|Donating blood likely has no short-term effects on heart rate, blood pressure, or blood chemistry (assuming the donor doesn't pass out) because the human body has homeostatic mechanisms that constrict blood vessels to increase blood pressure as well as kidney functions that increase fluid retention. It takes about 8 weeks to regenerate a pint of donated blood.
Blood transfusion recipients typically get just one pint. A normal human body contains about 10-12 pints of blood. Children have about the same volume of blood as adults. Except newborn babies, who have about a cup.
Blood donor DNA is detectable in recipients, but only through specialized tests that specifically look for it. Otherwise it's in small enough quantities that it can be ignored. #science