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20 Cards in this Set
- Front
- Back
1. List and describe the components and organization of the pulmonary circulation
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a. Pulmonary artery
i. Branch with airways 1. Mesh of capillaries at respiratory bronchioles a. Pulmonary venules i. Pulmonary veins |
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Describe the hemodynamic characteristics of the pulmonary circulation, including
typical mean internal pressures, blood flow and vascular resistance. |
• Pulmonary circulation is high flow, the pressure is very low (in contrast to the system pressure; 15 vs. 100)
• This means the right ventricle doesn’t have to work as hard • Additionally, there is less smooth muscle in pulmonary circulation o You don’t need to direct the blood to different organs, just need to have a thin sheet of blood across alveoli, so you don’t need to redirect the blood |
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. Explain why pulmonary capillaries are considered ‘alveolar vessels’. Explain why
these vessels can collapse or distend depending on the values of internal capillary pressure and alveolar pressure. |
• Capillaries are sensitive to alveolar pressure
o If it is great enough, the capillaries can be squeezed shut o If the internal capillary pressure is greater than the alveolar pressure, the capillary will be distended o Thus the capillary is sensitive to the amount of alveolar gas This is why they are referred to as alveolar vessels |
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List the pulmonary vessels that are considered to be ‘extra-alveolar’ vessels.
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• The veins are not subject to alveolar pressure
o Making them extra-alveolar These are the pulmonary arteries and veins • Instead, they are subject to radial traction (as the lung expands, it pulls open the veins to increase their caliber) |
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Describe the dependence of the caliber of the extra-alveolar vessels on lung volume.
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• Alveolar vessels (capillaries)
o Caliber determined by balance between internal and alveolar pressures • Extra-alveolar vessels (pulmonary artery and vein) o Caliber determined by lung volume |
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How does resistance in pulmonic vasculature differ from systemic?
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• Pulmonary vascular resistance is 1/10th of the system vascular resistance
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Describe how pulmonary vascular resistance changes with increases in pulmonary
arterial or venous pressure and cardiac output. |
• As you increase pulmonary arterial/venous pressure you decrease pulmonary vascular resistance
o This is due to increased cardiac output o THUS: Increased cardiac output or pulmonary arterial/venous pressure will DECREASE pulmonary vascular resistance |
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• What are the two things that underlie the reduced pulmonary vascular resistance?
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o Recruitment (open more capillaries)
o Distension (distend the already open capillaries) |
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Describe and explain the variation in pulmonary vascular resistance with changes in
lung volume. |
o At low lung volume
The extra alveolar vessels aren’t well expanded (the lung isn’t so no traction) Thus they are the main site of vascular resistance o At high lung volume The extra alveolar vessels are open due to radial traction (thus their resistance is NOT limiting) But now the alveoli are expanded, which is compressing (it’s actually a stretching, but w/e it acts to pinch them) the capillaries • Now this is the site of resistance |
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Describe and explain the variation in blood flow from lung apex to lung base in an
upright lung at rest. |
• Blood flow at the base of the lung is much greater than at the apex
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discuss the blood flow, alveolar pressure, venous pressure and arteriole pressure in ZONE 1
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• At the top of the lung, ZONE 1
o The blood flow is very low o The alveoli pressure is greater than arteriole pressure, this collapses the capillaries PA>Pa>Pv VESSELS COLLAPSED |
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discuss the blood flow, alveolar pressure, venous pressure and arteriole pressure in ZONE 2
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• In the middle of the lung, ZONE 2
o Some of the capillaries are open, arteriole pressure is greater than the alveoli o So the blood flow is determined by the pressure difference between the alveolar pressure and the capillaries o Venous pressure plays NO ROLE HERE Pa>PA>no role of venous pressure SOME VESSELS OPEN |
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discuss the blood flow, alveolar pressure, venous pressure and arteriole pressure in ZONE 3
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o Arteriole and venous pressure are greatest here
o You will see distension of the capillaries o Venous pressure now (as opposed to alveolar) is what is determining the rate of flow Pa>Pv>PA a-v difference important |
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Explain the
mechanism by which hypoxic vasoconstriction is thought to occur. |
• Pulmonary vasoconstriction occurs in hypoxia
• As alveolar PO2 is reduced, blood flow decreases due to vasoconstriction o This is hypoxic vasoconstriction • You have K+ channels that are sensitive to O2, when it drops, the channels close o You get depolarization of vascular smooth muscle Leads to contraction, and thus vasoconstriction • Not sensitive to arteriole, only alveolar |
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Explain why
hypoxic vasoconstriction is useful |
o Normally this mechanism is used to direct blood away from under-ventilated areas (such as in obstruction)
o This limits the amount of pulmonary shunt there is It redirects the blood to better areas of the lung |
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Explain why
hypoxic vasoconstriction is problematic |
o High altitude
Less O2 in atmosphere Alveolar O2 in lung is much lower • Get more generalized hypoxic vasoconstriction o Thus the blood has nowhere to go It backs up into the pulmonary artery • Get pulmonary hypertension and edema o HAPE: high altitude pulmonary edema o COPD Same idea that there is an inequality in gas exchange generalized in the lung • Mechanism basically works the same as above |
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What is HAPE?
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high altitude pulmonary edema
-due to hypoxic vasoconstriction -get back up of fluid (b/c whole lung is constricted) -will back up into pulmonary artery and leak out |
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Explain why keeping the alveoli dry is essential for efficient gas exchange
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• If you have a wet alveoli, you will decrease gas exchange (increase surface tension-->decrease compliance)
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List the pressures which determine the extent of fluid leakage from the pulmonary capillaries (that will play a role in increasing/decreasing surface tension)
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• Pressure pushing fluid out of capillaries
o Hydrostatic pressure and surface tension (trying to suck water out of capillary) • Pressure pushing on the capillary to keep it out of the alveoli o Alveolar pressure (trys to push fluid back into the capillaries) o Colloid osmotic pressure (COP!) |
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. Describe how fluid that leaks out of pulmonary capillaries is removed from the
interstitial space. Describe what happens to leaked fluid in the early and late stages of pulmonary edema. |
• Lymphatics are in the interstitial space
o They drain the fluid away • If the lymphatics are blocked o Interstitium will engorge (early edema) Fluid can then cross into the alveoli and mess with gas exchange (late edema) |