush border enzymes

Enterocyte surface hydrolases (lactase, sucrase, etc.).

Chylomicrons

Lipid-transport particles formed in enterocytes.

Lymph lacteals

Central lymphatics in villi for fat absorption.

Gastric rugae

Gastric folds—allow stomach expansion.