Arteries and arterioles have smooth muscle surrounding their endothelial walls that allows vasoconstrictors, such as angiotensin II or epinephrine, to increase blood pressure. Veins and venules may have limited constrictive abilities due to small amounts of smooth muscle interaction, but their effects on blood pressure are extremely small compared to those exerted by arteries and arterioles. Capillaries do not have smooth muscle, and are comprised of a singular layer of endothelial cells.

It is important to understand the relative sizes of the vessels through which blood flows. After exiting the heart from the left ventricle, the blood enters the aorta, the largest artery. The blood then flows into smaller arterioles, into capillaries, back into venules, and eventually into the vena cavae, which return the blood to the heart.

The larger veins contain the largest volume of blood because they are the most distensible, meaning they can stretch to accommodate large volume. Arteries and arterioles are hampered by the smooth muscle surrounding them. Veins contain about 64% of the circulating blood, acting as blood reservoirs. Blood is constantly pushed through the arteries and arterioles from the pumping heart, but the pulse does not have a large effect on the veins. The veins instead rely on the actions of shunts to help return slow-flowing blood to the heart. The combination of slow blood flow and vessel flexibility allow the veins to store large blood volumes.

The smooth muscle that surrounds arteries and arterioles constricts when acted upon by sympathetic nervous stimulation (alpha-adrenergic receptors) and by the tyrosine-based hormones epinephrine and norepinephrine, which are produced and secreted from the adrenal medulla.

Beta-adrenergic receptors, in contrast, promote smooth muscle relaxation.

The hydrostatic pressure becomes much lower as blood travels through capillary beds. This is because the fluid pressue lessens as fluid leaves the inside of the capillaries and is forced into the interstitial fluid. The oncotic presssure remains relatively constant, since proteins are large and do not readily move across vessel walls. As fluids exit the capillary, the concentration of proteins within the vessel increases.

The correct path of a drop of blood through the vascular system is right atrium, right ventricle, pulmonary arteries, lungs, pulmonary veins, left atrium, left ventricle, aorta, arteries, arteriorles, capillaries, venules, veins, vena cavae.

The right atrium and ventricle transfer deoxygenated blood to the lungs via the pulmonary arteries. Blood is oxygenated and returned to the left artium via the pulmonary veins. The left ventricle then pumps the oxygenated blood to the body, exiting the heart through the aorta. Systemic circulation flows through arteries, then arterioles, then capillaries where gas exchange occurs to tissues. Blood is then returned to the heart through venules and veins, which merge into the superior and inferior vena cavae and empty into the right atrium to complete the circuit.

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.