Small and Large Intestine Anatomy PDF

Small bowel It is the section of bowel between the stomach and the colon and is made up of three functional units (duodenum, jejunum and ilium) (Fig 1.27): Gross anatomy The total length of the jejunum and ileum varies from 3 to 10 m with an average length of 6 m. Both jejunum and ileu...

Small bowel It is the section of bowel between the stomach and the colon and is made up of three functional units (duodenum, jejunum and ilium) (Fig 1.27): Gross anatomy The total length of the jejunum and ileum varies from 3 to 10 m with an average length of 6 m. Both jejunum and ileum are attached to mesentery. So called small intestine proper. The root of mesentery extends from duodeno-jejenal junction (the left of L2 vertebrae) to the right sacroiliac joint. The valvulae conniventes are the mucosal folds of the small intestine, starting from the second part of the duodenum, they are large and thick at the jejunum and considerably decrease in size distally in the ileum to disappear entirely in the distal ileal bowel loops. Fig (1.27): A diagram showing the gross anatomy of the small bowel. Radiographic features: Abdominal X-ray: Air/fluid levels may be seen normally; up to five are allowed on an erect abdominal x ray. Generally, the small bowel lies centrally within the abdomen. The valvulae conniventes are thin, circular, folds of mucosa, some of which are circumferential and are seen on an X-ray to pass across the full width of the lumen. (fig 1.28) Jejunum Ileum o Shorter (Occupies proximal o Longer (Occupies distal 3/5 Length 2/5 of small intestine). of small intestine) Narrower (2.5 cm), often Diameter Wider (3-3.5) often empty loaded Wall thickness Thicker thinner Position Left upper abdomen Right iliac fossa Valvulae Thicker and more prominent Thinner and less prominent conniventes Fig (1.28) Small bowel gas pattern on abdominal x-ray Barium studies of small bowel loops: 1. Small bowel follow through (SBFT) (fig 1.29& 1.30) o It is often performed after an upper GI fluoroscopic study, as the contrast column moves from the stomach and duodenum into the small bowel. A small bowel follow through may also be performed by itself, without the upper GI investigation of the esophagus, stomach, and proximal duodenum, but this is less common. o It gives excellent mucosal detail. o Density of valvulae is high in the jejunum with a gradual reduction in the proximal ileum to relative paucity of folds distally. 2. Small bowel enema A naso-jejunal tube is passed to the duodenojejunal flexure and barium is passed directly into the small intestine. Excellent double-contrast images of the small bowel. Fig (1.29) barium follow through. Fig (1.30) barium meal with follow through Large Bowel The large intestine (also known as the large bowel) is a 1.5 meter muscular tube that extends from the cecum to the rectum. It has three outer longitudinal muscular layers called taenia coli, which are about 30 cm shorter than the length of the large bowel causing characteristic sacculations interrupted by incomplete rings called haustra. The large bowel is divided into the following parts (Fig.1.31): The caecum: is the proximal blind pouch of the ascending colon, lying at the level of the ileocecal junction. The terminal ileum opens into the cecum on the medial wall, and the ileocecal valve guards this opening. The appendix: a thin cylindrical organ with a blind attachment to the cecum. The base of the appendix lies on the posteromedial wall of the cecum about 1 to 2 centimeters below the ileocecal junction. The ascending colon: runs superiorly on the right side of the abdomen from the right iliac fossa to the right lobe of the liver where it makes a left turn at the right colic flexure (hepatic flexure) Transverse colon: the third, most mobile, and longest part of the large intestine. It is found between the right and left colic flexures. Descending colon: From the splenic flexure to the sigmoid colon. Sigmoid colon: an S-shaped loop that links the descending colon to the rectum.. The rectum: from the sigmoid colon till the anal canal. It occupies the concavity of the sacrococcygeal curvature. The anal canal: It is a narrow, muscular canal. This is directed posteriorly almost at right-angles to the rectum.  Fig. (1.31): A diagram showing the gross anatomy of the large bowel. Radiographic features: 1-Abdominal X-ray: The retroperitoneal structures of the colon (ascending colon, descending colon, and rectum) are relatively constant in position. These are often more readily identified than the transverse colon or sigmoid colon which is more variable in position. If visible, the caecum is often the widest segment. It too has a variable position but is most often confined to the right iliac fossa. The longitudinal muscles (taenia coli) and circular muscles of the colon form sacculations called haustra, which have characteristic radiographic appearance. There is no haustra within the rectum. Another characteristic feature of large bowel is that it contains faces. This has a mottled appearance due to its part gaseous content. Normal large bowel has the following features (Fig.1.31): 1. Peripheral in position. 2. Hustra. 3. Contains feces.  Fig (1.31): Large bowel gas pattern on abdominal x-ray. Small intestine Large intestine Loops Several loops Few loops Length 3-10m 1.5m caliber Narrower wider Position of loops Central Peripheral Taneia coli Absent Present Haustra Absent Present valvulae conniventes Present Absent Feces Absent Present 2-Barium Enema. (Fig.1.32 &1. 33) It is method of imaging the colon with fluoroscopy May be single or double-contrast, the views obtained from rectum to caecum. The contrast is injected a catheter and multiple views are taken. Appendix and terminal ileum may also fill.  To achieve adequate filling patient needs to be rolled into different positions to allow barium to coat the whole colon. Fig. (1.32) normal barium enema (asterisk (cecum)& squares (terminal ileum) Fig. (1.33): Single and double contrast barium enema showing different parts of the large bowel.