GI Bleeding — Anatomy Segment (Under 5 Minutes)

Slide Structure & What to Say

Slide 1 — The Anatomical Landmark: Ligament of Treitz (~45 sec)

• The ligament of Treitz (suspensory muscle of the duodenum) is the dividing line between upper and lower GI bleeding.
• Upper GI bleeding (UGIB): any source proximal to the ligament of Treitz — oesophagus → stomach → duodenum (1st–4th parts)
• Lower GI bleeding (LGIB): any source distal to it — jejunum, ileum, colon, rectum, anus

This distinction drives everything clinically — how the patient presents (haematemesis vs. rectal bleeding), how you investigate, and how you manage.

Slide 2 — Upper GI Tract: Key Anatomy (~1.5 min)

Slide 3 — Lower GI Tract: Key Anatomy (~1.5 min)

• SMA territory: cecum, ascending colon, proximal 2/3 transverse colon — diverticulae most common here
• IMA territory: distal transverse, descending, sigmoid — angioectasia common here
• Watershed zones (Griffiths' point at splenic flexure, Sudeck's point at rectosigmoid) — most vulnerable to ischaemia

Slide 4 — Why Anatomy Matters Clinically (~1 min)

• Haematemesis → UGIB (proximal to Treitz)
• Melaena → usually UGIB (blood digested over ~8 hours), occasionally proximal LGIB
• Haematochezia → usually LGIB, but massive UGIB can also cause it
• Knowing the arterial supply tells you where to look on angiography/CT angiography and where to embolise
• Knowing venous drainage explains portal hypertension varices (portal → azygos at GOJ)

Images to Use in Your Slides

Image 1 — Lower GI Vascular Territories (use on Slide 3)

Image 2 — Upper GI Tract Schematic (use on Slide 2)

Image 3 — Suggested external resource

Timing Summary

The Clash Risk

• Why varices bleed (portal hypertension → pressure → rupture)
• Why peptic ulcers bleed (mucosal breakdown → vessel erosion)
• The mechanism behind haematemesis vs. melaena vs. haematochezia

How to Reframe Slide 4 (Keep It, Change the Angle)

Practical Tip

"I'll cover what the symptoms tell us about where the bleeding is anatomically — the why it bleeds is coming up in the next section."

Full Presentation Script

Slide 1 — The Ligament of Treitz (~45 seconds)

"Good morning everyone. I'll be covering the anatomy of the gastrointestinal tract as it relates to GI bleeding.

Before we talk about any specific structure, there is one anatomical landmark that underpins everything in GI bleeding — the ligament of Treitz, also called the suspensory muscle of the duodenum. It marks the junction between the fourth part of the duodenum and the jejunum.

This single structure divides GI bleeding into two categories. Everything proximal to it — the oesophagus, stomach, and duodenum — is upper GI bleeding. Everything distal — the jejunum, ileum, colon, rectum, and anus — is lower GI bleeding.

Keep that landmark in mind, because every structure I discuss from here sits on one side of that line."

Slide 2 — Upper GI Tract Anatomy (~1 min 30 seconds)

"Starting with the upper GI tract.

The oesophagus is the first structure of note. Its lower third is where you find oesophageal varices — these develop in the submucosal venous plexus at the gastro-oesophageal junction, a site where the portal and systemic circulations meet. The gastro-oesophageal junction itself is also where Mallory-Weiss tears occur — linear mucosal splits at that junction.

Moving into the stomach — it has an extraordinarily rich arterial supply from the coeliac axis: the left and right gastric arteries along the lesser curve, the left and right gastroepiploic arteries along the greater curve, and the short gastric arteries supplying the fundus. This is why gastric bleeding can be brisk and difficult to control.

Finally the duodenum, specifically the first part or the bulb — this is the most common site for peptic ulcer disease. What makes it surgically important is the gastroduodenal artery, which runs directly posterior to the first part of the duodenum. A posterior duodenal ulcer that erodes into the GDA produces one of the most catastrophic bleeds we see — high volume, arterial, and potentially life-threatening."

Slide 3 — Lower GI Tract Anatomy (~1 min 30 seconds)

"Now the lower GI tract, distal to the ligament of Treitz.

The small bowel — jejunum and ileum — is supplied by the superior mesenteric artery via long vasa recta. Bleeding here is uncommon but serious, and it's notoriously difficult to access endoscopically.

The colon is where most lower GI bleeding originates, and its anatomy is best understood through two arterial territories — which you can see on this diagram.

(point to image)

The superior mesenteric artery supplies the small bowel, caecum, ascending colon, and proximal two-thirds of the transverse colon — shown in red. The inferior mesenteric artery supplies the distal transverse, descending, and sigmoid colon — shown in green. The rectum has a dual supply from the IMA above and the internal iliac arteries below — shown in blue.

Two points on the colon worth highlighting: the splenic flexure and the rectosigmoid junction are watershed zones — where the terminal branches of two arterial systems meet. These areas are most vulnerable to ischaemia when blood pressure drops.

Finally the anal canal — internal haemorrhoids arise from the superior rectal venous plexus above the dentate line. External haemorrhoids arise from the inferior rectal plexus below it. A simple anatomical line — the dentate line — separates them."

Slide 4 — Anatomy Maps the Bleeding Source (~1 minute)

"So to bring it all together — and I want to be clear this is purely the anatomical perspective, my colleagues will be explaining the mechanisms behind why these sites bleed.

When a patient presents with haematemesis, you are dealing with a source proximal to the ligament of Treitz — the oesophagus, stomach, or duodenum.

Melaena — dark, tarry stool — tells you the source is anatomically far enough proximal that blood undergoes digestion during transit. That typically means proximal to the splenic flexure.

Bright red blood per rectum localises the source to the distal colon or rectum — short transit, no time for digestion.

And knowing the arterial supply — coeliac axis for the upper tract, SMA and IMA for the lower — tells the surgical team where to look on CT angiography and where to target for embolisation.

So the anatomy does not just describe the structures — it tells you where the patient is bleeding from before you even pick up a scope.

I'll hand over now to my colleague who will cover the pathophysiology."

Timing Summary

• Speak to the audience, not the slide — glance at the image to direct attention, then look back up
• The GDA line on Slide 2 is your "wow moment" — slow down there, surgeons love it
• Your last line is a clean handoff — it signals to the examiner that the team is coordinated and you know your scope