Ventilation and lungs

Plueral Membranes

Plueral membranes are two, thin, moist membranes that separate the inside of the thorax from the lungs.

They make up a continunous envelope around the lungs, forming an airtight seal.

Between the two membranes is a space called pleural captivity, filled with a thin layer of liquid called plueral fluid. 

This acts as a lubrication, so that the surfaces of the lungs don't stick to the inside of the chest wall when we breath.

Breathing in

Intercostal muscles contract

Ribs move up and out

Diaphram contracts and moves down

Volume of the thorax increases

Pressure of the thorax decreases

Air rushes in along its pressure gradient

Breathing Out

Intercostal muscles relax

Ribs moven down and in

Diaphram relaxes and moves up

Volume of the thorax decreases 

Pressure of the thorax increases

Air rushes out along its pressure gradient

Elastic tissue in the lungs recoils

Smoking

Smoking affects lungs. For the lungs to be able to exchange gas properly, the air passages need to be clear, the alveoli free from dirt and bacteria, and they must have as big a surface area as possible in contact with the blood. The airways are kept clear by the action of mucus and cilia. Smoking destroys cilia so the mucus isn't swept away from the lungs, but clogs the air passages. This is made worse by the smoke irratating the lining of the airways, stimulating the cells to secrete more mucus. Irritation of the bronchial tree along with infections from bacteria in the mucus can cause bronchitis, which blocks normal air flow.

Smoking Diseases

Emphysema is a lung disease that kills around 20,000 people in Britain every year. Smoke damages the walls of the alveoli, which break down and fuse together, forming enlarged irregular air spaces. This greatly reduces the surface area for gas exchange which becomes very inefficant, and so the blood carries less oxygen. 

Lung cancer is caused mainly by smoking-cigarette smoke contains a strongly addictive drug, nicotine, as well as 17 chemicals which cause cancer, which contain tar. Cancer happens when cells start to divide uncontrollably, forming a tumor which causes the cancer to spread to other tissues.