Alveoli: Anatomy, Function and Diseases

They are tiny 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 asleep or awake, conscious or unconscious.

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

Now, there are specific 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, it 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 us 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 a tube known as the trachea.

The bronchial tree: When we go to the lungs, the trachea branches into two main sections, each 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 resembling an upside-down tree, 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 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 – 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, a singular name for the alveoli. Several alveoli may come from a conduit, forming a small solid tree. These groups of alveoli resemble clusters of grapes, which are all united.

In the alveoli, one of the most important transfers of our entire body occurs. The respiratory system directly interacts 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. However, 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 diseases 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 daily 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 bronchi tubes, which in turn branch out to become smaller tubes through the lungs progressively. 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 are 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 of blowing air is its hallmark.

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

Cystic fibrosis: A genetic condition that causes insufficient clearance of bronchial mucus. The 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 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 lung’s small blood vessels to the air sacs and the surrounding area. One form is caused by heart failure and back pressure in the lungs’ blood vessels; in another form, the direct lesion to the lung causes fluid leakage.

Lung cancer has many forms and can develop anywhere in the lungs. This is often in the central part of the lung, in or near the air sacs. The type, location, and spread of lung cancer determine 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).