▶ The GI tract includes the esophagus, stomach, small intestine, large intestine, and the accessory organs that are developmental outgrowths of those organs.
Esophagus(Abdominal Portion)
The esophagus is a muscular, collapsible tube about 10 in. (25 cm) long that joins the pharynx to the stomach.
▶ The esophagus enters the abdomen through an opening in the right crus of the diaphragm. After a course of about 0.5 in. (1.25 cm), it enters the stomach on its right side.
Arterial supply: left gastric artery
Venous drainage: left gastric vein tributary of portal vein
Lymph Drainage: lymph vessels follow the arteries into the left gastric nodes
Gastroesophageal anastomosis:
The gastroesophageal anastomosis is an important portal–systemic venous anastomosis that occurs at the lower third of the esophagus. Here, the esophageal tributaries of the left gastric vein (which drains into the portal vein) anastomose with the esophageal tributaries of the azygos veins
STOMACH
The stomach is the expanded part of the digestive tract between the esophagus and small intestine.
▶ It is specialized for the accumulation of ingested food, which it chemically and mechanically prepares for digestion stomach acts as a food blender and reservoir; its chief function is enzymatic digestion.
▶ The gastric juice gradually converts a mass of food into a semiliquid mixture, chyme, which passes fairly quickly into the duodenum.
▶ It is capable of considerable expansion and can hold 2–3 L of food, other wise empty stomach is only slightly larger than the intestines.
Location and Description
The stomach is situated in the upper part of the abdomen, extending from beneath the left costal margin region into the epigastric and umbilical regions
▶ The stomach is relatively fixed at both ends but is very mobile in between.
▶ In the supine position, the stomach commonly lies in the right and left upper quadrants, or epigastric, umbilical, and left hypochondrium and flank regions.
▶ In the erect position, the stomach moves inferiorly.
▶ In thin individuals, the body of the stomach
may extend into the pelvis.
▶ In obese individuals it is transversely placed.
Gross Features:
Parts of the stomach:
Fundus: This is dome shaped and projects upward and to the left of the cardiac orifice. It is usually full of gas.
Body: This extends from the level of the cardiac orifice to the level of the incisura angularis, a constant notch in the lower part of the lesser curvature.
Pyloric antrum: This extends from the incisura angularis to
the pylorus.Pylorus: This is the most tubular part of the stomach. The thick muscular wall is called the pyloric sphincter, and the cavity of the pylorus is the pyloric canal.
The stomach can also be explained as having:
2 Sufaces:
Anterior surface Posterior surface
2 Curvatures:
Lesser curvature Greater curvature
2 Orifices:
Cardiac orifice Pyloric orifice
Cardiac orifice:
No anatomic sphincter exists at the lower end of the esophagus. But the circular layer of smooth muscle in this region serves as a physiologic sphincter.
The tonic contraction of this sphincter prevents the stomach contents from regurgitating into the esophagus.
Relaxation of the muscle at the lower end occurs ahead of the
peristaltic wave so that the food enters the stomach.
- The closure of the sphincter is under vagal control, and this can be augmented by the hormone gastrin and reduced in response to secretin, cholecystokinin, and glucagon.
Pyloric orifice:
The pyloric canal forms the pyloric orifice, which is about 1 inch long. The circular muscle coat of the stomach is much thicker here and forms the anatomic and physiologic pyloric sphincter. The pylorus lies on the transpyloric plane.
The pyloric sphincter controls the outflow of gastric contents into the duodenum.
- The sphincter receives motor fibers from the sympathetic
system and inhibitory fibers from the vagi.
- The pylorus is controlled by local nervous and hormonal influences, the stretching of the stomach because of filling will stimulate the myenteric nerve plexus in its wall and reflexly cause relaxation of the sphincter.
Interior of the stomach:
The mucous membrane of the stomach is thick and vascular and is thrown into numerous folds, or rugae, that are mainly longitudinal in direction. The folds flatten out when the stomach is distended.
▶ The muscular wall of the stomach contains three muscle layers outer longitudinal fibers, middle circular fibers, and inner oblique fibers.
▶ Visceral peritoneum completely surrounds the stomach. It leaves the lesser curvature as the lesser omentum and the greater curvature as the gastrosplenic ligament and the greater omentum.
Relations
Anteriorly:
- anterior abdominal wall
- left costal margin
- left pleura and lung
- diaphragm
- left lobe of the liver
Posteriorly: the posterior relations of the stomach are also called stomach bed:
- lesser sac
- diaphragm
- spleen
- left suprarenal gland
- upper part of the left kidney
- splenic artery
- pancreas
- transverse mesocolon
- transverse colon
Arterial Supply:
| Artery | Branch of | Supplies to |
| Left gastric artery | Celiac artery | Upper right part of the lesser curvature |
| Right gastric artery | Hepatic artery | lower right part of the lesser curvature |
| Short gastric artery | Splenic artery | fundus |
| Right gastroepiploic artery | Splenic artery | upper part of the greater curvature |
| Left gastroepiploic artery | Gastroduodenal branch of hepatic artery | lower part of the greater curvature. |
Venous Drainage
Right and left gastric
▶ Short gastric and left gastroepiploic Splenic vein Portal Vein
▶ Right gastrorpiploic superior mesenteric vein
Lymphatic Drainage
Lymph vessels anastomose freely in the stomach wall, but there are valves in the vessels that direct lymph in such a way that a line drawn parallel to the greater curvature and two thirds of the way down the anterior surface indicates a
‘watershed’
Nerve Supply
Sympathetics derived from celiac plexus carries a proportion of pain-transmitting nerve fibers
Parasympathetics from vagus nerve are secretomotor to the gastric glands and motor to the muscular wall of the stomach. They reach the stomach as anterior and posterior vagal trunks
The pyloric sphincter receives motor fibers from the sympathetic system and inhibitory fibers from the vagi.
SMALL INTESTINE
The small intestine, consisting of the duodenum, jejunum, and ileum, is the primary site for absorption of nutrients from ingested materials. It extends from the pylorus to the ileocecal junction where the ileum joins the cecum.
DUODENUM
The duodenum, the first and shortest (25 cm) part of the small intestine, is also the widest and most fixed part.
▶ It pursues a C-shaped course around the head of the pancreas.
▶ It begins at the pylorus on the right side and ends at the duodenojejunal flexure on the left side.
▶ This junction with jejunum occurs approximately at the level of the L2 vertebra, 2–3 cm to the left of the midline. This junction usually takes the form of an acute angle, the duodenojejunal flexure. ▶ Except for the first inch of duodenum, which has lesser and greater omentums covering the walls, all of the duodenum is retroperitoneal.
Parts
First Part of Duodenum:
The first part of the duodenum (5cm) begins at the pylorus and runs upward and backward on the transpyloric plane at the level of the first lumbar vertebra.
Second Part of Duodenum:
This part (10 cm) runs vertically downward in front of the hilum of the right kidney on the right side of the second and third lumbar vertebrae. About halfway down its medial border, the bile duct and the main pancreatic duct pierce the duodenal wall.
They unite to form the ampulla of vater that opens on the summit of the Major Duodenal Papilla. The accessory pancreatic duct, if present, opens into the duodenum a little higher up on the minor duodenal papilla.
*transverse mesocolon crosses here
Third Part of Duodenum:
The third part of the duodenum (8cm) runs horizontally to the left on the subcostal plane, passing in front of the vertebral column at level of L3 vertebrae and following the lower margin of the head of the pancreas
Fourth Part of Duodenum:
The fourth part of the duodenum (5cm) runs upward and to the left to the duodenojejunal flexure. The flexure is held in position by a peritoneal fold, the suspensory ligament of the duodenum (ligament of Treitz), which is attached to the right crus of the diaphragm
*root of proper mesentery crosses here
CLINICALS
Achalasia of the Cardia
▶ Gastroesophageal Reflux Disease
▶ Bleeding Esophageal Varices
▶ Gastric Ulcer (splenic artery)
▶ Peptic Ulcer (gastroduodenal artery)
▶ Esophageal Varices
▶ Hiatal Hernia
▶ Congenital Hypertrophic Pyloric Stenosis
▶ Carcinoma of Stomach TROSSIERS SIGN
▶ Gastrectomy
▶ Visceral Referred Pain
▶ Paraduodenal Hernias