Why does your body have a hidden blood bank inside the spleen?
Sprint for a bus and an organ on your left side quietly tops up your blood for you.
The spleen holds a reserve of concentrated red blood cells. When you exercise, dive, lose blood, or hit thin mountain air, sympathetic nerves squeeze it and it dumps those cells into your bloodstream, raising oxygen-carrying capacity by a few percent.
When you run to catch a bus in the heat, your spleen contracts and releases stored red cells - a tiny built-in transfusion you never feel.
The spleen is an on-demand blood reservoir, not a useless organ - it auto-transfuses you during stress.
It explains why breath-hold divers and high-altitude climbers get a real oxygen boost, and why losing a spleen is a genuine trade-off, not a free pass.
Spleen = a sponge full of blood that gets wrung out when you push hard.
Learn the idea and practice English at the same time.