The lungs are like big pink sponges that are protected by the rib cage. The diaphragm is a muscle that sits underneath the ribcage, it moves up when it relaxes and down when it contracts. This movement helps to get air in and out of your lungs. The air you breath in goes through the trachea, this splits into two tubes called the bronchi (each one is a bronchus) one going into each lung. The bronchi split into smaller tubes called the bronchiholes. The bronchioles end at small air sacs in the lungs called alveoli. These are where gas exchange takes place.
Air is inhaled into the lungs. Some of the oxygen in the inhaled air passes into the bloodstream to be used in respiration. Carbon dioxide is a waste product of respiration. In the lungs it passes out of the blood and is then breathed out. The gases pass into or out of the bloodstream by diffusion, where a substance moves from where there's lots of it to where there's less of it. The lungs are well adapted for gas exchange as they: are moist, have a good blood supply and the alveoli give the lungs big inside surface area.
When you breathe in the diaphragm moves down and the ribs move up. This increases the volume of the chest cavity which decreases the pressure, air rushes in to fill the lungs. When the diaphragm moves up and relaxes the volume gets smaller and the pressure increases so the ribs move down and air rushes out. Breathing in is called inhaling and your ribs are pulled up and out by intercoastal muscles and the diaphragm moves down as it contracts making the chest volume bigger. When you breathe out it's exhaling, the intercoastal muscles relax also the diaphragm relaxes so the volume of your chest gets smaller. Lung volume is the amount of air you can breathe into your lungs in a single breath and is different for different people. Lung volume can be measured using a spirometer. Some people have a smaller lung volume because they have a disease or condition like Asthma. Asthma is when people have lungs that are too sensitive to certain things e.g pet hair, pollen etc... If an asthmatic breathes these things in the muscles around their bronchioles contract so this narrows the airways and become inflamed and fluid builds up making it hard to breathe possibly causing an asthma attack. Sufferes use an inhaler that contain drugs that open up the airways. The symptons of the condition are difficulty breathing, wheezing or tight chest.
When doing exercise your breathing rate and depth of breathing increases so you can get more oxygen to your blood, if you exercise lots and regularly the muscles used to breathe get stronger, meaning your chest cavity can open up more when you breathe so you get more air into your lungs. Also exercising can increase the number and size of the small blood vessels in your lungs and in the number of alveoli, the gas exchange therefore gets more efficient. Cigarette smoke contains four main things: carbon monoxide, nicotine, tar and particulates. Tar is very bad for you as it covers the cilia(little hairs)on the lining of the air ways meaning it can't get rid of mucus, the mucus sticks to the airways so you cough more, this can all lead to bronchitis and emphysema - both diseases make it hard to breathe also tar contains carcinogens that could cause cancer in the lungs, throat and mouth