Final answer:
The atria are the thinner chambers of the heart, often referred to as the receiving chambers, responsible for pumping blood into the ventricles.
Step-by-step explanation:
The thinner chambers of the heart, which are sometimes called the receiving chambers, are known as the atria. The atria serve as the upper or receiving chambers of the heart and are responsible for pumping blood into the lower chambers, the ventricles.
The right atrium receives blood from the upper and lower body, while the left atrium receives blood from the lungs.