Large Intestine, Exercises of Anatomy

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D R. N A B I L K H O U R I , M D. P H. D

LARGE INTESTINE

ANATOMY AND HISTOLOGY

OF THE GIT HOLLOW

ORGANS III

LARGE INTESTINE

• The large intestine extends from the ileum to the anus. It is divided into the cecum, appendix, ascending colon, transverse colon, descending colon, and sigmoid colon.
• The rectum and anal canal are considered in the sections on the pelvis and perineum.
• The primary function of the large intestine is the absorption of water and electrolytes and the storage of undigested material until it can be expelled from

the body as feces.

CECUM

LOCATION AND DESCRIPTION

• The cecum is that part of the large intestine that lies below the level of the junction of the ileum with the large intestine.
• It is a blind-ended pouch that is situated in the right iliac fossa. It is about 6 cm long and is completely covered with peritoneum.
• It possesses a considerable amount of mobility, although it does not have a mesentery.
• Attached to its posteromedial surface is the appendix.
• The presence of peritoneal folds in the vicinity of the cecum creates the superior ileocecal, the inferior ileocecal, and the retrocecal recesses.

• As in the colon, the longitudinal muscle is restricted to three flat bands, the TENIAE COLI, which converge on the base of the appendix and provide for it a complete longitudinal muscle coat.
• The terminal part of the ileum enters the large intestine at the junction of the cecum with the ascending colon.
• This 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.

ILEO-CECAL VALVE

• The ileocecal valve consists of two horizontal folds of mucous membrane that project around the orifice of the ileum.
• The valve plays little or no part in the prevention of reflux of cecal contents into the ileum. - The circular muscle of the lower end of the ileum (CALLED THE ILEOCECAL SPHINCTER BY PHYSIOLOGISTS)
• serves as a sphincter and controls the flow of contents from the ileum into the colon.

The glands are lined with simple columnar epithelium and a high number of mucin producing goblet cells.

The lamina propria typically contains lymphocytes that partly obscure the underlying muscularis Mucosae. The submucosa is almost fully occupied by lymphoid tissue mainly arranged in lymphatic nodules. The center of the lymphoid nodules stain lighter and are termed germinal centers. The germinal center contains the larger dividing lymphoblasts, similar to the arrangement in lymph nodes. The outer portions of the submucosa harbor larger vessels and have less dense infiltrates of immune cells.

TRANSVERSE COLON

Location and Description

• 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 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 mesocolon, or mesentery of the transverse colon, suspends the transverse colon from the anterior border of the pancreas. The mesentery is attached to the superior border of the transverse colon, and the posterior layers of the greater omentum are attached to the inferior border

RELATIONS

• ■■ Anteriorly: The greater omentum and the anterior abdominal wall (umbilical and hypogastric regions)
• ■■ Posteriorly: The second part of the duodenum, the head of the pancreas, and the coils of the jejunum and the ileum

DESCENDING COLON

Location and Description

• 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..

Relations

• ■■ Anteriorly: Coils of small intestine, the greater omentum, and the anterior abdominal wall.
• ■■ Posteriorly: The lateral border of the left kidney, the origin of the transversus abdominis muscle, the quadratus lumborum, the iliac crest, the iliacus, and the left psoas. The iliohypogastric and the ilioinguinal nerves, the lateral cutaneous nerve of the thigh, and the femoral nerve also lie posteriorly.