Microcirculation and Capillaries
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Microcirculation and Capillaries

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Questions and Answers

What is the primary function of microcirculation in the body?

  • Transport of hormones across the body
  • Transport of nutrients and removal of cell excreta (correct)
  • Regulation of body temperature
  • Removal of carbon dioxide from tissues

    • Which blood vessels are considered components of microcirculation?

  • Large venules and arterioles
  • Meta arterioles and capillaries (correct)
  • Aorta and vena cava
  • Veins and arteries

    • What is the typical size range of capillaries?

  • 5-10 μm (correct)
  • 1-3 μm
  • 100-150 μm
  • 10-20 μm

    • Which type of capillary allows the passage of blood cells and serum proteins?

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

    What regulates the intermittent flow of blood in capillaries?

    <p>Oxygen concentration in tissue</p> Signup and view all the answers

    What is the primary difference in composition between interstitial fluid and plasma?

    <p>Lower concentration of proteins in interstitial fluid</p> Signup and view all the answers

    What does the NFP equation stand for in the context of fluid movement?

    <p>Net Fluid Pressure</p> Signup and view all the answers

    What type of substances can pass easily through the walls of capillaries?

    <p>Only lipid-soluble substances and gases</p> Signup and view all the answers

    Which mechanism is primarily responsible for the exchange in microcirculation?

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

    What pressure at the arterial end of capillaries primarily favors filtration?

    <p>30 mm Hg</p> Signup and view all the answers

    What is the typical thickness of the basement membrane surrounding capillaries?

    <p>0.5 micrometers</p> Signup and view all the answers

    What effect does a positive interstitial fluid pressure have on capillary filtration?

    <p>It promotes reabsorption</p> Signup and view all the answers

    What is the pressure moving fluid out of the capillary at the arterial end?

    <p>41 mmHg</p> Signup and view all the answers

    How much protein does the lymphatic system recover daily?

    <p>200 gm</p> Signup and view all the answers

    Which statement regarding plasma osmotic colloid pressure is correct?

    <p>Albumin generates the vast majority of oncotic pressure</p> Signup and view all the answers

    What is the net filtration rate in the entire body?

    <p>2 ml/minute</p> Signup and view all the answers

    How is interstitial fluid composition influenced by proteoglycan filaments?

    <p>They create a gel that inhibits fluid movement</p> Signup and view all the answers

    What primarily causes hydrostatic pressure in interstitial fluid to be slightly negative?

    <p>Increased lymphatic drainage</p> Signup and view all the answers

    What role does the lymphatic system play in fluid management?

    <p>It provides an accessory route for fluid to return to blood.</p> Signup and view all the answers

    What is the primary mechanism that aids lymphatic fluid flow towards the heart?

    <p>Presence of valves in lymphatic vessels</p> Signup and view all the answers

    Which of the following best describes the Starling forces?

    <p>They involve osmotic and hydrostatic pressures influencing fluid direction</p> Signup and view all the answers

    What is a consequence of lacking lymphatic drainage?

    <p>Quick death within 24 hours</p> Signup and view all the answers

    Which pressure primarily influences the absorption of fluid into the capillary at the venous end?

    <p>Oncotic pressure of plasma</p> Signup and view all the answers

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

    <p>To drain excess interstitial fluid back into the blood</p> Signup and view all the answers

    Under which condition is fluid absorbed most effectively by venous capillaries?

    <p>When oncotic pressure of plasma exceeds pressure of interstitial fluid</p> Signup and view all the answers

    Which factor does NOT contribute to lymphatic pumping?

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

    Which of these components is NOT associated with the role of the lymphatic system?

    <p>Production of red blood cells</p> Signup and view all the answers

    Which condition is most likely to cause extracellular edema related to venous issues?

    <p>High venous pressure</p> Signup and view all the answers

    Which of the following is a determinant of lymph flow?

    <p>Pressure on lymphatics from external sources</p> Signup and view all the answers

    Which factor is NOT a cause of extracellular edema?

    <p>Decreased blood volume</p> Signup and view all the answers

    What is the role of lacteals in the lymphatic system?

    <p>Absorbing and transporting lipids</p> Signup and view all the answers

    How much protein does the lymphatic system typically drain back into the blood daily?

    <p>195 grams</p> Signup and view all the answers

    Study Notes

    Microcirculation

    • The most important function of circulation is transport of nutrients to the tissues and removal of cell excreta
    • The microcirculation is the blood flow through blood vessels smaller than 100 µm
    • Components of microcirculation are meta arterioles, arterioles, capillaries, postcapillary venules
    • The whole body has 10 billion capillaries with 500 to 700 sq meters surface area

    Capillaries

    • The smallest of a body's blood vessels, measuring 5-10 μm
    • Connect arteries and veins
    • Closely interact with tissues
    • "CAPILLARY BED" is the network of capillaries supplying an organ.

    Structure of Capillaries

    • Walls composed of a unicellular layer of endothelium
    • Surrounded by a basement membrane
    • 0.5 micrometer thick
    • Lipids soluble substances and gases can pass easily through diffusion
    • Pores or intercellular cleft 6-7 nano m represents 1/1000th of total surface area
    • Allows for the passage of water soluble molecules except for proteins
    • Plasmalemmal vesicles play a role in transporting material from one surface of capillaries to other

    Types of Capillaries

    • Continuous capillaries have a sealed epithelium and only allow small molecules, water and ions to diffuse
    • Fenestrated capillaries have openings that allow larger molecules to diffuse
    • Sinusoidal capillaries are special forms of fenestrated capillaries. They have larger openings in the epithelium allowing RBCs and serum proteins to enter

    Vasomotion

    • Intermittent flow of blood in the capillaries due to intermittent constriction and dilation of regional arterioles
    • Oxygen concentration in tissue is the most important factor regulating circulation

    Capillary Functions

    • Exchange of water and nutrients between blood and interstitium
    • Mechanisms of exchange: diffusion, filtration (bulk flow)

    Diffusion

    • Principal mechanism of micro vascular exchange
    • Rate of diffusion is directly proportional to change in concentration, surface area, solubility
    • Rate of diffusion is inversely proportional to thickness of membrane, molecular weight
    • Lipids soluble – through endothelial cell membrane.- Water soluble – through intercellular pores
    • Size Dependent

    Interstitium

    • Spaces between the cells
    • Fluid in this space is interstitial fluid
    • Makes up 2/3rd of ECF, 1/6th of TBW
    • Composed of collagen fibers, proteoglycan filaments

    Interstitial Fluid

    • Interstitial fluid---same composition as of plasma except for lower concentration of proteins
    • Composed of interstitial gel and free fluid
    • Gel--- fluid that is entrapped in the small spaces among proteoglycan filaments. Difficult to flow easily
    • Free fluid**----fluid that is free from proteoglycan. Can flow easily. In the form of free fluid vesicle and rivulets

    Filtration and Reabsorption

    • Filtration is the movement of fluid from plasma into interstitium
    • Reabsorption is the movement of fluid from interstitium to plasma
    • Starling Forces are Hydrostatic and osmotic forces that determine direction of flow

    Starling Forces

    • NFP= Pc – Pif –Πp+ Πif

    Capillary Hydrostatic Pressure

    • Pressure in capillaries that favors the outward fluid movement
    • At arterial end : 30 mm Hg
    • At venous end : 10 mm Hg
    • The gradient favors filtration at arterial end and reabsorption at venous ends
    • Mean capillary pressure is sum of two 17 mmHg

    Interstitial Fluid Hydrostatic Pressure

    • Slightly negative
    • Promotes filtration
    • Intrapleural space -8mmHg
    • Epidural space -4 to -6mmHg
    • Average pressure in subcutaneous interstitial fluid is -3mmHg
    • Due to pumping of fluid by lymphatic system
    • Rises if the interstitial fluid volume increases e.g edema
    • Positive pressure prevents filtration from capillaries

    Plasma Osmotic Colloid Pressure

    • Osmotic pressure within the capillary is principally determined by plasma proteins that are relatively impermeable
    • Referred to as the "oncotic" pressure
    • Tends to favor reabsorption
    • Average value 28mmhg
    • 19 mm hg comes from protein
    • 9 mm hg by DONNAN effect i.e.Osmotic pressure exerted by sodium potassium and other ions held in plasma by proteins
    • Albumin generates about 70% of the oncotic pressure
    • Increases along the length of the capillary

    Interstitial Fluid Colloid Osmotic Pressure

    • Proteins cannot pass through endothelium into interstitium
    • Only a very small amount leaks through pores
    • 3gm/dl of protein exerts a pressure of 8 mmHg
    • Favors filtration of fluid

    Movement of Fluid at Arterial End of Capillary

    • Pressures moving fluid out of the capillary:
      • Capillary pressure 30
      • Pressure of interstitial fluid 3
      • Oncotic pressure of ISF 8 41
    • Pressures moving fluid into the capillary:
      • Oncotic pressure of plasma 28
    • Together 41-28=13 mmHg in direction out of the capillary

    Movement of Fluid at Venous End of Capillary

    • Pressures going out of the capillary:
      • Capillary pressure 10
      • Pressure of interstitial fluid 3
      • Oncotic pressure of ISF 8 21
    • Pressures going into the capillary:
      • Oncotic pressure of plasma 28
    • Together 28-21=7 mmHg in direction into the capillary.

    Movement of Fluid Throughout Capillary

    • Pressures going out of the capillary: - Mean Capillary pressure 17.3
      • Pressure of interstitial fluid 3 -Oncotic pressure of ISF 8 28.3
    • Pressures going into the capillary:
      • Oncotic pressure of plasma 28
    • Together 28-28.3= 0.3 mmHg in direction out of the capillary

    Net Filtration

    • Reabsorption pressure is considerably less than filtration pressure
    • Venous capillaries are more numerous and more permeable than arterial
    • Capillaries at their venous ends absorb 9/10th of fluid filtered at arterial end
    • Remaining is absorbed by lymphatic
    • Normal rate of net filtration ( 0.3 mm Hg ) in entire body is only 2 ml / minute

    Lymphatic System

    • Provide accessory route through which fluid flow from interstitial space to blood
    • Returning albumin and other interstitial macromolecules to the circulatory system
    • Recovers 200 gm proteins daily
    • Without lymphatic drain we would die in 24 hrs
    • Normal lymph flow is 2L/day for entire body

    Mechanism of Lymph Flow

    • Lymphatic fluid is pumped out of the tissues by contraction of large lymph vessels and skeletal muscle
    • Flow towards the heart because of presence of valves in vessels
    • This fluid is then transported to progressively larger lymphatic vessels culminating in the right lymphatic duct (for lymph from the right upper body) and the thoracic duct (for the rest of the body); these ducts drain into the circulatory system at the right and left subclavian veins.

    Functions of the Lymphatic System:

    • Carries excess of interstitial fluid from interstitium into the blood. Rate of lymph flow is more than 3 liters/day. This amount is drained by lymphatic system.
    • Drains proteins and electrolytes from Interstitial space into the lymphatic system. Lymphatic system drain 195 grams of blood proteins from interstitium back into the blood.
    • Provides lymphocytes and antibodies into the circulation.
    • Removes bacteria and other microorganisims from the tissues.
    • Lacteals are involved in the absorption and transport of lipids.
    • Many large enzymes which are produced in the tissues get entry into the circulation through lymphatic system like histaminases and lipase.
    • It maintains the negative interstitial fluid hydrostatic pressure.

    Determinants of Lymph Flow

    • The degree of activity of the lymphatic pump
      • smooth muscle filaments in lymph vessel cause them to contract
      • external compression also contributes to lymphatic pumping
    • Pressure on Lymphatics from outside:
      • Skeletal Muscle Contraction
      • Movements of different parts of body
      • Presure by objects which come in contact on the outer surface of the body
      • Pulsations of near by arteries

    Factors Controlling the Formation of Tissue Fluid

    • Starling Forces
    • Capillary permeability
    • Lymphatic obstruction

    Causes of Extracellular Edema

    • Increased capillary pressure
      • Excessive kidney retention of salt and water
        • Acute or chronic kidney failure
        • Mineralocorticoid excess
      • High venous pressure and venous constriction
        • Heart failure
        • Venous obstruction
        • Failure of venous pumps
          • Paralysis of muscles
          • Immobilization of parts of the body
          • Failure of venous valves
      • Decreased arteriolar resistance
        • Excessive body heat
        • Insufficiency of sympathetic nervous system
        • Vasodilator drugs
    • Increased capillary permeability
      • Inflammation
      • Toxins
      • Bacterial infections
      • Hypoxia
    • Decreased lymphatic drainage
      • Lymphatic obstruction by tumors
      • Lymphedema
      • Surgical removal

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    This quiz covers the essential aspects of microcirculation, focusing on the structure and function of capillaries. Discover how these tiny blood vessels play a critical role in nutrient transport and excretion. Test your knowledge on the components and characteristics of microcirculation.

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