Mammalian gaseous exchange system

Question 1

Exchange in the lungs

Answer 1

> gasses pass by diffusion through the thin walls of the alveoli
oxygen passes from the air in the alveoli to blood in the capillaries
CO2 passes from the blood to the air in the capillaries

Question 2

Large surface area

Answer 2

> alveoli are individually small but are numerous so have a large surface area (70m2)
lined with a thin layer of moisture which evaporates
reduces cohesive forces between water molecules which can cause alveoli to collapse

Question 3

Thin barrier

Answer 3

> alveolus wall is one cell thick
capillary wall is one cell thick
squamous flattened cells
capillaries are in close contact with alveoli
capillaries are narrow so red blood cells are squeezed against the wall

Question 4

Good blood supply

Answer 4

> blood system transports carbon dioxide from the tissues to the lungs
- ensures CO2 conc is higher in blood than in the alveoli
blood transports oxygen away from the lungs
- ensures conc of oxygen is lower in the blood than the alveoli - so O2 diffuses into the blood

Question 5

Ventilation

Answer 5

> ensures that concentrations of oxygen and carbon dioxide are maintained in the alveoli

Question 6

Inspiration (inhaling)

Answer 6

> diaphragm contracts to move down and becomes flatter
intercostal muscles contract to raise ribs
volume of chest cavity increases
pressure of chest cavity drops
air moves into lungs

Question 7

Expiration (exhaling)

Answer 7

> diaphragm relaxes and is pushed up
> intercostal muscles relax and ribs fall
> volume of chest cavity is decreased 
> pressure increases 
> air is moved out