Stomach

The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. On a microscopic level, the stomach wall has several layers, including a mucosa, submucosa, muscularis, and serosa. The stomach is filled with glands that secrete a variety of substances involved in the digestive process. The arterial supply to the stomach is primarily from vessels originating from the celiac trunk.

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Overview

The stomach is a muscular sac in the upper abdomen that plays a critical role in digestion.

Functions of the stomach

  • Storage of food
  • Digestion: 
    • Mechanically breaks up food
    • Mixes food with gastric secretions to produce chyme
  • Slow/controlled emptying of chyme into the small intestine
  • Secretion of:
    • Hydrochloric acid (HCl): 
      • Activates digestive enzymes
      • Breaks up connective tissue in food
      • Destroys bacteria and other pathogens
    • Pepsinogen: converted to pepsin by HCl, which digests proteins
    • Mucus: protects gastric cells from the HCl
    • Intrinsic factor: essential for absorption of vitamin B12
    • Gastrin: stimulates secretion of HCl and mucus
    • Ghrelin (the “hunger hormone”): stimulates appetite and promotes fat storage

Development of the stomach

  • Develops from the foregut
  • Begins as a longitudinal tube
  • Dorsal wall grows faster than its ventral wall → sac expands posteriorly and to the left → develops a C shape
  • Rotates along its longitudinal axis into its final position
  • Has a dorsal and ventral mesogastrium (early mesentery attaching the primitive foregut to the posterior body wall): 
    • Dorsal mesogastrium → greater omentum
    • Ventral mesogastrium → lesser omentum

Gross Anatomy

General characteristics

  • C-shaped sac-like organ
  • Internal volume:
    • Approximately 50 mL when empty
    • Up to 4 L when full

Parts of the stomach and anatomic landmarks

  • Cardia: 
    • Entrance of the stomach
    • Adjacent to the lower esophageal sphincter
  • Fundus: dome-shaped region located at the highest point of the stomach, above the cardiac opening
  • Body: 
    • Main section of the stomach 
    • Extends from the fundus to the pylorus 
    • Bordered by the lesser and greater curvatures
    • Contains thick folds called rugae
  • Pylorus (also called the antrum): 
    • Connects to the duodenum via the pyloric sphincter
    • Consists of a wider pyloric antrum and narrower pyloric canal
  • Lesser curvature: 
    • A concave curvature along the medial side of the stomach
    • Runs from the right edge of the esophagus to the superior border of the pylorus
  • Greater curvature: 
    • Convex curvature along the lateral side of the stomach
    • Runs from the left edge of the fundus to the inferior border of the pylorus
  • Cardiac notch: angle created between the esophagus and the fundus
  • Angular incisure: notch in the lesser curvature in the pyloric region
  • Lumen: space inside the stomach walls
Anatomical components of the stomach

Anatomical components of the stomach

Image by BioDigital, edited by Lecturio

Location

  • Upper left quadrant of the peritoneal cavity
  • Connected to:
    • The esophagus at its proximal end
    • The duodenum at its distal end

Anatomic relationships

The stomach is in direct contact with a number of other organs, including:

  • Diaphragmatic dome → fundus and greater curvature 
  • Left lobe of the liver → right and ventral side of the stomach
  • Spleen → posterior left half of the stomach
  • Tail of the pancreas → dorsal side of the stomach
  • Transverse colon → posterior and inferior surfaces of the body and pylorus
  • Left kidney and adrenal gland → posterior surface of the gastric body 
Stomach

Stomach in situ and the relations to its neighboring structures

Image by BioDigital, edited by Lecturio

Microscopic Anatomy

Layers of the stomach wall

  • Mucosa:
    • Consists of 3 sublayers:
      • Simple columnar epithelium (innermost lining)
      • Lamina propria
      • Muscularis mucosa
    • Gastric pits:
      • Depressions in the mucosa that lead down into gastric glands within the lamina propria 
      • Open into the lumen
    • Lies in folds, called rugae, when the stomach is empty
    • Rugae stretch and flatten when the stomach is filled.
  • Submucosa: 
    • Contains the submucosal nerve plexus (Meissner plexus), which controls the muscularis mucosa
    • Made up of connective tissue
  • Muscularis externa:
    • Has 3 layers:
      • Oblique layer (innermost)
      • Circular layer (middle)
      • Longitudinal layer (outer)
    • Contains (and controlled by) the myenteric nerve plexus (Auerbach plexus) between the longitudinal and circular layers
    • Important for motility and mechanical digestion 
  • Serosa: outer layer of connective tissue

Gastric glands

General characteristics:

  • Mostly exocrine glands (secrete products into a luminal space rather than the bloodstream)
  • Located beneath the gastric pits within the gastric mucosa
  • Multiple glands open into a single gastric pit (which opens into the stomach lumen).
  • Neck region: area where the gastric glands open into the gastric pits

Types of glands:

  • Cardiac and pyloric glands:
    • Located in the gastric cardia and pyloric regions, respectively
    • Secrete mucus
  • Gastric glands:
    • Glands in the fundus and body
    • Contain multiple cell types → multiple secretory products

Types of cells within the glands:

Comprises (from surface to deep): 

  • Surface mucous cells:
    • Line the gastric pits
    • Simple columnar cells
    • Appear clear on H&E stains
    • Secrete an insoluble mucus:
      • Forms a protective barrier against the acidic environment of the stomach
      • Concentrates bicarbonate in the mucus
  • Mucous neck cells:
    • Located in the neck of the glands, where they join the gastric pits
    • Secrete a soluble mucus
    • Darker-staining nuclei than surface mucous cells
  • Stem cells:
    • Found between the pits and the entrance of the glands
    • Produce new cells to replace both surface mucous cells in the pits and glandular cells below
    • Stomach epithelial cells are replaced every 3–6 days.
  • Parietal cells:
    • Located in the middle region of the glands
    • Eosinophilic (stain pink on H&E)
    • Secrete HCl and intrinsic factor
  • Chief cells:
    • Most numerous glandular cells
    • Located in the bases of the glands
    • Basophilic (stain blue on H&E)
    • Secrete pepsinogen and gastric lipase
  • Enteroendocrine cells:
    • Located in the bases of the glands
    • Produce different types of hormones

Neurovasculature

Arterial blood supply

  • Arterial supply is from the celiac trunk.
  • Vessels form 2 anastomotic loops along the lesser and greater curvatures.
  • Vascular arch of the lesser curvature: 
    • Left gastric artery: directly off the celiac trunk
    • Right gastric artery: off the hepatic artery (a branch of the celiac trunk)
  • Vascular arch of the greater curvature: 
    • Left gastroepiploic artery: branch off the splenic artery (which is a branch of the celiac trunk)
    • Right gastroepiploic artery: branches off the gastroduodenal artery (a branch off the hepatic artery)
    • Note: Left and right gastroepiploic arteries are also known as the gastro-omental arteries.
  • Short gastric arteries:
    • Arise from the terminal splenic artery and the left gastroepiploic artery 
    • Supply the fundus of the stomach
Arterial supply of the stomach

Image showing the blood supply of the stomach

Image by BioDigital, edited by Lecturio

Venous drainage

  • By homonymous veins that accompany the arteries
  • Lesser curvature: right and left gastric veins → drain into the portal vein
  • Greater curvature: 
    • Left gastroepiploic vein and the short gastric veins → drain into the splenic vein
    • Right gastroepiploic vein → drains into the superior mesenteric vein
Venous drainage of the stomach

Venous drainage of the stomach

Image by BioDigital, edited by Lecturio

Lymphatic drainage

Lymph nodes draining the stomach are arranged in a complex network.

  • Lymph vessels within the mucosa and submucosa collect lymph.
  • Drain into immediate surrounding perigastric lymph nodes:
    • Right and left paracardiac lymph nodes
    • Suprapyloric and infrapyloric lymph nodes 
  • Perigastric lymph nodes drain into the lymph nodes and vessels, which run along the vasculature supplying the stomach:
    • Left gastric artery
    • Common hepatic artery
    • Celiac vessels
    • Splenic artery 
  • Ultimately drain into the para-aortic lymph nodes

Innervation

The stomach is innervated by the autonomic nervous system.

  • Parasympathetic innervation: anterior and posterior trunks of the vagus nerve (stimulatory)
  • Sympathetic innervation: greater splanchnic nerve (inhibits digestive activity of the stomach)
Innervation of the stomach

Innervation of the stomach

Image by BioDigital, edited by Lecturio

Clinical Relevance

  • Acute gastritis: inflammation associated with gastric mucosal injury. The most common causes of acute gastritis include Helicobacter pylori infection and immune-mediated reactions, though alcohol, medications (such as NSAIDs), and ischemia can also be causative; frequently the etiology is unknown. Clinical signs and symptoms include vomiting, abdominal discomfort/pain, and heartburn. Endoscopy with gastric mucosal biopsy is the best tool for diagnosis. 
  • Gastric ulcer: defect of the gastric mucosa, extending into its muscular layer, most often in the lesser curvature and antrum of the stomach. The majority of gastric ulcers are caused by H. pylori infection. The most common symptoms are epigastric pain that worsens with eating, epigastric fullness, early satiety, fatty-food intolerance, nausea, and occasional vomiting. Diagnosis is confirmed with endoscopy.
  • Gastric cancer: neoplasm of the stomach. Adenocarcinoma is the most common type, but additional types include lymphoma and GI stromal and carcinoid tumors. Gastric cancer typically presents with weight loss, dysphagia, vague abdominal pain, nausea, and early satiety. Upper endoscopy with biopsy is the gold standard for diagnosis. 
  • Pyloric stenosis: characterized by hypertrophy and hyperplasia of the pyloric sphincter in the first months of life. Pyloric stenosis is the most common cause of gastric outlet obstruction in infants. Clinical presentation includes postprandial vomiting that is nonbilious and forceful (often described as “projectile” vomiting); an olive-shaped mass may be palpable in the epigastrium.

References

  1. Le, T., Bhushan, V., Sochat, M., et al. (Eds.) (2021). First Aid for the USMLE Step 1, 31st ed., pp. 371–372. McGraw-Hill Education.
  2. Vakil, N.B. (2020). Peptic ulcer disease: Clinical manifestations and diagnosis. UpToDate. Retrieved August 15, 2021, from https://www.uptodate.com/contents/peptic-ulcer-disease-clinical-manifestations-and-diagnosis
  3. Kapoor, V.K. (2017). Stomach anatomy. Medscape. Retrieved August 15, 2021, from https://emedicine.medscape.com/article/1899301-overview#a2
  4. Hebbard, P. (2021). Partial gastrectomy and gastrointestinal reconstruction. UpToDate. Retrieved August 16, 2021, from https://www.uptodate.com/contents/partial-gastrectomy-and-gastrointestinal-reconstruction 
  5. Lirosi, M. C., Biondi, A., Ricci, R. (2017). Surgical anatomy of gastric lymphatic drainage. Translational Gastroenterology and Hepatology 2(3):14. Retrieved August 18, 2021, from https://doi.org/10.21037/tgh.2016.12.06

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