The Stomach: Anatomy, Functions, and Role in Digestion

The stomach is a J-shaped muscular organ in the upper left abdomen. It connects the esophagus to the duodenum and performs mechanical and chemical digestion.

Anatomical Regions

• Cardia: Surrounds esophageal opening.
• Fundus: Superior dome; gas collection.
• Body (corpus): Main central region.
• Antrum: Distal, narrow; strong peristalsis.
• Pylorus: Sphincter controlling emptying into duodenum.

Key Functions

1. Storage: Holds 1.5 L (distensible); allows intermittent eating.
2. Mechanical digestion: Peristaltic waves (3/min) mix and grind food into chyme.
3. Chemical digestion:
   • Gastric juice (2–3 L/day): HCl (pH 1.5–3.5), pepsinogen → pepsin (protein digestion), intrinsic factor (B12 absorption), lipase (minor fat digestion).
   • HCl denatures proteins, kills microbes, activates pepsin.
4. Chyme formation: Semi-liquid mixture released gradually via pylorus.
5. Regulation of emptying: Feedback from duodenum (fat, acid, osmolarity) → enterogastric reflex + hormones (CCK, secretin, GIP) slow gastric emptying.
6. Absorption (limited): Water, alcohol, aspirin, some lipid-soluble drugs.
7. Protection: Mucus-bicarbonate barrier; prostaglandins maintain blood flow.
8. Endocrine: Ghrelin (hunger), gastrin (acid secretion), somatostatin.

Clinical Relevance

• Gastritis, peptic ulcer (H. pylori, NSAIDs).
• Gastroparesis (delayed emptying; diabetes, post-viral).
• Gastric cancer (adenocarcinoma, lymphoma).
• Dumping syndrome (post-gastrectomy).

The stomach is a dynamic bioreactor, not just a holding tank.