Spleen controls the blood

The spleen produces blood and prevents it from spilling out of the vessels. The spleen is the source of blood and qì formation, and when healthy, it ensures plentiful supplies of blood, and of qì, which moves the blood and keeps it within the vessels. Thus, the spleen engenders the blood and indirectly keeps it from spilling out of the vessels. The two phrases the spleen controls blood and qì contains blood are therefore essentially synonymous. See spleen failing to control blood.

Etymology

Chin 统 tǒng, to rule, dominate, hold together.