The Pulmonary Circulation L4 Flashcards
What are the primary differences between pulmonary and systemic circulation?
Pulmonary circulation operates under low pressure and resistance, whereas systemic circulation functions under high pressure and resistance to pump blood throughout the body. Pulmonary vessels are thinner and more compliant, while systemic vessels are thicker to sustain higher pressures.
Explain how hypoxic pulmonary vasoconstriction works.
Hypoxic pulmonary vasoconstriction is a mechanism where pulmonary arterioles constrict in response to low oxygen levels in alveoli. This redirects blood flow to better-ventilated areas of the lungs to optimize gas exchange.
Why is the pulmonary vascular resistance lower than systemic vascular resistance?
Pulmonary vascular resistance is lower because the pulmonary vessels are more compliant and the lungs are in close proximity to the heart. This reduces the need for high pressures to move blood through the pulmonary circuit.
What is the significance of the gravitational effects on pulmonary circulation?
Gravitational effects cause blood flow to vary within the lung zones:
Zone 1 (apex): minimal flow.
Zone 2 (middle): intermittent flow.
Zone 3 (base): maximal flow. This distribution optimizes ventilation-perfusion matching for efficient gas exchange.
Describe the three zones of pulmonary blood flow.
Zone 1: No blood flow due to alveolar pressure exceeding arterial pressure.
Zone 2: Intermittent blood flow as arterial pressure exceeds alveolar pressure during systole.
Zone 3: Continuous blood flow as both arterial and venous pressures exceed alveolar pressure.
Describe the functional and structural differences between pulmonary and systemic circulations, emphasizing their adaptations for gas exchange.
Pulmonary circulation is designed for gas exchange, operating under low pressure (15 mmHg compared to systemic pressure of 120 mmHg). The vessels are thin-walled, compliant, and capable of accommodating large blood volumes with minimal resistance. These characteristics minimize the risk of fluid leakage into the alveoli, preserving the efficiency of oxygen-carbon dioxide exchange.
In contrast, systemic circulation is responsible for delivering oxygenated blood to tissues under high pressure. It features thick-walled arteries to withstand these pressures and maintain blood flow over long distances. The difference in resistance and pressure reflects the specific roles of each system.
Explain the concept of hypoxic pulmonary vasoconstriction and its significance in pulmonary circulation.
Hypoxic pulmonary vasoconstriction (HPV) is a protective mechanism where pulmonary arterioles constrict in regions of the lung with low oxygen (hypoxia). This diverts blood flow to better-ventilated alveoli, ensuring optimal oxygen uptake.
Significance: HPV maintains efficient ventilation-perfusion matching and prevents hypoxemia (low blood oxygen). However, in global hypoxia (e.g., high altitude or chronic lung diseases), widespread vasoconstriction can lead to pulmonary hypertension and right heart strain.
Discuss the factors affecting pulmonary blood flow distribution and their implications for ventilation-perfusion matching.
Gravity: Blood flow increases from apex (Zone 1) to base (Zone 3) due to hydrostatic pressure differences.
Alveolar pressure: Determines whether capillaries are compressed, limiting blood flow in certain lung regions (Zone 1).
Cardiac output: Higher output increases blood flow throughout the lung.
Implications: Proper ventilation-perfusion (V/Q) matching ensures efficient gas exchange. Mismatches can lead to hypoxemia (low blood oxygen), as seen in conditions like pulmonary embolism or chronic obstructive pulmonary disease (COPD).
Evaluate the role of pulmonary circulation in maintaining fluid balance and preventing pulmonary edema.
Operating under low pressure, reducing hydrostatic forces that can push fluid out of capillaries.
Thin-walled capillaries allow efficient gas exchange without excessive fluid leakage.
The lymphatic system removes excess fluid from the interstitial space, preventing accumulation. Pulmonary edema occurs when these mechanisms fail, such as in left heart failure or increased capillary permeability, impairing gas exchange and causing respiratory distress.
