GI Tract and Abdominal Anatomy - Quick Reference Notes

Peritoneum and Spaces

  • Peritoneal cavity: potential space between parietal and visceral peritoneum; surfaces of organs contact the parietal peritoneum in life.
  • Two portions: greater sac (main body) and lesser sac (omental bursa).
  • Lesser sac has superior recess behind the lesser omentum and an inferior recess behind the stomach, extending into the greater omentum.
  • Epiploic foramen (foramen of Winslow) connects the greater and lesser sacs.

Stomach and Omenta

  • Stomach curvatures: greater curvature and lesser curvature.
  • Greater omentum: gastrocolic ligament attaches to greater curvature; three portions: gastrocolic, gastrophrenic, gastrosplenic (gastrolienal).
  • Lesser omentum: attaches along lesser curvature and first part of duodenum to the liver; two parts: hepatogastric and hepatoduodenal.
  • Stomach regions: cardiac (cardia), body, fundus, pyloric region (pyloric antrum and pyloric canal).
  • Esophageal estraction: anterior left vagus; posterior right vagus.
  • Angular notch (incisura angularis) marks junction of body and pyloric region on the lesser curvature.
  • Gastric mucosa folds: rugae; pattern varies by region (fundus/body crisscross; pyloric antrum parallel to stomach long axis).

Duodenum and Small Intestine

  • Duodenum: 4 parts (superior, descending, horizontal, ascending); first part mobile with a mesentery; rest largely retroperitoneal.
  • Major and minor duodenal papillae; hepatopancreatic ampulla (of Vater) opens at major papilla; sphincter of Oddi.
  • Main and accessory pancreatic ducts: main joins common bile duct at hepatopancreatic ampulla; accessory drains uncinate process/head and usually joins main duct or opens at minor papilla.
  • Hepatoduodenal ligament attaches to first part of the duodenum; forms part of the portal triad enclosure.
  • Duodenojejunal junction (DJ junction): located at the duodenojejunal flexure; suspended by the suspensory ligament of Treitz.
  • Jejunum vs ileum: jejunum has thicker wall; ileum thinner; wall organization makes differentiation variable in situ; ileocecal junction marks transition to large intestine.
  • Root of the mesentery: oblique, from left upper quadrant to right lower quadrant; contains vessels and nerves.
  • Large intestine: cecum (ileocecal valve), appendix; taeniae coli; haustra; appendices epiploicae.
  • Rectum: lacks taeniae coli, haustra, and appendices epiploicae.

Large Intestine Details

  • Large intestine frames small intestine on three sides: right (cecum, ascending), superior (transverse), left (descending, sigmoid).
  • Cecum: ileocecal orifice and valve; vermiform appendix opens into cecum below the ileocecal valve; mesoappendix contains appendicular artery.
  • Teniae coli converge at base of appendix.
  • Appendix positions may vary; most common: retrocecal.
  • Sigmoid colon: long mesentery (sigmoid mesocolon); rectosigmoid junction ~ S-3.
  • Features unique to large intestine: taeniae coli, haustra, appendices epiploicae (except rectum).

Liver, Gallbladder, and Biliary System

  • Liver surfaces: diaphragmatic and visceral; bare area; coronary ligaments; falciform ligament; right/left triangular ligaments.
  • Porta hepatis: hilum where vessels/ducts enter/exit liver; contains portal triad components.
  • Portal triad (at hepatoduodenal ligament): portal vein (posterior), hepatic artery proper (medial), common bile duct (lateral).
  • Lesser omentum: extends from lesser curvature to visceral surface of liver; hepatoduodenal ligament contains portal triad.
  • Gallbladder: attached to visceral surface of liver; fundus projects below inferior border of liver; body and neck lead to cystic duct which joins the common hepatic duct to form the common bile duct.
  • Common hepatic duct and cystic duct merge to form the common bile duct; common bile duct opens into second part of the duodenum at the major duodenal papilla after joining with main pancreatic duct at hepatopancreatic ampulla.
  • Cystic artery typically within cystohepatic (Calot) triangle (cystic duct, common hepatic duct, liver).
  • Clinical correlation: cholecystoenteric fistula and gallstone impaction at hepatopancreatic ampulla can cause biliary or GI symptoms.

Portal Circulation and Pancreatic/Biliary Ducts

  • Portal vein formed behind the neck of the pancreas by union of superior mesenteric vein (SMV) and splenic vein; inferior mesenteric vein may drain into SMV, splenic vein, or their junction.
  • Marginal artery (Drummond) runs along the inner border of the large intestine, formed by SMA and IMA branches.
  • Portal hypertension can cause varices: esophageal (via left gastric), rectal, and caput medusae around the umbilicus.

Superior Mesenteric Syndrome (Nutcracker)

  • Left renal vein and third part of the duodenum pass between aorta posteriorly and SMA anteriorly; compression can occur, producing symptoms.

Abdominal Blood Vessels

  • Abdominal aorta: begins at T12, ends at L4 by bifurcating into right and left common iliac arteries.
  • Celiac trunk: three branches – common hepatic artery, left gastric artery, splenic artery.
  • Common hepatic artery branches: hepatic artery proper (gives right/left hepatic arteries and right gastric); gastroduodenal artery (gives supraduodenal, superior pancreaticoduodenal, right gastroepiploic).
  • Splenic artery: short gastric arteries (fundus) and left gastroepiploic.
  • Superior mesenteric artery (SMA): first major branch is inferior pancreaticoduodenal; other branches to the small intestine and right/mid transverse colon (ileocolic artery with appendicular branch; right colic; middle colic).
  • Inferior mesenteric artery (IMA): left colic; sigmoid arteries; superior rectal.
  • Note: SMA lies posterior to neck of pancreas and anterior to the third part of the duodenum and left renal vein; IMA arises about 3 cm above aortic bifurcation.

Portal Venous System and Drainage

  • Superior mesenteric vein, splenic vein, and inferior mesenteric vein form the portal vein (behind the neck of the pancreas or via its confluence).
  • Paraumbilical veins in falciform ligament connect portal circulation to systemic veins around the umbilicus; caput medusae seen in portal hypertension.

Kidneys, Suprarenal Glands, and Urinary System

  • Kidneys: retroperitoneal; right kidney lower than left due to liver.
  • Renal hilus: renal vein anterior, artery between veins and ureter posterior.
  • Renal fascia divides perirenal fat (inside fascia) and pararenal fat (outside fascia).
  • Left renal vein longer; may be compressed between aorta (posterior) and SMA (anterior).
  • Tributaries of left renal vein: left testicular/ovarian veins.
  • Renal arteries: usually multiple; posterior to renal veins; right renal artery typically longer.
  • Ureter: crosses the pelvic brim near bifurcation; descends to bladder.
  • Suprarenal (adrenal) glands: right gland posterior to IVC; left gland near left kidney; multiple arterial sources; venous drainage: left suprarenal vein to left renal vein; right suprarenal vein drains to IVC.

Nerves and Posterior Abdominal Wall

  • Lumbar plexus nerves: subcostal (T12); iliohypogastric (L1); ilioinguinal (L1); lateral femoral cutaneous (L2-L3); femoral (L2-L4); genitofemoral (L1-L2); obturator (L2-L4); accessory obturator (occasionally); lumbosacral trunk (L4-L5).
  • Four branches arise at the lateral border of psoas major; two at the medial border; one pierces the psoas.
  • Posterior abdominal wall muscles: psoas major, psoas minor (absent in ~40%), iliacus, quadratus lumborum, transversus abdominis.

Diaphragm

  • Four portions: sternal, costal, lumbar, central tendon.
  • Lumbar portion formed by two crura: left and right.
  • Esophageal hiatus formed by crus; Treitz ligament (suspensory muscle of duodenum) extends from the right crus.
  • Arcuate ligaments: medial, lateral, and median (transversalis fascia thickenings).
  • Openings: vena caval foramen (level varies), esophageal hiatus, aortic hiatus; higher openings are more anterior.
  • Structure passes through openings: standard list includes IVC, esophagus, aorta with accompanying structures; details depend on level.

Spermatic Cord, Scrotum, and Testis

  • Spermatic cord contents: vas deferens; testicular artery; pampiniform plexus; cremasteric artery; artery to vas deferens; genital branch of genitofemoral nerve; autonomic fibers; lymphatics.
  • Coverings of the spermatic cord (from external to internal): external spermatic fascia (from external oblique aponeurosis), cremasteric fascia/muscle (from internal oblique), internal spermatic fascia (from transversalis fascia).
  • Processus vaginalis and tunica vaginalis: remnants post-descent; gubernaculum testis forms scrotal ligament.
  • Scrotum: dartos fascia/muscle; skin with possible folds; fasciae continuous with abdominal wall structures.
  • Testis: tunica vaginalis covers most surfaces except posterior; tunica albuginea is the fibrous capsule; septa subdivide the interior into lobules.