Alveoli: Anatomy, Function and Diseases

They are small sacs within our lungs that allow oxygen and carbon dioxide to move between the lungs and the bloodstream.

Purpose of the Alveoli

Our bodies perform certain functions every second of the day and night without our conscience or direct command. For example, breathing is a job our body does for us, whether we are asleep or awake, conscious or unconscious.

But what is the real purpose of breathing? You probably already know that it consists in taking oxygen from the environment and getting rid of the carbon dioxide that we produce.

Now, there are certain tiny organs that help our bodies get the oxygen we breathe and get rid of the carbon dioxide we do not need. These organs are what are called alveoli.

The Alveoli and the respiratory system

Our bodies need oxygen to live. We get our oxygen from the air we breathe.

However, for our bodies to use this oxygen, they must get from our lungs into our bloodstream. This will eventually happen through the alveoli.

To understand the alveoli, we must first examine the main parts of the respiratory system. Let’s go then.

The Alveoli in the respiratory system: Diagram of the Respiratory System

Our respiratory system includes structures involved in our breathing. When you take a breath, the air is drawn into your mouth and nose and into a tube known as the trachea.

The bronchial tree: When we go to the lungs, the trachea branches into two main sections, each one called the bronchus.

There is a right primary bronchus that goes to the right lung, and a left primary bronchus that goes to the left lung. Each of these bronchi (plural for the bronchi) branches into more bronchi.

These, in turn, branch into smaller tubes called bronchioles. All this branching finally results in a structure that really resembles an upside down tree; being the trachea the trunk, with all the branches coming from it. For that reason, it is known as the bronchial tree.

Although this branching does not continue forever, it happens approximately 25 times after the first branching of the trachea.

The last bronchioles are divided into what are called respiratory bronchioles, each of which is divided into small openings called alveolar ducts.

This is how each tube becomes smaller and smaller, since it has branched off. When we reach the alveoli, the tubes are microscopic – and there are millions of them!

The Alveoli in our anatomy

At the end of each of the many tiny branches of our bronchial tree, we find openings to microscopic sacs. Each small sac is an alveolus, singular name for the alveoli. There may be several alveoli that come from a conduit, forming a small solid tree. These groups of alveoli resemble clusters of grapes a little, which are all united.

It is in the alveoli that one of the most important transfers of our entire body takes place. This is where the respiratory system comes into direct contact with the circulatory system, or blood vessels.


We breathe oxygen so that the parts of our body can use it in many different cellular functions. But we must somehow get the oxygen from our lungs to reach our bloodstream.

Pulmonary diseases are some of the most common medical conditions in the world. Tens of millions of people suffer from some lung disease in the United States. Smoking, infections and genetics are responsible for most lung diseases.

The lungs are part of a complex apparatus, expanding and relaxing thousands of times each day to bring oxygen and expel carbon dioxide. Pulmonary diseases can result from problems in any part of this system.

Lung diseases that affect the airways

The trachea is formed in tubes called bronchi, which in turn branch out to progressively become smaller tubes through the lungs. Diseases that affect the respiratory tract include:

Asthma: The airways become inflamed persistently, and occasionally they can cause spasms, causing wheezing and shortness of breath. Allergies, infections or contamination can trigger asthma symptoms.

Chronic Obstructive Pulmonary Disease (COPD): Lung conditions defined by an inability to exhale normally, which causes difficulty in breathing.

Chronic bronchitis: A form of COPD characterized by a chronic productive cough.

Emphysema: Lung damage allows air to be trapped in the lungs in this form of COPD. The difficulty to blow air is its hallmark.

Acute bronchitis: A sudden infection of the respiratory tract, usually caused by a virus.

Cystic fibrosis: A genetic condition that causes insufficient clearance of bronchial mucus. Accumulated mucus results in repeated lung infections.

Lung Diseases Affecting Air Sacs (Alveoli)

The airways eventually branch into tiny tubes (bronchioles) that end in clusters of air sacs. These air sacs, the alveoli, make up most of the lung tissue. Other lung diseases that affect the alveoli are:

Pneumonia: An infection of the alveoli, usually by bacteria.

Tuberculosis: A slowly progressive pneumonia caused by the bacterium Mycobacterium tuberculosis.

Emphysema, which is the result of damage to the fragile connections between the alveoli. Smoking is the usual cause of emphysema. (Emphysema also limits the flow of air, also affecting the airways).

Pulmonary edema: The fluid leaves the small blood vessels of the lung to the air sacs and the surrounding area. One form is caused by heart failure and back pressure in the blood vessels of the lungs; in another form, the direct lesion to the lung causes the leakage of fluid.

Lung cancer has many forms and can develop anywhere in the lungs. Very often this is in the main part of the lung, in or near the air sacs. The type, location and spread of lung cancer determines the treatment options.

Acute Respiratory Distress Syndrome (ARDS): severe and sudden injury to the lungs caused by a serious illness. Life support with mechanical ventilation is usually necessary to survive until the lungs recover.

Pneumoconiosis: A category of conditions caused by inhaling a substance that damages the lungs. Examples include lung disease caused by inhaled black carbon dust and asbestosis (inhaled asbestos powder).