I spent all day attending an online medical conference to keep my continuing education up-to-date. Towards the end of the day I realized that I had no picture yet and was worn down enough mentally that my photographer's eye wasn't going to be working well. So I used my pocket camera and grabbed this shot of one of the presenter's graphics.
This, for the uninitiated, is the business end of your lungs. Those things that look like bunches of grapes are called alveoli (the plural of alveolus). This is where oxygen in the air you breathe in gets into your blood stream, and where carbon dioxide gets from your blood cells to your lungs so you can exhale it. All of that exchange takes place in those little sacs.
