Blood circulation in a double circulatory system is divided into the pulmonary circuit and the systemic circuit (Starr, 126). The pulmonary circuit creates a link between the heart and the lungs. It is through the pulmonary circuit that blood absorbs oxygen and carbon dioxide diffuses from blood in the lungs (Starr, 126). The pulmonary circuit is composed of the right atrium, the atrioventricular valve, the right ventricle, the semilunar valve, the pulmonary artery, the lungs, the pulmonary vein, and the left atrium. The pulmonary vein carries blood highly concentrated in oxygen and lowly concentrated in carbon dioxide from the alveoli to the heart (Starr, 126). The blood flow in the pulmonary circuit starts with deoxygenated blood getting in to the right atrium of the heart via the vena cava. Blood in the vena cava is then drained to the right ventricle via the atrioventricular valve. The atrioventricular valve is located between the ventricle and the atrium. When the right ventricle is filled with blood, the ventricle muscles contract closing the atrioventricular valve. This prevents blood from flowing back into the atrium (Starr, 126). During the contraction of the right ventricle, blood in the right ventricle is pushed to the pulmonary artery via the semilunar valve (Starr, 126). The semilunar valve stops blood flowing backwards from the pulmonary artery to the right ventricle (Starr, 126). The pulmonary artery then carries blood into the lungs. From the lungs, blood is transported to the heart via the pulmonary vein (Starr, 126). This cycle ends with blood being drained into the left atrium.
Chronic pulmonary heart disease is a disease that causes the right ventricle to enlarge (Starr, 134). The disease can take place in two phases: a short time phase or built up over a long period. The chronic type of this disease, which builds up over a period, is caused by cigarette smoking (Starr, 134). The disease is initiated with inability of the lungs to supply enough oxygen to the blood. This disease results due to the lack of enough oxygen in the body forcing the heart to pump the blood faster in order to supply the body with enough oxygen. This results in an enlarged right ventricle. A person suffering from this disease has breathing problems, irregular heartbeat, pain in the chest, discolored fingertips, and swollen feet. Prolonged exposure to this disease causes the right ventricle of the heart to fail hence resulting in a heart failure (Starr, 135).
Arteries are large blood vessels that are hose-like. The walls of the arteries are masculine and thick. Arteries are elastic to allow the blood to flow through it during systole and diastole without difficulties (Starr, 130). Arteries lack valves because they carry blood at high pressure. Arteries transport blood away from the heart. All arteries accept pulmonary arteries carry oxygenated blood that is low in carbon dioxide concentrations. Blood pressure is increased in the arteries through vasoconstriction, where the walls contract to reduce the internal diameter of the blood artery (Starr, 130). The reverse of this process is called vasodilation, this lowers the blood pressure.
Arterioles are small and narrow branches of the arteries (Starr, 130). They have thinner walls compared to the arteries. Arterioles are less masculine than arteries. They are found in between the arteries and the capillaries. They are therefore wider than the capillaries but narrower compared to arteries. The narrow lumen of the arterioles causes blood to flow through the arterioles with a higher pressure compared to the arteries. The blood pressure is controlled by vasodilation and vasoconstriction processes (Starr, 130). The pressure in the arterioles is lowered through vasodilation. Vasoconstriction increases blood pressure in the arterioles.