What is the study of the circulatory system called?

Compare the statements $A$ and $B$.
$Statement A$: Blood sugar level falls rapidly after hepatectomy.
$Statement B$: The glycogen of the liver is the principle source of blood sugar.
Select the correct description:

The process of blood clot formation within the circulatory system is known as:

All of the following are vasoconstrictor agents except:

$A$: In an open circulatory system,the volume of blood is high,but blood pressure is low and irregular.
$R$: In a closed circulatory system,the volume of blood is limited,and blood pressure is high and regular.

Which organ remains functional for a few hours even after clinical death?