Perfusion of the Lung and the Alveolar Gas-Blood interface

Why is pulmonary circulation a low-pressure system?

lungs have low vascular resistance, so blood can flow through them without high pressure

What is the mean pulmonary artery pressure?

14mmhg

Why is low pulmonary pressure important?

prevents pulmonary edema

What happens to pulmonary blood pressure as blood moves through the lungs?

decreases from pulmonary artery to capillaries to left atrium

What is vessel distension?

blood vessels widen when pressure increases

What is vessel recruitment?

less used capillaries open to carry more blood

What is the effect of distension and recruitment on pulmonary resistance?

decrease vascular resistance

Why are distension and recruitment important during increased blood flow?

allow for more blood flow without a large rise in pulmonary pressure

What happens to pulmonary blood vessels when alveolar O₂ is low?

constrict

What is pulmonary hypoxic vasoconstriction?

low alveolar o2 causes pulmonary blood vessels to constrict

Why does hypoxic vasoconstriction occur?

redirect blood away from poorly ventilated alveoli

What is the effect of gravity on pulmonary blood flow?

blood flow greater at bottom of lung

What are the 5 factors affecting gas movement across the respiratory surface?

surface area, tissue thickness, partial pressure difference, gas solubility, molecular weight

How does surface area affect gas diffusion?

bigger surface area increases diffusion

Approximately how many alveoli are in the lungs?

300 million

What is the approximate total alveolar surface area?

50-100m2

How does membrane thickness affect gas diffusion?

thinner membrane, faster diffusion

Approximately how thick is the alveolar gas-blood barrier?

0.5 um

What drives O₂ from the alveoli into the blood?

partial pressure gradient

What are the approximate O₂ partial pressures across the respiratory membrane?

alveoli 100mmhg, blood 40mmhg

What drives CO₂ from blood into the alveoli?

partial pressure gradient

What are the approximate CO₂ partial pressures?

blood 46mmhg, alveoli 40mmhg

Which gas has the larger partial pressure driving force?

o2

How does the O₂ driving force compare with CO₂?

o2 has a 10x greater driving force

Which gas is more soluble in blood?

co2

How much more soluble is CO₂ than O₂?

25 x more soluble

Which is more important for gas diffusion: solubility or molecular weight?

solubility

Why can CO₂ diffuse effectively despite having a smaller pressure gradient?

co2 more soluble than o2