Week 24-38: Saccular Phase

• Occurs at about the 36th week of the gestational age.
• Surfactant production begins in the lungs.
• Surfactant is a soapy substance that helps keep the lung tissue from sticking to itself and prevents tearing during exhalation or lung compression.
• Air sacs begin to fill
  

In the diagram, the capillaries multiply around the acini. They push close to the surface and form a common basal membrane with that of the epithelium.

http://www.embryology.ch/anglais/rrespiratory/phasen05.html ttp://www.livestrong.com/article/163935-fetal-lung-development-stages/