The volume of air in the dead space fo human lungs is normally

Options

A. 230 mL
B. 210 mL
C. 190 mL
D. 159mL

Answer

To determine the volume of air in the dead space of human lungs, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Dead Space**:
- Dead space refers to the portion of the respiratory system where air does not participate in gas exchange. This includes the conducting airways such as the trachea and bronchi.

2. **Identifying Tidal Volume**:
- Tidal volume is the amount of air inhaled or exhaled during normal breathing. For an average adult, the tidal volume is approximately 500 ml.

3. **Calculating Dead Space Volume**:
- It is known that about 30% of the tidal volume does not reach the alveoli (the site of gas exchange) and remains in the conducting airways.
- To find the volume of air in the dead space, we calculate 30% of the tidal volume:
\[ \text{Dead Space Volume} = 0.30 \times \text{Tidal Volume} = 0.30 \times 500 \, \text{ml} = 150 \, \text{ml} \]

4. **Considering Additional Dead Space**:
- Besides the conducting airways, there is a negligible amount of air that remains in the alveoli and bronchioles that does not participate in gas exchange. This is estimated to be around 8-10 ml.
- Therefore, we can add this negligible volume to the dead space volume calculated earlier:
\[ \text{Total Dead Space Volume} = 150 \, \text{ml} + 8-10 \, \text{ml} \approx 158-160 \, \text{ml} \]

5. **Final Answer**:
- Based on the calculations, the total volume of air in the dead space of human lungs is approximately 150 ml, plus a negligible amount, leading to a total of about 159 ml.

### Conclusion:
- The volume of air in the dead space of human lungs is approximately **159 ml**.