Q.24 Internal respiration occurs in
1. nose
2. lungs
3. heart
4. tissue throughout the body
Internal respiration is the gas exchange process where oxygen diffuses from blood capillaries into body tissues, while carbon dioxide moves from tissues into blood, supporting cellular metabolism.
Correct Answer
4. tissue throughout the body
This occurs at systemic capillaries surrounding metabolically active cells everywhere in the body (e.g., muscles, organs), driven by partial pressure gradients: PO2 drops from ~100 mmHg in blood to ~40 mmHg in tissues.
Option Analysis
Nose (Option 1)
The nose handles air conditioning, filtration, and humidification during inhalation but no gas exchange with blood—it’s part of the conduction zone, not respiration proper.
Lungs (Option 2)
Lungs host external respiration (alveolar gas exchange with pulmonary capillaries), loading O2 into blood and unloading CO2—not internal respiration.
Heart (Option 3)
The heart pumps blood but doesn’t perform gas exchange; its role is circulation, not respiration (coronary capillaries supply its own tissue needs).
Tissue Throughout the Body (Option 4)
Correct: Internal respiration happens universally in tissues via diffusion across capillary walls, fueling ATP production body-wide.
| Option | Role in Respiration | Gas Exchange Site |
|---|---|---|
| Nose | Air conduction/humidification | None |
| Lungs | External respiration | Alveoli/capillaries |
| Heart | Blood circulation | None |
| Tissue Throughout | Internal respiration | Capillaries/tissues |
Clinical Relevance
Distinguishing internal (tissue-level) from external (lung-level) respiration is vital for exams like NEET, as disruptions (e.g., hypoxia, shock) impair tissue oxygenation despite normal lungs.
