Gas Exchange in mammals

Question 1

What is the order of the active process?

Answer 1

1) External intercostal muscles contract, moving ribcage up & out, internal intercostal relax
2) Diaphragm muscle contracts, causing diaphragm to flatten.
3) Volume of thorax increases
4) Pressure inside thorax decreases below atmospheric pressure, air enters lungs along pressure gradient

Question 2

What is the gas exchange system in mammals?

Answer 2

• The trachea which is supported by incomplete rings of cartilage and divides into two bronchi that divide into bronchioles
• The alveoli at the ends of the bronchioles which provide a large surface area where gaseous exchange occurs.

Question 3

How are the alveolus adapted?

Answer 3

-Shape and large number produce a large SA
-Fluid lining the alveolus allows gases to dissolve and diffuse across
-2 cell layers: flattened epithelial cells & endothelial cells
-Extensive network of blood capillaries, large SA
for absorbing O2 and releasing CO2.

Question 4

How does oxygen diffuse out off the alveolar space?

Answer 4

• Dissolves into the fluid lining of the epithelium of the alveolus
• O2 diffuses across the 2 layers
• O2 combines with haemoglobin, forming oxyhaemoglobin, transported away from lungs
• CO2 diffuses from the blood in the opposite direction into the alveolar space
• Blood flow ensure that deO2 blood continually reaches the alveoli and that O2 blood is removed, maintaining a high diffusion gradient.
• Ventilation mechanism continuously replenishes air

Question 5

How does Ventilation occur in mammals?

Answer 5

• Air is passed over the respiratory surface, ensuring a high gradient.
• Brain sends nerve impulses to stimulate muscles involved in inspiration
• External and Intercostal muscles act antagonistically

Question 6

What is the sequence of the passive process? (Expiration)

Answer 6

1) External intercostal relax and the ribcage moves down and in. Intercostal muscles contract
2) Diaphragm muscle relaxes and returns to dome shape.
3) Volume of thorax decreases
4) Pressure inside thorax increases above atmospheric pressure, air is forced out of lungs
5) Elastic recoil of lung tissue helps to force air out of the lungs during expiration

Question 7

What is the equation for pulmonary ventilation?

Answer 7

Total volume of air moved into the lungs in 1 min
Pulmonary Ventilation = Tidal Volume x Ventilation
(dm^3min^-1) (dm^3) (min^-1)