AS - Gas Exchange System

Detailed notes with highlights of key points.

HideShow resource information
Preview of AS - Gas Exchange System

First 497 words of the document:

James Alberts
Biology ­ Gas Exchange
Diffusion is required to supply oxygen to all organisms; the efficiency of diffusion is increased if there is;
1. A large surface area ­ In which exchange of molecules can take place
2. A concentration gradient ­ In which the principle of diffusion works
3. A thin surface - Easy to pass through
4. Warmer temperature ­ More energy therefore move faster
Fick's law is used to measure the rate of diffusion;
(The symbol means `proportional to')
So in ideal situations the larger the area and difference in concentration and the thinner the surface the
quicker the rate of diffusion of molecules through cell membranes, or the phosolipid layer.
In the mammals (humans) the gas exchange surface is called the alveolus
There are numerous alveoli which are basically sacs of air which are supplied by a system of tubes from the
trachea splitting into two bronchi, which mammals have two one for each lung, within these there are
numerous amounts of bronchioles which are in a general sense all connected to the outside by the mouth
and nose.
The alveoli provide a huge surface area in which gases can diffuse, along with this the thickness of the
surface they diffuse through is very thin, in fact only one cell thick between the lung lining and the blood
The blood supply flowing to the lungs is very extensive meaning that oxygen is near-less instantly carried
away and diffused into the blood.
Ventilation is the name given to the movements between the concentration gradients because air is regularly
moving between the atmosphere and lungs.
This breathing in or named as inspiration and breathing out named as expiration is controlled by nervous
impulses from the respiratory centre in the medulla of the brain, located at the centre back. From this both
the intercostals muscles which are located in between the ribs and the diaphragm receive impulses from the
respiratory centre. Stretch receptors in the lungs send impulses to the respiratory centre in the brain giving
information about the state of the lungs
The process of breathing in or as I mentioned is called inspiration, the process is shown below;
1. External intercostals muscles contract
2. Ribs move up and out
3. Thorax width increases in both measurement ways
4. Diaphragm contracts and moves down to flatten
From these stages the volume that the thorax has increased which means pressure between the pleural
surfaces decreases, air pressure in alveoli is less than atmospheric pressure, which air is then forced into the
lungs due to the lower pressure within them.
As the lungs fill with air the stretch receptors send impulses to the expiratory part of the respiration centre to
end breathing in.
The process of breathing out is called expiration, the process is shown below;

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

External intercostals muscles relax
2. Ribs move down and inwards
3. Thorax decreases in both measurement ways
4. Diaphragm relaxes and moves up
From these stages the volume of the thorax has decreased, which means pressure between the pleural
surfaces increases, air pressure is more than atmospheric pressure, which air is then forced back out of the
lungs, due to the higher pressure within them.…read more


No comments have yet been made

Similar resources:

See all resources »See all resources »