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Anatomy of lower GIT& its

blood supplyDr. NEHAL MOHAMMED

MD, Ph.D

Assistant professor of Anatomy &Embryology

KFMC-FOM

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Contents:-

Small intestine

Large intestine:

Colon

Rectum

Anal canal

Blood supply of the GIT

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Fig. 24.22a

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Small Intestine:-

3 regions

a. Duodenum (10 in long):

3 accessory organs associated:-Pancreas (Pancreatic duct)

-Gall Bladder (Cystic D.)

-liver (Hepatic D.)

b.Jejunum (middle portion) between duodenum & ileum

8 ft. long

larger lumen > ileum

absorption of nutrients

c.Ileum longest section of SI (12 ft.)

posterior portion

Terminates at the Ileocecal Valve (opens into the cecum)

Contains Peyers Patches

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Fig. 24.17a

-Duodenum:

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Four parts of the duodenum:-

Superior (first) part:-

at the level of vertebra L1. it lies in the

transverse plane.

Descending (second) part :

at the level of L2. The bile duct and the

pancreatic duct drain in this part.

Horizontal (third) part :

at the level of L3. It lies anterior to theinferior vena cava and the abdominal

aorta. The horizontal part of the duodenumis crossed anteriorly by the superiormesenteric vessels.

Ascending (fourth) part :

ascends to the level of L2. It turnsanteriorly to join the jejunum at theduodenojejunal junction.

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Fig. 24.22bJejunum:--It is widerbored, thickerwalled than the ilium because the plica

circularis are larger, and more numerous than the ileum.

-Simple arterial arcades in its mesentery.

-Less fat and more windows in its mesentery.

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-Ilium:Narrowerlumen, thinnerwall, smooth mucous membrane, more fat ,less

.Peyer patcheswindows and contains

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Jejunum versus Ilium:

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Ileocecal region:-

-Different positions of the appendix:Retrocecal (the commonest).

Sub cecal.

Anteileal.

Retroileal.

Pelvic.

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LARGE INTESTINE:-

The large intestine frames the

small intestines and extends from

the ileocecal valve to the anus. Its

diameter, is greater than that of

the small intestine and it is 1.5m

long.

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Large intestine is formed of 4 regions:-

a. Cecum

-1st region of LI

-Sac-like portion beneath ileocecal valve-Appendix hangs from its postero medial surface.

b. Colon

c. Rectum

d. Anal Canal

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Fig. 24.27

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Pelvic peritoneum:-

The anterior abdominal wall (1)

Superior to the pubis (2)

The superior surface of the urinary

bladder(3)

The vesicouterine pouch (4)

The fundus and body of the uterus (5)

The rectouterine pouch (6)

Anterior surface and sides of

the rectum (7)

The sigmoid mesocolon (8)

Laterally, a paravesical fossa is

Apparent on each side of the urinary bladder. Further posteriorly, a pararectal fossa is

apparent on each side of the rectum.

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Rectum:-

The rectum begins at the levelof the third sacral vertebra.

It is curving forward with a loopto the left.

It has a peritoneal covering on

the front and sides of itsproximal third; only on its frontfor the middle third; and nocovering for the distal third.

Blood supply; Superior, middle& inferior rectal arteries.

Its a site for porto systemicanastomosis.

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Anal Canal:

(1) Opens to exterior via anus.

(2) Has 2 anal sphincters:-Internal Anal Sphincter (smooth m.) = involutary

-External Anal Sphincter (skeletal m.)= voluntary

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Anal Canal and Hemorrhoidal veins:-

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Arterial supply of GIT

CELIAC TRUNK:You should realize that

arteries are named by their region ofdistribution, not by their

origin or branching pattern.

Celiac trunk arises from the anteriorsurface of the abdominal aorta

at the level of the twelfth thoracicvertebra. The celiac trunk is veryshort (less than 2 cm in mostcases) and divides into threebranches:

Common hepatic artery Left gastric artery

Splenic artery

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-SUPERIOR MESENTERIC ARTERY:

The superior mesentericartery arises from theanterior surface of theabdominal aorta

approximately 1 cminferior to the celiac trunk.

Branches:-

Ileocolic artery

Right colic artery

Middle colic artery

Jejunal& ileal branches

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Superior mesentric A.

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INFERIOR MESENTERIC ARTERY:The origin of the inferior mesenteric artery lies posterior

to the third part of the duodenum.

Itarises from the anteriorsurface of the abdominal aortaat the level of the intervertebraldisk between vertebrae L2 andL3.

Branches:

Left colic artery

Sigmoid arteries Superior rectal artery:

It is the continuation of the inferiormesenteric artery.

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Inferior mesentric A.

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:Veins of the stomach

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-Portal vein :

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