During the contraction of heart, what prevents backflow of blood?

Which one of the following is the mechanism of action of oral contraceptive pills?

Pulse is felt due to the rhythmic contraction and relaxation of the

In the human body, blood flows through a process of double circulation. Which one of the following statements is true in this regard ?

Which one of the following radio elements is used to measure the speed of the blood flow in the human body?

Which part of nephron of the human kidney is responsible for filtration of blood for excretion?