Blood flow in capillaries Approaching the tissues, arteries branch into smaller and smaller arteries - arterioles, which pass into the capillaries (

Blood flow in veins and capillaries [Hemodynamics]

Blood flow in capillaries

Approaching the tissues, arteries branch into smaller and smaller arteries — arterioles, which pass into the capillaries (from the Latin “hair”).

Through the capillary walls carries out the essential life processes — cells and tissues supply with oxygen and nutrients and removal waste products of metabolism and carbon dioxide. Mediator of this exchange is the intercellular fluid.

Capillary walls are permeable for oxygen, carbon dioxide, various nutrients and leukocytes that are dissolved in the blood, and impervious, in normal, for erythrocytes, platelets and plasma proteins. Oxygen and carbon dioxide, nutrients and waste products of metabolism pass from the capillaries into the extracellular fluid and then into the cells and tissues or in the opposite direction as a result of diffusion and osmosis. The total area of ​​the capillaries in the human body is approximately 1500 hectares. On this surface with thickness of 7-8 mm is only 250 ml (one cup) of blood.

The capillaries were discovered 300 years ago, by Italian physiologist Marcello Malpighi. Having seen capillaries under the microscope and blood flow in them, he said: "Truly unusual and large I see with my own eyes!" Taken from

Blood flow in veins

After taking cells waste products and carbon dioxide out from the intercellular substances, capillaries, first, merge into a small (called venules), and then into a large veins. Unlike arteries, veins walls have a layer of smooth muscle light fibers and cannot actively pump blood to the heart. Therefore, it slowly at a rate of 0.05-0.1 m/s moves up the veins of the lower and upper limbs, mainly due to contractions of skeletal muscles. When these muscles relax, the valves, which are in the veins, prevent blood flow in the reverse direction. Due to the small thickness of the smooth muscle layer, and the presence of elastic fibers, the walls of veins have a feature of considerable stretching. Therefore, they can contain (deposit) a lot of blood.

The pressure formed during the contraction of the ventricles and transmitted to the arteries (residual pressure), is not enough for veins. Because of this pressure there is very low — only 2-5 mmHg. So the veins that are located near the thoracic cavity and in the neck, at the time of inhalation have a negative blood pressure (relative to atmospheric pressure).

  • Explain the mechanism of blood flow in capillaries and their involvement in metabolism.

  • Due to what the physical and chemical processes does the exchange of substances between capillaries and interstitial fluid go?

  • Describe the relationship of capillaries structure and functions.

  • What vessels are in the venous system?

  • Describe the relationship of veins structure and functions.

  • Identify the relationship of the venous system and the skeletal muscles. What does this show?

  • What prevents the opposite direction blood flow in the veins?

  • Why do vein walls stretch significantly? What biological importance it has?