The large Intestine



The large Intestine

Extends from the termination of the ileum to the anus. It is divided into cecum, colon and rectum.

The cecum: is the first part of the large intestine, is the blind sac extend from ileocecal opening to the beginning of the colon at the cecocolic orifice found at the right side of abdominal cavity in all, domestic animals except pigs found in the left side.

In horse:

1-it is great cul-de-sac intercalated between the small intestine and the colon.

2-it is curved like a comma shape.

3-it is situated chiefly to the right side of the median plane, extend from the right side iliac and sub lumber regions to abdominal floor.

4-both extremities are blind.

5-it have two openings are placed at the concave curvature are ileocecal orifice and cecocolic orifice.

6-it has base, body and apex:

Base:-cranial on right side. Apex:-on abdominal floor. Body:-ventrally and cranially.

7-it has greater curvature begin dorsal, the lesser curvature ventral, connected with the lateral are the termination of ileum and origin of the colon.

8-it has four surfaces which are:

A-dorsal and ventral surface.

B-right or parietal surface: related to the right abdominal wall, diaphragm and liver.

C-the left or visceral surface: related to the terminal part of colon, the root of mesentery and small intestine.

9-the base attached dorsally by peritoneum with pancreas and right kidney, medially with transverse colon, ventrally to the origin of great colon.

10-the body is attached dorsolaterally to the 1st part of colon by the cecocolic fold.

11-the apex is free end.

12-the cecum has 4 longitudinal bands situated on the dorsal, ventral, right, left surface; these cause 4 rows of sacculation.

In ruminants: it has S-shaped.

1-it has an average length of 12cm in ox, 8cm in sheep and goats.

2-the cecum extends caudodorsally along the right flank. It is blind end lies at the right side of the pelvic inlet. The apex on left side on inlet and the base cranially.

3-dorsally it is attached by short cecocolic fold to the proximal loop of the colon.

4-ventrally by the ileocecal fold to the ileum.

5-it opens at the region between joins the ileum with colon by opening called ileocolic opening.

6-it doesn’t have longitudinal bands and sacculations except of the free end.

The colon: begins at the cecocolic orifice and terminates at the rectum at the pelvic inlet (there is no demarcations between the colon and rectum).

According to its position in man it divided into:

1-ascending colon: directed cranially on the right side.

2-transverse colon: directed from right to left side cranially to cranial mesenteric artery.

3-descending colon: directed caudally on left side.

1-Ascending colon:

A-in horse: called great colon, begins at the cecocolic orifice and terminates in the transverse colon, it consists of two parallel parts which connected by peritoneum, it is folded as u-shaped loops, so that it consist of four parts which are named according to their position or numerically.

The three parts are termed the flexures:

1-the right ventral colon: begins at the lesser curvature of the base of the cecum directed cranially. It forms initial curve and this part is in contact with the flank. It has four bands and sacculation it ends at the sternal flexure.

2-the left ventral colon: passes caudal on the abdominal floor to the left part of the cecum and reaching the pelvic inlet, bends sharply and dorsally and cranially forming the pelvic inlet flexure, it has 4 bands and sacculation.

3-the left dorsal colon: This passes cranial and dorsal to the left ventral colon and on reaching the diaphragm and the left lobe of liver, turns to the right to the right and caudal forming the diaphragmatic flexure, it have one bands and sacculations.

4-the right dorsal colon and on reaching, the medial surface of the base of the cecum, it turns to the left and dorsally caudal to the left sac of stomach where it becomes the short and narrow transverse colon, it has 3 bands and 3 rows of sacculations.

B-In ruminants (ascending colon):

1-located on the right side of the mesentery connecting the cecum to the transverse colon, it is longer than other parts of colon. This elongation forms a loop and coils up in conical spiral on the left side of the mesentery, this loops include:

A-proximal loop: begins as the direct continuation of the cecum at ileocecal orifice.

B-spiral loop:

1-centripetal turns: coil toward central and form central flexure, it has two coils.

2-centrifugal turns: coming back out from the central flexure.

C-distal loop: proceeds from the last centrifugal loop, on the right side medial to the proximal loop, it is continuous with the transverse colon.

2-it doesn’t has band and sacculation and don’t have sub division.

Transverse colon: is the constricted portion between the large and small colons, which passes from right to left around the cranial surface of the cranial surface of the cranial mesenteric artery and continuous caudally as descending colon. In horse have 2 bands and 2 sacculations but in ruminant doesn’t has bands.

Descending colon:

In horse: located in left side of abdominal cavity known as small colon, begins at the termination of the transverse colon and is continued by the rectum at the pelvic inlet, there are 2 bands and 2 sacculations.

In ruminant: has sigmoid flexure near the pelvic inlet and joins the rectum. It help to rectal palpation, it is attached to the sub lumber region by the colic mesentery and to the duodenum by duodenocolic fold.

The rectum: found on the pelvic cavity on the left side of median plane. It is the terminal part of the bowel, it extend from the pelvic inlet to the anus. In horse, dog and ox it details terminal to form the rectal ampullae. The major clinical value of the rectum is its use in palpation, rectal prolapsed occur in several species. It has two parts: parietal part and retro peritoneal part, which form flask-shaped dilation called the ampulla’s recti (develop in horse and do not found in cat, sheep and goats).

Anal canal:

It is the terminal part of the alimentary canal; it is situated below the roof of the tail. It is separated from rectum by line called Anorectal line and separated from skin (which covered the anus by line called Anocutaneous line. In dog and cat, the cutaneous zone of it has two openings lead to two sacs, which considered the storage of the secretions which have hate odor, which secreted from the gland surrounded the anal sacs.

Muscles of the anus:

1-muscle sphincter ani internus (involuntary muscles)

2-muscle sphincter ani externus (voluntary muscles)

3-retractor ani muscle (elevator ani muscle) which is retract partial prolapsed the anus undergoes during defecation.

Large intestine in dog:

1-slightly larger in diameter than small intestine.

2-the cecum is an irregular twisted tube which is attached to the ileum and ascending colon by short peritoneal folds, is located on the right, directed caudally, but it is blind end is bent and often points caudally.

3-the colon is short and its three segments: ascending, transverse and descending colon are arranged as their names indicate parts.

The ascending colon is the shortest of three parts begin at the cecum; it is closely applied to the roof of the abdominal cavity and the right kidney.

The transverse colon passes to the left between the stomach and cranial mesenteric artery, crossing the median plane at the level of the 12th thoracic vertebra.

The descending colon which follows extends to the pelvic inlet where it is continued by the rectum. It is longest of the three parts and has slightly wider mesocolon, found in the left side and related medially to the ascending duodenum by the doudocolic fold.

4-Rectum: it is shorter and continued with the colon in the pelvic cavity followed by short anal canal (the retroperitoneal part of rectum is wider slightly to make the ampullae recti.

5-Anal canal: in dog divided into three zones:

A-columinare zone lined by stratified squamous epithelial tissue and have longitudinal fold between it grooves and anal glands.

B-intermediate zone is correspond the continuous with skin, it covers with cornified stratified squamous epithelium has hair and circumnal glands and Para nasal sinus which open in it, Para nasal gland duct which secreted secretion have hate odor.

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