Problem 58 - Objective Biology for NEET

Question

Which is not true? (a) \(\mathrm{pCO}_{2}\) of deoxygenated blood is \(95 \mathrm{~mm} \mathrm{Hg}\). (b) \(\mathrm{pCO}_{2}\) of alveolar air is \(40 \mathrm{~mm} \mathrm{Hg}\). (c) \(\mathrm{pO}_{2}\) alveolar air is \(104 \mathrm{~mm} \mathrm{Hg}\). (d) \(\mathrm{pO}_{2}\) of oxygenated blood is \(95 \mathrm{~mm} \mathrm{Hg}\). (e) \(\mathrm{pO}_{2}\) of deoxygenated blood is \(40 \mathrm{~mm} \mathrm{Hg}\).

Step-by-Step Solution

Answer

The statement that is not true is (a). The pCO2 of deoxygenated blood is typically around 45-46 mmHg, not 95 mmHg.

Step 1: Understanding physiology and standard partial pressures

It is important to understand physiology behind partial pressures. In normal conditions and at sea level, the partial pressure of oxygen (pO2) in alveolar air is approximately 104 mmHg and in oxygenated blood is about 100 mmHg, and the partial pressure of oxygen in deoxygenated blood is around 40 mmHg. Similarly, the partial pressure of carbon dioxide (pCO2) in deoxygenated blood is approximately 45-46 mmHg and in alveolar air it's around 40 mmHg.

Step 2: Analyze each statement

Now let's analyze each statement with respect to the standard values. (a) pCO2 of deoxygenated blood is 95 mmHg. The standard value is 45-46 mmHg, so this statement is incorrect. The other statements: (b) pCO2 of alveolar air is 40 mmHg, (c) pO2 alveolar air is 104 mmHg, (d) pO2 of oxygenated blood is 95 mmHg and (e) pO2 of deoxygenated blood is 40 mmHg are in alignment with the standard values and are therefore accurate.

Step 3: Determining the incorrect statement

By comparing each statement with the standard values, we determine that statement (a) is incorrect. The typical pCO2 of deoxygenated blood is around 45-46 mmHg, not 95 mmHg.

Key Concepts

Respiratory Physiology

Respiratory physiology is the study of how our lungs and respiratory system deliver oxygen to the blood and remove carbon dioxide. The process involves inhaling oxygen-rich air and exhaling carbon dioxide-laden air. This exchange happens in our lungs, specifically within tiny air sacs called alveoli. To understand how efficient this process is, one can look into partial pressures of gases. Partial pressure is a measure of a specific gas's concentration, like oxygen or carbon dioxide, in the blood. At sea level, the normal ranges for oxygen (pO2) and carbon dioxide (pCO2) partial pressures can be examined to assess respiratory function. Variations in these values can indicate underlying respiratory disorders or inefficiencies in gas exchange.

Gas Exchange

Gas exchange is a critical biological process where oxygen is absorbed and carbon dioxide is expelled. This happens through diffusion in the alveoli, where blood coming from the heart picks up oxygen and releases carbon dioxide. Each gas moves from an area of higher partial pressure to one of lower partial pressure.

In normal conditions:

• The partial pressure of alveolar oxygen (pO2) is about 104 mmHg.
• The pCO2 in alveolar air is typically around 40 mmHg.

This process ensures that oxygen enters the bloodstream while carbon dioxide is removed from the body. If the gas exchange process is not optimal, it can lead to symptoms of respiratory distress or other complications.

Blood Oxygenation

Blood oxygenation refers to the process of getting oxygen from the lungs into the blood. This starts when oxygen enters the alveoli and diffuses into the pulmonary capillaries. In oxygenated blood, the partial pressure of oxygen (pO2) is about 95-100 mmHg as it circulates back to the heart to be pumped throughout the body. This oxygen-rich blood ensures that tissues can function properly.

Even in deoxygenated blood returning to the lungs, the pO2 is around 40 mmHg. This stark difference is crucial as it represents how efficiently the body is utilizing and then replenishing its oxygen supply. Monitoring blood oxygen levels can help detect lung and heart conditions.

Carbon Dioxide Transport

Carbon dioxide transport is just as important as oxygen delivery. This process begins after body tissues produce carbon dioxide as a byproduct of metabolism. The venous blood carries carbon dioxide to the lungs to be expelled. Normally, the pCO2 in deoxygenated blood is about 45-46 mmHg.

Within the lungs:

• Carbon dioxide diffuses from the blood into the alveolar air, where it has a partial pressure of about 40 mmHg.

Efficient carbon dioxide transport is vital to maintain the body's pH balance and prevent acidosis. Any disturbances in this process can have significant effects on overall health, potentially leading to respiratory or metabolic disorders.