Pulmonary Circulation Quiz
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Questions and Answers

What is the average diameter of pulmonary capillaries?

  • 8 μm
  • 4 μm
  • 10 μm
  • 6 μm (correct)

    • Which of the following statements is true regarding red blood cells (RBCs) passing through pulmonary capillaries?

  • RBCs do not engage in gas exchange until they exit the lungs.
  • RBCs retain their shape while passing.
  • RBCs must change shape slightly as they pass through. (correct)
  • RBCs pass through only one pulmonary capillary at a time.

    • What initiates gas exchange in pulmonary circulation?

  • At the alveoli exclusively.
  • In smaller pulmonary arterial vessels. (correct)
  • Only at the level of capillaries.
  • Along the entire length of the pulmonary arteries.

    • What influences changes in pulmonary vascular resistance (PVR)?

    <p>Neural and humoral influences.</p> Signup and view all the answers

    Which of the following components is NOT part of the pulmonary capillary structure as described?

    <p>Arterial smooth muscle cell</p> Signup and view all the answers

    What is the primary function of the pulmonary system?

    <p>Facilitating gas exchange between environmental air and the circulatory system</p> Signup and view all the answers

    Which factor does NOT influence the diffusion rate of gases in the lungs?

    <p>Type of muscle fibers present in the lungs</p> Signup and view all the answers

    What occurs at the surface of the alveoli?

    <p>Diffusion of oxygen from the air into pulmonary arterioles</p> Signup and view all the answers

    Hypoxic pulmonary vasoconstriction primarily serves to:

    <p>Redirect blood flow away from poorly ventilated areas</p> Signup and view all the answers

    What anatomical feature of the lungs is essential for adequate gas exchange?

    <p>Alveolar surface area</p> Signup and view all the answers

    Which statement about CO2 and O2 diffusion in the lungs is true?

    <p>O2 diffusion is dependent on the total alveolar surface area.</p> Signup and view all the answers

    What significant effect does increased lung volume have on pulmonary vascular resistance?

    <p>It decreases pulmonary vascular resistance.</p> Signup and view all the answers

    Elevated intravascular pressures generally lead to:

    <p>Increased pulmonary vascular resistance.</p> Signup and view all the answers

    What characterizes the arterial circuit compared to systemic vessels?

    <p>Thinner walls and larger diameter</p> Signup and view all the answers

    Where does the venous circuit start in the pulmonary circulation?

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

    How much blood is typically found in the pulmonary circulation per square meter of body surface area?

    <p>250-300 mL/m2</p> Signup and view all the answers

    What is the role of lymphatics in the pulmonary circulation?

    <p>To maintain a dry alveolar membrane</p> Signup and view all the answers

    How long does it typically take for a red blood cell to travel through the pulmonary circulation?

    <p>4-5 seconds</p> Signup and view all the answers

    Which structure drains into the left atrium in the venous circuit?

    <p>Pulmonary veins</p> Signup and view all the answers

    What feature makes pulmonary veins different from systemic veins?

    <p>Thinner walls and greater compliance</p> Signup and view all the answers

    In terms of structure, what role does the alveolar septum play in the pulmonary circulation?

    <p>It facilitates gas exchange by holding capillaries</p> Signup and view all the answers

    What condition can lead to hypoxia during exercise?

    <p>Impaired movement of O2 from alveoli to pulmonary vasculature</p> Signup and view all the answers

    Which of the following describes the function of the bronchial circulation?

    <p>Supplies oxygenated blood to lung structures</p> Signup and view all the answers

    What happens to pulmonary blood flow during exercise?

    <p>It is equal to approximately 3.5 L/min/m2</p> Signup and view all the answers

    What impact does lung fibrosis have on diffusion?

    <p>Decreases surface area for gas exchange</p> Signup and view all the answers

    Which of the following best explains V/Q mismatching?

    <p>The ratio of blood flow to air flow in the lungs</p> Signup and view all the answers

    Which part of the pulmonary blood flow participates in gas exchange?

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

    What is the blood flow percentage of the bronchial circulation compared to the left ventricle output?

    <p>2%</p> Signup and view all the answers

    What happens to oxygenation when pulmonary blood flow is blocked, as in a pulmonary embolus?

    <p>Oxygenation is supplied solely by bronchial flow</p> Signup and view all the answers

    What is typically observed in the pulmonary circulation in terms of pressure?

    <p>It is noteworthy for low pressure</p> Signup and view all the answers

    What does diffusion limitation refer to in the context of pulmonary function?

    <p>Impaired oxygen transfer from alveoli to blood</p> Signup and view all the answers

    What primarily regulates pulmonary blood flow?

    <p>Changes in arteriolar smooth muscle tone</p> Signup and view all the answers

    What is the main factor influencing hypoxic vasoconstriction in pulmonary circulation?

    <p>Partial pressure of O2 in alveolar gas</p> Signup and view all the answers

    What occurs as an adaptive mechanism during hypoxia in the lungs?

    <p>Pulmonary vasoconstriction to poorly ventilated regions</p> Signup and view all the answers

    What happens to pulmonary blood flow in widespread lung disease?

    <p>The compensatory mechanism of directing blood fails</p> Signup and view all the answers

    What mechanism allows O2 to affect vascular smooth muscle in pulmonary arterioles?

    <p>High lipid solubility of O2</p> Signup and view all the answers

    How does normal PAO2 affect arteriolar smooth muscle cells?

    <p>It induces vaso-relaxation and dilation</p> Signup and view all the answers

    What formula defines pulmonary vascular resistance (R)?

    <p>R = P1 - P2 / Q</p> Signup and view all the answers

    Which of the following statements is true regarding hypoxic vasoconstriction?

    <p>It does not affect overall pulmonary vascular resistance</p> Signup and view all the answers

    Study Notes

    Pulmonary Circulation Physiology

    • Pulmonary circulation facilitates gas exchange between the environment and the circulatory system
    • Oxygen (O2) is inhaled, diffuses into the blood, enters systemic circulation, and produces ATP for cellular energy
    • Carbon dioxide (CO2) and metabolic byproducts are exhaled
    • Lungs contain alveoli (air sacs), approximately 300 million in healthy lungs
    • Gas diffusion occurs at the alveoli surface into pulmonary arterioles

    Learning Objectives

    • Understand bronchial and pulmonary circulation, anatomy, and physiology
    • Compare and contrast pulmonary and systemic circulation
    • Describe effects of lung volume on pulmonary vascular resistance
    • Explain effects of elevated intravascular pressures on pulmonary vascular resistance
    • Identify neural and humoral factors that influence pulmonary vascular resistance
    • Describe interrelationships of alveolar, pulmonary arterial, and pulmonary venous pressure, and their effects on pulmonary blood flow
    • Describe hypoxic pulmonary vasoconstriction and its role in localized and widespread alveolar hypoxia

    Diffusion

    • Diffusion is passive movement from higher to lower concentration
    • Ventilation moves air into and out of the lungs
    • Oxygen is high in concentration in the lung and lower in pulmonary capillaries
    • Carbon dioxide is lower in concentration in the lung and higher in pulmonary capillaries
    • Diffusion rate depends on gas solubility, density, and available surface area in the lung

    Diffusion (part 2/4)

    • Carbon dioxide is highly soluble, so oxygen is the primary limiting factor in diffusion
    • Total available surface area is a key factor in pulmonary pathology
    • Reduced alveolar surface area relative to arteriolar perfusion decreases oxygen diffusion into the blood, potentially causing hypoxia

    Diffusion (part 3/4)

    • Diffusion limitation occurs when oxygen movement from alveoli to pulmonary blood vessels is impaired
    • Lung fibrosis and parenchymal destruction reduce alveolar surface area
    • Perfusion is blood flow through the lungs
    • Ventilation/perfusion ratio (V/Q) measures gas exchange efficiency in the lungs
    • V/Q mismatching often coexists with diffusion abnormalities, prevalent during exercise

    Diffusion (part 4/4)

    • Resting blood flow in lung arterioles is slow, allowing sufficient diffusion time
    • Exercise increases cardiac output, reducing oxygenation time and possibly causing transient hypoxia
    • Lung fibrosis and COPD are examples of limited diffusion diseases

    Pulmonary Circulation

    • The lung receives blood flow via bronchial and pulmonary circulation
    • Bronchial blood flow is part of systemic circulation, supplying oxygenated blood to the lungs
    • Pulmonary blood flow carries deoxygenated blood to the lungs for oxygenation and returns oxygenated blood to the heart

    Bronchial Circulation

    • Bronchial arteries arise from the aorta, or intercostal arteries
    • They supply arterial blood to the tracheobronchial tree and terminal bronchioles
    • They also supply blood to hilar lymph nodes, visceral pleura, pulmonary vessels, vagus, and esophagus
    • Lung tissues distal to terminal bronchioles receive oxygen directly through diffusion from alveolar air and nutrients from mixed venous blood in pulmonary circulation
    • Bronchial blood flow accounts for about 2% of the left ventricle output
    • Bronchial artery pressure is similar to other systemic arteries, but higher than pulmonary artery pressure

    Blood Flow to the Lung

    • Histologists have identified anastomoses between bronchial and pulmonary capillaries and arteries
    • These connections are generally minor in healthy individuals but can be important in pathological conditions
    • Blood flow to a portion of the lung can be impacted by either bronchial or pulmonary occlusion, with bronchial flow to that area increasing

    Pulmonary Circulation (Part 2)

    • Pulmonary blood flow undergoes gas exchange within pulmonary capillaries
    • Blood flow equals approximately 100% of left ventricular output
    • Approximately 3.5 L/min/m² of blood flow at rest with 280 billion pulmonary capillaries supplying ~300 million alveoli
    • One arteriole and venule supply and drain a pulmonary lobule

    Pulmonary Circulation: A Low-Pressure System

    • Diagram illustrating the pulmonary circulation and its low-pressure system flow

    Pulmonary Circulation Divisions

    • Pulmonary circulation is divided into 3 parts: arterial circuit, venous circuit, and lymphatics

    Arterial Circuit

    • Originates from the main pulmonary artery, arising from the right ventricle
    • It runs a short course (~5cm), then divides into the right and left main branches further dividing into smaller arteries, arterioles, and capillaries
    • The vessels are thinner than systemic vessels (1/3 thickness) and have a larger diameter, making them more distensible and compliant

    Venous Circuit

    • Venules drain capillaries forming smaller veins ultimately connecting to the main pulmonary veins, draining into the left atrium
    • Pulmonary veins are also thinner and more distensible than systemic veins, accommodating more blood due to greater compliance

    Lymphatics

    • Lymphatics are crucial in maintaining a dry alveolar membrane, preventing the accumulation of tissue fluid around the pulmonary circulation
    • They are located near terminal bronchioles
    • They drain mediastinal lymphatics and ultimately empty into the right lymphatic duct

    Pulmonary Veins and Arteries

    • Diagram showing the pulmonary veins and arteries within the lungs

    Pulmonary Vascular Resistance

    • PVR is calculated as (MPAP-MLAP)/PBF, which is equal to the cardiac output, reflecting the resistance to flow in the pulmonary vascular system

    Pulmonary Vascular Resistance (Part 2)

    • Pulmonary blood flow is pulsatile and can be turbulent
    • Pulmonary circulation is distensible and compressible
    • Complex branching structure of the pulmonary circulation impacting the pressure gradient
    • Mean left atrial pressure might not accurately represent downstream pressure in various lung conditions

    Pulmonary Vascular Resistance (Part 3)

    • Right and left ventricular outputs must be approximately equal for prolonged stability preventing fluid buildup in the lung or periphery
    • Given a drop in pressure across systemic and pulmonary circulation of about 98 mmHg vs 10 mmHg for the respective systems, pulmonary vascular resistance is ~1/10th of systemic vascular resistance

    Pulmonary Vascular Resistance (Part 4)

    • Low resistance in pulmonary circulation relates to thinner walls with less vascular smooth muscle, offering greater distensibility than systemic circulation

    Distribution of Pulmonary Vascular Resistance

    • Pressure distribution of the pulmonary vasculature is evenly distributed throughout the pulmonary arteries, capillaries, and veins
    • Pulmonary vasculature differs from systemic vasculature by uneven pressure distribution across the lung areas

    Distribution of Pulmonary Blood Flow

    • Blood flow in the lungs is unevenly distributed and influenced by gravity
    • Supine position results in a more uniform distribution
    • Upright positions exhibit the lowest flow at the apex and highest at the base due to gravitational influence on hydrostatic blood pressure

    Zone 1 Distribution of Pulmonary Blood Flow

    • Gravity-dependent arterial pressure can be lower than alveolar pressure at the lung apex
    • This compression can cause capillary closure, although perfusion still occurs at low flows

    Zone 2 Distribution of Pulmonary Blood Flow

    • Higher arterial pressure than alveolar pressure due to gravity's effect, with blood flow driven by the difference between arterial pressure and alveolar pressure, not arterial vs venous, unlike systemic blood flow
    • Capillary compression isn't a concern

    Zone 3 Distribution of Pulmonary Blood Flow

    • Gravity-dependent increased arterial and venous pressure, and both are higher than alveolar pressure
    • Blood flow is driven by the difference between arterial and venous pressure

    Common Pathologies of the Pulmonary Circulation

    • Pulmonary edema: any disturbance in the pulmonary circulation causing fluid accumulation in alveoli and respiratory distress; causes can be cardiogenic or non-cardiogenic
    • Pulmonary embolism: dislodged clot causing ischaemia and potential lung parenchyma infarction due to impaired gas exchange; common origin is a deep vein thrombosis
    • Pulmonary hypertension: elevation of MPAP above 25mmHg, leading to impaired gas exchange and exertional dyspnea
    • Pleural effusion: accumulation of fluid in the pleural space leading to pleuritic chest pain and respiratory distress

    Conclusion

    • Compared to systemic arteries, pulmonary arteries have significantly less vascular smooth muscle, resulting in lower resistance to blood flow due to the lower vascular transmural pressure gradient
    • Passive factors play a more prominent role in pulmonary vascular resistance than neural and humoral factors in contrast to those in systemic circulation
    • PVR typically decreases in relation to increase in pulmonary blood flow, pulmonary artery pressure, left atrial pressure, and pulmonary capillary blood volume due to vessel distention
    • Blood flow in lower lung regions is typically more ample than in the upper regions
    • Alveolar hypoxia or hypercapnia causes constriction of pre-capillary vessels diverting blood away from poorly ventilated regions of the lungs
    • "Physiology" by Linda S. Costanzo (6th Edition) is recommended for further study

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    Pulmonary Circulation Physiology PDF - Feb 2021

    Description

    Test your knowledge on the anatomy and physiology of pulmonary circulation. This quiz covers key concepts such as the diameter of pulmonary capillaries, gas exchange initiation, and factors influencing pulmonary vascular resistance. Answer questions to deepen your understanding of the pulmonary system.

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