When the body temperature is too high, peripheral vasodilation can help exchange heat from the body to the environment. Warm blood from the center of the body is pumped to the extremities, which have a high surface area. The surface area is used to allow the heat from the blood to dissipate before it returns to the center of the body.

Peripheral vasoconstriction and shivering help increase the body temperature. Hyperventilation have no noticeable effect on body temperature.

Capillaries are minute blood vessels that connect the arterial and venous systems. The walls of these vessels are extremely thin, allowing easy diffusion of gases, nutrients, and waste particles between the capillary and adjacent cells. Oxygen diffuses into cells from the capillary, and carbon dioxide diffuses into the capillary from the cells.

Vasoconstriction is a function of the smooth muscle that surrounds the vasculature. In order to reroute blood, the vessel needs to have a substantial amount of smooth muscle.

Arterioles have a relatively small diameter and a relatively large amount of smooth muscle. When contracted, this smooth muscle can obstruct the arteriole and route blood away from connected capillary beds. Capillaries do not have smooth muscle linings, and cannot constrict or reroute blood on their own. Arteries have a relatively large diameter; contraction of the surrounding smooth muscle can affect blood pressure, but will rarely be capable of rerouting the blood flow.

Veins contain a series of one way valves that prevent blood from flowing backwards. This is particularly important in larger veins in the legs that are further below the heart, and must oppose gravity to get blood back to the heart. Almost all of the blood pressure produced by the heart is lost along capillaries, thus the blood pressure in the veins is almost zero. Blood is "squished up" a little at a time due to the contraction of the skeletal muscles around veins and the presence unidirectional valves.

The venae cavae are the largest veins in the body. They return deoxygenated blood to the heart. The pulmonary veins bring oxygenated blood from the lungs to the left atrium. The pulmonary arteries bring deoxygenated blood from the right ventricle to the lungs to become oxygenated. The left ventricle hold oxygen-rich blood, and pumps it to the rest of the body. The left atrium is where freshly oxygenated blood is received via the pulmonary veins.

The stable pH of blood is around 7.5 and is maintained by buffers, especially carbon dioxide/bicarbonate. Note that the blood pH is very tightly regulated and is adjusted by the respiratory and urinary systems.

The correct answer is pulmonary veins. The pulmonary veins transfer the newly oxygenated blood towards the heart. Blood in these veins is highly concentrated with oxygen unlike any of the other locations mentioned. The pulmonary arteries bring oxygen-poor blood towards the lungs to be oxygenized.

The vagus nerve is responsible for slowing down the heart rate, and is able to "override" the faster, natural pace of the sinoatrial node. When the vagus nerve is severed from the heart, the heart will pump at the pace of the SA node.

Note that innervation is not necessary for the heart to continue beating; it is self-sustaining, but can be affected by innervation from the vagus nerve.

The chordae tendinae (tendinous chords or heart strings) are physical structures located in the heart lumen that connect the muscular wall of the heart to the tricuspid and mitral valves via papillary muscles.

The other answer options are examples of cell bundles and tissues that orchestrate the electrical conduction through the heart. Signals begin at the sinoatrial node and transition to the atrioventricular node. They then pass through the atrioventricular bundle (or bundle of His) to the purkinje fibers, which coordinate simultaneous ventricular contraction.

The sinoatrial node is responsible for initiating the contraction of the heart. Depolarization of the sinoatrial node coincides with atrial contraction. The depolarization travels very quickly to the atrioventricular node during this period. The atrioventricular node delays the spread of the impulse, preventing it from triggering ventricular contraction. This time delay allows the atria to fill the ventricles with blood before the impulse causes the ventricles to contract. Without this delay, an inadequate amount of blood would be pumped from the ventricles.