Alveoli are tiny, balloon-shaped air sacs in your lungs. The function of the alveoli is to move oxygen and carbon dioxide (CO2) molecules into and out of your bloodstream. Alveoli are an important part of your respiratory system, which includes the parts of your body that help you breathe. This article discusses the structure and function of the alveoli. It also describes some of the medical conditions that can affect alveoli. Verywell / JR Bee Alveoli are the endpoint of the respiratory system. When you breathe, the air moves through different parts of your respiratory system as follows:
Alveoli are lined by a fluid called surfactant. This fluid maintains the shape of the air sac and helps keep it open so that oxygen and CO2 can pass. Alveoli in the lungs. Dorling Kindersley / Getty Images Your diaphragm is the muscle that controls your breathing. When you inhale, your diaphragm contracts. This creates negative pressure in your chest, causing the alveoli to expand and pull in air.
When you exhale, your diaphragm relaxes. This causes the alveoli to recoil or spring back, pushing out air. Alveoli are the smallest structures in the respiratory system. They are arranged in clusters throughout the lungs at the ends of the branches of your respiratory tree, which is the tree-like structure of passageways that brings air into the lungs. The walls of the alveoli are very thin. This lets oxygen and CO2 pass easily between the alveoli and capillaries, which are very small blood vessels. Oxygen can pass from the alveoli to the capillaries because the concentration of oxygen is lower in the capillaries than in alveoli. Similarly, CO2 moves the other way because the concentration of carbon dioxide is lower in the alveoli than in the capillaries. The alveoli are made up of two different types of cells. Each type has different functions:
Alveoli also contain immune cells called alveolar macrophages. Macrophages are like the garbage trucks of the immune system. These cells phagocytize, or eat debris. Macrophages clean up any particles that are breathed in and make it to the alveoli. They also remove dead cells and bacteria. The alveoli will only work correctly if their tissue is healthy. Certain medical conditions can negatively impact alveoli by causing inflammation, scarring, infection, and fluid (water, pus, or blood) build-up. Known as alveolar lung diseases, these include:
Alveoli function also depends on the sacs being inflated the right amount. Some conditions and injuries can cause this balance to be off by causing either overdistention or surfactant dysfunction. Overdistention is the overstretching of the alveoli. A healthy connective tissue support system usually prevents this. The use of mechanical ventilation, or a respirator that helps a patient breathe, can cause overdistention. Surfactant prevents the alveoli from collapsing between breaths. Medical conditions like respiratory distress syndrome in infants can cause surfactant dysfunction.
Certain genetic conditions can also cause this. These problems can cause alveoli to collapse, making it harder for the lungs to work.
Pneumonia is a lung infection. It can be caused by bacteria, viruses, or fungus. Pneumonia causes inflammation in the alveoli in one or both lungs. The inflamed alveoli fill with pus, which makes breathing difficult. Emphysema is a chronic, or long-term lung disease. It usually develops in people with a long history of smoking. Emphysema patients have inflammation in their lungs. This causes the destruction of alveoli. The alveoli that remain do not work as well. They lose their ability to stretch or spring back when a patient exhales. This leads to a condition called air trapping, which means air remains in the lungs even after exhaling.
Emphysema patients usually have more trouble exhaling than inhaling. The inability to expel air from the lungs leads to more stretching of the alveoli. This increases the loss of function. Tuberculosis (TB) is an infectious disease caused by bacteria. The disease causes the growth of nodules (masses) in lung tissue. TB bacteria multiply in the alveoli. The disease can cause the destruction of alveolar cells. Pulmonary alveolar proteinosis (PAP) is a rare disease. PAP causes proteins to accumulate in the alveoli. It is most often an autoimmune condition, in which the immune system attacks healthy cells. PAP usually occurs in adults aged 20 to 50. It may also occur as a congenital condition. Congenital conditions are present at birth. Bronchioloalveolar carcinoma (BAC) is a type of lung cancer. It is a subtype of lung adenocarcinoma, one of the most common types of lung cancer. BAC begins in the alveoli and is often found in one or both lungs. Acute respiratory distress syndrome (ARDS) is a life-threatening lung condition. In ARDS, fluids accumulate in the alveoli. This prevents oxygen from getting to the lungs. ARDS is common in critically ill patients. Respiratory distress syndrome (RDS) is seen in premature babies. Babies born too early do not have enough surfactant lining the alveoli. This means there is less surface area available for the exchange of oxygen and CO2. Pulmonary edema is a condition caused by excess fluid in the lungs. This fluid collects in the alveoli and can cause respiratory failure. Respiratory failure is when your blood does not get enough oxygen.
Cigarette smoke affects how the alveoli work and causes damage down to the molecular level. It disrupts your body's ability to repair itself after an infection or trauma. If exposure to smoke continues, alveolar damage continues to worsen. The alveoli are an important part of the respiratory system. They are responsible for moving oxygen into, and CO2 out of, the bloodstream. Diseases that affect the alveoli can cause serious health problems. These include chronic lung conditions like emphysema and tuberculosis. Certain cancers can also begin in the alveoli. Other diseases, like pneumonia, are short-term but still serious. Some conditions that affect the alveoli can lead to respiratory failure.
Smoking is an important risk factor for lung disease. Quitting smoking can lower your risk of developing diseases related to the alveoli. The alveoli perform one of the body's most important functions. They are the gateway through which oxygen enters the bloodstream. They are also the primary way that the waste product carbon dioxide exits the body. Diseases that damage the alveoli affect the entire body. Damaged alveoli deliver less oxygen to tissues. This is called hypoxia. Hypoxia can cause damage to every major organ. Frequently Asked Questions
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