1.5 Microcirculation and Capillary Exchange
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Questions and Answers

What is the typical internal diameter range of arterioles?

  • 10 to 15 micrometers (correct)
  • 6 to 7 nanometers
  • 4 to 9 micrometers
  • 0.5 micrometers

    • Which of these structures has a pre-capillary sphincter?

  • Arterioles (correct)
  • Capillaries
  • Arteries
  • Veins

    • What is the typical thickness of a capillary wall that allows for rapid diffusion?

  • 5 to 9 micrometers
  • 6 to 7 nanometers
  • 0.5 micrometers (correct)
  • 10 to 15 micrometers

    • Which of the following structures have pores called intracellular clefts?

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

    What is the approximate uniform spacing of the intercellular clefts in capillaries?

    <p>6 to 7 nanometers (A)</p> Signup and view all the answers

    In which organ are the intercellular clefts the widest?

    <p>Liver (D)</p> Signup and view all the answers

    What causes the intermittent flow of blood through capillaries?

    <p>Contractions of arterioles and pre-capillary sphincters (C)</p> Signup and view all the answers

    What is the most important factor affecting the opening and closing of arterioles?

    <p>Concentration of oxygen (C)</p> Signup and view all the answers

    What is a primary factor that directly influences the diffusion rate of a substance across a capillary membrane?

    <p>The molecular weight of the substance (D)</p> Signup and view all the answers

    What is a defining characteristic of the interstitial space that impacts fluid flow?

    <p>The presence of collagen, fiber bundles, and proteoglycan filaments forming a tissue gel (C)</p> Signup and view all the answers

    Which of the following is NOT one of the Starling forces that determine fluid movement across the capillary membrane?

    <p>Lymphatic flow rate (D)</p> Signup and view all the answers

    How does a positive net filtration pressure typically affect fluid movement across capillaries?

    <p>It results in fluid filtration from the capillaries. (A)</p> Signup and view all the answers

    What is the typical relationship between filtration and reabsorption in capillaries under normal conditions?

    <p>Filtration at the arterial end is almost equal to reabsorption at the venous end. (D)</p> Signup and view all the answers

    What is the primary function of the lymphatic system in relation to interstitial fluid?

    <p>Draining excess fluid from the interstitial spaces back into the blood. (A)</p> Signup and view all the answers

    What is the average amount of fluid, in liters, that is returned to the lymphatic system per day?

    <p>2 - 3 (C)</p> Signup and view all the answers

    Which of these processes can lead to increased lymph flow?

    <p>Increased interstitial fluid pressure (C)</p> Signup and view all the answers

    What causes the pumping action of lymphatics in the tissues?

    <p>External compression and negative interstitial fluid pressure. (A)</p> Signup and view all the answers

    What is the approximate ratio of water diffusion, across the capillary membrane, compared to the rate of capillary blood flow?

    <p>80 times greater (B)</p> Signup and view all the answers

    Flashcards

    Diffusion

    The movement of molecules from an area of high concentration to an area of low concentration across a membrane.

    Membrane Permeability

    The ability of a substance to pass through a membrane.

    Capillary Hydrostatic Pressure

    The pressure exerted by the fluid within a capillary.

    Interstitial Fluid Hydrostatic Pressure

    The pressure exerted by the fluid surrounding a capillary.

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    Plasma Colloid Osmotic Pressure

    The pressure exerted by proteins in the blood, pulling water into the capillary.

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    Interstitial Fluid Colloid Osmotic Pressure

    The pressure exerted by proteins in the interstitial fluid, pulling water out of the capillary.

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    Net Filtration Pressure

    The net force driving fluid movement across a capillary membrane.

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    Filtration

    The movement of fluid from the capillaries into the interstitial space.

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    Reabsorption

    The movement of fluid from the interstitial space back into the capillaries.

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    Lymphatic System

    A system of vessels that collects excess fluid from the interstitial space and returns it to the blood.

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    Capillaries

    Tiny blood vessels that connect arterioles and venules, facilitating exchange of nutrients and waste products between blood and tissues.

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    Microcirculation

    The microscopic circulation of blood within an organ, tailored to the specific needs of that organ.

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    Arterioles

    Small blood vessels that branch off from arteries, characterized by a muscular wall and a diameter of 10-15 micrometers.

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    Capillaries

    Small blood vessels that connect arterioles and venules, characterized by a thin wall and a diameter of 4-9 micrometers.

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    Intercellular Clefts

    Small openings between cells in the capillary wall that allow for the passage of fluids and small molecules.

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    Vessel Motion

    The intermittent flow of blood through capillaries, controlled by the opening and closing of precapillary sphincters.

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    Precapillary Sphincter

    A ring of smooth muscle that controls the flow of blood into a capillary.

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    Diffusion Through Capillary Membrane

    The process by which substances move between the blood in capillaries and the surrounding tissues.

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    Study Notes

    Microcirculation

    • Arteries entering an organ branch 6-8 times into arterioles (10-15 μm diameter).
    • Arterioles branch 2-5 times into capillaries (5-9 μm diameter).
    • Arterioles are highly muscular; arterioles have intermittent smooth muscle.
    • Precapillary sphincters regulate capillary blood flow. Capillaries (4-9 μm diameter) have thin walls (0.5 μm) for rapid diffusion.
    • Capillary walls have intracellular clefts (6-7 nm spacing) enabling fluid and small molecule passage.
    • Brain capillaries have tight junctions restricting passage to small molecules (water, O2, CO2).
    • Other capillary types have variable permeability (e.g., GI tract, kidney).

    Capillary Exchange

    • Blood flow through capillaries is intermittent, regulated by arteriole and precapillary sphincter contraction.
    • Oxygen concentration in tissues is a key regulator of capillary sphincter opening/closing.
    • Diffusion is the primary mechanism for substance exchange between plasma and interstitial fluid.
    • Lipid-soluble molecules (e.g., O2, CO2) diffuse directly through cell membranes.
    • Water-soluble substances pass through intracellular clefts.
    • Diffusion rate depends on substance's molecular weight and concentration gradient.
    • Water diffuses much faster than blood flow.

    Interstitial Fluid

    • Interstitial fluid (ISF) fills spaces between cells, constituting about 1/6 of the body's total volume.
    • ISF is a tissue gel containing collagen fibers and proteoglycans, creating a viscous environment.
    • Fluid movement across capillary walls is governed by Starling forces.

    Starling Forces

    • Capillary hydrostatic pressure (CHP): 17 mmHg, pushes fluid outward.
    • Interstitial fluid hydrostatic pressure (IFHP): -3 mmHg, opposes outward flow.
    • Plasma colloid osmotic pressure (PCOP): 28 mmHg, draws fluid inward.
    • Interstitial fluid colloid osmotic pressure (IFCOP): 8 mmHg, draws fluid outward.
    • Net filtration pressure determines fluid movement. Positive net pressure causes filtration; negative net pressure causes reabsorption.
    • Normal conditions result in slightly positive net pressure, balancing filtration and reabsorption amounts.

    Lymphatic System

    • The lymphatic system is an accessory pathway for fluid return to the blood.
    • Lymphatic capillaries collect approximately 2-3 liters of interstitial fluid daily.
    • This fluid, often containing nutrients (esp. fats) and other substances, is returned from interstitial spaces to the blood.
    • Factors increasing interstitial pressure increase lymphatic flow.
    • External compression forces open lymphatic valves to facilitate movement and return interstitial fluid.

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    Description

    This quiz explores the intricate processes of microcirculation and capillary exchange in the human body. Understand the structural characteristics of arterioles, capillaries, and how they facilitate the exchange of substances crucial for tissue health. Test your knowledge on the regulatory mechanisms involved in blood flow and exchange.

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