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. When the right ventricle contracts, blood is forced through the pulmonary semilunar valve into the pulmonary artery. Then it travels to the lungs.

Detailed explanation-2: -Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium. As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.

Detailed explanation-3: -The period of time that begins with contraction of the atria and ends with ventricular relaxation is known as the cardiac cycle. The period of contraction that the heart undergoes while it pumps blood into circulation is called systole.

Detailed explanation-4: -During ventricular contraction, the atria relax (atrial diastole) and receive venous return from both the body and the lungs. Then, in ventricular diastole, the lower chambers relax, allowing initial passive filling of the thick-walled ventricles and emptying of the atria.

Detailed explanation-5: -The impulse spreads through the walls of the right and left atria, causing them to contract, forcing blood into the ventricles. The impulse then reaches the atrioventricular (AV) node, which acts as an electrical bridge for impulses to travel from the atria to the ventricles.