Lung alveoli: anatomy and structure

Author: Scott A. Sheffield MS

Last update:

The alveoli of the lung are small air sacs that have extremely thin tissue walls. The alveoli have a large surface area and receive oxygen from the blood that goes through an exchange of gases, allowing carbon dioxide to be removed.

A zoom-in of the secondary lobule and alveolar duct

An alveolus with blood supply, duct and sac.
alveoli labeled respiratory bronchiole
An alveolus labeled alevolus ducts
1
2
3
  • Protruding from the thin walls of the alveolar ducts and respiratory bronchioles are many cup-shaped image descriptionalveoli, each measuring about 0.2 – 0.5 mm in diameter.

Want to master anatomy of the respiratory system? Look no further than these interactive quizzes, worksheets and labeled diagrams.

An alveolus with blood supply, duct and sac.
alveoli
1
2
  • At the distal end of an alveolar duct, the alveoli are arranged into grape-like clusters called image descriptionalveolar sac. The alveoli share a common opening to the alveolar duct.
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar Sacs
Alveolar sacs.

Lung Alveolus Structure – Lung Alveoli Anatomy

 

A magnified view of an alveolar sac

  • About 95% of the alveolar surface consists of simple squamous epithelial image descriptiontype I cells, and the remaining 5% is occupied by image descriptiontype II cells (or septal cells).
Zoom in view of a lung alveolus
Simple squamous epithelial type I cells
Simple squamous epithelial type 2 cells
1
2
3
  • These large, rounded cells are located between the type I cells and  image descriptionsecrete the pulmonary surfactant. The complex of phospholipids and proteins in the surfactant reduces surface tension inside the alveoli, which keeps the alveolar walls from sticking together as they deflate during exhalation.
  • Small openings called image descriptionalveolar pores perforate the interalveolar wall and allow air to pass between alveoli. They provide alternative routes to and from the alveoli if an obstruction occurs.
  • A network of image descriptioncapillaries and many supportive collagen and elastic fibers are found in the narrow interstitial spaces that separate the alveoli.
  • Numerous image descriptionmacrophages (or dust cells) protect the lungs from damage. click  image descriptionhere to see a histological demonstration of the alveoli

Want to learn respiratory system anatomy, fast? Look no further than these interactive quizzes, diagrams and labeling exercises.

Zoom in view of a lung alveolus
Small openings called alveolar pores perforate the interalveolar wall
A lung alveolus demonstrating the network of capillaries
A lung alveolus with a macrophage labeled
Microscope slide demonstrating the capillary, type 1 cell, type 2 cell and macrophage
1
2
3
4
5
  • Macrophages (dust cells) image descriptionmove about the air spaces and between the alveoli, where they remove (engulf) inhaled particles, foreign invaders, and other types of harmful substances.

An Overview of the Location of Alveolar Ducts and Alveolar Sacs:

image descriptionShow/image descriptionHide answers

Test Yourself on alveolar ducts and sacs with answers hidden
Test Yourself on lung alveoli - alveolar ducts and sacs with answers shown
Test yourself while observing Alveolar Ducts and Alveolar Sacs
1
2

An Overview of the Structure of a Lung Alveolus:

image descriptionShow/image descriptionHide answers

Test yourself on lung alveolus with answers shown
1
2