Guyton and Hall Physiology Chapter 17 - Local and Humoral Control of Tissue Blood Flow
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Questions and Answers

What percentage of cardiac output is supplied to the heart under basal conditions?

  • 4% (correct)
  • 2%
  • 14%
  • 22%

    • Which organ receives the highest percentage of cardiac output?

  • Muscle (inactive state)
  • Brain
  • Liver (correct)
  • Kidneys

    • How much blood flow, in ml/min, does the brain receive under basal conditions?

  • 200 ml/min
  • 100 ml/min
  • 1100 ml/min
  • 700 ml/min (correct)

    • What is the blood flow (ml/min/100 g of tissue) to the kidneys?

    <p>360 ml/min</p> Signup and view all the answers

    What is the overall blood flow percentage to muscles in an inactive state?

    <p>15%</p> Signup and view all the answers

    Which of the following organs receives the lowest blood flow percentage?

    <p>Bronchi</p> Signup and view all the answers

    What percentage of the cardiac output is supplied to the liver?

    <p>27%</p> Signup and view all the answers

    How does the blood flow through an isolated dog leg change with decreasing arterial oxygen saturation?

    <p>It decreases</p> Signup and view all the answers

    What is the major function of vasopressin in the body?

    <p>Enhancing water reabsorption from renal tubules</p> Signup and view all the answers

    Where is vasopressin ultimately secreted into the blood?

    <p>Posterior pituitary gland</p> Signup and view all the answers

    Which of the following substances is considered a potent vascular constrictor?

    <p>All of the above</p> Signup and view all the answers

    What role does vasopressin play during severe hemorrhage?

    <p>To markedly increase circulating blood vasopressin concentration</p> Signup and view all the answers

    What is the relationship between humoral control and vascular function?

    <p>Humoral control involves substances that can affect circulation across the body</p> Signup and view all the answers

    What effect does a high flow rate in the radial artery have on its luminal diameter?

    <p>It increases progressively.</p> Signup and view all the answers

    How does angiotensin II affect arterial pressure?

    <p>It can increase arterial pressure by 50 mm Hg or more.</p> Signup and view all the answers

    What is the primary role of angiotensin II in the body?

    <p>To regulate arterial pressure and increase total peripheral resistance.</p> Signup and view all the answers

    What happens to the vascular wall when blood flow is chronically reduced?

    <p>The thickness of the vascular wall usually decreases.</p> Signup and view all the answers

    What type of remodeling occurs in large blood vessels as a result of long-term increases in vascular wall tension?

    <p>Outward hypertrophic remodeling.</p> Signup and view all the answers

    How does increased shear stress affect the radial artery's cross-sectional area?

    <p>It increases the cross-sectional area.</p> Signup and view all the answers

    What role does vasopressin play in the body related to blood pressure?

    <p>It is involved in regulating blood volume and pressure.</p> Signup and view all the answers

    What is a characteristic effect of the sympathetic stimulation on blood flow in the radial artery?

    <p>It increases the blood flow rate significantly.</p> Signup and view all the answers

    What occurs in the venous side of the fistula in response to increased blood pressure?

    <p>The wall thickness increases.</p> Signup and view all the answers

    What is the main consequence of norepinephrine and epinephrine release into circulation?

    <p>They amplify the effects of direct nerve stimulation.</p> Signup and view all the answers

    What is the primary result of increased local metabolism in tissues that are highly active?

    <p>Dilation of local blood vessels</p> Signup and view all the answers

    How much can local muscle blood flow increase during intense exercise?

    <p>Up to 20-fold</p> Signup and view all the answers

    What happens during reactive hyperemia?

    <p>An immediate rise in blood flow after a period of blockage</p> Signup and view all the answers

    What is the effect of a rapid increase in arterial pressure on blood flow in tissues?

    <p>Blood flow increases initially and then normalizes</p> Signup and view all the answers

    What physiological process occurs to meet the metabolic needs of highly active tissues?

    <p>Active hyperemia</p> Signup and view all the answers

    What substance is released in large quantities by active tissues to facilitate increased blood flow?

    <p>Vasodilator substances</p> Signup and view all the answers

    What describes active hyperemia?

    <p>Increased blood flow relative to tissue metabolic needs</p> Signup and view all the answers

    What can a deficiency of certain vitamins lead to in highly active tissues?

    <p>Diminished contractile ability</p> Signup and view all the answers

    During which condition does blood flow through a tissue increase four to seven times normal levels?

    <p>After a brief blockage of blood supply</p> Signup and view all the answers

    What could lead to local vasodilation in specific tissues?

    <p>High oxygen demand</p> Signup and view all the answers

    What is the effect of high altitude on blood flow in the tissues?

    <p>It markedly increases blood flow through the tissues.</p> Signup and view all the answers

    How does pneumonia affect blood flow through the tissues?

    <p>It may increase blood flow to compensate for reduced oxygenation.</p> Signup and view all the answers

    What is the consequence of carbon monoxide poisoning on hemoglobin?

    <p>It impairs hemoglobin’s ability to transport oxygen.</p> Signup and view all the answers

    Which of the following conditions would likely cause an increase in blood flow to tissues?

    <p>High altitude exposure</p> Signup and view all the answers

    What occurs to blood flow as arterial oxygen saturation drops to around 25%?

    <p>Blood flow increases about threefold.</p> Signup and view all the answers

    What is cyanide poisoning primarily known to impair?

    <p>Tissues' ability to utilize oxygen</p> Signup and view all the answers

    During which condition does blood flow through the tissues often increase as a compensatory mechanism?

    <p>Carbon monoxide poisoning</p> Signup and view all the answers

    What is the main reason for increased blood flow during tissue hypoxia?

    <p>To maintain a relatively constant oxygen supply to tissues</p> Signup and view all the answers

    What physiological effect does cold weather have on skin blood flow?

    <p>It decreases blood flow to maintain core temperature.</p> Signup and view all the answers

    How does the body respond to decreased oxygen supply due to high altitude?

    <p>There is a significant increase in blood flow to tissues.</p> Signup and view all the answers

    What is the result of acute mechanisms for local blood flow regulation when arterial pressure suddenly increases?

    <p>Blood flow increases instantaneously by about 100%.</p> Signup and view all the answers

    What happens to blood flow through tissues when arterial pressure remains elevated for a prolonged period?

    <p>Blood flow approaches almost exactly the normal level over weeks.</p> Signup and view all the answers

    How does increased endothelin release affect blood flow regulation?

    <p>It contributes to vasoconstriction when the endothelium is damaged.</p> Signup and view all the answers

    What characterizes long-term blood flow regulation compared to acute mechanisms?

    <p>It involves control over hours, days, or weeks to normalize blood flow.</p> Signup and view all the answers

    Which of the following statements regarding endothelin receptor blockers is true?

    <p>They are utilized in managing pulmonary hypertension but not systemic hypertension.</p> Signup and view all the answers

    What controls the cyclical opening and closing of precapillary sphincters?

    <p>The metabolic needs of the tissue for nutrients</p> Signup and view all the answers

    What happens to precapillary sphincters when oxygen levels increase in the tissue?

    <p>They close until oxygen is consumed</p> Signup and view all the answers

    Which theory suggests that blood flow is regulated by the metabolic requirements of tissues?

    <p>Oxygen demand theory</p> Signup and view all the answers

    Which of the following describes the cyclical opening and closing of blood vessels due to nutrient needs?

    <p>Vasomotion</p> Signup and view all the answers

    What is the primary reason that smooth muscle remains contracted in precapillary sphincters?

    <p>Increased oxygen concentration</p> Signup and view all the answers

    What is the primary consequence of collateral blood vessels developing in response to corollary insufficiency?

    <p>They prevent heart attacks.</p> Signup and view all the answers

    Which type of remodeling is associated with chronic elevation of blood pressure?

    <p>Outward remodeling</p> Signup and view all the answers

    What vascular change occurs as a result of long-term exercise training?

    <p>Increased blood flow demands</p> Signup and view all the answers

    What can happen if collateral blood vessels do not develop quickly enough during coronary insufficiency?

    <p>Serious heart attacks can occur.</p> Signup and view all the answers

    What is a significant adaptive response of blood vessels to chronic changes in blood flow?

    <p>Vascular remodeling</p> Signup and view all the answers

    What structural changes can occur in blood vessels due to chronic hypertension?

    <p>Decreased elasticity</p> Signup and view all the answers

    Which type of remodeling occurs in tissues with increased capillary density due to sustained exercise?

    <p>Hypertrophic remodeling</p> Signup and view all the answers

    What role does remodeling play in blood vessels in response to increased mechanical stress?

    <p>It allows accommodation for higher pressure.</p> Signup and view all the answers

    What occurs in the coronary vessels of many individuals by the age of 60 years?

    <p>Closure or partial occlusion of vessels.</p> Signup and view all the answers

    What type of arterial remodeling is characterized by a decrease in lumen size in response to reduced blood flow?

    <p>Inward remodeling</p> Signup and view all the answers

    Total cyanide poisoning can cause local blood flow to increase as much as threefold.

    <p>False</p> Signup and view all the answers

    The mechanisms by which oxygen availability alters tissue blood flow are fully understood.

    <p>False</p> Signup and view all the answers

    The vasodilator theory suggests that a higher rate of metabolism leads to the formation of more vasodilator substances.

    <p>True</p> Signup and view all the answers

    The oxygen demand theory is one of the two main theories proposed to explain changes in tissue blood flow.

    <p>True</p> Signup and view all the answers

    An increase in blood flow during tissue hypoxia is primarily due to reduced oxygen and nutrient availability.

    <p>True</p> Signup and view all the answers

    Increasing tissue metabolism decreases blood flow to the affected area.

    <p>False</p> Signup and view all the answers

    Adenosine is one of the vasodilator substances believed to diffuse to precapillary sphincters.

    <p>True</p> Signup and view all the answers

    Carbon monoxide exposure is known to enhance blood flow by improving oxygen availability.

    <p>False</p> Signup and view all the answers

    The blood flow can increase fourfold with an increase in metabolism up to eight times the normal level.

    <p>True</p> Signup and view all the answers

    Lactic acid is released into tissue spaces during oxygen deficiency and promotes vasodilation.

    <p>True</p> Signup and view all the answers

    Inadequate oxygen levels result in blood vessels relaxing and dilating.

    <p>True</p> Signup and view all the answers

    The glucose deficiency in blood can cause local tissue vasodilation.

    <p>True</p> Signup and view all the answers

    Only oxygen is responsible for local blood flow regulation.

    <p>False</p> Signup and view all the answers

    The oxygen demand theory is the only explanation for variations in local blood flow.

    <p>False</p> Signup and view all the answers

    Local vasodilation can be impacted by the metabolism of nearby tissues.

    <p>True</p> Signup and view all the answers

    Local blood flow does not change in response to nutrient deficiencies.

    <p>False</p> Signup and view all the answers

    As a result of increased metabolism, oxygen availability to smooth muscle fibers can decrease.

    <p>True</p> Signup and view all the answers

    The vaso-dilator substance theory and oxygen demand theory have no overlap.

    <p>False</p> Signup and view all the answers

    Other nutrients beyond oxygen do not affect blood vessel behavior.

    <p>False</p> Signup and view all the answers

    In the absence of specific nutrients, local blood flow may be regulated differently.

    <p>True</p> Signup and view all the answers

    Match the organs with their corresponding percentage of cardiac output under basal conditions:

    <p>Brain = 14% Heart = 4% Kidneys = 22% Liver = 27%</p> Signup and view all the answers

    Match the organs with their corresponding blood flow in ml/min under basal conditions:

    <p>Brain = 700 ml/min Heart = 200 ml/min Liver = 1350 ml/min Bone = 250 ml/min</p> Signup and view all the answers

    Match the organs with their blood flow in ml/min per 100 g of tissue:

    <p>Heart = 70 ml/min Kidneys = 360 ml/min Liver = 95 ml/min Muscle (inactive state) = 4 ml/min</p> Signup and view all the answers

    Match the organs with their blood flow percentage during rest:

    <p>Bronchi = 2% Muscle (inactive state) = 15% Bone = 5% Heart = 4%</p> Signup and view all the answers

    Match the blood flow percentages of organs with their proper functions:

    <p>Brain = Cognitive functions Kidneys = Filtration of blood Liver = Metabolism and detoxification Muscles = Movement and support</p> Signup and view all the answers

    Match the following phenomena with their descriptions:

    <p>Reactive hyperemia = Increased blood flow after temporary occlusion Active hyperemia = Increased blood flow due to elevated metabolic rate Vasodilation = Widening of blood vessels Vitamin deficiency = Reduced blood flow and increased peripheral resistance</p> Signup and view all the answers

    Match the following nutrients with their related diseases:

    <p>Thiamine = Beriberi Niacin = Pellagra Riboflavin = Ariboflavinosis Vitamin C = Scurvy</p> Signup and view all the answers

    Match the type of blood flow response with its condition:

    <p>Reactive hyperemia = Following temporary occlusion of blood supply Active hyperemia = During intense exercise Local vasodilation = Due to tissue hypoxia Nutrient deficiency = In beriberi</p> Signup and view all the answers

    Match the blood flow regulation mechanisms with their impact:

    <p>Increased arterial pressure = May cause increased blood flow temporarily Reactive hyperemia = Restores blood flow following occlusion Active hyperemia = Supports tissues with high metabolic activity Vitamin deficiencies = May lead to reduced blood flow</p> Signup and view all the answers

    Match the following terms with their effects on blood flow:

    <p>Occlusion = Leads to reactive hyperemia Metabolic activity = Increases blood flow demands Vasodilation = Promotes increased blood flow Nutrient deficiency = May restrict blood flow capacity</p> Signup and view all the answers

    Study Notes

    Local Blood Flow Regulation

    • Blood flow to tissues is regulated by metabolic needs and changes in arterial pressure.
    • Metabolic mechanisms: local vasodilation and vasoconstriction occur based on tissue metabolic demand.
    • Reactive hyperemia: increased blood flow after a period of tissue blood supply blockage.
    • Active hyperemia: increased blood flow during tissue activity, like exercising muscle.

    Humoral Control of Circulation

    • Humoral control involves substances secreted into body fluids, like hormones.
    • Vasoconstrictors: substances that narrow blood vessels, increasing blood pressure
    • Norepinephrine and Epinephrine: these hormones cause vasoconstriction, contributing to blood pressure regulation.
    • Angiotensin II: powerful vasoconstrictor, regulating blood pressure by constricting arterioles and decreasing sodium and water excretion by kidneys.
    • Vasopressin (Antidiuretic hormone): extremely potent vasoconstrictor, also important for water reabsorption in kidneys.

    Vascular Remodeling

    • Long-term changes in blood pressure and flow lead to vascular remodeling.
    • Increased blood flow and shear stress cause outward remodeling and increased luminal diameter of arteries.
    • Chronic reductions in blood pressure and flow lead to decreased luminal diameter and wall thickness.

    Autoregulation of Blood Flow

    • Autoregulation: the ability of tissues to maintain relatively constant blood flow over a range of arterial pressures.
    • Myogenic mechanism: blood vessels constrict in response to stretch, triggered by increased arterial pressure.
    • Metabolic mechanism: accumulation of vasodilator substances in response to increased metabolic activity, counteracting pressure-induced vasoconstriction.

    Precapillary Sphincters and Blood Flow Regulation

    • Precapillary sphincters are normally completely open or closed, and the number that are open is proportional to the tissue's nutritional needs.
    • They open and close cyclically several times per minute, with the duration of the open phases proportional to the metabolic needs of the tissues.
    • This cyclical opening and closing is called vasomotion.

    Oxygen Demand Theory for Local Blood Flow Control

    • This theory suggests that the need for oxygen and other nutrients drives blood flow regulation.
    • As oxygen demand increases, vasodilators are released, leading to vasodilation and increased blood flow.
    • When oxygen concentration falls below a certain level, precapillary and metarteriole sphincters open to increase blood flow and restore oxygen levels.

    Endothelin and Vasoconstriction

    • Endothelin is a potent vasoconstrictor.
    • Increased endothelin release contributes to vasoconstriction when the endothelium is damaged, such as by hypertension.

    Long-Term Blood Flow Regulation

    • This type of regulation adjusts blood flow over a longer time scale, spanning hours, days, and weeks.
    • It provides more complete control of blood flow than short-term mechanisms.

    Vascular Remodeling

    • This is a process of adaptation in response to chronic changes in blood pressure or blood flow.

    Vascular Remodeling in Response to Chronic Changes in Blood Flow or Blood Pressure

    • Chronic exercise training increases vascularity in trained muscles to accommodate higher blood flow requirements.
    • Chronic hypertension leads to remodeling of arteries and arterioles to accommodate increased mechanical wall stress.
    • Inward eutrophic remodeling occurs in small arteries and arterioles in response to increased blood pressure, decreasing lumen diameter and thickening the vascular wall.
    • Hypertrophic remodeling occurs in larger arteries that do not constrict in response to increased pressure, increasing the thickness and cross-sectional area of the vascular wall.
    • Outward remodeling occurs when blood vessels are chronically exposed to increased blood flow, increasing lumen diameter and cross-sectional area of the vascular wall without significant wall thickening.
    • Outward hypertrophic remodeling occurs in response to both chronic increases in blood pressure and blood flow, increasing both lumen diameter and wall thickness.

    Vascular Remodeling in Response to A-V Fistula Creation

    • Creation of an A-V fistula, bypassing high-resistance small vessels and capillaries, causes remodeling in the affected artery and vein.
    • The artery undergoes outward remodeling, increasing its lumen diameter.
    • The vein undergoes hypertrophy, thickening its wall to withstand the increased pressure.
    • The vein's wall thickness becomes similar to that of an artery several months after implantation.

    Vascular Remodeling in Response to Chronic Changes in Blood Flow or Blood Pressure

    • Chronic dialysis in patients with renal failure requires an A-V fistula creation.
    • This fistula increases blood flow to the affected area.

    Local Blood Flow Regulation

    • Oxygen deficiency and blood flow: Total cyanide poisoning can increase local blood flow up to sevenfold due to oxygen deprivation.

    • Vasodilator Theory: Increased metabolic rate or reduced oxygen availability leads to the formation of vasodilator substances like adenosine, carbon dioxide, and potassium ions.

      • These substances dilate precapillary sphincters, metarterioles, and arterioles, increasing blood flow.
      • Adenosine and lactic acid are released in response to oxygen deficiency, causing intense vasoconstriction.

    • Oxygen Demand Theory: Increased tissue metabolism theoretically decreases oxygen availability to smooth muscle fibers in blood vessels, leading to local vasodilation.

    Other Factors Influencing Local Blood Flow

    • Glucose Deficiency: Lack of glucose in the perfusing blood can cause local tissue vasodilation.
    • Other Nutrient Deficiencies: Deficiencies in amino acids or fatty acids could potentially cause vasodilation.

    Acute vs. Long-Term Blood Flow Regulation

    • Acute Regulation: Primarily governed by vasodilator substances and oxygen demand, which are mainly responsible for rapid changes in blood flow.

    • Long-Term Regulation: Involves changes in tissue vascularity to match increased or decreased metabolic needs.

    Mechanisms of Long-Term Blood Flow Regulation

    • Angiogenesis: Increased tissue metabolism for a prolonged period leads to an increase in the number and size of arterioles and capillary vessels.
    • Vascular Regression: Decreased tissue metabolism leads to a decrease in tissue vascularity.

    Nitric Oxide (NO) and Blood Flow Regulation

    • NO Release: Shear stress and vasoconstrictors stimulate the release of NO from endothelial cells.
    • NO Function: NO dilates upstream blood vessels, enhancing the effectiveness of local blood flow control.
    • NO Protection: NO protects against excessive vasoconstruction.

    Timeframe for Long-term Blood Flow Regulation

    • Rapid Adjustment: Vascularity can change rapidly in young animals and growing tissues.
    • Slower Adjustment: Changes occur more slowly in older tissues.

    Importance of Long-Term Blood Flow Regulation

    • Metabolic Needs: Long-term regulation ensures that tissues receive adequate blood flow to meet their ongoing metabolic demands.

    Local Control of Blood Flow

    • Local control of blood flow refers to the ability of tissues to regulate their own blood supply.
    • Tissues can regulate their blood flow in response to changes in their metabolic needs, such as increased oxygen demand or accumulation of metabolic byproducts.
    • Metabolic mechanisms play a crucial role in local blood flow control, responding to the metabolic demands of tissues.
    • These mechanisms include autoregulation, reactive hyperemia, and active hyperemia.

    Autoregulation

    • Autoregulation ensures that blood flow remains relatively constant despite fluctuations in arterial pressure.
    • If arterial pressure rises, blood flow through the tissue also increases initially.
    • However, the blood vessels constrict, reducing blood flow back to its normal level within a minute, despite persistent high arterial pressure.
    • Autoregulation involves both metabolic and myogenic mechanisms.

    Reactive Hyperemia

    • Reactive hyperemia occurs after a brief period of blood flow blockage to a tissue.
    • When blood flow is restored, the tissue experiences a rapid increase in blood flow four to seven times the normal rate, which can last for several minutes.
    • This excess blood flow compensates for the oxygen deficit accumulated during the blockage.

    Active Hyperemia

    • Active hyperemia occurs when tissue metabolic activity increases.
    • Active tissues, such as exercising muscles, demand a greater supply of oxygen and nutrients.
    • To meet this demand, local blood vessels dilate, expanding blood flow to the active tissue.
    • Active hyperemia can increase muscle blood flow up to 20 times during intensive exercise.

    Vasoactive Substances – Nitric Oxide

    • Nitric oxide (NO) is a potent vasodilator that plays a critical role in regulating blood flow.
    • NO is produced by endothelial cells in response to various stimuli, including shear stress from blood flow, and certain pharmacological agents.
    • NO activates soluble guanylate cyclases in vascular smooth muscle cells, leading to the production of cGMP, which causes relaxation of blood vessels.

    Vasoactive Substances – Endothelin

    • Endothelin is a potent vasoconstrictor produced by endothelial cells.
    • It is released in small amounts under normal conditions but increases significantly when the endothelium is damaged, such as during injury or inflammation.
    • Endothelin helps prevent excessive bleeding from injured blood vessels.

    Vasoactive Substances - Other Vasodilators and Vasoconstrictors

    • Bradykinin: A powerful vasodilator and increases capillary permeability, playing a role in regulating blood flow in inflamed tissues and salivary/gastrointestinal glands.
    • Histamine: Released in response to tissue damage, inflammation or allergic reactions, causing vasodilation and increased permeability.
    • Carbon dioxide: Causes moderate vasodilation in most tissues, but marked vasodilation in the brain.
    • Angiotensin II: A powerful vasoconstrictor, chronically infused angiotensin II has a long-term effect on blood flow.
    • Most Vasodilators and Vasoconstrictors Have Little Effect on Long-Term Blood Flow: Chronic infusion of potent vasoactive agents generally does not alter long-term blood flow, indicating robust autoregulation mechanisms in most tissues.

    Key Points

    • Local blood flow control is vital for maintaining tissue function and oxygen delivery.
    • Metabolic mechanisms play a central role in regulating blood flow in response to the body's needs.
    • Vasoactive substances, including nitric oxide, endothelin, bradykinin, and histamine, contribute to the intricate regulation of blood flow.
    • Understanding these local control mechanisms is essential for comprehending the overall regulation of blood flow and cardiovascular function.

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    Description

    This quiz covers the mechanisms of local blood flow regulation and the humoral control of circulation. It includes metabolic processes like vasodilation, reactive hyperemia, and the effects of hormones such as norepinephrine and angiotensin II. Test your knowledge on how blood flow is adjusted to meet the metabolic needs of tissues.

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