Organisms Exchange Substances with their Environment: Gas Exchange - Humans (Ventilation)

Question 1

Define ventilation

Answer 1

• Breathing in and out

- Inhalation / expiration

Question 2

What structures are involved in ventilation?

Answer 2

• Intercostal muscles
• Diaphragm
• Ribcage
• Thorax

Question 3

What is the thorax?

Answer 3

• The ribs and upper backbone, and the organs found in the chest

Question 4

Describe the process of inhalation

Answer 4

• Inspiration is an active process
• External intercostal muscles contract (while internal relax), pulling the ribs up and out
• Diaphragm contracts and flattens
• Volume of the thorax increases
• Atmospheric pressure is higher than pressure in lungs, so air moves into lungs - down a pressure gradient

Question 5

Describe the process of expiration

Answer 5

• Expiration is a passive process
• External intercostal muscles relax (while internal contract), bringing the ribs down and in
• Diaphragm relaxes and domes upwards
• Volume of the thorax decreases
• Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance

Question 6

Describe forced expiration

Answer 6

• Expiration can be forced e.g when blowing out candles
• During forced expiration, external intercostal muscles relax and internal intercostal muscles contract
• This pulls ribs further down and in