How many alveoli are found in each lung

Overview of Alveoli

Alveoli are small, thin-walled air sacs found in the lungs. These air sacs are highly elastic and important for gas exchange, allowing oxygen to move from the lungs into the bloodstream. There are approximately 300 million alveoli in adult human lungs – 600 million in total.

In this article, we’ll discuss the structure and function of alveoli and how they work to facilitate respiration.

Definition of Alveoli

Alveoli are microscopic air sacs found in the lungs and found in very large numbers. They are clustered together where the tiny bronchioles divide, and these sacs point inward towards the center of an organ allowing for effective and efficient autonomous respiration.

The alveoli contain capillaries that allow oxygen molecules to diffuses into the bloodstream, where they can be used to exchange gases between the lungs and other organs.

The alveoli are incredibly small, ranging from 0.2-0.5 μm in diameter, and very fragile structures consisting of just a pouch of elastic fibers known as alveolar walls. The number of alveoli within each lung varies significantly but on average carries 150 million per lung which equates to roughly 300 million total per person if both lungs are considered. They have a high surface area-to-volume ratio which allows them to quickly absorb oxygen from the surrounding air, providing rapid respiration rates throughout our body while we’re at rest or exercising.

Function of Alveoli

Alveoli are tiny air sacs found within the lungs. They play a major role in providing oxygen to the body, as well as getting rid of carbon dioxide. The human body can contain up to 300 million alveoli, along with an extensive network of capillaries.

Each alveolus is surrounded by blood capillaries, which helps facilitate gas exchange. Oxygen breathed in from outside is moved into the alveoli and then enters the surrounding capillaries where it can be dispersed throughout the body. At the same time, carbon dioxide moves out of the blood and into the surrounding alveoli where it will eventually be exhaled out of your lungs.

The function of alveolar walls is twofold: they form a physical barrier to keep foreign material out and act as an interface for gas exchange during respiration. The countless small respiratory pores on their surface also help increase surface area for efficient gas exchange while making them less susceptible to blockage or accumulation of dust or fungi particles that could lead to infection or irritation of air sacs. All this makes alveolar walls extremely important for maintaining proper breathing and efficient respiration overall.

Number of Alveoli in Each Lung

The alveoli are tiny air sacs found in the lungs, which are responsible for the exchange of oxygen and carbon dioxide. They are typically about 0.2 millimeters in diameter and make up the majority of the lungs’ surface area. Knowing the exact number of alveoli in each lung can provide helpful information for medical practitioners.

In this article, we will take a closer look at the number of alveoli found in each lung:

Average Number of Alveoli in Each Lung

The lungs contain an astronomical number of tiny, thin-walled air sacs called alveoli. These air sacs line the walls of the bronchial tubes and are responsible for exchanging oxygen and carbon dioxide between the lungs and bloodstream.

The number of alveoli in an individual lung varies from person to person, but on average, each lung contains about 300 million. During normal breathing, these millions of alveoli separate from one another during inhalation and compress together during exhalation.

Besides just being incredibly numerous, the size of these tiny structures makes them incredibly efficient at performing gas exchange – each alveolus is only about 0.2 millimeters across. Additionally, due to their delicate structure, they provide a tremendous amount of surface area for oxygen molecules to be absorbed into the bloodstream – totalling roughly 70–120 square meters!

Overall, alveoli within our lungs provide critical respiratory functions that make it possible for us to absorb life-sustaining oxygen while expelling waste carbon dioxide. Their delicate shape allows them to easily collapse when we exhale and expand when we inhale; ensuring an efficient process for gas exchange between our lungs and bloodstream each time we breathe.

Variations in Alveoli Numbers

The exact number of alveoli in lungs can vary from person to person, even in healthy individuals. Studies have found that the number of alveoli can range anywhere from 300 million to over 700 million per lung. The larger the lung size, the more alveoli it is likely to contain. While this difference may seem minute, it can have a major impact on how an individual breathes and their overall respiratory health.

The number of alveoli increases with age due to a process called “budding” where small capillaries grow out from preexisting cells making new branches with more alveolar sacs at the end. When left untreated, certain respiratory illnesses such as emphysema can cause a decrease in the amount of alveoli present in either or both lungs—increasing shortness of breath and potentially leading to other health complications.

Smoking cigarettes has been found to be one of the largest contributors to these reduced numbers due to its damaging affects on lung tissue as well as airways and its potential for obstructing air flow altogether. Other factors such as chronic bronchitis, cystic fibrosis and asthma can also extraordinarily reduce the number of available alveoli for proper respiration to take place normally.

Therefore, it is important for individuals who are at risk for any sort of respiratory illness or discomfort seek regular medical attention so that any changes in their bronchial tree (which includes alveoli) may be monitored closely.

Factors That Affect Alveoli Numbers

The total number of alveoli in each lung can vary depending on several factors. Age, gender, lifestyle, and lung health can all have an effect on the number of alveoli present. This article will discuss all the factors that have an impact on alveoli numbers and how the number of alveoli in the lungs changes over time.


Age is one of the most important factors that can have a significant impact on the number of alveoli found in each lung. Studies have shown that, during infancy and childhood, the total number of alveoli increases rapidly and reaches its peak in the beginning of adulthood. This rapid growth can be attributed to an increase in cell division, as well as improved airflow due to broader chest cavity size in children.

This peak continues until about 40-50 years old when a gradual decrease sets in due to age-related damage and destruction from environmental factors such as cigarette smoking. The number then continues to decline at an accelerated rate as we age resulting in fewer alveoli and therefore a reduction in pulmonary function capacity.


Smoking is one of the primary factors that can reduce alveoli numbers in the lungs. This is because inhaling tobacco smoke decreases lung capacity and can lead to airway irritations and bronchitis, resulting in destruction of alveoli due to lack of oxygen, directly affecting their numbers. Also, smoking may interfere with normal alveolar growth, leading to a decrease in alveolar counts.

Long-term smoking results in an increase production of mucus within the lungs by stimulating the mucus-producing cells and impairing the cilia, which further decreases lung capacity and increases destruction of small airways and alveoli.


Certain diseases and medical conditions can cause a decrease in the number of alveoli. Among these conditions are emphysema and cystic fibrosis.

  • Emphysema is a form of chronic obstructive pulmonary disease (COPD) characterized by inflammation and destruction of the alveoli. This can result in an insufficient number of alveolar sacs to exchange oxygen through the lungs.
  • Cystic fibrosis is a genetic disorder that affects many organs throughout the body, including the lungs, causing excessive mucus production which can lead to blockages or collapses of the airways and alveolar sacs.
  • Additionally, certain infections such as pneumonia can damage vast numbers of alveoli, ultimately leading to a reduced number in each lung.


Alveoli are the tiny air sacs in our lungs that allow oxygen to pass into the bloodstream. Each human lung can contain between 300 million to 600 million alveoli, which makes up the largest respiratory organ. The total surface area of a single lung is estimated to be between 70 and 140 square meters.

In this article, we will take a closer look at this specialist organ and explore the different elements that make up the alveoli.

Summary of Alveoli and Their Numbers

Alveoli are microscopic, thin-walled air sacs found in the lungs. These tiny structures are vitally important, as they allow the exchange of oxygen and carbon dioxide between the lungs and the bloodstream.

A single alveolus is a simple, cup-like sac made up of a single layer of flattened cells surrounded by numerous small capillaries. Each alveolus measures only about 0.1–0.2 millimeters in diameter yet within each lung there are roughly 300 million alveoli! This all makes for an impressive 70 square meters of alveolar surface area available for gas exchange within each lung—an area that is about half the size of a tennis court!

The walls between neighboring alveoli also help keep inhaled oxygen together as it diffuses across them into nearby capillaries and following that same pattern carbon dioxide diffuses outward from the capillaries into neighboring alveoli to be exhaled back out of your body.

Within each lung, gas exchange takes place quickly because of these specialized air sacs and their efficient way of passing oxygen from inhaled air to your blood stream. The large number, size and surface area allows maximum exposure to oxygen which all together helps keep us alive day in, day out.