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 and out
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 in and out (2)
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 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.
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.