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3.2 Transport in Animals - Coggle Diagram

- - - - The atria contract while the ventricles relax. This decreases the volume inside the atria which increases the pressure. This increased pressure forces the atrioventricular valves open and pushes blood into the ventricles.
    - - The ventricles contract while the atria are relaxed. This decreases the volume inside the ventricles which increases the pressure. The pressure is higher in the ventricles compared to the atria, which forces the atrioventricular valves closed and causes the semi-lunar valves to open. The closure of the AV valve is important because it prevents the back-flow of blood into the atria. Blood is forced out of the ventricles and into the arteries (the aorta and the pulmonary artery).
    - - Both the atria and ventricles are relaxed so the pressure is low in both chambers. Since the pressure is higher in the arteries than in the heart chambers, the semi-lunar valves are forced closed which prevents blood flowing backwards into the ventricles. Blood is returned to the heart and the atria fill with blood.