The stomach protects itself from self-digestion primarily through a thick mucus lining produced by specialized epithelial cells. This acts as a protective barrier. However, multiple mechanisms are involved to ensure the stomach's integrity.
Here's a breakdown of the stomach's defenses:
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Mucus Layer:
- The epithelial cells lining the stomach secrete a thick layer of mucus rich in bicarbonate.
- This mucus layer physically shields the stomach lining from the harsh acidic environment (hydrochloric acid) and digestive enzymes like pepsin.
- The mucus also acts as a neutralizer.
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Bicarbonate Secretion:
- The epithelial cells secrete bicarbonate ions (HCO3-) into the mucus layer.
- Bicarbonate is alkaline and neutralizes the acid closest to the stomach lining, creating a pH gradient from the highly acidic lumen (stomach cavity) to a near-neutral pH at the epithelial surface.
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Tight Junctions:
- Stomach epithelial cells are connected by tight junctions, which are specialized cell-cell junctions that prevent acid and enzymes from seeping between cells and damaging deeper tissues.
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Rapid Cell Turnover:
- The cells lining the stomach have a high turnover rate. They are constantly being replaced every few days. This allows the stomach to quickly repair any damage caused by acid or enzymes.
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Prostaglandins:
- Prostaglandins play a crucial role in protecting the stomach lining. They:
- Stimulate mucus and bicarbonate secretion.
- Promote blood flow to the stomach lining, which helps deliver nutrients and remove waste products.
- Inhibit acid secretion.
- NSAIDs (nonsteroidal anti-inflammatory drugs) inhibit prostaglandin production and can therefore increase the risk of stomach ulcers.
- Prostaglandins play a crucial role in protecting the stomach lining. They:
In summary, the stomach avoids digesting itself through a multi-layered defense system, including a protective mucus barrier, bicarbonate secretion, tight junctions between cells, rapid cell turnover, and the protective effects of prostaglandins.
