Gastrointestinal (GI) Viscera

Gastrointestinal (GI) Viscera Esophagus (abdominal portion) Is a muscular tube (about 10 inches or 25 cm long) that extends from the pharynx to the stomach, but the short abdominal part (1/2 inch long) extends from the diaphragm to the cardiac orifice of the stomach, entering the abdomen through an opening in the right crus of the diaphragm. Has a physiologic esophageal sphincter , which is the circular layer of smooth muscle at the terminal portion of the esophagus. The tonic contraction of this sphincter prevents the stomach contents from regurgitating into the esophagus. It is also known that, at the gastroesophageal junction, the diaphragmatic musculature forming the esophageal hiatus functions as a physiologic esophageal sphincter. Stomach Rests, in the supine position, on the stomach bed , which is formed by the pancreas, spleen, left kidney, suprarenal gland, transverse colon and its mesocolon, and diaphragm. Is covered entirely by peritoneum and is located in the left hypochondriac and epigastric regions of the abdomen. Has greater and lesser curvatures , anterior and posterior walls, cardiac and pyloric openings, and cardiac and angular notches. Is divided into four regions: cardia, fundus, body , and pylorus. The fundus lies inferior to the apex of the heart at the level of the fifth rib. The pylorus is divided into the pyloric antrum and pyloric canal. The pyloric orifice is surrounded by the pyloric sphincter , which is a group of thickened circular smooth muscles and controls the rate of discharge of stomach contents into the duodenum. The sphincter is constricted by sympathetic stimulation and relaxed by parasympathetic action. Receives blood from the right and left gastric, right and left gastroepiploic, and short gastric arteries. Undergoes contraction, which is characterized by the appearance of longitudinal folds of mucous membrane, the rugae. The gastric canal , a grooved channel along the lesser curvature formed by the rugae, directs fluids toward the pylorus. Produces hydrochloric acid (which destroys many bacteria in food and drink) and a protein-digesting enzyme, pepsin (which converts proteins to polypeptides), in its fundus and body. Produces the hormone gastrin (which stimulates gastric acid secretion) in its pyloric antrum. Parasympathetic fibers in the vagus nerve stimulate gastric secretion. Small Intestine Extends from the pyloric opening to the ileocecal junction. Is the location of complete digestion and absorption of most of the products of digestion, electrolytes, and minerals such as calcium and iron. Consists of the duodenum, jejunum , and ileum. Duodenum Is a C-shaped tube surrounding the head of the pancreas and is the shortest (25cm) long but widest part of the small intestine. Is retroperitoneal except for the beginning of the first part, which is connected to the liver by the hepatoduodenal ligament of the lesser omentum. Receives blood from the celiac (foregut) and superior mesenteric (midgut) artery. Is divided into four parts: I. Superior (first) part Has a mobile or free section, termed the duodenal cap (because of its appearance on radiographs), into which the pylorus invaginates II. Descending (second) part Contains the junction of the foregut and midgut, where the common bile and main pancreatic ducts open. Contains the greater papilla, on which terminal openings of the bile and main pancreatic ducts are located and the lesser papilla, which lies 2 cm above the greater papilla and marks the site of entry of the access of the pancreatic duct. III. Transverse (third) part Is the longest part and crosses the IVC, aorta, and vertebral column to the left. Is crossed anteriorly by the superior mesenteric vessels. IV. Ascending (fourth) part Ascends to the left of the aorta to the level of the second lumbar vertebra and terminates at the duodenojejunal junction, which is fixed in position by the suspensory ligament, a surgical landmark. This fibromuscular band is attached to the right crus of the diaphragm. Jejunum Makes up the proximal two fifths of the small intestine (the ileum makes up the distal three fifths). Is emptier, larger in diameter, and thicker walled than the ileum. Has the plicae circulares (circular folds), which are tall and closely packed. Has translucent areas called windows between the blood vessels of its mesentery. Has less prominent arterial arcades (anastomotic loops) in its mesentery compared with the ileum. Has longer vasa recta (straight arteries, or arteriae rectae) compared with the ileum. Ileum Is longer than the jejunum and occupies the false pelvis in the right lower quadrant of the abdomen. Is characterised by the presence of Peyer's patches (lower portion), shorter plicae circulares and more mesenteric fat and arterial arcades when compared with the jejunum. Large Intestine Extends from the ileocecal junction to the anus and is approximately 1.5 m (5 feet) long. Consists of the cecum, appendix, colon , rectum and anal canal. Functions to convert the liquid contents of the ileum into semisolid feces by absorbing water, salts , and electrolytes. It also stores and lubricates feces with mucus. Colon Has ascending and descending colons that are retroperitoneal and transverse and sigmoid colon surrounded by peritoneum. The ascending and transverse colons are supplied by the superior mesenteric artery and the vagus nerve; the descending and sigmoid colons are supplied by the inferior mesenteric artery and the pelvic splanchnic nerves. Is characterised by the following: Teniae coli: three narrow bands of the outer longitudinal muscular coat. Sacculations or haustra: produced by the teniae, which are slightly shorter than the gut. Epiploic appendages: peritoneum-covered sacs of fat, attached in rows along the teniae. Cecum Is the blind pouch of the large intestine. It lies in the right iliac fossa and is usually surrounded by peritoneum but has no mesentery. Appendix Is a narrow, hollow, muscular tube with large aggregations of lymphoid tissue in its wall. Is suspended from the terminal ileum by a small mesentery, the mesoappendix , which contains the appendicular vessels. Causes spasm and distention when inflamed , resulting in pain that is referred to the periumbilical region and moves down and to the right. Has a base that lies deep to McBurney's point, which occurs at the junction of the lateral one third of the distance between the right anterior superior iliac spine and the umbilicus. This is the site of maximum tenderness in acute appendicitis. Rectum and anal canal Extend from the sigmoid colon to the anus. Are described as pelvic organs ◄.....Go back to the Gross Anatomy homepage