Blood Viscosity Vessel Length and Vessel Radius Affect Resistance

To understand the importance of smooth muscle in the control of SVR, we will consider the role of each factor expressed in Poiseuille's law (see Chapter 12):

Viscosity increases with hematocrit, especially when the hematocrit is above the normal range of 38 to 54% (Fig. 15.9). An increase in viscosity raises vascular resistance and, thereby, limits flow. Because oxygen delivery depends on blood flow as well as blood oxygen content, a limited flow can negate the increase in oxygen content resulting from the increased number of red blood cells. In individuals with polycythemia (an increased number of red blood cells), less oxygen may actually be delivered to tissues because of increased viscosity,- this occurs despite the enhanced oxygen-carrying capacity provided by the extra red blood cells. A normal hematocrit reflects a good balance between sufficient red blood cells for oxygen transport and the viscosity caused by red blood cells.

Circulation Pulse

Capillaries

^jpBHHPlI^ Pressures in different vessels of the sys-mtmmU^mmJ temic circulation. Pulse pressure is greatest in the aorta and large arteries. The greatest drop in pressure occurs in the arterioles.

Capillaries

^jpBHHPlI^ Pressures in different vessels of the sys-mtmmU^mmJ temic circulation. Pulse pressure is greatest in the aorta and large arteries. The greatest drop in pressure occurs in the arterioles.

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Responses

  • bisrat
    Is vessel length important to resistance of blood flow?
    8 years ago
  • janne
    How is vessel resistance and viscosity related?
    8 years ago
  • lukas
    How is the flow of blood resistance affected by length?
    8 years ago
  • Jasmine
    What is the function of blood viscosity, vessel lenght and vessel radius?
    8 years ago
  • katrin
    Is vessel length an important source of resistance to blood flow?
    7 years ago
  • mary watson
    How is resistance related to blood vessel radius?
    7 years ago
  • tom
    Is resistance to blood flow affected by polycythemia?
    7 years ago
  • rita
    How does vessel radius affect viscosity?
    8 months ago

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