Matching of ventilation and blood flow in alveoli

Question 1

cause of inadequate oxygen movement between alveoli and pulmonary capillary blood

Answer 1

major disease-induced

not a problem with diffusion, but with mismatching of air supply and blood supply in individual alveoli

Question 2

how many alveoli in the lungs?

Answer 2

~300 million

Question 3

ventilation-perfusion inequality

Answer 3

correct proportion of alveolar airflow (ventilation) and capillary blood flow (perfusion) should be available to each alveolus, for increased efficiency - mismatching is ventilation-perfusion inequality

Question 4

major effect of v-p inequality

Answer 4

decrease Po2 of systemic arterial blood

Question 5

v-p in healthy adults

Answer 5

gravitational effects causing v-p can decrease arterial Po2 by ~5mmHg
upright posture - increase filling of blood vessels at bottom of lung - Po2 in pulmonary veins and systemic arteries are 5mmHg less than alveolar air

Question 6

causes of v-p inequalities in disease states

Answer 6

regional changes in lung compliance
airway resistance
vascular resistance

ventilated alveoli with no blood flow (dead space)
blood flow through areas with no ventilation, e.g. due to collapsed alveoli (shunt)

Question 7

co2 and v-p inequalities

Answer 7

elimination is impaired, not as significantly as o2 supply

small increases in arterial Pco2 increase alveolar ventilation, which reduces arterial Pco2

Question 8

flowchart for local control of v-p matching

Answer 8

decreased airflow to region of lung -> decreased Po2 in pulmonary blood -> vasoconstriction of pulmonary vessels -> decreased blood flow - local perfusion decreased to match a local decrease in ventilation -> diversion of blood flow and airflow away from disease area to healthy areas

decreased bloodflow to region of lung -> decreased alveolar Pco2 -> bronchoconstriction -> decreased airflow - local ventilation decreased to match local decrease in perfusion -> diversion of bloodflow and airflow away from disease area to healthy area

Question 9

separation of systemic arterial blood from interstitial fluid

Answer 9

thin capillary wall - highly permeable to oxygen and carbon dioxide

Question 10

separation of interstitial fluid from intracellular fluid

Answer 10

plasma membrane - permeable to oxygen and carbon dioxide

Question 11

gaseous values in cells and blood

Answer 11

intracellular Po2 is higher and Pco2 lower than in arterial blood - in mitochondria Po2 it’s the lowest (less than 5mmHg) so net diffusion of oxygen from blood into cells and mitochondria, and carbon dioxide from cells into blood