LO 2 — Anatomical Relationships

Serous Sac Anatomy

Peritoneal cavity normally contains only ___

Free air rises to ___ in upright patient; fluid collects in ___ (F) or ___ (M)

Pneumoperitoneum on CXR always indicates ___

Visceral peritoneum differs from parietal: visceral = ___, parietal = ___

Intraperitoneal vs Retroperitoneal — Classify Each Organ

Organ / Structure	IP or Retro?	Organ / Structure	IP or Retro?
Stomach		Duodenum D2–D4
Pancreas head/body/neck		Pancreas tail
Jejunum & ileum		Ascending colon
Transverse colon		Descending colon
Sigmoid colon		Kidneys & ureters

Greater & Lesser Sacs

Lesser sac (omental bursa) is located ___

Greater and lesser sacs communicate via ___

Borders of omental foramen — anterior: ___; posterior: ___

Acute pancreatitis fluid / pancreatic pseudocyst collect in ___

Superior border of omental foramen = ___; inferior = ___

Greater & Lesser Omenta

Greater omentum attaches to ___, nicknamed ___

Lesser omentum = ___ ligament + ___ ligament

Hepatoduodenal ligament contents (portal triad: 3 structures)

Hepatogastric ligament connects ___ to ___, contains ___

Pringle maneuver = compress ___ to temporarily occlude ___

LOs 1 & 2 — GI Tract Segments & Clinical Relationships

Esophagus — Regional Blood Supply

Region	Arterial Supply	Venous Drainage
Cervical
Thoracic
Abdominal

Esophageal Varices & Achalasia

Abdominal esophageal veins drain into ___ system → in portal HTN, diverted to ___ system

Esophageal varices risk = ___ → clinical presentation: ___

Achalasia = failure of ___ to relax → dysphagia to ___

Achalasia barium swallow sign = ___

Achalasia in Chagas disease: T. cruzi destroys ___

Stomach Anatomy (HY per Dr. Uren)

Stomach regions in order: ___

Lesser curvature blood supply: ___ arteries (within ___ omentum)

Greater curvature blood supply: ___ arteries (within ___ omentum)

GDA runs ___ to D1; erosion by posterior ulcer → ___

Short gastric arteries arise from ___ and supply the ___

Duodenum — 4 Parts

Part	Peritoneal Status	Key Anatomical Fact / Clinical Relevance
D1 (superior)
D2 (descending)
D3 (horizontal)
D4 (ascending)

Jejunum vs Ileum — Key Differences

Jejunum: few, simple arcades; ileum: ___

Jejunum: long vasa recta; ileum: ___

Peyer's patches found in ___ (absent in ___)

Jejunum: plicae circulares tall & packed; ileum: ___

LO 1 — Vasculature, Lymphatics & Portal System

Foregut / Midgut / Hindgut — Master Table

Division	Extent (start → end)	Artery	Aortic Level
Foregut
Midgut
Hindgut

Celiac Trunk Branches

Celiac trunk 3 daughters: ___, ___, ___

Left gastric artery: supplies ___ + gives off ___ to distal esophagus

Splenic artery: supplies spleen + gives off ___ (fundus) + ___ (left greater curvature)

GDA branches: ___ (right greater curvature) + ___ (pancreas/duodenum)

Hepatic artery proper → ___ hepatic (gives off cystic artery → gallbladder) + ___ hepatic

SMA Branches (Midgut Supply)

Branch	Supplies
Inferior pancreaticoduodenal arteries
Middle colic artery
Right colic artery
Ileocolic artery
Jejunal / ileal arteries

IMA Branches (Hindgut Supply)

Branch	Supplies
Left colic artery
Sigmoid arteries
Superior rectal artery

Hepatic Portal System & Lymphatics

Portal vein formed by ___ + ___ + ___

3 portosystemic anastomoses in portal HTN: ___, ___, ___

Cisterna chyli located at ___, gives rise to ___ duct → empties at ___

Virchow's node = enlarged ___ lymph node; signals ___

LOs 1 & 3 — Innervation, Referred Pain, Meckel's

Enteric Nervous System — Two Plexuses

Plexus	Location in Wall	Function
Myenteric (Auerbach's)
Submucosal (Meissner's)

Hirschsprung Disease

Hirschsprung = congenital absence of ___ in ___ of colon/rectum

Barium enema shows ___ between narrow ___ and dilated proximal colon (___)

Caused by failure of ___ cell migration; gene mutation = ___

Autonomic Innervation Table (Dr. Uren: Must Memorize!)

⚠ Pelvic splanchnic nerves (S2–S4) = PSNS — NOT sympathetic! This is a classic trap.

GI Division	SNS Nerve	PSNS Nerve
Foregut
Midgut
Hindgut

Referred Pain — Abdominal Patterns

Pain Location	GI Origin (organ + embryological division)	Spinal Levels
Epigastric
Periumbilical
Hypogastric / suprapubic

Meckel's Diverticulum — Rule of 2's

Meckel's = true diverticulum; embryological origin: persistence of ___ duct

Rule of 2's: 2% population, 2 inches long, ___ feet from ileocecal valve, first ___ years of life

Most common ectopic tissue = ___; causes ___ → ulceration → bleeding

Meckel's scan: radiotracer = ___; taken up by ___; hot spot in ___

Classic presentation in children: ___; mimics appendicitis because both are ___

Meckel's vs appendicitis: Meckel's → ___; appendicitis → fever, rebound tenderness at ___

Practice Questions — GI08 USMLE-Style

Q1. During cholecystectomy, the surgeon compresses the hepatoduodenal ligament between thumb and finger to stop liver bleeding (Pringle maneuver). Which 3 structures are occluded?

A. Portal vein, hepatic artery, common bile duct
B. Portal vein, IVC, cystic duct
C. Hepatic veins, hepatic artery, cystic duct
D. SMA, portal vein, cystic duct
E. Hepatic artery, celiac trunk, common bile duct

✅ A — Portal vein, hepatic artery proper, and common bile duct (portal triad). The hepatoduodenal ligament is the free edge of the lesser omentum and forms the anterior border of the omental foramen. All three structures in it are temporarily occluded to control hepatic inflow.

Q2. Which list contains ONLY retroperitoneal structures?

A. Stomach, duodenum D1, sigmoid colon, rectum
B. Suprarenal glands, aorta, duodenum D2–D4, pancreas body/tail
C. Suprarenal glands, kidneys, duodenum D2–D4, ascending colon
D. Liver, gallbladder, pancreas head, cecum
E. Spleen, transverse colon, sigmoid colon, appendix

✅ C — SAD PUCKER: Suprarenal glands, Aorta/IVC, Duodenum D2–D4, Pancreas (except tail), Ureters, Colon (ascending & descending), Kidneys, Esophagus, Rectum. Pancreas tail is intraperitoneal (splenorenal ligament). Stomach, spleen, transverse colon, sigmoid colon, liver, and gallbladder are intraperitoneal.

Q3. During trauma laparotomy, a surgeon enters the lesser sac. Through which structure did they most likely pass?

A. Through the greater omentum directly
B. Via the epiploic foramen (foramen of Winslow), posterior to the hepatoduodenal ligament
C. Through the left gastroepiploic vessels
D. Via the falciform ligament
E. Through the transverse mesocolon

✅ B — The epiploic foramen (foramen of Winslow) is the natural communication between the greater and lesser peritoneal sacs. Bounded anteriorly by the hepatoduodenal ligament, posteriorly by IVC, superiorly by caudate lobe of liver, inferiorly by D1.

Q4. Endoscopy shows a dilated esophagus with bird-beak narrowing at the GEJ. Manometry confirms failure of the LES to relax. What cell type is lost?

A. Interstitial cells of Cajal
B. Myenteric plexus inhibitory nitrergic neurons
C. Submucosal plexus secretomotor neurons
D. Chief cells of the gastric fundus
E. Parietal cells of gastric body

✅ B — Achalasia = loss of inhibitory neurons (NO/VIP) in the myenteric (Auerbach's) plexus at the LES → tonic contraction → failure of relaxation → progressive dysphagia to BOTH solids and liquids from onset. Chagas disease (T. cruzi) destroys these neurons → secondary achalasia.

Q5. A 72-year-old woman with atrial fibrillation develops sudden abdominal pain and bloody diarrhea after colonoscopy shows ischemic changes at the splenic flexure. Why is this location vulnerable?

A. Splenic flexure has a long mesentery prone to volvulus
B. Watershed area between SMA and IMA territories with limited collateral supply
C. Splenic flexure receives blood exclusively from IMA with no collaterals
D. Retroperitoneal; compressed by left kidney
E. Site of transition between taeniae coli and continuous longitudinal muscle

✅ B — The splenic flexure is a watershed zone between SMA territory (middle colic artery) and IMA territory (left colic artery). The marginal artery of Drummond is often tenuous here → most vulnerable during low-flow states, embolism, or AAA repair.

Q6. A patient with cirrhosis vomits bright red blood. Endoscopy reveals varices at the GEJ. These varices arise from dilation of which portosystemic anastomosis?

A. Superior rectal vein ↔ middle/inferior rectal veins
B. Paraumbilical veins ↔ superficial epigastric veins
C. Left gastric (coronary) vein ↔ azygos/esophageal veins
D. Splenic vein ↔ left renal vein
E. SMV ↔ inferior epigastric veins

✅ C — Esophageal varices form where the left gastric (coronary) vein (portal) meets the azygos/esophageal system (systemic). Most dangerous portosystemic shunt — rupture → massive hematemesis. Anorectal varices = superior rectal ↔ inferior/middle rectal; caput medusae = paraumbilical ↔ superficial abdominal.

Q7. A 3-day-old infant fails to pass meconium. Barium enema shows megacolon proximal to a narrow rectosigmoid segment. Rectal biopsy: absent ganglion cells. What is the underlying mechanism?

A. Neural crest cell migration failure → tonically constricted aganglionic segment
B. Hypertrophy of myenteric plexus → excessive peristalsis
C. Loss of pacemaker cells (ICC) in sigmoid colon
D. Overactivation of Meissner's plexus → hypersecretion
E. Absence of internal anal sphincter smooth muscle

✅ A — Hirschsprung disease: neural crest cells fail to migrate to the distal colon → absent myenteric AND submucosal plexus ganglion cells → aganglionic segment stays tonically contracted → functional obstruction → proximal colon dilates (megacolon). RET proto-oncogene mutation.

Q8. A 30-year-old man has painless rectal bleeding. Colonoscopy finds a 2 cm outpouching 2 feet proximal to the ileocecal valve with ectopic gastric and pancreatic tissue on biopsy. Where would a Meckel's scan show a hot spot?

A. Right upper quadrant
B. Left upper quadrant
C. Left lower quadrant
D. Right lower quadrant
E. Periumbilical region

✅ D — ⁹⁹ᵐTc-pertechnetate is taken up by ectopic gastric mucosa → hot spot in the RLQ where the terminal ileum lies (2 feet from ileocecal valve). Painless rectal bleeding in a child = Meckel's diverticulum until proven otherwise (Rule of 2's).

Abdominal Viscera I: GI Tract — Active Recall