expression, noun
blood circulation
Literal physiological sense; often used in set phrases like 血の巡りが良い/悪い.
運動すると血の巡りが良くなる。
Exercise improves blood circulation.
expression, noun
quickness of mind; apprehension
Figurative extension from blood circulation; almost always used in the negative phrase 血の巡りが悪い to mean slow-witted or dense.
See also: 血の巡りが悪い
He's slow on the uptake and doesn't get jokes.
More technical term for blood circulation; 血の巡り is a colloquial phrase.
Refers to mental quickness; 血の巡りが悪い is a more colorful, somewhat old-fashioned way to say someone is slow-witted.
Compound of 血 (blood) + の (possessive particle) + 巡り (circulation, going around). The figurative sense derives from the idea that poor blood flow to the head causes slow thinking.