Morphofunctional classification of blood vessels

Role of the heart and cushioning vessels

The heart functions as the main pump of the vascular system, performing rhythmic ejection of blood into the aorta.

Cushioning vessels include the aorta, as well as large and medium elastic-type arteries. Due to the high distensibility (elasticity) of their walls, they smooth out pressure pulsations. Their main task is to transform intermittent cardiac output into a continuous and uniform blood flow. This mechanism is often called the "windkessel effect" («compression chamber» effect).

Resistance vessels ("main taps")

Resistance vessels include pre-capillary pathways — small arteries and arterioles. Their walls contain many smooth muscle fibers.

• They possess pronounced myogenic basal tone and account for the bulk of vascular resistance.
• It is in the arterioles that the greatest pressure drop in the vascular bed occurs (more significant than in capillaries due to the greater length of the arterioles).
• The tone of these vessels is regulated by the sympathetic nervous system and biologically active substances (metabolites, hormones).

I.M. Sechenov aptly called arterioles the "main taps" of the circulatory system, as they control tissue blood supply.

A special role is played by pre-capillary sphincters — small smooth-muscle structures that determine how many capillaries will function (be perfused) at any given moment. Their tone depends primarily on local metabolites (most commonly vasodilators). By contracting, the sphincter closes the lumen and limits blood inflow into the capillary network.

Exchange and shunt pathways

Exchange vessels are capillaries. This is where transcapillary exchange of gases and nutrients between blood and surrounding tissues takes place. The main mechanisms of this exchange are filtration, diffusion, and osmosis.

Shunt vessels (arteriovenous anastomoses) perform a direct bypass function. They allow arterial blood to flow directly into the venous bed, bypassing the capillary network.

Capacitance vessels and blood return

Capacitance vessels are represented by the venous bed. Their role in creating resistance to blood flow is minimal. However, they are able to change their capacity by altering the shape and diameter of their lumen. Even a slight change in the lumen of veins leads to a significant redistribution of blood volume in the body.

Return vessels (small, medium, and large veins) are responsible for delivering blood back to the heart. They can accommodate up to 20% of all circulating blood. Venous hemodynamics is determined by blood volume, central venous pressure (CVP), and the magnitude of venous return. In the venae cavae, pressure is minimal and can reach negative values (from -3 to -5 mm Hg). These factors ultimately determine the volume of subsequent cardiac output.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of basal myogenic tone of arterioles.
• Sympathetic and humoral regulation of vascular tone.
• Processes of filtration, diffusion, and osmosis in capillaries.
• Influence of central venous pressure on cardiac output.

Other topics in "Vascular Bed Hemodynamics"

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