mechanism of ventilation in mammals

Question 1

Explain the mechanism of inspiration

Answer 1

1. The external intercostal muscles contract causing the rib cage to move up and out
2. The diaphragm muscle contracts, pulling it downwards
3. The volume of the thorax increases
4. The pressure inside the thorax decreases
5. The pressure inside the thorax is lower than the atmospheric air pressure, so air is drawn into the lungs from the trachea to equalise the pressure difference
6. This is a pressure difference

Question 2

Explain the mechanism of expiration

Answer 2

1. The external intercostal muscles relax, moving the rib cage dowards and inwards
2. The diaphragm muscle relaxes, moving upwards into its natural dome shape
3. The volume of the thorax decreases
4. The pressure inside the thorax increases
5. The pressure inside the thorax is greater than the atmospheric air pressure and so air is drawn out of the lung to equalise the pressure difference
6. This is a passive process

Question 3

Describe how a spirometer is used to measure breathing rate

Answer 3

1. A person breathes through a tube which is connected to a floating container of oxygen
2. The exhaled air passes through a drum of soda lime which absorbs the carbon dioxide in the exhaled air to maintain a normal breathing rate and to prevent harm that could be caused by increasing levels of carbon dioxide
3. As the person breathes, the floating oxygen container rises up and down
4. A pen attatched to the container draws a trace on a rotating drum of graph paper
5. The oxygen in the container gradually decreases over time.
6. Breathing rate can be measured by looking at the trace and seeing the number of breaths per minute

Question 4

Explain why a spirometer trace gradually decreases

Answer 4

As the person breathes, they release carbon dioxide which is absorbed by the soda lime, so the total volume of air in the spirometer decreases gradually over time.

Question 5

What is the equation for ventilation rate

slash oxygen uptake rate

Answer 5

tidal volume x breathing rate per minute

Question 6

What is ventilation rate?

Answer 6

The volume of air inhaled per minute

Question 7

What is breathing rate?

Answer 7

The number of breaths per minute

Question 8

What is tidal volume?

Answer 8

• The volme of air inhaled and exhaled
• in each breath
• during regular breathing

Question 9

What is inspiratory reserve volume?

Answer 9

The maximum volume of air inhaled in one breath above normal inhalation volume

Question 10

What is expiratory reserve volume?

Answer 10

The maximum volume of air exhaled in one breath above normal exhalation volume

Question 11

What is vital capacity?

Answer 11

Tidal volume + Inspiratory reserve volume + expiratory reserve volume

Question 12

What is residual capacity

Answer 12

The volume of air left in the lungs after maximum exhalation

Question 13

What is total lung capacity?

Answer 13

Vital capacity + residual volume