Lung

From ArticleWorld

In animal vertebrates, the lung (or lungs) is the primary organ responsible for the extraction of oxygen from the air that is breathed into it and for the release into the air of carbon dioxide, one of the waste products from oxygen use in our body tissues. The lungs also cushion the heart and filter out tiny blood clots that may be formed inside the veins during the transfer of blood back to the heart and lungs.

Anatomy

In humans and mammals, the lungs come as a pair. In humans, the right lung contains 3 lobes and the left lung is made of 2 lobes. Oxygen-rich air is able to enter the lungs via the trachea, a large tube that is kept open by being surrounded by rings of cartilage. The trachea divides into the right and left main stem bronchi that further divide throughout the lungs into smaller bronchioles. The air eventually fills clusters of tiny air sacs called alveoli where the exchange of oxygen and carbon dioxide into and out of the blood takes place.

Mammalian lungs are able to push air in and out of the lungs via the act of breathing or, more specifically, the contraction and release of the muscles of the diaphragm which draw the air through the trachea and the bronchial “tree”.

Physiology

The main physiological function of the lungs is that of respiration. All higher animals rely on oxygen for the production of energy and produce carbon dioxide as a byproduct of metabolism. When oxygen-poor, carbon dioxide-rich blood enters the lungs via the pulmonary vein, the blood is sent down multiple channels into smaller and smaller blood vessels until it reaches the small capillaries that surround the surface of millions of tiny alveoli or air sacs. These alveoli have extremely thin walls that allow for hemoglobin in the blood to pick up the oxygen and for carbon dioxide to enter the alveoli in a gaseous form.

The exchange of these gases occurs during each and every breath. Depending on the animal species, the act of breathing can involve the muscles of the diaphragm and intercostal muscles (in mammals), the pharyngeal muscles (lower animals) or through the use of other muscular structures (in birds and reptiles).

Diseases

There are many lung conditions that impair respiratory function. Infections, such as pneumonia, can fill the lungs with fluid, lowering the degree of gas exchange. The lung can collapse, affecting respiration. Emphysema causes excess mucus and damages the alveoli, destroying the available space for gas exchange. Diseases like asthma can interfere with air entering and leaving the lungs. A blood clot, or “pulmonary embolus”, can prevent blood from entering the lung for proper gas exchange. Finally, the heart muscle can be weak, resulting in excess fluid build-up in the lungs.