Gas Exchange in the body

Breathing in Diaphragm muscles contract and diaphragm is pulled flat. Intercostal muscles contract and rib cage is pulled up and out. Volume of the thorax increases  Pressure of the thorax decreases  Air moves from high pressure outside to a low pressure inside, down a pressure gradient Air is drawn into the lungs

Breathing out Diaphragm muscles relax and diaphragm springs back up  Intercostal muscles relax and rib cage sinks down and in  Volume of the thorax decreases Pressure in the thorax increases Air moves from high pressure inside to low pressure outside, down a pressure gradient Air is forced out of the lungs

The journey of the air to the lungs  Air enters the body through either the mouth or the nose. It is better to breath through your nose as the hairs in your nose filter the air, it is warmed because the membrane in close contact with blood vessels, and moistened by the mucus in the naval cavity From the nose the air goes to the trachea. - rings of cartilage around the trachea stop it from collapsing especially when food is swallowed. In the thorax the trachea divides into 2 main different branches - bronci These divide into broncus  which when in the lung divide into many smaller branches called bronchiole. At the of the bronchiole are tiny air sacs called alvioli This is where diffusion into the blood takes place.

Why is the rate of diffusion high in the alvioli?... high surface to volume ratio distance over which diffusion takes place is very small: walls of the alvioli are only 1 cell thick and is in contact with capillary so only 2 cells separating air and blood rich blood supply: alvioli's are surrounded by capillaries big difference in concentration of gas: ventilation in the lungs helps to maintain a steep diffusion gradient. Air conc. of O2 is always much higher in the air passages than in the capillaries because air is being replaced by breathing. 

Cilia which line the airways push mucus containing trapped dust and microbes towards the throat and mouth. Smoking destroys the cilia meaning that mucus slides downwards into the lungs. This results in a cough. Coughing inflames lining on the lungs resulting in bronchitis. 

Tar is a mixture of harmful chemicals. It is an irritant which makes coughing more likely leading to bronchitis (swelling of the bronchiles). Some chemicals in tar cause cancer this causes the linings of the bronchus and the bronchioles to divide out of control = tumour

Chemicals in cigarette smoke cause white blood cells to destroy alveoli, leading to emphysema -  a disease which results in the breaking down of walls of the alvioli reducing the surface area available for gas exchange

the lungs

the alvioli

smoking