Guyton and Hall Physiology Chapter 21 - Muscle Blood Flow and Cardiac Output During Exercise
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Questions and Answers

What effect does strenuous exercise have on muscle capillaries?

  • All capillaries open to increase blood flow (correct)
  • Some capillaries remain dormant
  • Capillaries overflow with blood during rest
  • All capillaries close completely

    • How does decreased oxygen in muscle tissue influence blood flow?

  • It has no effect on blood flow
  • It decreases blood flow significantly
  • It enhances blood flow greatly (correct)
  • It only affects blood flow during rest

    • What is the primary mechanism of blood flow regulation in skeletal muscles during exercise?

  • Blood pressure changes in systemic circulation
  • Local control of vascular resistance (correct)
  • Systematic hormone release
  • Neural control from the central nervous system

    • What role does the sympathetic nervous system play during exercise?

    <p>It increases cardiac output through blood vessel constriction</p> Signup and view all the answers

    What impact does norepinephrine have on blood vessels during exercise?

    <p>It leads to vasoconstriction in non-exercising muscles</p> Signup and view all the answers

    During which condition does the heart receive increased coronary blood flow?

    <p>During strenuous exercise</p> Signup and view all the answers

    What physiological change occurs in the capillary surface area during exercise?

    <p>Capillary surface area increases twofold to threefold</p> Signup and view all the answers

    What primarily causes pain associated with angina pectoris?

    <p>Insufficient oxygen delivery to the heart muscle</p> Signup and view all the answers

    What is the primary purpose of placing stents in coronary arteries?

    <p>To hold the artery open and prevent restenosis</p> Signup and view all the answers

    What physiological response occurs in the coronary artery after stent placement?

    <p>Endothelium grows over the stent surface</p> Signup and view all the answers

    How much can blood flow through a vessel increase after the relevant procedure?

    <p>3-fold to 4-fold</p> Signup and view all the answers

    What percentage of patients typically experience relief from coronary ischemic symptoms after the procedure?

    <p>More than 75%</p> Signup and view all the answers

    What is a common subsequent requirement for many patients who have undergone the procedure?

    <p>Coronary bypass surgery</p> Signup and view all the answers

    In the context of exercise, what mechanism regulates hyperemia to muscles?

    <p>Neural control</p> Signup and view all the answers

    What role does norepinephrine play in blood flow regulation?

    <p>Causes vasoconstriction</p> Signup and view all the answers

    What happens to the coronary artery during angioplasty?

    <p>It is dilated to improve blood flow</p> Signup and view all the answers

    What is a potential long-term complication after stent placement?

    <p>Restenosis of the artery</p> Signup and view all the answers

    How does the body typically respond to increased metabolic demands during exercise?

    <p>Increased vasodilation in active muscles</p> Signup and view all the answers

    What is primarily responsible for the vasodilation of active muscles during exercise?

    <p>Local vasodilator effects</p> Signup and view all the answers

    What is the effect of sympathetic vasoconstrictor nerve fibers on resting muscles?

    <p>They reduce blood flow to resting muscles.</p> Signup and view all the answers

    Which of the following statements about norepinephrine is correct?

    <p>It can decrease blood flow through resting muscles.</p> Signup and view all the answers

    What happens to blood flow in nonmuscular areas during intense exercise?

    <p>Blood flow is temporarily reduced.</p> Signup and view all the answers

    How does the body respond to stress during circulatory shock?

    <p>It enhances sympathetic vasoconstrictor effects to maintain arterial pressure.</p> Signup and view all the answers

    What is the potential consequence of sympathetic vasoconstriction during emergency situations?

    <p>Greater ability to run faster in critical conditions.</p> Signup and view all the answers

    Which circulatory systems are spared from the vasoconstrictor effect of sympathetic nerves?

    <p>Cerebral and coronary systems</p> Signup and view all the answers

    What is the role of the adrenal glands during exercise?

    <p>They secrete increased amounts of hormones.</p> Signup and view all the answers

    What is the physiological significance of reducing blood flow to resting muscles during exercise?

    <p>To allocate blood to actively working muscles.</p> Signup and view all the answers

    Which nerve transmitter is primarily involved in sympathetic vasoconstriction?

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

    What primarily causes the increase in blood flow during skeletal muscle activity?

    <p>Local chemical effects from reduced oxygen levels</p> Signup and view all the answers

    During extreme exercise, how much can blood flow increase in well-trained athletes compared to resting levels?

    <p>25 to 50 times normal</p> Signup and view all the answers

    Which of the following best describes the blood flow during muscle contractions?

    <p>Blood flow increases and decreases with each contraction.</p> Signup and view all the answers

    How much does resting skeletal muscle blood flow typically average per 100g of muscle?

    <p>3 to 4 ml/min/100 g</p> Signup and view all the answers

    What is the primary chemical factor resulting from active muscles that causes vasodilation?

    <p>Reduced oxygen levels</p> Signup and view all the answers

    What is the primary purpose of the coronary arteries in the heart?

    <p>To provide a significant blood supply to heart tissue</p> Signup and view all the answers

    Which coronary artery primarily supplies the anterior portion of the left ventricle?

    <p>Left coronary artery</p> Signup and view all the answers

    What happens to coronary blood flow during the diastole phase?

    <p>It decreases sharply until the next systole</p> Signup and view all the answers

    How does the sympathetic nervous system influence coronary blood flow?

    <p>It increases oxygen consumption of the myocardium</p> Signup and view all the answers

    What percentage of oxygen in the coronary arterial blood is typically extracted by the heart muscle?

    <p>70%</p> Signup and view all the answers

    During exercise, which factor is most significant in regulating blood flow in the coronary arteries?

    <p>The oxygen demand of cardiac musculature</p> Signup and view all the answers

    What role does norepinephrine play in cardiac physiology?

    <p>It enhances myocardial oxygen consumption</p> Signup and view all the answers

    What is likely to happen to blood flow in the coronary capillaries if muscle oxygen demand increases?

    <p>It increases to meet the higher oxygen needs</p> Signup and view all the answers

    What portion of the left ventricle does the right coronary artery primarily supply in most individuals?

    <p>Posterior section in 80-90% of people</p> Signup and view all the answers

    Which statement about cardiac muscle nutrition is accurate?

    <p>The primary source of nutrition is from coronary blood flow</p> Signup and view all the answers

    Which coronary artery is responsible for supplying the anterior portion of the left ventricle?

    <p>Left coronary artery</p> Signup and view all the answers

    What mechanism primarily regulates blood flow in the coronary arteries?

    <p>Oxygen demand of cardiac muscle</p> Signup and view all the answers

    During which phase of the cardiac cycle does coronary blood flow typically decrease significantly?

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

    Which of the following statements about cardiac muscle nutrition is correct?

    <p>Only a small portion of cardiac muscle gets direct nutrition from coronary blood supply.</p> Signup and view all the answers

    What percentage of the oxygen in the coronary arterial blood is typically removed as it flows through the heart muscle?

    <p>70%</p> Signup and view all the answers

    What is the typical average ratio of coronary blood flow to total cardiac output in a resting individual?

    <p>4% to 5%</p> Signup and view all the answers

    During severe exercise, how much can coronary blood flow increase relative to its normal state?

    <p>3-fold to 4-fold</p> Signup and view all the answers

    Which statement accurately describes the blood flow behavior during exercise in patients with weakened hearts?

    <p>Marked increases in right atrial pressure occur.</p> Signup and view all the answers

    What is the normal coronary blood flow per 100 grams of heart tissue in a healthy individual?

    <p>70 ml/min/100 g</p> Signup and view all the answers

    What happens to the work output of the heart during strenuous exercise in a young adult?

    <p>It may increase 6-fold to 9-fold.</p> Signup and view all the answers

    What is a common characteristic of pain experienced during a myocardial infarction?

    <p>Hot, pressing, and constricting pain</p> Signup and view all the answers

    Which class of drug is commonly administered during an acute anginal attack for immediate relief?

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

    What effect do beta blockers have on the heart during exercise?

    <p>They block sympathetic beta-adrenergic receptors.</p> Signup and view all the answers

    What is a potential outcome for a heart that has recovered from a large myocardial infarction?

    <p>Pumping capability may be permanently decreased.</p> Signup and view all the answers

    What is the usual rate of restenosis in patients treated with angioplasty?

    <p>25% to 40%</p> Signup and view all the answers

    Which class of drugs may be beneficial for treating chronic stable angina pectoris?

    <p>Calcium channel blockers</p> Signup and view all the answers

    What causes restenosis after angioplasty?

    <p>Scar tissue formation under new endothelium</p> Signup and view all the answers

    How do angiotensin-converting enzyme inhibitors affect heart function?

    <p>They dilate blood vessels and reduce workload.</p> Signup and view all the answers

    What percentage of cardiac output is capable of being increased by a normal heart during rest?

    <p>300% to 400%</p> Signup and view all the answers

    What is the significance of understanding heart function after recovery from a myocardial infarction?

    <p>To acknowledge that recovery does not guarantee full functionality.</p> Signup and view all the answers

    Strenuous exercise causes a reduction in the number of open muscle capillaries.

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

    Decreased oxygen levels in muscle tissue significantly enhance blood flow to those muscles.

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

    The primary mechanism for regulating blood flow in the skeletal muscles during exercise is systemic control from the brain.

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

    At rest, some muscle capillaries may have little or no blood flowing through them.

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

    The pain associated with angina pectoris is solely caused by increased blood flow to the heart.

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

    During strenuous exercise, the coronary blood flow increases from 3-fold to 7-fold.

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

    A normal resting person's coronary blood flow averages about 4% to 5% of total cardiac output.

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

    The heart can increase its work output by 6-fold to 9-fold under severe conditions.

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

    Approximately one-third of deaths in industrialized nations are due to coronary artery disease.

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

    In patients with weakened hearts, even moderate exercise does not affect right atrial pressure significantly.

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

    The cardiac muscle cell membrane is highly impermeable to adenosine.

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

    Sympathetic innervation of coronary vessels is less extensive than parasympathetic innervation.

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

    Adenosine is released primarily during periods of coronary hypoxia.

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

    Alpha receptors in coronary vessels are primarily responsible for vasodilation.

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

    Loss of adenosine from cardiac muscle cells has no significant cellular consequences.

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

    Norepinephrine and epinephrine can only have vasoconstrictor effects in coronary vessels.

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

    Beta receptors are more prevalent in epicardial coronary vessels compared to intramuscular arteries.

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

    Coronary ischemia lasting for over 30 minutes can be critical for cardiac cell survival.

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

    The synthesis rate of new adenine in cardiac muscle cells is approximately 20% per hour.

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

    The coronary arteries primarily receive signals from sympathetic nerve fibers.

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

    Match the following coronary arteries with their primary areas supplied:

    <p>Left coronary artery = Nutrient capillaries of the left ventricle Right coronary artery = Posterior part of the left ventricle</p> Signup and view all the answers

    Match the following descriptions with their corresponding terms:

    <p>Subendocardial arterial plexus = Deep coronary blood supply Epicardial coronary arteries = Outer layer blood supply Coronary capillaries = Site of oxygen extraction Cardiac muscle = Tissue requiring oxygen nutrition</p> Signup and view all the answers

    Match the following phases of the cardiac cycle with their effects on coronary blood flow:

    <p>Systole = Decreased blood flow Diastole = Increased blood flow Cardiac muscle contraction = Compression of coronary arteries Relaxation = Maximum blood flow</p> Signup and view all the answers

    Match the following physiological responses during exercise with their effects:

    <p>Sympathetic vasoconstriction = Increases mean arterial pressure Vasodilation in active muscles = Decreases arterial pressure increase Increased cardiac output = Supports enhanced blood flow to muscles Increased arterial pressure = Facilitates oxygen delivery</p> Signup and view all the answers

    Match the following concepts with their definitions:

    <p>Oxygen demand = Primary factor in regulating coronary blood flow Nutritional blood supply = Source of muscle oxygen for cardiac tissue Coronary capillary function = Site of oxygen transfer Endocardial surface = Minimal direct blood nutrition source</p> Signup and view all the answers

    Match the following types of exercise with their typical effects on arterial pressure:

    <p>Strenuous exercise = Increase of 20 to 40 mm Hg Tense situations with few muscles = Increase as high as 170 mm Hg Massive whole-body exercise = Minimal increase in mean arterial pressure Moderate exercise = Stabilization of arterial pressure</p> Signup and view all the answers

    Match the percentage of oxygen extraction with the respective cardiac scenario:

    <p>70% = Oxygen extracted by the heart muscle 80%-90% = Individuals supplied by right coronary artery 1/10 mm = Depth of endocardial surface for nutrition Absolute zero = Oxygen remaining after coronary blood flow</p> Signup and view all the answers

    Match the following blood flow components with their descriptions:

    <p>Venous return = Amount of blood returning to the heart Cardiac output = Volume of blood pumped by the heart per minute Right atrial pressure = Pressure in the chamber receiving blood from the body Arterial pressure = Pressure exerted by circulating blood on vessel walls</p> Signup and view all the answers

    Match the following exercises with the relevant vasculature response:

    <p>Running = Extreme vasodilation in large muscle groups Swimming = Balanced blood flow distribution Weightlifting = Localized vasoconstriction in inactive muscles Yoga = Moderate increases in arterial pressure</p> Signup and view all the answers

    Match the following physiological changes during exercise to their triggers:

    <p>Vasodilation = Increased metabolic demand in muscles Sympathetic nervous response = Tense conditions during activity Increased arterial pressure = Extreme exercise conditions Cardiac output increase = Maximal muscle stimulation</p> Signup and view all the answers

    Study Notes

    Blood Flow in Skeletal Muscles

    • During exercise, the skeletal muscles require a large amount of blood flow to meet their oxygen demands.

    Local Control of Blood Flow

    • Decreased oxygen levels in muscle tissues cause vasodilation, increasing blood flow to the muscles.
    • This dilation happens primarily through the opening of dormant capillaries.
    • The distance oxygen must diffuse from capillaries to muscle fibers decreases during exercise, improving oxygen delivery.

    Nervous Control of Blood Flow

    • Sympathetic vasoconstrictor nerves: Secrete norepinephrine, reducing blood flow to resting muscles.
    • This mechanism can decrease blood flow to as little as one-half to one-third of normal levels.

    Cardiac Output During Exercise

    • Increased oxygen demand by skeletal muscles results in a need for an increased cardiac output.
    • Cardiac output can increase to four to five times normal in non-athletes and six to seven times normal in trained athletes.

    Coronary Circulation

    • Coronary arteries supply the heart muscle with blood and oxygen.
    • The left coronary artery nourishes the anterior and left lateral parts of the left ventricle.
    • The right coronary artery supplies most of the right ventricle and the inferior part of the left ventricle in most people.
    • Coronary blood flow is closely tied to the metabolic needs of the heart muscle, especially oxygen demand.

    Cardiac Muscle Compression

    • The heart muscle compresses coronary blood vessels during systole, reducing blood flow.

    Factors Affecting Coronary Flow

    • Heart rate, blood pressure, and contractility all contribute to changes in coronary blood flow.

    Skeletal Muscle Blood Flow Rate

    • At rest, skeletal muscle blood flow averages 3 to 4 ml/min/100 g of muscle.
    • During intense exercise, this flow can increase 25 to 50-fold, reaching 100 to 200 ml/min/100 g of muscle.
    • Peak blood flows as high as 400 ml/min/100 g of muscle have been reported in endurance athletes.

    Blood Flow During Muscle Contractions

    • Blood flow to the muscle fluctuates with each contraction, increasing and decreasing with the rhythm of the exercise.
    • After exercise, blood flow to the muscles remains elevated for a few seconds before returning to normal.

    Coronary Blood Flow Regulation in Heavy Exercise

    • Despite increased cardiac output, coronary venouse flow decreases during heavy exercise
    • Sympathetic stimulation of the heart increases blood flow back into the heart through the Thebesian veins

    Normal Coronary Circulation

    • Makes up about 5% of cardiac output.
    • At rest, blood flow is 70 ml/min/100g of heart weight, or about 225 ml/min.
    • During strenuous exercise, cardiac output increases by 4- to 7-fold.
    • The heart works harder, pumping blood against higher arterial pressure.
    • Coronary blood flow increases 3- to 4-fold to meet the increased metabolic demands of the heart muscle.

    Cardiac Muscle Compression

    • Compression of the heart muscle during systole reduces coronary blood flow.
    • During diastole, coronary blood flow increases as the heart relaxes.

    Oxygen Demand and Coronary Blood Flow

    • Coronary blood flow is regulated to meet the oxygen demand of the heart muscle.
    • About 70% of oxygen in the coronary arterial blood is removed as blood flows through the heart muscle.
    • Coronary blood flow increases proportionate to the need for oxygen in the heart muscle.

    Angina Pectoris

    • Pain associated with insufficient coronary blood flow.
    • Pain is described as hot, pressing, and constricting.
    • This type of pain usually causes the patient to cease unnecessary activity.

    Drug Treatment for Angina Pectoris

    • Vasodilators like nitroglycerin can relieve pain during an acute anginal attack.
    • Chronic stable angina can be treated with drugs like angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, calcium channel blockers, and ranolazine.
    • Beta blockers block sympathetic beta-adrenergic receptors, reducing heart rate and metabolic demand.

    Surgical Treatment of Coronary Artery Disease

    • Aortic-coronary bypass surgery involves grafting a vein from the aorta to a coronary artery beyond a blockage.
    • Stents are placed inside dilated coronary arteries to prevent restenosis.
    • Drug-eluting stents release drugs to prevent excessive scar tissue formation.
    • Laser therapy can dissolve atherosclerotic lesions without damaging the arterial wall.

    Blood Flow Regulation in Skeletal Muscle

    • Strenuous exercise requires significant blood flow to skeletal muscles.
    • Exercise increases blood flow to skeletal muscles by opening dormant capillaries
    • This increases the diffusion surface area for oxygen and nutrients.

    Control of Skeletal Muscle Blood Flow

    • Increased metabolic demand in muscles during exercise reduces oxygen levels.
    • Low oxygen levels activate vasodilators that increase local blood flow.

    Coronary Circulation

    • Coronary artery disease is a leading cause of death in developed countries.
    • Coronary arteries deliver blood to the heart muscle.
    • About 5% of cardiac output is dedicated to the coronary circulation.

    Coronary Blood Flow

    • During exercise, the heart pumps 4-7 times more blood than at rest.
    • Coronary blood flow increases by 3-4 times during exercise.

    Physiology of Cardiac Muscle Metabolism

    • Cardiac muscle metabolism is similar to other muscle tissue.
    • Sympathetic nervous system stimulation generally constricts coronary vessels but can also cause dilation.
    • Metabolic factors override direct nervous system stimulation.

    Ischemic Heart Disease

    • Ischemic heart disease is the most common cause of death in developed countries.
    • Atherosclerosis is a major cause of ischemic heart disease.
    • Atherosclerosis reduces coronary blood flow, leading to heart attacks.

    Myocardial Infarction

    • A large ischemic area can lead to the death of heart muscle cells (necrosis)
    • The area of myocardial infarction is surrounded by a zone of nonfunctional muscle and a zone of weakly contracting muscle.
    • Cardiac muscle cells in the infarcted area are replaced by scar tissue.

    Coronary Ischemia

    • A significant portion of the coronary arteries may become blocked due to atherosclerosis.
    • Blockage of the coronary arteries causes pain, known as angina pectoris.
    • Ischemia can lead to abnormal conduction pathways within the heart.

    Cardiac Output Control During Exercise

    • Exercise places a considerable strain on the circulatory system.
    • Increased blood flow in skeletal muscle requires a significant increase in cardiac output.
    • During exercise, cardiac output increases by 4- to 7-fold.

    Effects of Coronary Ischemia

    • Loss of adenosine, an important vasodilator, can exacerbate ischemia.
    • Myocardial ischemia damages and kills cardiac muscle cells.
    • Ischemia can lead to arrhythmias and heart failure.

    Blood Flow and Cardiac Output During Exercise

    • Venous return increases with strenuous exercise resulting in rise in cardiac output.
    • Increase in venous return during strenuous exercise leads to a rise in right atrial pressure.
    • Sympathetic nervous response is activated during exercise resulting in vasodilation in active muscles.
    • During tense conditions vasodilation occurs in a few active muscles but vasoconstriction occurs in other areas of the body.
    • Increase in mean arterial pressure is minimal during massive whole-body exercise due to vasodilation in active muscle masses.
    • Mean arterial pressure can increase to as high as 170 mm Hg during tense conditions with limited muscle activity.

    Coronary Blood Flow and Regulation

    • The heart receives its blood supply through coronary arteries.
    • Only the inner one-tenth millimeter of the endocardial surface receives nutrition directly from the blood inside the cardiac chambers.
    • The left coronary artery supplies blood to the anterior and left lateral portions of the left ventricle.
    • The right coronary artery supplies most of the right ventricle as well as the posterior part of the left ventricle in 80-90% of people.
    • Coronary blood flow is regulated in proportion to the need of the cardiac musculature for oxygen.
    • During systole, capillary blood flow in the left ventricle muscle falls to a low level due to cardiac muscle compression.
    • About 70% of the oxygen in the coronary arterial blood is removed as blood flows through the heart muscle.

    Nervous Stimuli & Coronary Vasculature

    • Parasympathetic stimulation releases acetylcholine which dilates coronary arteries.
    • Sympathetic innervation of coronary vessels is more extensive than parasympathetic innervation.
    • Norepinephrine and epinephrine can dilate coronary vessels depending on the presence of receptor types.
    • Alpha receptors are more prevalent in epicardial coronary vessels and cause vasoconstriction.
    • Beta receptors are more prevalent in intramuscular arteries and cause vasodilation.
    • Anastomoses among the smaller arteries (20-250 micrometers in diameter) provide collateral flow during coronary artery occlusion.
    • Collateral flow can reach normal or almost normal coronary flow within a month following coronary artery occlusion.

    Ischemic Heart Disease

    • Myocardial infarction occurs when blood flow to an area of cardiac muscle becomes insufficient.
    • Infarcted areas are characterized by engorged blood vessels, bluish-brown hue, and edema.
    • Cardiac muscle cells die within a few hours of almost no blood supply.
    • Cardiac muscle requires 1.3 ml of oxygen/100 g of muscle tissue/min to remain alive.
    • 8 ml oxygen/100 g are delivered to the normal resting left ventricle each minute.
    • 15-30% of normal resting coronary blood flow is sufficient to prevent cardiac muscle death.
    • Coronary steal syndrome occurs when increased workload of the heart during exercise diverts blood flow away from ischemic areas, worsening the condition.
    • The recovery process for myocardial infarction requires absolute body rest to prevent further damage.

    Angina Pectoris

    • Angina pectoris is characterized by severe pain typically felt beneath the upper sternum.
    • Angina pectoris pain is often referred to other areas of the body, such as the left arm, shoulder, neck, and face.
    • Episodes of angina pectoris usually last for a few minutes, but can be constant in severe cases.
    • The pain is intensified by exercise, emotional strain, cold temperatures, and a full stomach.

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    Guyton and Hall Physiology - Muscle Blood Flow and Cardiac Output During Exercise PDF

    Description

    This quiz explores the mechanisms of blood flow in skeletal muscles during exercise. It covers local and nervous control of blood flow, the role of cardiac output, and how these factors adjust to meet the increased oxygen demands of muscles. Test your understanding of these physiological concepts!

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