Large intestine

Large Intestine Length: is about 1.5 meters. Parts: - Caecum and appendix. - Colon: (ascending,transverse,descending and pelvic) - Flexures (right and left colic flexures). - Rectum. - Anal Canal.

The Main Differences between Small and Large intestine: Tenia Coli: are the longitudinal outer muscle layer which is represented by 3 bands. They are not found in the appendix and rectum. Sacculations: this due the length of tenia coli is shorter than the length of the large intestine. Appendices Epiploicae: small sacs of peritoneum-covered fat hanging from the surface of the colon.

Caecum It is a mobile blind sac at the beginning of the large intestine. Position: It occupies the right iliac fossa and is completely covered with peritoneum.  

Caecum Relations: Anteriorly: anterior abdominal wall, greater omentum, and coils of small intestine. Posteriorly: 2 Muscles: Psoas major and iliacus. 2 Arteries: Right gonadal and External iliac artery. 3 Nerves: Femoral, genitofemoral, and lateral cutaneous nerve of the thigh.

Blood supply of caecum Arterial supply: anterior and posterior caecal arteries from ileocolic artery which is a branch from superior mesenteric artery. Venous drainage: into superior mesenteric vein then into portal vein.

Vermiform appendix It is a worm like tube, about 10 cm long, opens by its base into posteromedial aspect of the caecum below the terminal ileum. It has a mesentery known as mesoappendix which is a triangular peritoneal fold, containing the appendicular artery in its free border.

Positions of the Appendix 1. Retrocecal (65%) 2. Pelvic (30%) 3. Subcecal (3%) 4. Pre or post- ileal (2%)

Blood supply of the appendix Arterial supply: appendicular artery from ileocolic artery. Venous drainge: into superior mesenteric vein.

Surface anatomy of the Base of the appendix (McBurney’s point): It is represented by a point at the junction of lateral 1/3rd and medial 2/3rd of a line connecting anterior superior iliac spine and the umbilicus.

Clinical note Inflammation of the appendix (appendicitis) causes ill-defined colicky pain, felt in the umbilical region (referred pain) why? Because, the appendix is supplied with sympathetic fibers from 10ththoracic spinal cord segment, and the 10th thoracic somatic nerve supplies the skin of umbilical region.

Ascending colon It begins as a continuation of the cecum and ends just below the liver, here it continues with the transverse colon at the right colic (hepatic) flexure. Peritoneal covering: It is covered by peritoneum anteriorly and on each side.

Blood supply of ascending colon Arterial supply: From superior mesenteric artery Ileocolic artery Right Colic artery Venous drainage: It drains its venous blood into the veins corresponding to the arterial supply.

Transverse colon It runs from the right colic (hepatic) flexure across the abdomen to the left colic (splenic) flexure. It is completely covered with peritoneum which forms transverse mesocolon and it is freely mobile. Relations: Anterior relations: Liver, stomach and greater omentum. Posterior relations: Second part duodenum, head of pancreas, jejunum and left kidney.  

Transverse mesocolon Transverse colon is suspended from the posterior abdominal wall by its transverse mesocolon which is attached to the anterior border of pancreas. Contents of transverse mesocolon: 1. Transverse colon. 2. Middle colic artery. 3. Extra-peritoneal fat. 4. sympathetic nerves.

Blood supply of transverse colon Arterial supply: - Right 2/3 by right and middle colic arteries of superior mesenteric artery. - Left 1/3 by ascending branch of left colic artery from inferior mesenteric artery. Venous drainage: It drains its venous blood into the veins corresponding to the arterial supply.

Descending colon   It runs from the left colic (splenic) flexure and descends till the pelvic brim to continue as sigmoid (pelvic) colon. It is covered by peritoneum anteriorly and on each side.

Relations of descending colon Anteriorly: Coils of small intestine, the greater omentum. Posteriorly: 1 viscera: the lateral border of left kidney, 4 Muscles: the transversus abdominis muscle, the quadratus lumborum,, the iliacus, and the left psoas. 1 bone: the iliac crest 4 nerves: The iliohypogastric and the ilioinguinal nerves, the lateral cutaneous nerve of the thigh, and the femoral nerve

Blood supply of descending colon Arterial Supply: Upper and lower left colic arteries (inferior mesentric). They form marginal arteries (vasa recti) at the wall of the colon. Venous drainage: to inferior mesentric vein which ends in splenic vein.

Pelvic (sigmoid) colon - It begins at the left side of the pelvic brim. - It ends at the 3rd sacral piece where the rectum begins. - It describes S-shaped course. - It is completely covered with peritoneum and suspended by the sigmoid mesocolon.

Blood supply of sigmoid colon Arterial supply: sigmoid branches of the inferior mesenteric artery. Venous drainage: It drains its venous blood into the veins corresponding to the arterial supply.

Sigmoid meso-colon It is a peritoneal fold which is attached to the posterior pelvic wall by an inverted V- shaped root. Contents of the sigmoid mesocolon: 1. Sigmoid colon in the free border. 2. Sigmoid vessels in the lateral limb. 3. Superior rectal vessels in the medial limb.

Inferior mesenteric artery Origin (start): From the front of the aorta opposite the L3. It runs obliquely down to the pelvic brim. Termination: in the root of the pelvic mesocolon as the superior rectal artery.

Branches of inferior mesentric artery Left colic artery: It passes up to the left towards the splenic flexure. It divides into two branches; ascending and descending branches which anastomose with the left branch of the middle colic artery and with the sigmoid branches.

2- Sigmoid arteries: 3-4 branches pass forwards between the layers of the pelvic mesoclon to anastomose at the wall of the pelvic colon. 3- Superior rectal artery.

THANK YOU Prof. Dr. Shawky Tayel