Control of Breathing and Values

1. Where is the medullary respiratory centre located

In the medulla oblongata of the brainstem.

2. What are the two main neuron groups in the medullary respiratory centre

The dorsal respiratory group (DRG) and ventral respiratory group (VRG).

3. What is the main role of the dorsal respiratory group (DRG)

It generates impulses that drive normal inspiration.

4. Which muscles does the DRG activate during quiet breathing

The diaphragm through the phrenic nerve and the external intercostal muscles through intercostal nerves.

5. What is the main role of the ventral respiratory group (VRG)

It helps activate additional muscles during forceful breathing.

6. What happens during quiet, normal breathing

The DRG drives inspiration, then nerve impulses stop and the inspiratory muscles relax during expiration.

7. How long does a normal breath take in the lecture's example

Approximately five seconds.

8. How long does inspiration take in the lecture's example

Approximately two seconds.

9. How long does expiration take in the lecture's example

Approximately three seconds.

10. What happens during forceful breathing

The DRG activates the VRG to recruit additional respiratory muscles.

11. Which muscles are used during normal inspiration

The diaphragm and external intercostals.

12. What causes normal quiet expiration

Relaxation of the inspiratory muscles and elastic recoil of the lungs and thoracic wall.

13. Which additional muscles assist forceful inspiration

The scalenes and sternocleidomastoids.

14. Which muscles assist forceful expiration

The internal intercostals and abdominal muscles.

15. Why are abdominal muscles used during forceful expiration

They increase abdominal pressure and push the diaphragm upward, helping expel air.

16. Why is quiet expiration usually passive

Elastic recoil reduces lung volume without requiring active contraction of expiratory muscles.

1. What is normal tidal volume

500 mL.

2. What is inspiratory reserve volume

3,000 mL in the lecture.

3. What is expiratory reserve volume

1,000 mL in the lecture.

4. What is residual volume

1,200 mL in the lecture.

5. What is functional residual capacity

2,200 mL in the lecture.

6. What is vital capacity

4,500 mL in the lecture.

7. What is total lung capacity

5,700 mL in the lecture.

8. What is average resting respiratory frequency

12 breaths/min.

9. What is average resting minute ventilation

6 L/min.

10. What is anatomical dead space

Approximately 150 mL per breath.

11. How much fresh air reaches the alveoli with a 500 mL tidal volume

Approximately 350 mL.

12. What is atmospheric pressure at sea level

760 mmHg.

13. What is atmospheric PO₂ at sea level

Approximately 160 mmHg.

14. What is the partial pressure of water vapour in humidified respiratory air

47 mmHg.

15. What are typical alveolar partial pressures

PO₂ = 100 mmHg and PCO₂ = 40 mmHg.

16. What are typical venous blood partial pressures entering the lungs

PO₂ = 40 mmHg and PCO₂ = 46 mmHg.

17. What is the O₂ partial-pressure difference between alveoli and incoming venous blood

60 mmHg.

18. What is the CO₂ partial-pressure difference between incoming venous blood and alveoli

6 mmHg.

19. What proportion of oxygen is transported by haemoglobin

Approximately 98.5%.

20. What proportion of CO₂ is transported as bicarbonate

Approximately 80–90%.

21. What are the four major factors that promote oxygen unloading

Increased CO₂, increased H⁺, increased temperature, and increased 2,3-BPG.

22. How long does a normal breath take in the lecture's example

Five seconds: two seconds of inspiration and three seconds of expiration.