Extrinsic Regulation of Blood Flow

The term extrinsic regulation refers to control by the autonomic nervous system and endocrine system. Angiotensin II, for example, directly stimulates vascular smooth muscle to produce generalized vasoconstriction. Antidiuretic hormone (ADH) also has a vasoconstrictor effect at high concentrations; this is why it is also called vasopressin. This vasopressor effect of ADH is not believed to be significant under physiological conditions in humans.

Regulation by Sympathetic Nerves

Stimulation of the sympathoadrenal system produces an increase in the cardiac output (as previously discussed) and an increase in total peripheral resistance. The latter effect is due to alpha-adrenergic stimulation (chapter 9; see fig. 9.10) of vascular smooth muscle by norepinephrine and, to a lesser degree, by epinephrine. This produces vasoconstriction of the arterioles in the viscera and skin.

Even when a person is calm, the sympathoadrenal system is active to a certain degree and helps set the "tone" of vascular smooth muscles. In this case, adrenergic sympathetic fibers (those that release norepinephrine) activate alpha-adrenergic receptors to cause a basal level of vasoconstriction throughout the

Cardiac Output, Blood Flow, and Blood Pressure 421

Cardiac Output, Blood Flow, and Blood Pressure 421

Renal Circulation

■ Figure 14.16 A diagram of the systemic and pulmonary circulations. Notice that with few exceptions (such as blood flow in the renal circulation) the flow of arterial blood is in parallel rather than in series (arterial blood does not usually flow from one organ to another).

body. During the fight-or-flight reaction, an increase in the activity of adrenergic fibers produces vasoconstriction in the digestive tract, kidneys, and skin.

Arterioles in skeletal muscles receive cholinergic sympathetic fibers, which release acetylcholine as a neurotransmitter. During the fight-or-flight reaction, the activity of these choliner-gic fibers increases. This causes vasodilation. Vasodilation in skeletal muscles is also produced by epinephrine secreted by the adrenal medulla, which stimulates beta-adrenergic receptors. During the fight-or-flight reaction, therefore, blood flow is decreased to the viscera and skin because of the alpha-adrenergic effects of vasoconstriction in these organs, whereas blood flow to the skeletal muscles is increased. This diversion of blood flow to the skeletal muscles during emergency conditions may give these muscles an "extra edge" in responding to the emergency. Once exercise begins, however, the blood flow to skeletal muscles increases far more due to other mechanisms (described shortly under Intrinsic Regulation of Blood Flow).

Parasympathetic Control of Blood Flow

Parasympathetic endings in arterioles are always cholinergic and always promote vasodilation. Parasympathetic innervation of blood vessels, however, is limited to the digestive tract, external genitalia, and salivary glands. Because of this limited distribu tion, the parasympathetic system is less important than the sympathetic system in the control of total peripheral resistance.

The extrinsic control of blood flow is summarized in table 14.4.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

Get My Free Ebook


Responses

  • Daniel
    What is "extrinsic regulation"?
    8 years ago
  • eric
    What is extrinsic regulation controlled by in humans?
    7 years ago
  • dino boni
    Is flight or fight intrinsic or extrensic?
    7 years ago
  • mustafa
    Is vasoconstriction extrinsic or intrinsic?
    6 years ago
  • Veijo
    How is fight or flight related to vasodilation?
    6 years ago
  • clorinda
    What organs are extrinsic regulations for blood flow?
    5 years ago
  • brancaleone
    What is intrinsic and extrinsic control of arterioles?
    5 years ago
  • Robel Negassi
    Does extrinsic control of blood cause vasoconstiction?
    4 years ago
  • Yasmin Fleming
    Is blood pressure extrinsic?
    4 years ago
  • Arvid
    Why have extrinsic control of blood vessels?
    3 years ago
  • nile
    What is intrinsic control of renal blood flow?
    3 years ago
  • MEHRET NASIH
    How is blood flow regulated in the body?
    3 years ago
  • andreas
    What are the extrinsic control in the medulla?
    3 years ago
  • mari
    Is increased blood flow to skeletal muscles during exercise intrinsic or extrinsic?
    3 years ago
  • alisha
    Is exerciding intrinsic or extrinsic regulation?
    2 years ago
  • stanislao
    What is the intrinsic mechanism of blood pressure regulated by kidney?
    2 years ago
  • cora
    Is thermoregulatoin intrinsic or extrinsic control?
    2 years ago
  • andrea
    What is the difference between intrinsic and extrinsic control of blood pressure?
    2 years ago
  • cillian
    Which of the following is not directly associated with extrinsic regulation of blood flow?
    2 years ago
  • MEAZA
    What are regulators that control blood flow pdf?
    1 year ago
  • teodros mehari
    Are execises intrinsic or extrinstic regulation?
    10 months ago
  • kia
    What are two extrinsic factors that increase cardiac output?
    10 months ago
  • donte
    Is the shivering response of skeletal muscle intrinsic or extrinsic?
    9 months ago
  • huriyyah
    What is the main purpose of extrinsic control of blood flowa.?
    9 months ago
  • DIAMANDA
    Does exercise cause extrinsic regulation?
    8 months ago
  • kathrin
    Is extrinsic regulation involved during exercise?
    8 months ago
  • kenzie
    What are some intrinsic and extrinsic regulators of blood flow?
    7 months ago
  • wilda
    What intrinsic and extrinsic controls that determine blood flow?
    6 months ago
  • Janet Rivera
    Is an exersise considered an extrinsic regualtion?
    6 months ago
  • maddison
    What is intrinsic and extrinsic control of the cardia cycle?
    5 months ago
  • semhar abaalom
    Which of the following is an example of extrinsic control of heart activity?
    5 months ago
  • longo
    What is the effect of extrinsic stimulation on the heart?
    3 months ago
  • linda
    What is the intrinsic and extrinsic control of the urinary?
    3 months ago
  • viviana
    Which organs is blood diverted to in emergency?
    3 months ago

Post a comment