Arteriolar Control in Specific Organs

Figure 14-41 summarizes the factors that determine arteriolar radius. The importance of local and reflex controls varies from organ to organ, and Table 14-8 lists for reference the key features of arteriolar control in specific organs.

Neural controls

Hormonal controls

Local controls

Neural controls

Hormonal controls

Local controls

Parenteral Epinephrine Mode Action

FIGURE 14-41

Major factors affecting arteriolar radius. Note that epinephrine can be a vasodilator or vasoconstrictor, depending on the tissue.

FIGURE 14-41

Major factors affecting arteriolar radius. Note that epinephrine can be a vasodilator or vasoconstrictor, depending on the tissue.

PART THREE Coordinated Body Functions

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART THREE Coordinated Body Functions

TABLE 14-8 Reference Summary of Arteriolar Control in Specific Organs

Heart

High intrinsic tone; oxygen extraction is very high at rest, and so flow must increase when oxygen consumption increases if adequate oxygen supply is to be maintained.

Controlled mainly by local metabolic factors, particularly adenosine, and flow autoregulation; direct sympathetic influences are minor and normally overridden by local factors.

Vessels are compressed during systole, and so coronary flow occurs mainly during diastole.

Skeletal Muscle

Controlled by local metabolic factors during exercise.

Sympathetic nerves cause vasoconstriction (mediated by alpha-adrenergic receptors) in reflex response to decreased arterial pressure.

Epinephrine causes vasodilation, via beta-adrenergic receptors, when present in low concentration and vasoconstriction, via alpha-adrenergic receptors, when present in high concentration.

CI Tract, Spleen, Pancreas, and Liver ("Splanchnic Organs")

Actually two capillary beds partially in series with each other; blood from the capillaries of the GI tract, spleen, and pancreas flows via the portal vein to the liver. In addition, the liver also receives a separate arterial blood supply.

Sympathetic nerves cause vasoconstriction, mediated by alpha-adrenergic receptors, in reflex response to decreased arterial pressure and during stress. In addition, venous constriction causes displacement of a large volume of blood from the liver to the veins of the thorax.

Increased blood flow occurs following ingestion of a meal and is mediated by local metabolic factors, neurons, and hormones secreted by the GI tract.

Kidneys

Flow autoregulation is a major factor.

Sympathetic nerves cause vasoconstriction, mediated by alpha-adrenergic receptors, in reflex response to decreased arterial pressure and during stress. Angiotensin II is also a major vasoconstrictor. These reflexes help conserve sodium and water.

Brain

Excellent flow autoregulation.

Distribution of blood within the brain is controlled by local metabolic factors.

Vasodilation occurs in response to increased concentration of carbon dioxide in arterial blood.

Influenced relatively little by the autonomic nervous system.

Skin

Controlled mainly by sympathetic nerves, mediated by alpha-adrenergic receptors; reflex vasoconstriction occurs in response to decreased arterial pressure and cold, whereas vasodilation occurs in response to heat.

Substances released from sweat glands and noncholinergic, nonadrenergic neurons also cause vasodilation.

Venous plexus contains large volumes of blood, which contributes to skin color.

Lungs

Very low resistance compared to systemic circulation.

Controlled mainly by gravitational forces and passive physical forces within the lung.

Constriction, mediated by local factors, occurs in response to low oxygen concentration—just opposite that which occurs in the systemic circulation.

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Responses

  • Marissa
    What organs control skin color?
    8 years ago
  • ruaraidh
    What organ controls oxygen levels?
    8 years ago
  • taija hahli
    What is the organ that controls certain body functions?
    8 years ago
  • matilda gammidge
    What organ controls vasoconstriction?
    8 years ago
  • fre-swera
    How is arteriolar radius controlled?
    8 years ago
  • dodinas
    Can arterioles vasodilate or vasoconstrict?
    7 years ago
  • lily
    How is arterial radius controlled?
    7 years ago
  • bellisima
    Which organ receives least blood supply during exercise?
    7 years ago
  • kati warelius
    Which organ receives least oxygen supply during exercise?
    7 years ago
  • fre-qalsi
    What is arteriolar reflex?
    5 years ago
  • hilda
    What controls which specific organs are perfused?
    6 months ago

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