AP BIOLOGY

Detailed explanation-1: -Blood first enters the heart’s right atrium. A muscle contraction forces the blood through the tricuspid valve into the right ventricle.

Detailed explanation-2: -Your heart chambers are four hollow spaces within your heart. Your upper chambers are called your right atrium and left atrium. Your lower chambers are called your right ventricle and left ventricle. Your chambers work together to manage your heartbeat.

Detailed explanation-3: -The right atrium is the first chamber of the heart that the blood comes into contact with as it returns from the systemic circulation, and from the blood supply to the heart.

Detailed explanation-4: -atrium, in vertebrates and the higher invertebrates, heart chamber that receives blood into the heart and drives it into a ventricle, or chamber, for pumping blood away from the heart. Fishes have one atrium; amphibians, reptiles, birds, and mammals, two. In humans the atria are the two upper chambers of the heart.