Which of the following mechanisms helps prevent gastric juice from destroying stomach lining?

The correct answer is: Secretion of mucus and bicarbonate ions.

The gastric juice in our stomach is highly acidic (pH 1-2) and can potentially damage the stomach lining. To protect itself from this acidic environment, the stomach has several defense mechanisms, including:

- Secretion of mucus: The stomach lining secretes a thick layer of mucus that acts as a physical barrier between the acidic gastric juice and the sensitive stomach cells. This mucus layer helps to prevent the acid from coming into direct contact with the stomach lining and causing damage.

- Secretion of bicarbonate ions: The stomach also secretes bicarbonate ions (HCO3-) which help to neutralize the acidity of the gastric juice. Bicarbonate ions react with hydrogen ions (H+), the main component of gastric acid, to form water (H2O) and carbon dioxide (CO2). This process helps to reduce the acidity of the gastric juice and protect the stomach lining.

- Tight junctions between stomach cells: The cells that line the stomach have tight junctions that prevent the acidic gastric juice from seeping between them and reaching the deeper layers of the stomach wall. These tight junctions help to maintain the integrity of the stomach lining and prevent damage from the acidic environment.

- Regeneration of stomach cells: The stomach lining is constantly being replaced by new cells that are produced in the pits of the gastric glands. This process of cell regeneration helps to maintain the health of the stomach lining and allows it to withstand the harsh acidic environment.