The left ventricle is more muscular than the right ventricle because it must keep the blood in the aorta at high pressure. The high blood pressure in the aorta helps to continue pushing the rest of the blood in the general circulation through the body and back to the heart. The blood in the pulmonary artery is actually at lower pressure than blood in the aorta, since pulmonary capillaries would easily rupture otherwise.

Note that both ventricles pump the same volume of blood, as any blood passing through one ventricle will ultimately return to the other. Blood can be thought of as the current flow in a series circuit.

When blood returns to the heart via the superior and inferior vena cavae, it is deoxygenated. It remains this way as it passes through the right atrium, the right ventricle, and the pulmonary arteries, through which it travels to the lungs to conduct gas exchange with the alveoli. Both the right ventricle and the pulmonary artery contain deoxygenated blood.

All of the other answer choices contain at least one component that carries oxygenated blood.

The heart is composed of two circuits: the pulmonary circulation on the right side of the heart, and the systemic circulation on the left side of the heart. Keep in mind that these simplified pathways are ignoring the arterioles, capillaries, and venules that are present in each circulation.

Pulmonary circulation is ordered from the right ventricle to the pulmonary arteries, through the lungs, to the pulmonary veins, and reenters the heart in the left atrium.

Systemic circulation is ordered from the left ventricle to the aorta, through the structures of the body, to the superior or inferior vena cava, and reenters the heart in the right atrium.

The velocity of blood is inversely proportional to the size of the vessel. Although capillaries are the smallest individually, they have the largest combined cross-sectional area. Blood is slowest therefore slowest in the capillaries, which is necessary for gas and nutrient exchange to occur. Blood is fastest in the aorta, and as the vessels branch and have a larger cross sectional area the velocity deceases.

The pulmonary arteries carry deoxygenated blood from the right ventricle to the lungs for oxygenation. Arteries always carry blood away from the heart, while veins always carry blood toward the heart. The pulmonary arteries are the only arteries to carry deoxygenated blood. After traveling to the lungs, blood is returned to the left atrium via the pulmonary veins, the only veins to carry oxygenated blood.

The aorta carries blood from the left ventricle to the body for systemic circulation. The vena cavae return the blood from systemic circulation to the right atrium. The superior vena cava returns blood from the head upper extremities, while the inferior vena cava returns blood from the abdomen and lower extremities.

The systemic circulation refers to the path that carries blood from the left ventricle, through the body, back to the right atrium. In contrast, the pulmonary circuit refers to the path from the right ventricle, through the lungs, and back to the left atrium.

The femoral artery is a major systemic artery found in the leg and thigh. The hepatic portal system delivers oxygenated blood to the liver. The vasa recta refers to the capillaries surrounding the nephrons in the kidney, which help to regulate the ion gradient responsible for concentrating urine.

The pulmonary veins carry oxygenated blood from the lungs to the left atrium, and are part of the pulmonary circuit.

When an obstruction causes a restriction of flow, increased pressure will occur upstream of the blockage. In the cardiopulmonary system blood flows from the right atrium to the right ventricle, then through the pulmonary artery, lungs, and pulmonary vein, before re-entering the heart at the left atrium.

Should a blockage occur in the pulmonary artery, blood will pool behind the blockage (upstream) in the right ventricle, increasing the pressure in this chamber.

Oxygen partial pressure is likely to be highest in the lung capillaries, as this is where oxygen will be "loaded" on to hemoglobin molecules for transportation to the tissues. Since binding affinity increases with oxygen partial pressure, one would also expect red blood cells in lung capillaries to bind the strongest to oxygen, which allows hemoglobin saturation in the lungs.

Increased pulmonary resistance means that it will be more difficult to pump blood into the lungs. The right ventricle, which performs this function, will compensate by increasing in muscle mass. The left atrium will not increase in muscle mass because it receives blood from the lungs and pumps blood into the left ventricle; its muscle mass will likely be unaffected.

All of the venous blood will ultimately drain into the vena cava. From the vena cava, blood is then drained into the right atrium, the right ventricle, the pulmonary artery and finally to the lungs to exchange carbon dioxide for oxygen.