Abdomin

Small intestine

The jejunoileum
It is the portion of the small intestine which is suspended from the posterior abdominal wall by the mesentery . There is no clear line of demarcation between the 2 parts . the upper two fifths ( 8 feet ) is the jejunum, the lower three fifths ( 12 feet ) is the ileum . The jejunum is wider-bored, thicker walled and redder than ileum. In addition, jej. mesentery contains less fat so that the vessels are more clearly visible than in the ileal mesentery.
Small intestine is mainly located in the center of the abdominal cavity. The distal part of the ileum ends in the medial aspect of cecum .
The Mesentery :
It is a double layer of peritoneum which covers the jejunoileum and connects it to the posterior abdominal wall. It carries mesenteric blood & lymphatic vessels as well as nerves to the intestine & organs. It contains fat and areolar tissue .
Its intestinal border is 20 feet while its root (attached border to post. abd wall) is about 6 inches. The root of the mesentery starts over the distal end of the 4th part of duodenum (duodenojejunal flexure) to the left of L2 vertebra , and it ends in the right iliac fossa ant. to the right sacroiliac joint . between these two points the root of the mesentery crosses the 3rd part of duodenum , aorta , inferior vena cava , right ureter & the right psoas muscle.

THE LARGE INTESTINE

The large intestine is continuous with the ileum . it is about 5 feets long & composed of : cecum / vermiform appendix/ ascending colon / transverse colon / descending colon / sigmoid colon / rectum / anal canal
_ These parts form an arch which surrounds the small intestine.
Differences between small and large intestine
In the large intestine there are :
Teniae coli : longitudinal musculature of large intestine in the form of 3 bands arise at root of appendix.
Saculation (haustrations) : bulges between teniae due to shortening of teniae in comparison with the large intestine .
Epiploic appendages : fat filled tabs lie adjacent to teniae .

The vermiform appendix :

A narrow tube in adult having an average length of 8 cm. Originally it is the tapered tip of the cecum. It is completely peritonized & it has a mesoappendix. It most commonly lies retrocecally .
The cecum :
It is the blind pouch of the large intestine , lies below the junction of the ileum and the colon . located in the right iliac fossa. It opens above into the ascending colon. The cecum is completely peritonized .
The ileocecal valve :
Is formed by the infolding of the end of ileum into the cavity of the cecum.
The ascending colon :
It is the part of large intestine between ileocecal valve &right colic flexure. lies retroperitoneally along the right side of the post. abd. wall.
The transverse colon :
It is the largest & most movable part of large intestine. It begins from the right colic (hepatic) flexure to the left colic ( splenic ) flexure opposite to the spleen .
It is attached posteriorly by its meso colon on a line which crosses the 2nd part of duodenum & pancreas.
The descending colon :
It passes inferiorly from the Lt colic flexure to reach Lt iliac fossa, where it curves downward ending at the Lt side of pelvic brim in sigmoid colon .
The sigmoid colon :
It has S- shape loop and has mesocolon . It begins at the brim of pelvis and ends at midline opposite to 3rd segment of sacrum, where it becomes the rectum. Sigmoid colon usually occupies the pelvis , it may rest on the bladder in male or uterus in female .
Blood supply :
Superior mesenteric artery : It arises from the aorta at the level of lower part of L1 vertebra (above 3rd part of duodenum) .it passes behind the neck of pancreas crossing the uncinate process of pancreas & crosses the 3rdpart of the duod. It runs within the mesentery and descends downward toward right iliac fossa . It gives the following branches :
Inferior pancreaticoduodenal artery.
Intestinal branches {for ileojejunum} .
Middle colic artery : it is divided into Rt & Lt branches for ( T. colon ) .
Right colic artery : it divides into ascending & descending branches (for ascending colon ) .
Ileocolic artery : it divides at the ileocecal junction into: -colic branch -ant. cecal branch -post. cecal -ileal branch -appendicular branch .
The superior mesenteric artery ends by anastomosing with the ileal branch of the ileocolic artery . The sup. mesenteric art. supplies the distal part of duodenum ,ileojejunum ,cecum ,appendix , asc.colon and Rt 2/3 of T.colon


Inferior mesenteric artery :
It is the 3rd unpaired ventral branch of abd. aorta, arises from aorta , about 4 cm above its bifurcation, just below the 3rd part of duodenum at the level of L3 . the artery descends downward to the left & crosses the Lt common iliac artery to be the sup. rectal artery . It gives the following branches :
Left colic artery : it divides into ascending & descending branches ( for descending colon ) .
Sigmoid arteries : 2-3 branches .
Superior rectal artery : it is the continuation of the artery , it will divide into two branches . descending along the rectum .
The artery supplies the left 1/3 of T.colon , descending colon , sigmoid colon, rectum & upper part of anal canal .
(branches of superior & inferior mesenteric arteries will anastomose with each other forming the marginal artery).
Venous drainage :
To portal circulation (through superior and inferior mesenteric veins which have tributaries similar to the branches of the arteries)
lymphatic drainage :
To superior and inferior mesenteric lymph nodes around sup. and inf. mesenteric arteries.
Nerve supply:
Sympathetic: by superior and inferior mesenteric plexuses around same arteries (from celiac plexus and lumbar splanchnic nerves from sympathetic trunks).
Parasympathetic: by celiac plexus (to part of intestine supplied by superior mesenteric artery).
And by pelvic splanchnic nerves (to part of intestine supplied by inferior mesenteric artery).

Portal vein and portal circulation

It is formed by the union of sup.mesenteric.vein (begins at the ileocecal junction) & splenic vein behind the neck of the pancreas . it passes upward to the right behind the 1st part of duodenum , then in the free margin of lesser omentum ( posterior to the common bile duct & hepatic artery ) & anterior to epiploic foramen to reach the porta hepatis of liver where it divides into Right and Left branches . Portal vein drains blood from GIT. It ends by emptying blood into the sinusoids of liver. The portal venous blood traverse the liver & drains into the I.V.C of the systemic venous circulation by way of hepatic veins , & this is the direct (main) route . however, there are smaller communications between the portal & systemic circulations which become important when the direct route blocked. these communications are :
At the gastroesophageal junction: through the esophageal veins of left gastric vein (portal tributaries) and azygos vein (systemic tributaries).
In the anal canal: through the superior rectal veins ( portal tributaries) and middle + inferior rectal veins (systemic tributaries ).
At the umbilicus: through the paraumbilical veins (portal tributaries) and superior + inferior epigastric veins ( systemic tributaries ).
Lymphatic drainage of the abdomen
Parietal lymphatics : go to
■External iliac L.N ■ common iliac L.N ■lumbar chain L.N (Lt & Rt hain)
The lymph. vessels from these 3 groups form the lumbar trunk on each side (Rt & Lt) & then the Rt & Lt trunks drain into cisterna chyli (found below diaphragm) which continues as the thoracic duct .
Visceral lymphatics : go to
■Celiac lymph node ■ sup.mesenteric L.N ■inf.mesenteric L.N
The lymphatics from the 3 groups form the intestinal trunk which empties into left lumbar trunk .