Vascular Resistance to Blood Flow

The rate of blood flow to an organ is related to the resistance to flow in the small arteries and arterioles that serve the organ. Vasodilation decreases resistance and increases flow, whereas vasoconstriction increases resistance and decreases flow. Vasodilation and vasoconstriction occur in response to intrinsic and extrinsic regulatory mechanisms.

The amount of blood that the heart pumps per minute is equal to the rate of venous return, and thus is equal to the rate of blood flow through the entire circulation. The cardiac output of 5 to 6 L per minute is distributed unequally to the different organs. At rest, blood flow is about 2,500 ml/min through the liver, kidneys, and gastrointestinal tract; 1,200 ml/min through the skeletal muscles; 750 ml/min through the brain; and 250 ml/min through the coronary arteries of the heart. The balance of the cardiac output (500 to 1,100 ml/min) is distributed to the other organs (table 14.3).

Cardiac Output, Blood Flow, and Blood Pressure

Table 14.3 Estimated Distribution of the Cardiac Output at Rest

Organs Blood Flow

Table 14.3 Estimated Distribution of the Cardiac Output at Rest

Organs Blood Flow

Milliliters

Percent

per Minute

Total

Gastrointestinal tract and liver

1,400

24

Kidneys

1,100

19

Brain

750

13

Heart

250

4

Skeletal muscles

1,200

21

Skin

500

9

Other organs

600

10

Total organs

5,800

100

Source: From O.L. Wade and J.M. Bishop, Cardiac Output and Regional Blood Flow. Copyright © 1962 Blackwell Science, Ltd. Used with permission.

Source: From O.L. Wade and J.M. Bishop, Cardiac Output and Regional Blood Flow. Copyright © 1962 Blackwell Science, Ltd. Used with permission.

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Responses

  • kirstie
    Why the kidney is at 1100 ml/min at rest?
    8 years ago
  • sabina
    How can blood flow through the skin increase from 50ml to 2500 ml per minute?
    8 years ago

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