The alveoli move oxygen and carbon dioxide (CO2) molecules into and out of your bloodstream.
This article discusses the structure and function of the alveoli.
What the Alveoli Do
Alveoli are the endpoint of the respiratory system.
Verywell / JR Bee
Yourdiaphragmis the muscle that controls your breathing.
When you breathe in, your diaphragm contracts and creates negative pressure in your chest.
When this happens, the alveoli expand and pull in air.
When you breathe out, your diaphragm relaxes.
The alveoli then recoil or spring back, pushing out air.
Structure of the Alveoli
Alveoli are the smallest structures in the respiratory system.
Cells of the Alveoli
The alveoli are made up of two different types of cells.
Each key in has different functions:
Alveoli also have immune cells in them (alveolarmacrophages).
These are like the garbage trucks of the immune system because they eat (phagocytize) debris.
What Causes Damage to the Alveoli?
The alveoli only work if the tissue is healthy.
Some conditions and injuries can cause overdistention or surfactant dysfunction, which cause the alveoli to collapse.
This makes it harder for the lungs to work.
Diseases that hurt the alveoli can affect more than just your respiratory health.
Damaged alveoli deliver less oxygen to tissues (hypoxia), which can damage every major organ.
Pneumonia
Pneumoniais a lung infection that can be brought on by bacteria, viruses, or fungi.
Pneumonia causesinflammation in the alveoliin one or both lungs.
The inflamed alveoli fill with pus, which makes it hard to breathe.
Emphysema
Emphysemais a chronic, or long-term lung disease.
It usually develops in people with a long history of smoking.
People with emphysema have inflammation in their lungs that causes the destruction of the alveoli.
The alveoli that remain do not work as well.
They lose their ability to stretch or spring back when a person exhales.
This leads to a condition called air trapping, which meansair remains in the lungs even after exhaling.
People with emphysema usually have more trouble exhaling than inhaling.
Tuberculosis
Tuberculosis(TB) is an infectious disease because of bacteria.
The disease causes thegrowth of masses (nodules) in lung tissue.
TB bacteria multiply in the alveoli, so the disease can cause the destruction of alveolar cells.
It is most often anautoimmunecondition, meaning the immune system attacks healthy cells.
PAP usually occurs in adults ages 20 to 50.
It can also be a condition that is present at birth (congenital condition).
Bronchioloalveolar Carcinoma
Bronchioloalveolar carcinoma(BAC) is atype of lung cancer.
It is a subtype oflung adenocarcinoma, one of the most common types of the disease.
BAC begins in the alveoli and is often found in one or both lungs.
Acute Respiratory Distress Syndrome
Acute respiratory distress syndrome(ARDS) is a life-threatening lung condition.
In ARDS,fluid builds up in the alveoliand prevents oxygen from getting to the lungs.
ARDS is common in critically ill patients.
Respiratory Distress Syndrome
Respiratory distress syndrome (RDS) is seen in premature babies.
Infants born too early have aninsufficient amount of surfactantlining the alveoli.
This means there is less surface area available for the exchange of oxygen and CO2.
Pulmonary Edema
Pulmonary edemais a condition that is brought on by extra fluid in the lungs.
Thefluid collects in the alveoliand can cause respiratory failure.
Respiratory failure is when your blood does not get enough oxygen.
Summary
The alveoli are an important part of your respiratory system.
They are responsible for moving oxygen into, and CO2out of, the bloodstream.
Health problems like emphysema and tuberculosis can affect how the alveoli function.
Certain cancers can also start in the alveoli.
Even short-term lung diseases like pneumonia can still be very serious.
Some conditions that affect the alveoli can even lead to respiratory failure.
Frequently Asked Questions
One cubic millimeter of lung tissue contains around 170 alveoli.
Human lungs have a surface area of roughly 70 square meters.
Pulmonary surfactant is a fluid made of phospholipids and proteins that lines the alveoli in the lungs.
It helps air sacs maintain their shape and allows oxygen and carbon dioxide to pass through.
Gas exchange occurs in the alveoli, which are tiny, balloon-shaped structures in the lungs.
It is when oxygen is absorbed into the bloodstream and carbon dioxide is released.
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