What is the main buffer system responsible for maintaining the pH of human blood?

RML 2023

Applied Physiology

Easy

Appeared in: RML 2023

Explanation

The bicarbonate-carbonic acid system is the most important chemical buffer in the blood plasma (extracellular fluid).
It accounts for approximately 65% of the buffering capacity in plasma.
Its high efficiency is due to its components being independently regulated by the lungs (controlling CO₂) and the kidneys (controlling HCO₃⁻).
This 'open system' allows the body to make rapid respiratory compensations and slower, but more powerful, renal (metabolic) compensations to pH changes.

Option A: The phosphate buffer system's concentration in the blood plasma is very low, which limits its effectiveness as a primary blood buffer.
Option B: While proteins are the most abundant buffers in the body by quantity, they are primarily located inside cells (intracellular fluid). Plasma proteins like albumin contribute to buffering, but their role is minor compared to the bicarbonate system.
Option D: The hemoglobin buffer is a specialized protein buffer that functions exclusively inside red blood cells. It does not directly buffer the blood plasma.

Clinical Relevance

Nursing practice connection: Knowing Acid-Base Balance and Blood Buffer Systems helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding the bicarbonate buffer system is fundamental for interpreting Arterial Blood Gas (ABG) results, which measure pH, pCO₂ (the respiratory component), and HCO₃⁻ (the metabolic component).
Nurses use ABG values to identify acid-base imbalances (acidosis or alkalosis), determine if the cause is respiratory or metabolic, and assess the degree of physiological compensation.
What if? - A patient has chronic kidney disease (CKD). Their ability to excrete acid and regenerate bicarbonate (HCO₃⁻) would be impaired. This compromises the metabolic component of the buffer system, leading to a high risk of chronic metabolic acidosis.

How to Approach the Question

First, identify the keywords in the question: 'main buffer system' and 'human blood'. In this context, 'human blood' primarily refers to the plasma, which is an extracellular fluid.
Second, evaluate each option based on its primary location and role in the body.
Recall that the bicarbonate system is unique because its components (CO₂ and HCO₃⁻) are actively and powerfully regulated by two major organ systems: the lungs and the kidneys.
Eliminate the other options based on their location: the phosphate and protein buffer systems are primarily intracellular, and the hemoglobin buffer is confined to red blood cells.
Conclude that the bicarbonate-carbonic acid system, being the primary buffer in the extracellular fluid and having robust physiological regulation, is the main buffer for blood pH.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 73-75

E6 Physiology Guyton 4SAE Part 2B p. 66-68

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 555-557