Difference Between Alveoli and Alveolar Sac (With Table)

Our body is made up of many complex things. Just like plants have a root system and shoot system, animals also have a digestive system, respiratory system, heart, lymphatic system, nervous system, bone, reproductive system, integument, etc which keeps our body moving and balanced. Our respiratory system helps us inhale and exhale. Amphibians like frogs breathe through their skin, fish breathe through their gills, similar to mammals have respiratory systems. Our respiratory system is made up of many things like the nose, mouth, pharynx, trachea, lungs, etc.

Alveoli vs Alveolar Sac

The difference between alveoli and the alveolar sac is that the alveoli are the last end of the tract of our respiratory system which is connected to the alveolar tubes while the alveolar sac is an air space in the alveolar duct. It occurs in the lungs, which open into two or more alveoli. It is surrounded by alveoli. It is lined by epithelium. 

The alveoli are the end of the respiratory tract which is in the lungs. It is attached to the alveolar ducts. It is like a thin-walled sphere where gas exchange takes place in the highest percentage. At least 700 million alveoli are present in each human lung. The surface area generated by the alveoli used for surface diffusion is about 80 m2, which is 42 times larger than the entire human surface area. 

The alveolar sac is also known as pulmonary alveolus which is a type of air sac or air space in a hollow sphere shape present in the cavity of the lungs. The main function of these air spaces is to provide space for the process of exchange of gas in the highest percentage. These gases are mainly carbon dioxide and oxygen. The pulmonary alveolus is a Latin name for the alveolar sac. 

Comparison Table Between Alveoli and Alveolar Sac

Parameters of comparisonAlveoliAlveolar Sac
DefinitionThe alveoli are the last end of the tract of our respiratory system which is connected to the alveolar tubes.The alveolar sac is also known as pulmonary alveolus which is a type of air sac or air space in a hollow sphere shape present in the cavity of the lungs.
NumberThe number of alveoli present in the lungs is approx. 700 million.The number of alveolar sacs is approx. 5-6 into which cluster of alveoli open.
FunctionThe alveoli mainly perform the function of gas exchange, where they carry carbon dioxide from the blood to the lungs and allow the oxygen present in the blood to reach the body’s cells.The main function of these air spaces is to provide space for the process of exchange of gas in the highest percentage. These gases are mainly carbon dioxide and oxygen.
Composed of The alveoli are mainly composed of epithelial layers and the extracellular matrix of capillaries.The alveolar sac is a type of space that forms the distal end of the alveolar ducts.
Biological nameThe biological name of alveoli is pulmonary alveolus. The biological name of alveolar sacs is Sacculi Alveolares.

What is Alveoli?

The alveoli are the end of the respiratory tract which is in the lungs. It is attached to the alveolar ducts. It is like a thin-walled sphere where gas exchange takes place in the highest percentage. At least 700 million alveoli are present in each human lung. The surface area generated by the alveoli used for surface diffusion is about 80 m2, which is 42 times larger than the entire human surface area. 

The space of air where two or more alveoli open is called the alveolar sac. Each alveolus is separated by a common wall called the interalveolar septum. This wall is made up of many cells and connective tissue which is a network of reticular fibers. This wall mainly provides space for gas exchange, which is a type 1 alveolar cell (simple squamous epithelium). In addition, it includes other things such as type II alveolar cells (septal cells), fibroblasts, and alveolar macrophages, etc. 

The function of fibroblasts is to produce reticular and elastic fibers. Type 2 alveolar cells secrete alveolar fluid that maintains the moisture of the respiratory surface. Macrophages block any foreign particles from entering and eliminate them there.

Alveoli are responsible for the filtration of air that we inhale. This mainly separates oxygen and carbon dioxide inside our lungs. The size of alveoli are very small but they are present in large number. 

What is Alveolar Sac?

Bronchioles are found in each lung, which is very numerous. A bronchiole divides into two or more respiratory bronchioles that divide with alveoli and each of these alveolar ducts and more alveoli are attached to them. Each alveolar duct is connected to a round of vacuoles in which alveoli, atria are already present. Each atrium is connected to 2-5 alveolar sacs attached to the periphery of the alveoli or air sac.

It is also known as Sacculi Alveolares which is a type of air sac or air space in a hollow sphere shape present in the cavity of the lungs. The main function of these air spaces is to exchange gas in the highest percentage. These gases are mainly carbon dioxide and oxygen. The Sacculi Alveolares is a biological name for the alveolar sac. 

The alveoli present in the lungs are in the form of pockets extending into the respiratory bronchioles which are present in their lumen. It is quite elongated and the alveolar tubules become increasingly alveolar with branches, which are further lined with alveoli. Two to eleven tubules are present in each bronchiole. Each duct opens into an alveolar sac which is a group of alveoli. The number of ducts is 5 to 6. 

Main Differences Between Alveoli and Alveolar Sac

  1. The alveoli are mainly composed of epithelial layers and the extracellular matrix of capillaries, while the alveolar sac is a type of space that forms the distal end of the alveolar ducts.
  2. Alveoli are mainly a cluster of collagen and elastic fibers whereas the alveolar sac is a group of alveoli where they communicate.
  3. The alveoli mainly perform the function of gas exchange, where they carry carbon dioxide from the blood to the lungs and allow the oxygen present in the blood to reach the body’s cells. Whereas the alveolar sac provides the space for this process to happen where this whole process is completed.
  4. The biological name of alveoli is pulmonary alveolus while the biological name of alveolar sacs is Sacculi Alveolares.
  5. The number of alveoli present in the lungs is approx. 700 million while the number of alveolar sacs is approx 5-6 into which cluster of alveoli open.

Conclusion

So here we conclude that both alveoli and alveolar sac are the part of the respiratory system which present inside the lungs. They are different from each other. The alveoli are the end of the respiratory tract which is in the lungs while the alveolar sac is a pouch-like structure that denotes the air space. Their function is also different. The alveoli mainly perform the function of gas exchange, where they carry carbon dioxide from the blood to the lungs and allow the oxygen present in the blood to reach the body’s cells. Whereas the alveolar sac provides the space for this process to happen where this whole process is completed. The number of alveoli is higher than the number of alveolar sacs. 

References

  1. https://www.tandfonline.com/doi/abs/10.3109/08958371003749939
  2. https://asmedigitalcollection.asme.org/biomechanical/article-abstract/143/8/081013/1106234
  3. https://journals.physiology.org/doi/pdf/10.1152/jappl.1974.37.2.249
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