JEJUNUM AND ILEUM
The jejunum and ileum together measure about 20 ft (6 m) long.
▶ The jejunum makes up the upper two fifths of this length. Each has distinctive features, but there is a gradual change from one to the other. The jejunum begins at the duodenojejunal flexure and continues into ileum.
▶ The third part, the ileum makes the lower three fifths of this length, ends at the ileocecal junction, the union of the terminal ileum and the cecum.
Location and Description
The coils of jejunum and ileum are freely mobile and are attached to the posterior abdominal wall by a fan-shaped fold of the peritoneum known as the mesentery of the small intestine.
▶ the jejunum lies in the left upper quadrant (LUQ) of the infracolic compartment, whereas most of the ileum lies in the right lower quadrant (RLQ).
Root of proper mesentery:
The short root (15cm) is continuous with the parietal peritoneum on the posterior abdominal wall along a line that extends downward and to the right from the left side of the second lumbar vertebra (duodenojejunal junction) to the region of the right sacroiliac joint (ileocecal junction).
The root of the mesentery crosses (successively) the ascending and inferior parts of the duodenum, abdominal aorta, IVC, right ureter, right psoas major, and right testicular or ovarian vessels
Between the two layers of the mesentery are the superior mesenteric vessels, lymph nodes, a variable amount of fat, and autonomic nerves.
Blood Supply:
Lymphatic Drainage
LARGE INTESTINE
The large intestine is where water is absorbed from the indigestible residues of the liquid chyme, converting it into semisolid stool or feces that is stored temporarily and allowed to accumulate until defecation occurs.
▶ The large intestine consists of the cecum; appendix; ascending, transverse, descending, and sigmoid colon; rectum; and anal canal.
The large intestine can be distinguished from the small intestine by:
▶ Omental appendices: small, fatty, omentum-like projections.
▶ Teniae coli: three distinct bands of smooth
muscle represent the longitudinal coat:
- mesocolic tenia, to which the transverse and sigmoid mesocolons attach;
- omental tenia, to which the omental appendices attach; and
- free tenia, to which neither mesocolons nor omental appendices are attached.
▶ Haustra: sacculations of the wall of the colon between the teniae
▶ A much greater caliber (internal diameter).
CECUM and APPENDIX
Location and description
The cecum is that part of the large intestine that lies below the level of the ileocecal junction. It is a blind-ended pouch that is situated in the right iliac fossa. It is about 6 cm long and wide and is completely covered with the peritoneum.
▶ The presence of peritoneal folds in the vicinity of the cecum creates the superior ileocecal, the inferior ileocecal, and the retrocecal recesses
The teniae coli, are the longitudinal muscle coat which converge on the base of the appendix and provide for it a complete longitudinal muscle coat.
▶ The cecum is often distended with gas and can then be palpated through the anterior abdominal wall in the living patient.
▶ The terminal part of the ileum enters the large intestine at the junction of the cecum with the ascending colon. The opening is provided with two folds, or lips, which form the so-called ileocecal valve
▶ The appendix communicates with the cavity of the cecum through an opening located below and behind the ileocecal opening.
Ileocecal valve:
the ileocecal valve consists of two horizontal folds of mucous membrane that project around the orifice of the ileum. These folds or lips of the valve meet laterally forming ridges called the frenula of the ileal orifice
▶ The smooth muscle tone is reflexly increased when the cecum is distended; the hormone gastrin, which is produced by the stomach, causes relaxation of the muscle tone.
APPENDIX
The appendix is a narrow, muscular tube containing a large amount of lymphoid tissue. It varies in length from 8 to 13 cm.
▶ The base is attached to the posteromedial surface of the cecum about 2.5 cm below the ileocecal junction. The remainder of the appendix is free.
▶ It has a complete peritoneal covering, which is attached to the mesentery of the small intestine by a short mesentery of its own, the mesoappendix. The triangular mesoappendix contains the appendicular vessels and nerves.
Location and Description
The appendix lies in the right iliac fossa.
▶ In relation to the anterior abdominal wall, its base is situated one third of the way up the line joining the right anterior superior iliac spine to the umbilicus (McBurney’s point).
▶ The base of the appendix is easily found by identifying the teniae coli of the cecum and tracing them to the base of the appendix, where they converge to form a continuous longitudinal muscle coat
Common Positions of Appendix Tip
The tip of the appendix is subject to a considerable range of movement and may be found in the following positions:
- retrocecal: coiled up behind the cecum,
- pelvic: hanging down into the pelvis against the right pelvic wall
- paracecal: projecting upward along the lateral side
of the cecum, and
- Pre ileal/post ileal: in front of or behind the terminal part of the ileum.
COLON
The colon has four parts—ascending, transverse, descending, and sigmoid—that succeed one another in an arch.
▶ The colon encircles the small intestine, the Ascending colon lying to the right of the small intestine, the transverse colon superior and/or anterior to it, the descending colon to the left if it, and the sigmoid colon inferior to it.
Ascending Colon
- The ascending colon is about 13 cm long and lies in the right lower quadrant. It extends upward from the cecum to the inferior surface of the right lobe of the liver, where it turns to the left, forming the right colic (hepatic) flexure, and becomes continuous with the transverse colon.
- The peritoneum covers the front and the sides of the ascending colon, binding it to the posterior abdominal wall. It is secondarily retroperitoneal
Transverse colon
The transverse colon is about 38 cm long and extends across the abdomen, occupying the umbilical region. It begins at the right colic flexure below the right lobe of the liver and hangs downward, suspended by the transverse mesocolon from the pancreas.
▶ It then ascends to the left colic (splenic) flexure below the spleen The left colic flexure is higher than the right colic flexure and is suspended from the diaphragm by the phrenicocolic ligament
The transverse colon and its mesentery, the transverse mesocolon, loops down, often inferior to the level of the iliac crests. The mesentery is adherent to or fuse with the posterior wall of the omental bursa.
▶ The root of the transverse mesocolon lies along the inferior border of the pancreas and is continuous with the parietal peritoneum posteriorly.
Descending Colon
The descending colon is about 25 cm long and lies in the left upper and lower quadrants. It extends downward from the left colic flexure, to the pelvic brim, where it becomes continuous with the sigmoid colon.
▶ The peritoneum covers the front and the sides and binds it to the posterior abdominal wall (secondarily retroperitoneal).
Blood supply
Lymphatic drainage
CLINICALS
▶ Mesenteric Arterial Occlusion
▶ Meckel Diverticulum
▶ Mesenteric Vein Thrombosis
▶ Colonoscopy
▶ Appendiceal Predisposition to Infection
▶ Appendiceal Predisposition to Perforation
▶ Appendicitis Pain
▶ Appendectomy
▶ Diverticulosis
▶ Cecostomy and Colostomy
▶ Volvulus
▶ Intussusception