The lungs are the primary organs of respiration in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into thebloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systemsin different species. The lungs are located in the chest on either side of the heart in the rib cage. They are conical in shape with a narrow apex at the top and a broad base that rests on the diaphragm. They stretch from close to the backbone in the rib cage to the front of the chest The left lung shares space with the heart, with an angular notch in its anterior border called the cardiac notch. The right lung has three lobes, whilst the left lung only has two. The lobes are further divided into bronchopulmonary segments and lobules. The lungs have a unique blood supply, receiving deoxygenated blood sent from the heart for the purposes of receiving oxygen and a separate blood supply of oxygenated blood The tissue of the lungs can be affected by a number of diseases, including pneumonia and lung cancer. Chronic diseases such as chronic obstructive pulmonary disease and emphysema can be related to smoking or exposure to harmful substances. Diseases such as bronchitis can also affect the respiratory tract.