Large Intestine[1]

8/18/2019 Large Intestine[1]

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4/25/2016 Large Intestine

http://www.wesnorman.com/largeintestine.htm

Large Intestine

The large intestine extendsfrom the ileocecal junctionto the anus and is about1.5m long. On the surface,you can identify bands of longitudinal muscle fibers

called taeniae coli, eachabout 5mm wide. Thereare three bands and theystart at the base of theappendix and extend fromthe cecum to the rectum.Along the sides of thetaeniae, you will find tagsof peritoneum filled withfat, called epiploic

appendages (orappendices epiploicae).The sacculations, calledhaustra, are characteristicfeatures of the largeintestine, and distinguish itfrom the rest of theintestinal tract.

The large intestine consists

of the following parts:

1. cecum2. ascending colon3. transverse colon4. descending colon5. sigmoid colon6. rectum Not seen in

diagram.7. anal canal Not seen in

diagram.


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8. anus Not seen indiagram.

There are two flexuresassociated with the colon:

1. right colic flexure orhepatic flexure

2. left colic flexure orsplenic flexure

The cecum isabout 6cm longand is a blind cul-de-sac which liesin the right iliacfossa. It is thepart of the colonbelow the

opening of theileum into thecolon. The cecumlies immediatelybehind theabdominal walland greateromentum. Thereis frequently aperitoneal recess

behind the cecumcalled theretrocecal recessand the appendixis sometimeshiding within thisrecess and mayextend as farsuperiorly as theliver.


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Hanging off thececum is thevermiformappendix whichopens into thececum about 2cmbelow theileocecal opening.The averagelength of theappendix is about10cm and may liein differentpositions. It hasits ownmesentery calledthemesoappendixwhich carries theappendicularartery.

If the cecum isopened, you canidentify theopening of theileum into thececum. Thisopening issurrounded bythickened musclewhich forms theiliocolic valve. Inthis image, youcan see the firstpart of theascending colon

with its semilunarfolds.


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Arterial Supply of the Colon

The colon is supplied bybranches of the superiormesenteric and inferiormesenteric arteries.

Superior mesentericarteryileocolic artery

superior branchthat joins theright coliccecal branchappendicularbranchileal branch

right colic arterydescendingbranch to jointhe superiorbranch of theileocolicascendingbranch that

joins the rightbranch of themiddle colic

middle colic arteryright branchleft branch that

joins with theascendingbranch of theleft colic artery

Inferior mesenteric

arteryleft colic

ascendingbranch that

joins the middlecolicdescendingbranch that

joins thehighest sigmoid


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branchsigmoid arteries (2-3)

superior sigmoidbranch join theleft colicinferior sigmoidbranch joins thesuperior rectal

superior rectal artery- not shown in theimage

Venous Drainage of the

Gastrointestinal TractThe venous drainage of the gastrointestinal tract, from the lower esophagus to theupper rectum is by way of the portal venous system. This system also drains thespleen and pancreas.

The portal vein is usuallydescribed as being formedby the splenic andsuperior mesenteric veins.

The inferior mesentericvein then joins the splenicvein. However, there arevariations to this patternand might exist. Two of these are that the inferiormesenteric vein may joinat the junction of thesplenic with the superiormesenteric or the inferior

mesenteric veins may jointhe superior mesentericvein before it merges withthe splenic. Identify the:

superior rectal veininferior mesentericveinsplenic veinsuperior mesenteric


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veinesophageal veinsleft gastric veinportal vein

The numbered stars

represent the areas wherethe portal venous systemanastomoses with thecaval venous system andare clinically important inportal or cavalhypertension.

1. esophageal plexus -caval drainage into

azygos veins, portaldrainage into the leftgastric vein

2. rectal plexus - cavaldrainage into middleand inferior rectalveins and then intothe pudendal andinternal iliac veinsback to inferior vena

cava, portal drainageinto the superiorrectal, the inferiormesenteric and thesplenic

3. paraumbilical veins -caval drainagedownward to thesuperficial inferiorepigastric vein to the

femoral vein, to theexternal iliac, to theinferior vena cava,upward to thethoracoepigastricvein, the lateralthoracic vein,subclavian vein,superior vena cava,portal drainage


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through theparaumbilical vein tothe portal vein.

Clinical Consideration

Portal obstruction. In cases of liver disease where the portal blood can no longerpass through the liver, the blood will try to get back to the heart any way it canand this usually involves the superior or inferior venae cavae. One possible causeof liver disease is chronic alcoholism. When the liver becomes impassable, it willpass backwards through the portal vein into the left gastric, paraumbilical orsuperior rectal. At each of these sites, the veins become enlarged and will result inother clinical signs and symptoms.

In case of the esophageal plexus (*1), esophageal varices will develop andmassive hemorrhage may occur resulting in death.

In case of the rectal plexus (*2), hemorrhoids occur, resulting in pain andbleeding.

In case of the paraumbilical veins (*3), visible signs of venous enlargement andtortuosity occur on the abdomen and these are referred to the caput medusae.

Caval blockage. In cases where tumors or other pathologies compress the vena

cava, the blood will utilize the above connections to return blood to the heart butthis time through the caval system.

Jejunum and Ileum

Liver

Abdominal CavitystomachDuodenumIleum and JejunumLiverPancreasSpleen

http://www.wesnorman.com/spleen.htmhttp://www.wesnorman.com/pancreas.htmhttp://www.wesnorman.com/liver.htmhttp://www.wesnorman.com/jejunumileum.htmhttp://www.wesnorman.com/duodenum.htmhttp://www.wesnorman.com/stomach.htmhttp://www.wesnorman.com/abdominalcavity.htmhttp://www.wesnorman.com/liver.htmhttp://www.wesnorman.com/jejunumileum.htm

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Large Intestine[1]