Cardiovascular Physiology: Microcirculation
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Questions and Answers

What is the primary function of interstitial fluid hydrostatic pressure (Pif)?

  • To promote filtration
  • To increase capillary oncotic pressure
  • To regulate blood pressure
  • To drive fluid out of the interstitial space into the capillaries (correct)

    • What type of pressure is responsible for pushing fluid out of the capillaries?

  • Interstitial fluid hydrostatic pressure
  • Hydrostatic pressure (correct)
  • Capillary oncotic pressure
  • Blood pressure

    • What is the approximate pressure of the capillary venous end?

  • 20 mmHg
  • 17 mmHg (correct)
  • 10 mmHg
  • 25 mmHg

    • What is the primary function of albumin molecules in capillary fluid exchange?

    <p>To carry charged particles and attract Na ions</p> Signup and view all the answers

    What is the result of the interaction between albumin and Na ions?

    <p>A strong attraction of Na ions</p> Signup and view all the answers

    What is the primary force opposing filtration in capillary fluid exchange?

    <p>Interstitial fluid hydrostatic pressure</p> Signup and view all the answers

    What is the typical value of interstitial fluid hydrostatic pressure (Pif)?

    <p>Near zero or slightly negative</p> Signup and view all the answers

    What is the function of capillary oncotic pressure (πp)?

    <p>To pull fluid back into the capillaries</p> Signup and view all the answers

    What is the relationship between albumin and capillary oncotic pressure?

    <p>Albumin increases capillary oncotic pressure</p> Signup and view all the answers

    What is the primary plasma protein responsible for colloid osmotic pressure in the intravascular space?

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

    Which pressure favors filtration at the arterial side of the capillaries?

    <p>Capillary hydrostatic pressure</p> Signup and view all the answers

    What is the net filtration pressure (NFP) when arterial hydrostatic pressure is 35 mmHg and interstitial fluid oncotic pressure is 0 mmHg?

    <p>10 mmHg</p> Signup and view all the answers

    What is the consequence if the net filtration pressure (NFP) is negative?

    <p>Fluid is reabsorbed into the capillaries</p> Signup and view all the answers

    What condition can increase the permeability of capillary walls?

    <p>Capillary injury</p> Signup and view all the answers

    How much fluid is typically reabsorbed back into the circulation each day from the capillaries?

    <p>17 liters</p> Signup and view all the answers

    What is the role of the lymphatic system in fluid exchange?

    <p>It carries proteins and large particles away from tissues</p> Signup and view all the answers

    What does the term 'hydraulic conductance' (Kf) refer to?

    <p>The water permeability of the capillary wall</p> Signup and view all the answers

    What proportion of colloid osmotic pressure is typically exerted by albumin?

    <p>80%</p> Signup and view all the answers

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

    <p>Drain excess interstitial fluid and proteins.</p> Signup and view all the answers

    What mechanism prevents interstitial fluid and proteins from leaving the lymphatic capillaries?

    <p>The presence of one-way flap valves.</p> Signup and view all the answers

    How does the lymphatic system contribute to fluid balance in the body?

    <p>By draining excess interstitial fluid and proteins.</p> Signup and view all the answers

    What is the primary role of the lymphatic system in fat transport?

    <p>Absorbing fats from the intestines and transporting them to the blood.</p> Signup and view all the answers

    How does the lymphatic system contribute to the immune system?

    <p>Transporting foreign material to lymph nodes for immune response.</p> Signup and view all the answers

    What is the main factor responsible for the flow of lymph through the lymphatic vessels?

    <p>The contraction of smooth muscle in the lymph vessels and surrounding skeletal muscle.</p> Signup and view all the answers

    Which of the following is NOT a function of the lymphatic system?

    <p>Transporting oxygen to the tissues.</p> Signup and view all the answers

    What is the primary characteristic of edema?

    <p>An increase in interstitial fluid volume.</p> Signup and view all the answers

    Which of the following is a potential cause of edema?

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

    What is the primary function of terminal arterioles in the microcirculation?

    <p>To supply blood to capillaries</p> Signup and view all the answers

    Which statement about metarterioles is true?

    <p>They lack a continuous muscular coat.</p> Signup and view all the answers

    What regulates the entrance of blood into capillaries?

    <p>Precapillary sphincters</p> Signup and view all the answers

    How do the pressures in venules compare to those in arterioles?

    <p>Venules have lower pressure than arterioles.</p> Signup and view all the answers

    What type of blood vessel has a wall composed of a single layer of endothelial cells?

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

    What feature distinguishes the capillaries in the brain from those in the liver?

    <p>Capillaries in the brain have tight junctions limiting passage.</p> Signup and view all the answers

    Which type of capillaries allows almost all dissolved substances of plasma to pass?

    <p>Sinusoidal capillaries</p> Signup and view all the answers

    Which layer primarily constitutes the capillary walls?

    <p>Endothelial layer</p> Signup and view all the answers

    What is the role of smooth muscle fibers at the origin of capillaries from metarterioles?

    <p>To regulate capillary entrance</p> Signup and view all the answers

    What is a characteristic of an effusion?

    <p>It is an abnormal collection of fluid in a hollow space or between tissues.</p> Signup and view all the answers

    What is the main reason for fluid accumulation in congestive heart failure?

    <p>Increased blood pressure in the veins.</p> Signup and view all the answers

    Which of the following is NOT a type of edema or effusion mentioned in the text?

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

    What is the primary force that drives fluid movement out of the capillaries in congestive heart failure?

    <p>Increased capillary hydrostatic pressure</p> Signup and view all the answers

    What is the clinical application of the information regarding edema and effusion?

    <p>Diagnosing and managing congestive heart failure</p> Signup and view all the answers

    What is the term for the fluid buildup in the abdomen that is mentioned in the text?

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

    What is the mechanism by which fluid accumulates in the tissues in congestive heart failure?

    <p>The heart pumps blood too slowly, causing blood to back up and increase pressure in the capillaries.</p> Signup and view all the answers

    What is the key difference between edema and effusion?

    <p>Edema is a buildup of fluid in the tissues, while effusion is a buildup of fluid in a hollow space.</p> Signup and view all the answers

    What is the main factor contributing to the increased capillary hydrostatic pressure in congestive heart failure?

    <p>Increased blood volume in the capillaries.</p> Signup and view all the answers

    Study Notes

    Microcirculation Structure

    • The microcirculation of each organ is organized to serve the organ's specific needs
    • Each artery entering an organ branches 6-8 times before becoming small enough to be called arterioles
    • Arterioles branch 2-5 times until they become terminal arterioles that supply blood to capillaries
    • Terminal arterioles are called metarterioles
    • Metarterioles do not have a continuous muscular coat, but smooth muscle fibers encircle the vessel at intermittent points

    Precapillary Sphincter

    • The point where each true capillary originates from a metarteriole has a smooth muscle fiber that usually encircles the capillary, called a precapillary sphincter
    • The precapillary sphincter can open or close the entrance of the capillary

    Capillaries

    • Not all capillaries are always perfused with blood, it depends on metabolic needs
    • The capillary wall is composed of a single layer of endothelial cells and a thin basement membrane
    • Special types of pores occur in the capillaries of certain organs, such as the brain, liver, and kidney

    Venous Structure

    • Venules are larger than arterioles and have a much weaker muscular coat
    • The pressure is lower and allows constriction despite the weak muscle

    Capillary Fluid Exchange

    • Capillary arterial pressure = 35 mmHg, capillary venous pressure = 17 mmHg
    • Interstitial fluid hydrostatic pressure (Pif) drives fluid out of the interstitial space into the capillaries
    • Capillary oncotic pressure (πp) is also called colloid osmotic pressure, and is exerted by plasma proteins (80% by albumin), favoring reabsorption
    • Interstitial fluid oncotic pressure (πif) is determined by the interstitial fluid protein concentration and favors filtration
    • Net filtration pressure = hydrostatic pressure - oncotic pressure

    Forces Involved in Fluid Exchange

    • Hydrostatic pressure pushes fluid out of the capillaries
    • Osmotic pressure pulls fluid inside of the capillaries
    • If the result of these forces is positive, there will be a net fluid filtration across the capillaries
    • If the result is negative, there will be a net fluid reabsorption from the interstitial fluid into the capillaries

    Permeability of the Capillary Wall

    • Permeability is increased in capillary injury (e.g. toxins, burns, inflammation), which increases permeability to water
    • Hydraulic conductance (Kf) is the water permeability of the capillary wall and varies among different types of tissues

    Lymphatic System

    • The lymphatic system is an accessory route through which fluid can flow from the interstitial spaces into the blood
    • Lymphatics carry proteins and large particle matter away from the tissue spaces
    • Lymphatic capillaries possess one-way flap valves that permit interstitial fluid and protein to enter but not to leave
    • Lymphatic capillaries merge into larger lymphatic vessels/thoracic duct, and lymph flow depends on contraction of the smooth muscle in the lymph vessels and compression of the lymph vessels by activity of the surrounding skeletal muscle
    • The lymphatic system plays a key role in controlling interstitial fluid protein concentration, volume, and pressure

    Clinical Application: Edema and Effusion

    • Changes in Starling forces can influence the direction and magnitude of fluid movement
    • Edema is an increase in interstitial fluid volume (swelling)
    • Effusion is an abnormal collection of fluid in a hollow space or between tissues (e.g. pleural effusion)
    • Congestive heart failure can lead to edema or effusion due to an increase in capillary hydrostatic pressure

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