Q.27 Which ofthe following are involved in buffering our blood system ?
1. Bicarbonate Phosphate buffers
2. Tris Hel buffer
3. MOPs buffer
4. Calcium/ Magnesium buffers

The primary buffers in human blood maintain pH between 7.35-7.45, with bicarbonate and phosphate systems playing key roles alongside proteins like hemoglobin.

Option Analysis

Blood buffering resists pH changes from metabolic acids/bases; the correct answer is option 1, as it names the two main non-protein systems operational in blood plasma and cells.

• Option 1: Bicarbonate Phosphate buffers – Correct. Bicarbonate (H2CO3/HCO3-) is the dominant plasma buffer, linked to CO2 excretion via lungs; phosphate (H2PO4-/HPO4^2-) aids intracellularly and in kidneys but contributes in blood.

• Option 2: Tris Hel buffer – Incorrect. Tris (tris(hydroxymethyl)aminomethane) is a synthetic lab buffer (pKa ~8.1) for cell culture; “Hel” likely means HEPES, another artificial Good’s buffer (pKa 7.5), neither physiological for blood.​

• Option 3: MOPs buffer – Incorrect. MOPS (3-(N-morpholino)propanesulfonic acid, pKa ~7.2) is a synthetic zwitterionic buffer used in labs/biochem experiments, not in vivo blood.​

• Option 4: Calcium/ Magnesium buffers – Incorrect. Ca^2+/Mg^2+ are electrolytes involved in signaling/muscle function, not acid-base buffering (no weak acid/conjugate pair); proteins bind them but aren’t “Ca/Mg buffers.”​

Buffers in blood system are essential for pH homeostasis (7.35-7.45), preventing acidosis/alkalosis from CO2, lactic acid, or ketones. This guide targets the key phrase “buffering our blood system,” decoding the MCQ on bicarbonate phosphate buffers versus lab synthetics like Tris or MOPS, ideal for competitive exams in physiology and biochemistry.

Core Blood Buffers: Bicarbonate and Phosphate

The bicarbonate buffer (CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-) dominates plasma (53% buffering power), with rapid lung/kidney regulation. Phosphate buffer (H2PO4- ⇌ H+ + HPO4^2-, pKa 6.8) supports intracellularly (35% power), especially in RBCs/renal tubules. Together, they handle ~90% of blood’s buffering alongside hemoglobin/proteins.

Why Not Synthetic Buffers?

Tris-HEPES (option 2) and MOPS (option 3) are Good’s buffers for lab use (e.g., PCR, electrophoresis), with pKa near physiological range but absent in vivo due to toxicity/non-regulation. Ca/Mg (option 4) ions don’t form buffers; they complex with proteins but lack H+/base neutralization capacity.

Buffer Comparison Table

For exams, prioritize bicarbonate-phosphate as blood’s key chemical buffers per standard physiology texts.