1. What are the main functions of the lung?

• Oxygenation

• Ventilation: elimination of carbon dioxide

• Acid-base balance: forms the respiratory component to acid-base homeostasis

• Endocrine: production of angiotensin converting enzyme

2. Broadly speaking, which parts of the brain are responsible for controlling the rate and depth of ventilation?

• The brainstem: pons and medulla involved mainly. These give ventilation its automacity and rhythmical nature

• Cerebral cortex: this gives some voluntary control

3. Which parts of the brainstem have been identified as being particularly important? Outline the role that each plays in control.

Note that these areas of the brainstem have collectively been termed the respiratory centre. They consist of:

• Medullary respiratory centre: found in the reticular formation. Composed of a dorsal group (involved in inspiration) and a ventral group (involved in expiration). The expiratory area in the ventral group is not normally active during quiet respiration, since expiration is predominantly a passive process

• Apneustic area: located in the pons. This area is thought to prolong the inspiratory phase of the respiratory cycle

• Pneumotaxic area: also located in the pons. This inhibits the activity of the inspiratory area of the medulla. It may be involved in ‘fine tuning’ of respiratory rate, depth and rhythm

4. Which physiologic variables form the basis for control of ventilation? Place them in order of importance.

• PaCO2: the most important regulatory factor

• PaO2

• pH of the blood and CSF: has some influence above and beyond the PaCO2

5. How are changes in these parameters detected?