Topic 6.4Gas Exchange

Topic 6: Human Health and Physiology

Definitions

• Breathing – inhaling and exhaling

• Ventilation – The muscle movements that bring about the movement of air into and out of the lungs.

• Gas Exchange – the exchange of oxygen (in) and carbon dioxide (out).

More on Gas exchange

• Air in lungs oxygen in blood• CO2 in blood air in lungs• Happens in alveoli• O2 water around cells• Alveoli cells capillary cell• Capillary cell erythrocyte• Erythrocyte takes O2 away to maintain

diffusion gradient

Maintaining concentration gradients

• Oxygen– Blood always moves

• Carbon dioxide– Air in lungs is always replaced

• Watch this animation.

Cellular respiration

• Cell respiration is the release of energy from large organic molecules such as glucose that happens in every cell in living organisms.

• It is a chemical reaction – not a physical action.

• Gas exchange, ventilation and respiration are all dependent on each other.

Why do we need a ventilation system?

• Remember the work on surface area to volume ratio from topic 2?

• Is bigger better for diffusion?

2.1.6 Surface area: Volume ratio

• As organisms get bigger both their volume and surface area get bigger

• However the increase is not by the same amount.

2.1.6 Surface area: Volume ratio

Each side is 1cm long

Volume =

Surface area =

Each side is 2cm long

Volume =

Surface area =

Volume x 8

Surface area x ?Surface area x 4

2.1.6 Surface area: Volume ratio

Consequences for organisms:• All organisms need to exchange substances with

surroundings by diffusion and osmosis– e.g. ??

• They can only do this through their surface – why?

• The amount of exchange needed depends on the organism’s volume– But the rate of exchange depends on what?

2.1.6 Surface area: Volume ratio

• Therefore, diffusion/osmosis decreases as the organism gets bigger.

• Trying to balance the rate of exchange and the needs of the organism becomes a deciding factor in the size of the organism.

• So the ability to meet the requirements of a cell depends on the

Surface area : Volume ratio

2.1.6 Surface area: Volume ratio

Each side is 1cm long

Volume =

Surface area =

Ratio =

Each side is 2cm long

Volume =

Surface area =

Ratio =

2.1.6 Surface area: Volume ratio

The bigger the organism, the smaller the surface area to volume ratio. So the less surface area there is (for

diffusion) for every unit of volume.

Why do we need a ventilation system?

• If oxygen can’t diffuse in through the surface of an organism then it needs to develop a different method to maintain concentration gradients for gas exchange.

• This is why we need a ventilation system.

Features of alveoli that adapt them for gas exchange

• In groups discuss what you remember from IGCSE.

• You should have come up with the following ideas:– Large surface area– Thin walls (short distance for diffusion)– Moist (so gases dissolve before diffusing)– Good blood supply (to maintain the

concentration gradient)

6.4.4 Ventilation System

• Homework:• Draw a diagram of the ventilation system

including the following parts:• trachea, lungs, bronchi, bronchioles and

alveoli.• The alveoli should be drawn as an inset at

a higher magnification.• DO NOT JUST PRINT IT OUT FROM

THE INTERNET!!! DRAW IT!!!

Ventilation

• Ventilation – The muscle movements that bring about the movement of air into and out of the lungs.

Diaphragm contracts and

gets ____________

Intercostal muscles contract.

Ribs move out and ______

Volume _____________

Pressure ____________

Air enters the lungs

Inhalation

Diaphragm _______ and

returns to its dome shape

Intercostal muscles ______.

Ribs move ___ and ______

Volume _____________

Pressure ____________

Air _____ the lungs

Exhalation

Lung volumes

• Tidal volume – the amount of air breathed in or out of the lungs. This is about 500cm3

• Inspiratory reserve volume – extra lung volume available if you breathe in as much as you can. This is about 3000cm3

• Expiratory reserve volume – extra lung volume available if you breathe in as much as you can. This is about 1100cm3

Lung volumes

• Vital capacity – this is the TV + IRV + ERV or the useable lung capacity. It is about 4500cm3

• Residual air – this is the amount of air that needs to stay in your lungs to stop them collapsing. It is about 1200cm3

Lung capacity practical

• Look at the instructions for how to use the lung volume kit.

• Try to measure your own lung volume

• Plan an investigation into a factor that could affect vital capacity. Due in next Wednesday.