Alveoli Diagram Labeled

The end of an airway, then one alveolus opened: 14 parts to name.

Alveoli Diagram Labeled

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1 2 3 4 5 6 7 8 9 10 11 12 13 14
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Write the name of each numbered part.Answer key

  1. Terminal bronchiole
  2. Respiratory bronchiole
  3. Alveolar duct
  4. Alveolar sac
  5. Alveolus
  6. Pulmonary arteriole
  7. Pulmonary venule
  8. Pulmonary capillary network
  9. Type I alveolar cell
  10. Type II alveolar cell
  11. Alveolar macrophage
  12. Respiratory membrane
  13. Red blood cell
  14. Alveolar pore

Drawn for this site by script, 2026-09-26. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: follow the blood back to the heart

All 14 parts on the diagram

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Start here: 8 main parts 8

  1. Terminal bronchiole The tiniest bronchiole of the conducting zone. There are more than 1000 in each lung, and each one leads on to a respiratory bronchiole.
  2. Respiratory bronchiole The smallest type of bronchiole. The respiratory zone, where gas exchange happens, starts where it joins the terminal bronchiole.
  3. Alveolar duct Opens into a cluster of alveoli. A tube of smooth muscle and connective tissue.
  4. Alveolar sac A cluster of many alveoli at the end of an alveolar duct. Together they are responsible for gas exchange.
  5. Alveolus One of the small grape-like sacs, about 200 micrometers across. Its elastic walls stretch as you breathe in.
  6. Pulmonary arteriole A small branch of the pulmonary artery. It brings deoxygenated blood to the lobule; one arteriole and one venule serve each pulmonary lobule.
  7. Pulmonary venule Drains the oxygenated blood from the alveoli toward the pulmonary veins.
  8. Pulmonary capillary network Tiny vessels that follow the alveoli. They have very thin walls and no smooth muscle. Where a capillary wall meets an alveolar wall, gas is exchanged.

Blood: 4 1

  1. Red blood cell Picks up oxygen in the capillary for transport to the body's tissues. Also called an erythrocyte.

The alveolar wall: 5 5

  1. Type I alveolar cell A flat squamous cell. These cells cover up to 97 percent of the alveolar surface and let gases pass easily.
  2. Type II alveolar cell Scattered among the type I cells, it secretes surfactant. Surfactant lowers the surface tension inside the alveolus.
  3. Alveolar macrophage A cell of the immune system that roams the alveolar wall. It removes debris and germs that reach the alveoli.
  4. Respiratory membrane The alveolar and capillary walls together, about 0.5 micrometres thick. Oxygen and carbon dioxide cross it by simple diffusion.
  5. Alveolar pore An opening that joins neighboring alveoli. It helps keep air pressure equal through the lung.

How this list was compiled: Read 2026-09-26. OpenStax Anatomy and Physiology 2e, section 22.1, Organs and Structures of the Respiratory System, https://openstax.org/books/anatomy-and-physiology-2e/pages/22-1-organs-and-structures-of-the-respiratory-system : terminal bronchioles (more than 1000 in each lung); the respiratory zone beginning where a terminal bronchiole joins a respiratory bronchiole, the smallest type; the alveolar duct of smooth muscle and connective tissue opening into a cluster of alveoli; the alveolar sac; an alveolus about 200 micrometres across with elastic walls; alveolar pores keeping air pressure equal; type I alveolar cells covering up to 97 percent of the surface; type II cells secreting surfactant; the alveolar macrophage; the respiratory membrane about 0.5 micrometres thick, crossed by simple diffusion. Section 22.2, The Lungs, https://openstax.org/books/anatomy-and-physiology-2e/pages/22-2-the-lungs : the pulmonary artery carrying deoxygenated blood and branching; one arteriole and an accompanying venule for each pulmonary lobule; the pulmonary capillary network with thin walls and no smooth muscle; erythrocytes picking up oxygen; oxygenated blood leaving by the pulmonary veins. The book was used to check names and facts only; no figure was traced. Licence: own work

The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work

How it works

An alveoli diagram labeled with 14 parts in two figures: the end of an airway with the blood vessels of one pulmonary lobule, and a single alveolus opened up. Start with the 8 main parts, then the wall.

Read the full guide

From airway to air sac

Air passes a terminal bronchiole, then a respiratory bronchiole, where the respiratory zone begins, then an alveolar duct that opens into an alveolar sac. Each alveolus is about 200 micrometres across.

Where the gas crosses

Type I cells make up most of the wall. Where one meets a capillary, the two walls form the respiratory membrane, about 0.5 micrometres thick, and oxygen and carbon dioxide cross it by simple diffusion.

  • Mind the direction: the arteriole brings blood low in oxygen to the alveoli, and the venule carries it away rich in oxygen.

Questions and answers

What is the difference between an alveolus and an alveolar sac?

An alveolus is one small grape-like sac. An alveolar sac is the whole cluster of alveoli at the end of an alveolar duct.

What do type II alveolar cells do?

They secrete surfactant, a mix of phospholipids and proteins that lowers the surface tension inside the alveoli. Type I cells, which cover up to 97 percent of the surface, do the gas exchange.

What are alveolar pores?

Openings that join neighbouring alveoli. They help keep the air pressure equal throughout the alveoli and the lung.

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