Question

1) which type of vessel has a greater compliance, arteries or veins? Why?

2) how does this relate to the blood volum reservior of the body?

Answer 1

1) Veins have a much higher compliance than arteries (largely due to their thinner walls.) Veins which are abnormally compliant can be associated with edema. Pressure stockings are sometimes used to externally reduce compliance, and thus keep blood from pooling in the legs.Veins are more compliant than arteries and expand to accommodate changing volume. (Wikipedia) However, arteries have more elastic tissue and are under more pressure than veins.Take for example the aorta; it has the most layers (around 50 layers) of elastin fibers in its tunica media which makes it the most elastic blood vessel in the body. If the aorta is compressed or stretched, it will recoil back to its normal shape. Compliance of a vessel is the opposite of its elastance.Therefore, veins can accommodate a large changes in blood volume with only a small change in pressure. ... Contraction of smooth muscle in arteries reduces their compliance, thereby decreasing arterial blood volume and increasing arterial blood pressure within the arterial system.

The veins have high compliance, meaning they're high-volume, low pressure vessels, and even a small increase in pressure expands the volume a loti. The arteries, on the other hand have low compliance, and are low-volume, high pressure vessels, meaning with same amount of pressure, their volume doesn't expand as much.A resistance artery is small diameter blood vessel in the microcirculation that contributes significantly to the creation of the resistance to flow and regulation of blood flow. Resistance arteries are usually arterioles or end-points of arteries.

Vascular Compliance. The ability of a blood vessel wall to expand and contract passively with changes in pressure is an important function of large arteries and veins. ... Therefore, compliance decreases at higher pressures and volumes (i.e., vessels become "stiffer" at higher pressures and volumes).The veins have high compliance, meaning they're high-volume, low pressure vessels, and even a small increase in pressure expands the volume a loti. The arteries, on the other hand have low compliance, and are low-volume, high pressure vessels, meaning with same amount of pressure, their volume doesn't expand as much.

Veins are called the "capacitance vessels" of the body because over 50 % of the blood volume is in veins. Veins are more compliant than arteries and expand to accommodate changing volume. However, arteries have more elastic tissue and are under more pressure than veins.

2) Blood Volume reservior of the body:

Venoconstriction is considerably greater in certain regions of the body than in others.The vascular beds of the liver, lungs, and spleen are also important blood reservoirs. In the dog, the spleen is packed with red blood cells, and it can constrict to a small fraction of its normal size.

Veins as Blood Reservoirs

In addition to their primary function of returning blood to the heart, veins may be considered blood reservoirs, since systemic veins contain approximately 64 percent of the blood volume at any given time.Jugular vein. Jugular vein, any of several veins of the neck that drain blood from the brain, face, and neck, returning it to the heart via the superior vena cava. The main vessels are the external jugular vein and the interior jugular vein.

The liver represents a major blood reservoir in the body; it has a crucial role in the response to blood loss or expanded fluid volume and has a recognized role in determining the response to pressor, antihypertensive, and afterload-reducing agents.The walls of the blood vessels (arteries and veins) are more richly innervated; the free nerve endings that are sensitive to nociceptive stimuli are located in the inner layers of the blood-vessel walls. The internal organs, protected by the skin, muscles, and bones, have even fewer nerve endings than the muscles.

As shown in circulatory data, nearly 60% of the total volume of blood in the human body is present within the veins. The blood in veins is referred to as a "Reservoir" because it can be mobilized to boost cardiac output and in turn systemic arterial pressure when physiological demands require so.

After capillary beds blood is collected in venules which are tributaries of veins. These vessels provide a low pressure blood reservoir through which blood returns to the heart. ... Veins often have a dead space around them to allow for dilation, so not sheathed as arteries are, but run in loose connective tissue.

Their ability to hold this much blood is due to their high capacitance, that is, their capacity to distend (expand) readily to store a high volume of blood, even at a low pressure.

Blood ejected from the left ventricle flows into the aorta (Fig 1), which branches into arteries, arterioles, and eventually capillaries. Arteries are low resistance vessels that serve as pressure reservoirs to maintain blood flow during diastole. All arteries have muscular walls.