Large arteries and veins are continuous with the heart at its base. Each side has an atrium and ventricle and each atrium has an extension known as the auricle Atria receive blood from veins and ventricles receive blood from atria. Venous blood enters the right atrium during the atrial relaxation phase of the cardiac cycle and is then directed through the tricuspid valve to the right ventricle. After circulation through the lungs the blood enters the left atrium via the pulmonary veins. Blood Vessels Inner aspect of the pericardium is described as the outer cell layer of the heart and is known as epicardium Middle layer of heart is cardiac muscle Inner layer of heart is endocardium which is continuous with the endothelium of all blood vessels.
Blood vessels provide for a continuous route for blood leaving The heart to return to the heart.
Veins are thin-walled tubes reinforced by connective Tissue. They also contain some smooth muscle fibers Valves are present in the veins at irregular intervals that are directed towards the heart prevents backflow Blood Circulatory Systems Pulmonary Circulates blood through the lungs Pressure for this system originates in the right ventricle Capillaries for this system lie in pulmonary alveoli Systemic circulation Carries blood that has returned from the lungs. Pressure for this system orginates in the left ventricle Blood traversing this system leaves the left ventricle through the aorta and is returned to the right atrium via the venae cavae. First branches of aorta supply heart muscle through coronary arteries. Within the systemic circulation are a few portal systems.