Hydrochloric Acid | Biology for GCSE/IGCSE - Year 11 PDF Download

Hydrochloric Acid

• The stomach produces various fluids collectively known as gastric juice.
• One of these fluids is hydrochloric acid.
• Hydrochloric acid kills bacteria in food and provides an acidic pH for enzymes to function in the stomach.
• The acidic environment activates pepsin, a protease enzyme, which begins the digestion of proteins.
• The acid helps to break down the connective tissues in meat and other foods, making them easier to digest.
• The presence of hydrochloric acid also assists in the absorption of certain minerals, such as iron and calcium, in the intestine.

How is a low pH helpful in the stomach?

• Activation of Pepsinogen: The low pH in the stomach activates pepsinogen, an inactive enzyme precursor, into its active form, pepsin. Pepsin is crucial for breaking down proteins into smaller peptides.
• Optimal Environment for Pepsin: The acidic environment (pH around 2) is essential for pepsin to function effectively. Without this low pH, pepsin would not be able to catalyze the hydrolysis of proteins efficiently.
• Breakdown of Tough Plant Material: The acidity helps to break down tough plant cell walls and connective tissues in meat, making it easier for enzymes to further digest the food in the small intestine.
• Prevention of Pathogen Proliferation: Besides killing bacteria, the acidic environment prevents the proliferation of potentially harmful pathogens that may have been ingested with the food.
• Enhancing Mineral Absorption: The low pH in the stomach facilitates the solubilization and absorption of certain minerals, such as iron and calcium, which are better absorbed in an acidic environment.
• Regulation of Stomach Emptying: The low pH helps regulate the rate at which the stomach empties its contents into the small intestine, ensuring that food is sufficiently digested before moving on.
• Denaturing Dietary Proteins: The acidity denatures the tertiary and quaternary structures of dietary proteins, making them more accessible to enzymatic breakdown by pepsin.
• Hydrochloric Acid Production: Parietal cells in the stomach lining produce hydrochloric acid, which lowers the pH and creates an inhospitable environment for most microorganisms, thereby protecting the body from infections.
• Bicarbonate Secretion: The stomach lining secretes bicarbonate ions into the mucus layer that coats the stomach, providing a buffer zone that protects the stomach tissue from being damaged by the acidic pH.