The urge to inhale in humans results from

Options

A. rising `pco_(2)`
B. rising `po_(2)`
C. falling `pcO_(2)`
D. falling `po_(2)`

Answer

**Step-by-Step Solution:**

1. **Understanding the Mechanism of Breathing:**
- Breathing is a vital process that involves inhaling oxygen and exhaling carbon dioxide. The urge to breathe is primarily regulated by the levels of carbon dioxide in the blood rather than the levels of oxygen.

2. **Role of Carbon Dioxide:**
- Carbon dioxide (CO2) is a byproduct of cellular metabolism. As cells perform their functions, they produce CO2, which then enters the bloodstream.

3. **Accumulation of Carbon Dioxide:**
- When CO2 accumulates in the blood, it leads to an increase in its partial pressure. This is known as hypercapnia. The body continuously monitors the levels of CO2 in the blood.

4. **Stimulation of the Respiratory Center:**
- The respiratory center, located in the brain (specifically in the medulla oblongata and pons), detects the rising levels of CO2. The accumulation of CO2 irritates the respiratory center, triggering impulses that stimulate the urge to inhale.

5. **Response to Increased CO2 Levels:**
- As CO2 levels rise, the body sends signals to initiate breathing. This ensures that oxygen is taken in and CO2 is expelled, maintaining homeostasis in the body.

6. **Conclusion:**
- Therefore, the urge to inhale in humans results from the increased partial pressure of carbon dioxide in the blood, which is a direct response to its accumulation due to metabolic processes.

**Final Answer:**
The urge to inhale in humans results from the increased partial pressure of carbon dioxide.

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