Overview
This lecture explains how pH varies throughout the body, the importance of buffer systems in maintaining appropriate pH, and how this impacts protein and enzyme function, especially in the digestive system.
pH Variation in the Body
- pH is not uniform throughout the body; different areas have different normal pH values.
- Stomach acid has a low (acidic) pH, while blood and other body fluids have higher pH values.
- There are very few places in the body with a neutral pH (7.0).
Importance of Buffers
- Buffers keep pH relatively constant, not necessarily neutral, in each area of the body.
- Buffers prevent drastic pH changes to protect protein structure and function.
- Common buffer in the digestive tract is the bicarbonate ion (HCO₃⁻).
Protein Structure and pH
- Proteins need a constant pH to maintain their specific three-dimensional shape.
- Changes in pH can denature (unravel/alter) proteins, causing loss of function.
Digestive System pH and Buffering
- The mouth, stomach, and small intestine each have different pH levels.
- Food moves from mouth (pH ≈ 6.8–7.4) to stomach (pH ≈ 1–2), then to small intestine (duodenum, pH ≈ 7.4–7.8).
- Stomach acid kills pathogens and starts protein digestion.
- Food is slowly released from the stomach into the duodenum, regulated by the pyloric sphincter based on pH.
- When acidic food enters the duodenum, buffers (mainly bicarbonate ions from the pancreas) are released to neutralize the acid and increase pH.
Enzymes and pH Sensitivity
- Digestive enzymes are proteins that work in a narrow pH range.
- If pH is too low (acidic), enzymes become denatured and can't function.
- Buffers must raise pH before enzymes enter the small intestine to ensure digestion occurs.
Key Terms & Definitions
- pH — a measure of hydrogen ion concentration; indicates acidity or alkalinity.
- Buffer — a substance that helps maintain a stable pH in a solution.
- Protein denaturation — structural change in a protein causing loss of function, often due to pH or temperature change.
- Enzyme — a protein that speeds up chemical reactions, sensitive to pH.
- Pyloric sphincter — muscle controlling food movement from stomach to small intestine.
- Bicarbonate ion (HCO₃⁻) — main buffer in the digestive system.
- Duodenum — first section of the small intestine, site of chemical digestion.
Action Items / Next Steps
- Review the process of food moving from stomach to small intestine and the role of pH and buffers.
- Prepare to explain why pH and buffers are vital for protein/enzyme function, especially in digestion.
- Remember this example for potential essay or short answer exam questions.