If the AV node delay where too long the blood would be pumped into the ventricles before it could be pumped into the blood vessels, causing too much volume of blood to concentrate in the ventricles . If the AV node delay were too short there would not be enough time for the blood to leave the ventricles before the next heart contraction.
THE blood group AB is called the universal receiver because any other blood group can be compatible with this blood group this is due to the absence of anti-bodies in this type
while blood group O is called the universal donor because it is compatible with all blood groups due to the absence of antigen (A and B)
while blood group A receives blood from itself and O and donates blood to itself and AB thesamethinggoeswithbloodgroupB
