## Gastric Acid-Secreting Cells **Key Point:** Parietal cells are the primary source of gastric acid (HCl) and are located predominantly in the fundic glands of the stomach. ### Cell Type Distribution and Function | Cell Type | Location | Primary Secretion | Function | |-----------|----------|-------------------|----------| | **Parietal cells** | Fundic glands (body & fundus) | HCl, Intrinsic factor | Acid secretion, B₁₂ absorption | | Chief cells | Base of fundic glands | Pepsinogen | Protein digestion (inactive form) | | Mucous neck cells | Neck of fundic glands | Mucus | Mucosal protection | | G cells | Antral glands | Gastrin | Hormonal regulation of acid | **High-Yield:** Parietal cells secrete: - Hydrochloric acid (HCl) — via H⁺/K⁺-ATPase pump - Intrinsic factor — required for vitamin B₁₂ (cobalamin) absorption in terminal ileum - Gastric intrinsic factor ### Mechanism of Acid Secretion 1. **Basal state:** Minimal acid secretion 2. **Stimulated state:** Three pathways activate parietal cells: - **Acetylcholine (ACh)** from vagal nerve endings → muscarinic M₃ receptors - **Gastrin** from G cells → gastrin receptors - **Histamine** from enterochromaffin-like (ECL) cells → H₂ receptors 3. **Final common pathway:** All three converge to increase intracellular cAMP and Ca²⁺, activating the **H⁺/K⁺-ATPase pump** in the apical membrane **Clinical Pearl:** Loss of parietal cells (autoimmune gastritis, gastrectomy) → achlorhydria, pernicious anemia, and hypergastrinemia due to loss of negative feedback. [cite:Guyton & Hall 13e Ch 64]
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