Anatomy of the Stomach

The Stomach

• The stomach is a dilated portion of the gastrointestinal tract with three functions: storing food, mixing food with gastric secretion to form chyme, and controlling the rate of discharge of the chyme to the small intestine.
• The stomach has a capacity of 1500 ml.
• The stomach lies in the upper part of the abdomen, extending from beneath the left costal margin to the epigastric and umbilical regions.
• It is relatively fixed at both ends but is very mobile in between.
• The stomach is a J-shaped organ with two openings (cardiac orifice and pyloric orifice), two surfaces (anterior and posterior), and two curvatures (lesser and greater).

Orifices of the Stomach

• Cardiac orifice:
  • Lies where the esophagus enters the stomach.
  • Located 10 cm posterior to the 7th left costal cartilage.
  • Located 2-3 cm to the left of the median plane (between the liver and the diaphragm).
• Pyloric orifice:
  • Is the distal end of the pyloric canal.

Curvatures of the Stomach

• Lesser curvature:
  • Forms the right border of the stomach.
  • Extends from the cardiac orifice to the pylorus.
  • Connected to the liver by the lesser omentum.
• Greater curvature:
  • Is much longer than the lesser curvature.
  • Forms the left border of the stomach.
  • Extends from the left of the cardiac orifice, over the dome of the fundus, to the pylorus.
  • The gastrosplenic omentum extends from the upper part of the greater curvature to the spleen.
  • The greater omentum extends from the lower part of the greater curvature to the transverse colon.

Parts of the Stomach

• Cardia:
  • The most fixed part of the stomach.
  • Surrounds the cardiac orifice.
  • Lies 2-3 cm to the left of the median plane at the level of the tenth thoracic vertebra.
• Fundus:
  • Dome-shaped and full of gas.
  • Projects upward to the left of the cardiac orifice.
  • In contact with the left dome of the diaphragm and may reach the level of the fifth rib in the midclavicular line (inferior to the apex of the heart).
• Body:
  • Extends from the cardiac orifice to the incisura angularis (notch in the lower part of the lesser curvature).
• Pyloric antrum:
  • Extends from the incisura angularis to the pylorus.
• Pylorus:
  • Tubular part of the stomach.
  • Lies 2-3 cm to the right of the median plane.
  • Has two parts: the pyloric canal (narrow canal) and pyloric sphincter (thick muscular wall that surrounds the distal opening of the stomach, the pyloric orifice).

Relation of the Stomach

• Anterior:
  • Anterior abdominal wall.
  • Left costal margin.
  • Left pleura and lung.
  • The diaphragm and left lobe of the liver.
• Posterior:
  • Behind the stomach are groups of structures comprising the stomach bed.
  • The posterior wall of the stomach is covered by the peritoneum of the anterior wall of the lesser sac.
  • The bed is covered by the posterior wall of the lesser sac.
  • The structures of the stomach bed are:
    • The spleen.
    • The left kidney.
    • Left suprarenal gland.
    • Splenic artery.
    • Pancreas.
    • Transverse colon.
    • Transverse mesocolon.
    • Diaphragm.

Blood Supply of the Stomach

• Arterial supply:
  • Derived from branches of the celiac trunk.
  • Left gastric artery: arises from the celiac trunk, passes upward and to the left to reach the esophagus, then descends along the lesser curvature (within the layers of the lesser omentum).
  • Right gastric artery: arises from the common hepatic artery at the upper border of the pylorus, then runs to the left along the lesser curvature.
  • Pyloric branch: passes down to the pylorus.
• Posterior vagal trunk: formed mainly by the right vagus nerve and enters the abdomen on the posterior surface of the esophagus, then runs on the posterior surface of the stomach and supplies:
  • Anterior and posterior surfaces of the stomach.
  • Gives large celiac branch to the celiac plexus.
• Sympathetic nerve supply: from the T6 through T9 segments of the spinal cord, passes to the celiac plexus through the greater splanchnic nerve.

Mucous Membrane of the Stomach

• Thick and vascular with numerous folds called rugae.
• These folds are flattened when the stomach is distended.

Peritoneum of the Stomach

• The visceral peritoneum completely surrounds the stomach.
• Leaves the greater curvature as the greater omentum and gastrosplenic omentum.
• Leaves the lesser curvature as the lesser omentum.

The Small Intestine

• The largest part of the G.I.T.
• Extends from the pylorus of the stomach to the ileocecal junction.
• Divided into three parts: the duodenum, the jejunum, and the ileum.

Duodenum

• A C-shaped tube, about 25 cm long.
• Joins the stomach to the jejunum.
• Curves around the head of the pancreas and receives the openings of the bile and pancreatic ducts.
• The first 2.5 cm of the duodenum resembles the stomach in that it is covered on its anterior and posterior surfaces with peritoneum and has lesser omentum attached to its upper border and greater omentum attached to its lower border.
• The remainder of the duodenum is retroperitoneal, being only partially covered by peritoneum.
• Divided into four parts: the first part, the second part, the third part, and the fourth part.

Parts of the Duodenum

• First part of the duodenum (superior part):
  • 5 cm (2 inches) long.
  • Begins at the pylorus and runs upward, backward, to the right.
  • The first 2.5 cm is covered with peritoneum.
  • Relations:
    • Anterior: quadrate lobe of the liver and the neck of the gall bladder.
    • Posterior: gastroduodenal artery, common bile duct, portal vein, and the inferior vena cava.
    • Inferior: the head of the pancreas.
    • Superior: epiploic foramen.
• Second part of the duodenum (descending part):
  • 7.5 cm (3 inches) long.
  • Runs vertically downward in front of the hilum of the right kidney.
  • Relations:
    • Anterior: right lobe of the liver, fundus of the gall bladder, coils of small intestine, and the transverse colon.
    • Posterior: right kidney, right ureter, right suprarenal gland, and the right psoas.
    • Lateral: right colic flexure, right lobe of liver, and the ascending colon.
    • Medial: head of pancreas, common bile duct, and the main pancreatic duct.
• Third part of the duodenum (horizontal part):
  • 10 cm (4 inches) long.
  • Adherent to the posterior abdominal wall.
  • Runs horizontally to the left, in front of the third lumbar vertebra.
  • Relations:
    • Anterior: coils of jejunum and the root of the mesentery of small intestine.
    • Posterior: right ureter, right psoas, inferior vena cava, aorta, inferior mesenteric artery, and the right gonadal vessels.
    • Inferior: jejunum.
    • Superior: head of pancreas.
• Fourth part of the duodenum (ascending part):
  • 2.5 cm (1 inch) long.
  • Runs upward and to the left to the duodenojejunal flexure.
  • Relations:
    • Anterior: coils of jejunum and the root of the mesentery.
    • Posterior: left psoas muscle, left gonadal vessels, inferior mesenteric vein, and the left margin of the aorta.
    • Medially: pancreas.
    • Lateral: left kidney and ureter.

Mucous Membrane of the Duodenum

• Thick with numerous circular folds called plica circulares (except the first 2.5 cm is smooth).

Arteries of the Duodenum

• The upper half is supplied by the superior pancreatic duodenal artery.
• The lower half is supplied by the inferior pancreatic duodenal artery.
• Also receives branches from the right gastric artery, right gastroepiploic artery, gastroduodenal artery, and the hepatic artery.

Venous Drainage of the Duodenum

• The upper half drains to the portal vein.
• The lower half drains to the superior mesenteric vein.

Lymph Drainage of the Duodenum

• The