Cardio Lec 05
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Questions and Answers

What is the primary function of the tunic media in blood vessels?

  • Connects the vessel to surrounding tissues
  • Forms a smooth lining that reduces friction between blood and the vessel wall.
  • Regulates blood flow by controlling smooth muscle contraction. (correct)
  • Provides structural support and flexibility to the vessel wall.

    • Which of the following accurately describes the Windkessel effect?

  • The elastic recoil of arteries that helps maintain blood flow during ventricular relaxation. (correct)
  • The ability of veins to expand and store blood, acting as a reservoir.
  • The increased pressure in the arteries due to the contraction of the heart.
  • The process by which capillaries exchange nutrients and waste products with surrounding tissues.

    • Which type of blood vessel is responsible for draining blood from capillaries?

  • Veins
  • Arteries
  • Venules (correct)
  • Capillaries

    • What is the primary function of valves in veins?

    <p>To prevent backflow of blood, ensuring unidirectional flow. (A)</p> Signup and view all the answers

    Which layer of a blood vessel is primarily composed of fibrous connective tissue?

    <p>Tunic externa (B)</p> Signup and view all the answers

    What is the primary role of large arteries in the circulatory system?

    <p>To act as reservoirs for blood, storing a significant volume. (B)</p> Signup and view all the answers

    How does the sympathetic nervous system influence arteriolar resistance?

    <p>By directly controlling the contraction of smooth muscle in the arterioles. (A)</p> Signup and view all the answers

    What is the primary function of the endothelium in blood vessels?

    <p>To form a smooth lining that reduces friction between blood and the vessel wall. (D)</p> Signup and view all the answers

    What two types of vessels comprise capillary beds?

    <p>Arteriovenous shunts and true capillaries (A)</p> Signup and view all the answers

    What is the relationship between flow and the pressure gradient?

    <p>Flow is directly proportional to the pressure gradient (D)</p> Signup and view all the answers

    Why does fluid flow only if there is a positive pressure gradient?

    <p>Fluid flows from a region of higher pressure to a region of lower pressure (B)</p> Signup and view all the answers

    What is the relationship between flow and resistance?

    <p>Flow is inversely proportional to resistance (C)</p> Signup and view all the answers

    Where is blood pressure the highest in the cardiovascular system?

    <p>Aorta (C)</p> Signup and view all the answers

    What is the key principle behind Poiseuille’s Law?

    <p>Resistance is influenced by viscosity, vessel diameter, and length (B)</p> Signup and view all the answers

    How does resistance affect flow through a tube?

    <p>As resistance increases, flow decreases (A)</p> Signup and view all the answers

    Which of the following factors does NOT influence fluid flow through a tube?

    <p>Temperature of the fluid (A)</p> Signup and view all the answers

    What is the relationship between the resistance to blood flow and the radius of a blood vessel?

    <p>Resistance is inversely proportional to the fourth power of the radius of the blood vessel. (B)</p> Signup and view all the answers

    If the radius of a blood vessel is doubled, what happens to the resistance to blood flow?

    <p>The resistance is reduced to one-sixteenth. (D)</p> Signup and view all the answers

    Which of the following is NOT a factor that alters arteriolar resistance?

    <p>Hormonal control (B)</p> Signup and view all the answers

    What is the effect of vasoconstriction on blood flow?

    <p>Vasoconstriction decreases blood flow. (B)</p> Signup and view all the answers

    What is the effect of vasodilation on blood flow?

    <p>Vasodilation increases blood flow. (D)</p> Signup and view all the answers

    Which of the following is NOT a paracrine that can alter arteriolar resistance?

    <p>Adrenaline (A)</p> Signup and view all the answers

    What is the role of the sympathetic nervous system in regulating arteriolar resistance?

    <p>The sympathetic nervous system causes vasoconstriction. (A)</p> Signup and view all the answers

    What is the primary mechanism of myogenic autoregulation?

    <p>Myogenic autoregulation is the mechanism by which blood vessels respond to changes in blood pressure. (C)</p> Signup and view all the answers

    What is the key difference between active hyperemia and reactive hyperemia?

    <p>Active hyperemia is caused by a buildup of metabolic byproducts, while reactive hyperemia is caused by a temporary blockage of blood flow. (B)</p> Signup and view all the answers

    Which of the following is NOT a factor that directly influences the frequency and velocity of calcium waves in vascular smooth muscle cells?

    <p>The presence of troponin in the smooth muscle cells (A)</p> Signup and view all the answers

    What is the key role of G protein-coupled receptors (GPCRs) in vascular smooth muscle cell contraction?

    <p>GPCRs trigger the release of calcium from intracellular stores through the activation of PLCb. (A)</p> Signup and view all the answers

    Which of the following is NOT directly involved in the regulation of vascular smooth muscle cell contraction?

    <p>Calcium oscillations within the smooth muscle cell cytoplasm (A)</p> Signup and view all the answers

    Flashcards

    Tunic layers of blood vessels

    Blood vessels have three layers: tunic intima, tunic media, and tunic externa.

    Tunic intima

    The inner layer of blood vessels, composed of endothelium.

    Tunic media

    The middle layer of blood vessels, containing smooth muscle, controlled by the sympathetic nervous system.

    Tunic externa

    The outer layer of blood vessels, primarily made of fibrous connective tissue.

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    Windkessel effect

    The ability of large elastic arteries to expand and store energy during ventricular contraction.

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    Elastic recoil

    The ability of arteries to return to their original shape, keeping blood moving during ventricular relaxation.

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    Venous return system

    Consists of venules and veins that drain blood and prevent backflow with valves.

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    Blood volume in veins

    Veins hold approximately 70% of the body’s blood and act as reservoirs during hemorrhage.

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    Capillary Beds

    Networks of small blood vessels involved in nutrient exchange.

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    Arteriovenous Shunt

    A direct connection between an arteriole and a venule.

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    True Capillaries

    Vessels allowing nutrient and gas exchange with tissues.

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    Blood Flow Equation

    Flow is determined by the formula Flow µ DP/R.

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    Pressure Gradient

    Difference in pressure that drives fluid flow.

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    Resistance and Flow

    Flow is inversely proportional to resistance (Flow µ 1/R).

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    Poiseuille’s Law

    Describes factors determining a vessel's resistance to flow.

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    Driving Pressure

    The pressure that maintains blood flow in the circulatory system.

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    Resistance (R)

    A measure of the opposition to flow in a tube, affected by length, viscosity, and radius.

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    Length (L) of tube

    Resistance is directly proportional to this factor; as L increases, R increases.

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    Viscosity (h)

    Resistance is directly proportional to this fluid property; thicker fluids increase R.

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    Tube radius (r)

    Resistance is inversely proportional to the radius raised to the fourth power; larger radius means less resistance.

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    Vasoconstriction

    A decrease in blood vessel diameter/radius that reduces blood flow and increases resistance.

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    Vasodilation

    An increase in blood vessel diameter/radius that enhances blood flow and reduces resistance.

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    Flow (Q) relationship

    Flow is inversely proportional to resistance; as resistance increases, flow decreases.

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    Factors altering arteriolar resistance

    Includes myogenic autoregulation, local paracrines, and sympathetic control affecting blood vessel behavior.

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    Adrenal Medulla

    The inner part of the adrenal gland that produces epinephrine.

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    Active Hyperemia

    An increase in blood flow in response to increased metabolic activity in tissues.

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    Reactive Hyperemia

    Increased blood flow following the removal of a blockage in blood vessels.

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    Sympathetic Regulation

    Control of arteriolar diameter by norepinephrine as part of the autonomic nervous system.

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    Calcium Oscillations

    Fluctuations in calcium levels that control contraction of vascular smooth muscle cells.

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    Study Notes

    Blood Flow Lecture Notes

    • Fluids and nutrients are circulated throughout the body.
    • Arteriolar resistance is regulated.
    • Silverthorn 8th edition pages 436-440, 476-482, 486-492

    Blood Vessels: Anatomy

    • Blood vessels have three layers (tunics).
    • Tunic intima contains endothelium and loose connective tissue, including an internal elastic lamina.
    • Tunic media is composed of smooth muscle, controlled by the sympathetic nervous system.
    • Tunic externa is largely fibrous connective tissue.
    • Arteries, arterioles, capillaries, venules, and veins are all types of blood vessels.
    • Valves prevent backflow in veins.

    Blood Vessel Structure: Major Types

    • Arteries have a large diameter and thick walls to withstand high pressure.
    • Arterioles have a smaller diameter and thicker walls than arteries.
    • Capillaries are the smallest blood vessels with thin walls, facilitating nutrient and gas exchange.
    • Venules collect blood from capillaries and gradually merge to form larger veins.
    • Veins have a lower pressure environment, thinner walls, and valves preventing backflow.

    Large Arteries and Large Veins

    • Large arteries (e.g., aorta) have low compliance and low capacitance and contain 15% of the blood.
    • Large veins (e.g., vena cava) have high compliance and high capacitance, containing 65-80% of the body's blood.
    • Arterioles and capillaries mediate gas and nutrient exchange with tissues.

    Large Elastic Arteries

    • During ventricular ejection, elastic arteries expand and store energy (Windkessel effect).
    • The expansion of the aorta and arteries generates pressure that propels blood forward even during ventricular relaxation.

    Elastic Recoil of Arteries

    • During ventricular relaxation, elastic recoil of arteries keeps blood moving throughout the circulatory system.
    • Semilunar valves prevent backflow of blood.

    Veins and Venous Return System

    • Venules emerge from capillaries and flow into larger veins.
    • Veins have less smooth muscle and connective tissue than arteries.
    • Veins have valves that prevent blood from flowing backward.
    • Veins function as a blood reservoir during hemorrhaging, containing approximately 70% of the body's blood.

    Capillary Beds

    • Capillary beds consist of arteriovenous shunts (connecting arterioles and venules) and true capillaries for nutrient exchange.
    • True capillaries permit oxygen and nutrient diffusion into cells and carbon dioxide and waste diffusion into blood.
    • Capillaries have very thin walls (single-cell layer) to facilitate rapid gas and nutrient exchange.

    Fluid Flow in Any System

    • Fluid flow (F) is directly proportional to the pressure gradient (ΔP) and inversely proportional to resistance (R).
    • Flow (F) = ΔP/R.

    Fluid Flow Through a Tube

    • Fluid flow is directly proportional to the pressure gradient (difference in pressure between two points).
    • Fluid flow occurs only with a positive pressure gradient.
    • Flow is determined by the pressure gradient, not the absolute pressure.

    Pressure Gradient in CV System

    • Blood pressure is highest in the aorta and progressively decreases through the circulatory system.
    • The heart maintains a positive driving pressure throughout the system.

    Resistance of a Vessel or System

    • Fluid flow is inversely proportional to resistance. Higher resistance leads to decreased flow, while lower resistance leads to increased flow.

    Poiseuille's Law

    • Poiseuille's law defines resistance (R) in a tube based on length (L), viscosity (η), and radius (r) as R = 8Lη/πr4.
    • Resistance increases with increasing length and viscosity.
    • Resistance decreases exponentially with increasing radius.

    Vessel Radius Changes

    • A small change in vessel radius has a substantial impact on resistance.
    • A 25% increase in radius reduces resistance significantly.
    • A 25% decrease in radius greatly increases resistance, resulting in significantly lower flow.

    Resistance: Blood Vessels

    • Small changes in radius drastically affect resistance to blood flow.
    • Vasoconstriction decreases blood vessel diameter and reduces blood flow.
    • Vasodilation increases blood vessel diameter and enhances blood flow.

    Effect of Resistance

    • When a blood vessel constricts (e.g., vessel B), resistance increases, reducing flow through that vessel. Blood is then diverted to other lower-resistance vessels.

    Factors Altering Arteriolar Resistance

    • Myogenic autoregulation
    • Local paracrines (e.g., active hyperemia, reactive hyperemia)
    • Sympathetic control (e.g., norepinephrine, epinephrine)

    Active Hyperemia

    • Increased tissue metabolism triggers the release of vasodilators (e.g., adenosine) into the extracellular fluid.
    • This causes arterioles to dilate, increasing blood flow to meet the metabolic demands of the tissue.

    Reactive Hyperemia

    • A physical obstruction temporarily reduces blood flow.
    • Once the obstruction is removed, metabolic vasodilators accumulate, causing arterioles to dilate, resulting in a temporary increase in blood flow.

    Sympathetic Regulation: Norepinephrine

    • The sympathetic nervous system (SNS) tonically releases norepinephrine to control arteriolar diameter.
    • Norepinephrine binds to α receptors on smooth muscle cells, triggering calcium-mediated contraction.
    • Changing the signal rate alters the amount of norepinephrine released, thereby influencing arteriolar constriction or dilation.

    GPCRs and Smooth Muscle Contraction

    • G-protein-coupled receptors (GPCRs) facilitate norepinephrine's role in smooth muscle contraction without requiring excitation-contraction coupling. Norepinephrine's binding causes a cascade of intracellular events leading to increased calcium levels and subsequent contraction.

    Calcium Oscillations and Vascular Smooth Muscle

    • Calcium oscillations regulate vascular smooth muscle contraction.
    • Basal tone is associated with low levels of calcium activity and a low frequency of calcium waves.

    Arteriolar Diameter and Flow

    • Arteriolar diameter influences blood flow between venous and arterial “bags".

    Structure of Smooth Muscle Cells

    • Arterial smooth muscle cells are spindle-shaped and long, typically measuring 100 μm in length and 5 μm in width.
    • They contain contractile proteins like actin and myosin, enabling length adjustments during contraction.

    Contractile Proteins in Smooth Muscle

    • Actin and myosin are the primary contractile proteins. Myosin structures have heavy and light chains. Actin structures are globular proteins arranged into double helices.

    Calcium and Contraction

    • Calcium triggers smooth muscle contraction via a calcium-dependent enzyme cascade involving calmodulin, MLCK, and other proteins.

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    PSL301H Lecture 5: Blood Flow 2022 PDF

    Description

    Test your knowledge on blood flow and the structure of blood vessels. Dive into the details of each type of blood vessel, including their unique characteristics and functions. This quiz covers key concepts from Silverthorn's anatomy textbooks.

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