mechanism of ventilation in mammals

Question 1

explain the process of inspiration and the changes that occur throughout the thorax

Answer 1

• external intercostal muscles contract (while internal relax), pulling the ribs up and out
• diaphragm contracts and flattens
• volume of thorax increases
• air pressure outside the lungs is therefore higher than the air pressure inside, so air moves in to rebalance

Question 2

explain the process of expiration and the changes that occur throughout the thorax

Answer 2

• external intercostal muscles relax (whilst internal contract), bringing the ribs down and in
• diaphragm relaxes and domes upwards
• volume of thorax decreases
• air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance