Sandbox 2

Lower GI bleeding is defined as any bleed that occurs distal to the ligament of Treitz.

Incidence

In the United States the incidence of LGIB ranges from 20.5 to 27 per 100,000 persons per year.

There is a greater than 200 fold increase from the third to the ninth decade of life.

Lower GI bleeding can be classified into 3 groups based on the severity of bleeding:
- Occult lower GI bleeding
- Moderate lower GI bleeding
- Severe lower GI bleeding

Midgut

The midgut is defined as all structures between the foregut and the hindgut. This includes

the distal duodenum, jejunum, ileum, appendix, cecum, ascending colon, hepatic

flexure, and proximal transverse colon. The superior mesenteric artery (SMA)

and its branches provide the blood supply to the midgut. Venous drainage is via the

portal system.

Hindgut

The hindgut includes the distal one-third of the transverse colon, the splenic flexure,

descending colon, sigmoid colon, and rectum. Blood supply is mainly via the inferior

mesenteric artery (IMA), with rectal perfusion through the superior, middle, and inferior

rectal arteries. Venous drainage is via the portal system, with the exception of the

lower rectum, which drains into the systemic circulation.

The SMA and IMA are connected by the marginal artery of Drummond. This vascular

arcade runs in the mesentery close to the bowel and is almost always present. As patients

age, there is increased incidence of occlusion of the IMA. The left colon stays

perfused, primarily because of the marginal arter

		Arterial supply	Venous drainage
Midgut	Distal duodenum, jejunum, ileum, appendix, cecum, ascending colon, hepatic flexure, and proximal transverse colon.	Superior mesenteric artery (SMA) and its branches	Portal system.
Hindgut	Distal one-third of the transverse colon, the splenic flexure, descending colon, sigmoid colon, and rectum	Inferior mesenteric artery (IMA)	Portal system, with the exception of the lower rectum, which drains into the systemic circulation.