1 gm of haemoglobin contains?

AIIMS BBSR SNO - 2019

Applied Physiology

Easy

Appeared in: AIIMS BBSR SNO - 2019

Explanation

This question tests a fundamental value in respiratory physiology: the oxygen-binding capacity of hemoglobin.
Each molecule of hemoglobin has four iron-containing heme groups, and each heme group can reversibly bind one molecule of oxygen.
Based on the molecular weight of hemoglobin and oxygen, it is calculated that 1 gram of chemically pure hemoglobin can bind a maximum of 1.39 mL of oxygen.
This value is the theoretical maximum. A slightly lower value of 1.34 mL/g is often used in clinical calculations to account for inactive forms of hemoglobin (e.g., methemoglobin) in the blood.
Since 1.39 mL is provided as an option, it represents the correct theoretical answer.

Option B: This value is significantly higher than the actual oxygen-binding capacity of hemoglobin. It is not a recognized physiological constant.
Option C: This value is also substantially overestimated and does not reflect the biochemical properties of hemoglobin.
Option D: This value is significantly lower than the established oxygen-carrying capacity. Such a low capacity would not be sufficient to meet the body's metabolic needs.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Oxygen-carrying capacity of hemoglobin as background academic context rather than a clinical decision trigger.
Understanding the oxygen-carrying capacity is crucial for nurses to interpret lab results (like Hb levels) and assess a patient's oxygenation status. For example, a patient with anemia (low Hb) has a reduced total oxygen-carrying capacity, even if their lungs are functioning perfectly.
This knowledge helps in managing conditions like hemorrhage, anemia, and respiratory failure, where oxygen delivery to tissues is compromised.
What if a patient has carbon monoxide (CO) poisoning? Even with normal hemoglobin levels, the oxygen-carrying capacity is drastically reduced. CO binds to hemoglobin with an affinity over 200 times that of oxygen, forming carboxyhemoglobin, which cannot transport oxygen. The answer to the question (1.39 mL/g) remains true for the available hemoglobin, but the effective amount of Hb is much lower.

How to Approach the Question

Identify the question type: This is a factual recall question that requires knowledge of a specific physiological value.
Scan the keywords: The key terms are '1 gm of haemoglobin' and 'oxygen'. This points directly to the concept of oxygen-carrying capacity.
Recall the specific value: Access your memory of respiratory physiology. The standard value for the maximum amount of oxygen that 1 gram of pure hemoglobin can carry is 1.39 mL.
Compare with options: Match the recalled value with the given options. Option A, 1.39 mL, is a direct match.
Eliminate other options: Quickly recognize that the other values (2.39, 3.39, 0.39) are incorrect and do not align with known physiological data.

Concept Tested & Keywords

QuO3rMEmASk-owpajNIkRz

E6 Physiology Guyton 4SAE Part 2A pp. 92-94, 90-93

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 11-13