Capillary Membrane Diffusion Processes
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Questions and Answers

What effect does increased metabolism have on interstitial concentration of chemical signals?

  • Has no effect
  • Fluctuates randomly
  • Decreases interstitial concentration (correct)
  • Increases interstitial concentration

    • Metabolic control of blood flow is a local mechanism that matches blood flow to metabolic rate.

    True

    What initiates vasodilation in a tissue?

    Accumulation of metabolic products and lack of oxygen

    Increased blood flow results in the rapid delivery of __________ to tissue cells.

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

    Match the process with its result:

    <p>Increased blood flow = Rapid removal of metabolic waste Accumulation of metabolic products = Vasodilation Decrease in oxygen levels = Increased blood flow Vasodilation = Opens more capillaries</p> Signup and view all the answers

    What happens to vascular resistance when arterioles dilate?

    <p>Vascular resistance decreases</p> Signup and view all the answers

    Which type of substances can readily diffuse through capillary walls?

    <p>Lipid-soluble substances</p> Signup and view all the answers

    Lipid-insoluble substances can diffuse directly through cell membranes.

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

    The mechanism of blood flow control uses positive feedback to match tissue needs.

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

    As tissues become more active metabolically, blood flow is __________ to regulate metabolite concentration.

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

    What is the primary route for the delivery of plasma proteins into the interstitial fluid?

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

    Lipid-insoluble substances pass through the capillary walls via the ______.

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

    Which of the following substances can easily diffuse through endothelial cell membranes?

    <p>Fatty acids</p> Signup and view all the answers

    Match the type of substance with its ability to diffuse through capillary walls:

    <p>Dissolved oxygen = Lipid-soluble Glucose = Lipid-insoluble Carbon dioxide = Lipid-soluble Amino acids = Lipid-insoluble</p> Signup and view all the answers

    Continuous capillaries have large pores that allow blood cells to pass through.

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

    What process involves the invagination of the capillary endothelial cell membrane to form vesicles?

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

    What factor is NOT mentioned as increasing filtration of water out of capillaries?

    <p>Increasing blood viscosity</p> Signup and view all the answers

    A higher capillary hydrostatic pressure always favors reabsorption of water into the capillaries.

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

    What term is used to describe the combination of hydrostatic and oncotic forces affecting water movement?

    <p>Starling forces</p> Signup and view all the answers

    The equation that quantifies the interaction of hydrostatic and oncotic forces is called the _______.

    <p>Starling equation</p> Signup and view all the answers

    Which of the following actions can decrease the osmotic tendency for water to be reabsorbed?

    <p>Decreasing protein levels in the blood</p> Signup and view all the answers

    A decrease in arteriolar resistance can result in a higher capillary hydrostatic pressure.

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

    What is the diameter range of the water-filled channels formed by endocytotic and exocytotic vesicles through endothelial cells?

    <p>50 to 80 nm</p> Signup and view all the answers

    What is the primary effect of increased central venous pressure on capillary filtration?

    <p>It raises capillary hydrostatic pressure.</p> Signup and view all the answers

    Match the following changes to their effect on capillary filtration:

    <p>Increase in arterial pressure = Increases filtration Decrease in arteriolar resistance = Increases filtration Increased protein levels = Decreases filtration Backed up venous blood = Increases filtration</p> Signup and view all the answers

    Fick's Law of Diffusion states that diffusion proceeds from an area of lower concentration to an area of higher concentration.

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

    What are the primary factors affecting the rate of diffusional exchange between capillary blood and interstitial fluid?

    <p>Concentration difference, area available for diffusion, distance over which diffusion must occur, and properties of the diffusing substance.</p> Signup and view all the answers

    The rate of diffusion of a substance depends on the concentration difference, the area available for diffusion, and the distance __________ must occur.

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

    Match the following factors with their corresponding definitions in Fick's Law of Diffusion:

    <p>Concentration difference = The difference in concentration between two areas Area available for diffusion = Total surface area of capillaries or area of clefts Distance = Distance from a tissue cell to the nearest capillary Properties of diffusing substance = Characteristics such as lipid-soluble versus lipid-insoluble</p> Signup and view all the answers

    Which type of substances can pass through the water-filled channels created by endocytotic and exocytotic vesicles?

    <p>Both lipid-soluble and lipid-insoluble substances</p> Signup and view all the answers

    Where are the water-filled channels formed from endocytosis and exocytosis typically found?

    <p>In areas where large amounts of fluid and solutes must pass, such as the gastrointestinal tract and endocrine glands.</p> Signup and view all the answers

    The size of the capillary pores directly impacts the rate of diffusion.

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

    When is blood flow through the coronary circulation highest?

    <p>During ventricular systole</p> Signup and view all the answers

    Mechanical compression does not significantly affect blood flow through the right coronary vessels during systole.

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

    What happens to left coronary blood flow during systole?

    <p>It is depressed and may even reverse momentarily.</p> Signup and view all the answers

    During ____, coronary vascular resistance decreases dramatically, allowing increased blood flow.

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

    Match the following terms with their definitions.

    <p>Ventricular Systole = Period of highest aortic pressure Diastole = Period when heart muscle relaxes Metabolic Rate = Rate of metabolism in tissue Coronary Resistance = Opposition to blood flow in coronary vessels</p> Signup and view all the answers

    What is the effect of increased heart rate and cardiac contractility during exercise on blood flow?

    <p>Increases flow but reduces diastolic time</p> Signup and view all the answers

    High coronary resistance occurs during diastole, making blood flow easier.

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

    Why do healthy coronary vessels suffice to supply blood flow even during maximal exercise?

    <p>They have sufficiently low resistance during diastole.</p> Signup and view all the answers

    Study Notes

    Lipid-soluble Substance Diffusion

    • Small, lipid-soluble substances (e.g., oxygen, carbon dioxide, fatty acids, ethanol, hormones) readily dissolve and diffuse through cell membranes of capillary endothelial cells

    Lipid-insoluble Substance Diffusion

    • Lipid-insoluble substances (e.g., ions, glucose, amino acids) cannot dissolve in cell membranes and require pores or clefts between endothelial cells for passage

    Capillary Wall Features

    • Continuous capillaries: endothelial cells form a continuous tube with tiny, water-filled pores (4 nm) between cells
      • Allows passage of water and small solutes
      • Plasma proteins and blood cells are too large to pass
    • Transcytosis: three-step process for moving plasma proteins into interstitial fluid
      1. Pinocytosis: invagination of capillary endothelial cell membrane forms a vesicle containing plasma, including proteins
      2. Vesicles cross the endothelial cell to the interstitial fluid side
      3. Exocytosis: vesicles fuse with membrane and release contents into interstitial space
    • Fenestrated capillaries: have larger pores (50-80 nm) with fine diaphragms
      • Allow passage of both lipid- soluble and -insoluble substances
      • Found in areas with high fluid and solute exchange (e.g., gastrointestinal tract, endocrine glands)

    Fick's Law of Diffusion

    • Rate of diffusion of a substance (S) depends on:
      • Concentration difference: between capillary and interstitial fluid; drives diffusion from high to low concentration
      • Area available for diffusion: total capillary surface area for lipid-soluble substances, only pore area for lipid-insoluble
      • Distance of diffusion (Δx): from tissue cell to nearest capillary; greater distance slows diffusion
      • Metabolism: increased metabolism increases diffusion rate due to higher demand and lower interstitial concentration

    Metabolic Control of Blood Flow

    • Low oxygen and high concentrations of metabolic products (e.g., K+) in tissues cause arteriole dilation, leading to:
      • Decreased vascular resistance
      • Increased blood flow
      • Relaxation of precapillary sphincters, opening more capillaries for better diffusion
      • Decreased diffusion distance between capillaries and cells
      • Increased capillary surface area for exchange
    • Results in faster delivery of oxygen and nutrients and removal of waste products
    • Mechanism involves negative feedback:
      • Accumulation of metabolic products and oxygen depletion trigger vasodilation, increasing blood flow
      • Increased blood flow removes accumulated products and delivers oxygen, restoring balance

    Starling Forces

    • Balance of hydrostatic and oncotic pressures affecting water movement across capillary walls
    • Hydrostatic pressure pushes water out of capillaries
    • Oncotic pressure pulls water into capillaries
    • Net pressure is typically small (1 mmHg), indicating near balance
      • Slight tendency for filtration
    • Starling equation accounts for water movement: water movement = Kf (filtration coefficient) x (hydrostatic pressure - oncotic pressure)

    Changes Affecting Starling Forces and Filtration

    • Increased capillary hydrostatic pressure (Pc) leads to greater filtration:
      • Increased arterial pressure
      • Decreased arteriolar resistance (dilation)
      • Increased venous pressure
      • Mechanical compression of veins (e.g., in skeletal muscle)
    • Mechanical compression can reduce blood flow despite higher perfusion pressure:
      • Left coronary vessels experience high resistance during systole due to ventricular muscle squeezing
      • Right coronary flow is less affected during systole because the right ventricle contracts less strongly
      • Adequate time during diastole allows for sufficient coronary blood flow in resting conditions
      • Exercise increases metabolic demands and heart rate, reducing diastole time
      • Healthy coronary vessels still provide sufficient blood flow during maximal exercise

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    VPSL 121 Module III Lecture 5,6 PDF

    Description

    This quiz explores the diffusion of lipid-soluble and lipid-insoluble substances across capillary membranes. It covers the features of capillary walls, including continuous capillaries and the process of transcytosis. Test your understanding of these vital biological processes related to membrane permeability.

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