Gross Anatomy of the Stomach and Esophagus

• The lecture broadly covers the gross anatomy of the gastrointestinal tract, specifically the stomach, including the esophagus, gastric mucosa, and pyloric sphincter.
• It delves into the structures, attachments, curvatures, blood supply, and nerve supply of the stomach

Esophagus

• The esophagus is a fibromuscular tube, about 25cm long, from the pharynx to the stomach.
• The esophagus has three main strictures which are cervical, thoracic, and oesophageal.
• The oesophageal constrictor is produced as the oesophagus passes through the diaphragm at the oesophageal hiatus (T10).
• The anterior and posterior vagal trunks join the oesophageal plexus surrounding the oesophagus, then follow it through the diaphragm into the abdomen.

Clinical Considerations: Hiatus Hernia

• A hiatus hernia results from the protrusion of part of the stomach into the mediastinum through the oesophageal hiatus of the diaphragm.
• Hernias occur when the diaphragm muscle weakens, widening the oesophageal hiatus and allowing parts of the stomach to move upwards.
• Hernias can involve the fundus alone, usually without regurgitation if the cardia is correctly positioned.
• When the cardia and parts of the fundus are involved, regurgitation is possible.

General Anatomy of Stomach

• The stomach is a J-shaped organ with 5 parts: cardia, fundus, body, antrum, and pylorus.
• It is located in the epigastric, umbilical, and left hypochondrium regions.
• The size and position of the stomach depend on body shape, degree of distension, and posture.

Oesophageal/Gastric Sphincter and Pyloric Sphincter

• Sphincters are located at the entry and exit of the stomach.
• The oesophagogastric junction lies to the left of the T11 vertebra on the horizontal plane through the tip of the xiphoid process.
• The Z-Line marks where the mucosa changes from oesophageal to gastric.
• Diaphragmatic musculature superior to the Z-line functions as a physiological sphincter that contracts and relaxes.
• The cardiac notch and the diaphragmatic musculature prevent reflux of stomach contents.

Reflux of Gastric Contents

• Reflux of gastric contents into the oesophagus is a common occurrence
• Deficient clearance of reflux material may result in heartburn and/or inflammation with ulceration.
• Chronic reflux can lead to metaplastic changes in the mucosa, resulting in Barrett's oesophagus.

Pyloric Sphincter

• The pyloric sphincter is a thickening of the circular muscle coat at the pyloric end of the stomach.
• The pyloric sphincter controls the discharge of stomach contents through the pyloric orifice into the duodenum.
• The pyloric sphincter allows small amounts of chyme to enter the duodenum at controlled rates.
• The pyloric sphincter prevents backflow of bile and intestinal contents into the stomach leading to more effective digestion.
• Pyloric sphincter helps ensures only properly digested food moves forward.

Hypotonic and Hypertonic Sphincter Conditions

• Hypotonic state: the sphincter weakens, leading to rapid gastric emptying (dumping syndrome) with symptoms like diarrhea, bloating, nausea, and dizziness.
• Hypertonic state: the sphincter becomes overly tight, causing delayed gastric emptying (gastroparesis) with symptoms like nausea, vomiting, bloating, early satiety, and acid reflux.

The Gastric Mucosa Histological Zones

• Gastric mucosa features longitudinal folds known as rugae.
• A gastric canal temporarily forms between gastric folds along the lesser curvature, facilitating the passage of saliva and fluids to the pylorus.
• The Gastric mucosa consists of 3 histologically distinct zones.
• Cardia which consists of neck cells that produce mucus.
• Fundus and Body consisting of neck cells (mucus), Parietal cells (acid), and Chief cells (pepsinogen).
• Pyloric which consists of neck cells (mucus) and G-cells (gastrin).

Peptic Ulcers

• Peptic ulcers are erosions or loss of continuity, often linked to hyperacidity and commonly found in the antrum along the lesser curvature.
• In severe cases, ulcers can perforate through layers.
• Perforation of ulcers leads to the leakage of gastric contents into the peritoneal cavity, potentially affecting abdominal structures such as the pancreas and blood vessels.

Gastric and Duodenal Ulcers

• Gastric ulcers cause pain on eating.
• Duodenal ulcers cause pain when hungry.

Anatomical Relationships

• Posterior wall ulcers can penetrate the gastroduodenal artery, causing bleeding.
• Anterior wall ulcers can penetrate the peritoneum, leading to perforation into the peritoneal cavity.

Greater and Lesser Omentum

• The greater omentum is a four-layered peritoneal fold that hangs down from the greater curvature of the stomach.
• After descending the greater omentum folds back and attaches to the anterior surface of the transverse colon and its mesentery.
• The lesser omentum is a double-layered peritoneal fold connects the lesser curvature of the stomach and the proximal part of the duodenum to the liver, and also connects the stomach to the portal triad.

Epiploic Foramen

• The greater and lesser sacs communicate through the omental foramen (epiploic foramen).
• The omental foramen is situated posterior to the free edge of the lesser omentum.
• The omental foramen can be located by running a finger along the gall bladder to free the edge of the lesser omentum. It typically admits 2 fingers.

Blood Supply

• The arterial blood supply to the stomach originates from the coeliac trunk and its branches.
• The coeliac trunk originates from the abdominal aorta.
• Arterial blood supply includes the left gastric, splenic, and common hepatic arteries along the lesser curvature.
• Coeliac trunk, left gastric, and common hepatic are also included as a blood supply.
• Coeliac trunk also includes splenic and left gastro-omental (epiploic)
• The coeliac trunk includes the common hepatic and gastroduodenal arteries along the greater curvature.
• The coeliac trunk further divides into splenic and posterior gastric/small gastric arteries (5-7) to supply the fundus and body.

Venous Drainage

• Venous drainage follows a path with the left and right gastric veins following the corresponding arteries and draining into the hepatic portal vein.
• Follows the corresponding arteries and draining into the hepatic portal vein.
• The short gastric vein drains into the splenic vein.
• The splenic vein then joins with the superior mesenteric vein to form the hepatic portal vein.
• The left gastro-omental vein drains into the splenic vein, which further joins the superior mesenteric vein to form the hepatic portal vein.
• Right gastro-omental vein drains into the superior mesenteric vein.
• The hepatic portal vein is formed when the superior mesenteric vein joins the splenic vein to form the hepatic portal vein.

Nerve Supply

• Sympathetic nerve supply to the stomach is derived from the T6 to T10 segments via the greater splanchnic nerve to the celiac plexus.
• The left and right vagus nerves enter the abdomen through the oesophageal hiatus (T10 vertebral level) and supply the stomach.
• The anterior vagus nerve supplies the anterior surface of the stomach ie Cardia & Lesser Curvature.
• It also gives off a hepatic branch for the liver, gall bladder, and pylorus.
• The posterior vagus nerve gives off a celiac branch (to the celiac plexus) and a posterior branch to the posterior surface of the stomach.
• Crow's feet innervate the antropyloric region.
• Two main nerve trunks branch into multiple nerves at the incisura, forming the crow's foot.
• These nerves innervate the antrum and are preserved in highly selective vagotomy.
• Vagus nerve innervation constitutes both the motor and secretory nerve supply of the stomach.

Inflammation of the Stomach: Gastritis

• Gastritis can be acute when it is caused by NSAIDs/Alcohol, resulting in exfoliation of surface epithelial cells and decreased secretion of protective mucus.
• Gastritis can be chronic when it is most commonly caused by infection with the Helicobacter pylori which causes inflammatory changes in the mucosa resulting in atrophy and epithelial metaplasia.

Stomach Post Wall

• Posterior gastric cancer or ulcer can erode the pancreas, leading to back pain.
• Ulceration into the splenic artery can result in severe haemorrhage.