Overview
This lecture explains the roles of acids, bases, and buffers in the body, focusing on how they maintain pH balance using key systems.
Ions in the Body
- Ions are charged atoms (e.g., sodium, potassium, calcium, hydrogen) essential for bodily functions.
- Hydrogen ions (H⁺) are much less concentrated in blood than other ions due to their high reactivity.
- H⁺ ions can damage proteins if not regulated because of their small size and high charge density.
Acids and Bases
- An acid is a substance that donates hydrogen ions (protons).
- When an acid donates a proton, it forms a conjugate base.
- A base absorbs hydrogen ions, reversing the acid reaction.
Physiological Acids and Conjugate Bases
- Common biological acids: hydrochloric acid, dihydrogen phosphate (phosphoric acid), carbonic acid, amino acids, lactic acid, pyruvic acid.
- Amino acids have both carboxy and amine groups that can donate or accept protons, acting as buffers.
pH, pKa, and Buffer Systems
- pH measures hydrogen ion concentration; normal blood pH is 7.4.
- pKa is the acid-specific value indicating its tendency to donate H⁺ at a certain pH.
- If pH ≈ pKa, the acid/base system acts as a buffer, resisting pH changes.
- If pKa < pH, the solution favors H⁺ production; if pKa > pH, H⁺ is mopped up.
Strong vs. Weak Acids
- Strong acids (e.g., HCl) fully dissociate in solution and cannot act as buffers.
- Weak acids have pKa values closer to physiological pH and can act as buffers by donating or accepting H⁺.
Major Buffer Systems in the Body
- Three main buffers: phosphate, protein (amino acid), and bicarbonate.
- Phosphate buffer is effective intracellularly and in renal tubules where pKa ≈ pH.
- Protein buffer is the most abundant intracellular buffer due to ionizable groups on amino acids.
- Bicarbonate buffer system is most important, as it can be regulated by both lungs (CO₂ exhalation—rapid) and kidneys (bicarbonate reabsorption—slow).
Key Terms & Definitions
- Ion — A charged atom or molecule.
- Acid — Donates hydrogen ions (protons) in solution.
- Base — Absorbs (binds) hydrogen ions.
- Conjugate base — The residue left after an acid donates a proton.
- pH — Measure of hydrogen ion concentration.
- pKa — Value indicating an acid’s tendency to donate protons at a given pH.
- Buffer — Solution that resists drastic changes in pH.
Action Items / Next Steps
- Review the bicarbonate buffer system in more detail for understanding acid-base imbalances like acidosis and alkalosis.
- Watch the next lecture for in-depth analysis of buffer systems and their clinical significance.