The velocity of blood
For the rate of blood flow is the total accumulated value of the cross section of the blood vessel.
The smaller total cross-section, the greater the velocity of the fluid. Conversely, the greater the total cross-section, the slower the flow of fluid. From this it follows that the amount of fluid flowing through any cross-section, is constant.
The amount of lumens of capillaries in the 600-800 times the lumen of the aorta. The cross sectional area of the aorta adult 8 cm2, so it is the bottleneck of the circulatory system – is the aorta. Resistance to large and medium arteries small. It rises sharply in the small arteries – arterioles. Arteriole lumen of the arterial lumen much smaller, but the total arteriolar lumen ten times higher than the total clearance of arteries and arterioles of the total inner surface greatly exceeds the inner surface of arteries, which considerably increases the resistance.
Greatly increases resistance in the capillaries (external friction). Especially great friction where the diameter of the lumen of the capillary have red blood cells that barely pushed through it. The number of capillaries of the systemic circulation – 2 billion. As the merger capillary venules and veins in the total clearance is reduced; lumen of the vena cava only 1.2-1.8 times the lumen of the aorta.
The linear velocity of the blood depends on the difference in blood pressure in initial and final part of the large or small circulation and the lumen of the total blood vessels. The greater total clearance, the speed is lower, and vice versa.
At the local expansion of blood vessels in any organ and blood pressure generally unchanged velocity of the blood through the body increases.
The highest rate of moving blood in the aorta. During systole, it is 500-600 mm / s, and during diastole – 150-200 mm / s. The arteries speed is 150-200 mm / s. In arterioles it drops abruptly to 5 mm / s in the capillaries is reduced to 0.5 mm / s. The average speed of the veins increases to 60-140 mm / s, and in the hollow veins – 200 mm / sec. Slow blood flow in the capillaries is very important for the exchange of substances and gases between the blood and tissues through the capillary walls.
The smallest time required for the blood has passed through the circulation, of a person with 21-22. In humans, while the circulation of the blood decreases during digestion and muscular work. When digestion increased blood flow through the organs of the abdominal cavity, and during muscular work – through the muscles.
Number of systolic in the continuation of one of the circuit in different animals is approximately the same.
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