CorpusHuman Anatomy
DigestiveFluid

Gastric juice

Succus gastricus

Gastric juice is the strongly acidic secretion of the gastric glands, about 1.5–2 L a day. It contains HCl, pepsinogen, gastric lipase, mucus and intrinsic factor.

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Overview

Volume≈1.5–2 L/day
pH≈1.5–3.5

Gastric juice is a mixture of a parietal component (HCl and KCl) and a non-parietal alkaline component (Na⁺, HCO₃⁻ and mucus). As the secretion rate rises, the parietal fraction dominates, so H⁺ rises and Na⁺ falls. K⁺ stays higher than in plasma at all rates (about 10–15 mmol/L).

Acid and pepsin together digest protein. Acid also kills most ingested microbes and frees vitamin B12 and iron from food. Chyme leaving the stomach is a semi-fluid mixture of partly digested food and gastric juice.

Parts & subdivisions

  1. Hydrochloric acid
    From parietal cells. Denatures proteins, activates pepsinogen, kills microbes and helps absorption of non-haem iron.
  2. Pepsinogen/pepsin
    From chief cells. Starts protein digestion.
  3. Intrinsic factor
    From parietal cells. Binds B12 in the duodenum for ileal uptake.
  4. Mucus and bicarbonate
    From surface and neck mucous cells. Form the protective gel layer.
  5. Gastric lipase
    Acid-stable lipase.

Function

  • Protein digestion.
  • Barrier against ingested pathogens.
  • Release of B12 and iron from food.
  • Formation of chyme.

Clinical significance

Vomiting and metabolic alkalosis

Losing gastric juice removes H⁺ and Cl⁻, which leaves a hypochloraemic metabolic alkalosis. Volume depletion activates aldosterone, which increases renal K⁺ and H⁺ loss. The result is hypokalaemia and "paradoxical aciduria". The classic example is pyloric stenosis.

Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.