Q. Which is the first (human) heart chamber into which blood enters? Where does the blood go after passing that chamber? What is the name of the valve that separates the compartments? Why is that valve necessary?

The tricuspid valve is necessary to prevent returning of blood to the right atrium during systole contraction of ventricles, the valve that separates the right ventricle from the right atrium is the tricuspid valve a valvular system made of three leaflets, the venous blood that comes from the tissues arrives in the right atrium of the heart and from the right atrium the blood goes to the right ventricle.