What are the small sac-like structures in the lungs where oxygen moves into the bloodstream and what is this process called?

The small sac-like structures in the lungs are called alveoli. This is where the exchange of oxygen and carbon dioxide occurs with the bloodstream, a process known as gas exchange. Oxygen diffuses from the alveoli into the bloodstream, while carbon dioxide moves from the bloodstream into the alveoli to be exhaled.