Biol 224 Lecture 23: Gas Exchange Partial Pressures

How are gases exchanged

By diffusion

across alveoli- capillary border

across capillary- interstitial fluid border

Diffusion in liquids

high concentration to low concentration

Diffusion in gases

high pressure to low pressure

O2 diffusion path

lungs → blood → intersitial fluid → cells (always lowest in oxygen 

CO2 diffusion path

cells → interstitial fluid → blood → lungs

Why dont we store o2?

Because we are constantly making ATP meaning we are constantly using oxygen

Reasons for efficient gas exchange?

Small diffusion distance

Large surface area of alveoli 

differences in partial pressure across blood air barrier are substantial

o2 and co2 are lipid soluble 

What can small diffusion distance be affected by?

Edema, pneumonia, pulmonary fibrosis disease, etc

What can large surface area of all alveoli be affected by?

Emphysema 

Efficiency of gas exchange

large differences in gas concentrations between air and blood 

what can differences in gas concs between air and blood be affected by?

changes in concentraiton of o2 and co2 in the air 

affected by changes in air pressure 

high pressure causes more gas to go into blood and altitude affects air pressure

Daltons Law

Each gas contributes to total pressure in proportion to its relative abundance

Partial pressure

pressure contributed by a single gas in a mixture

In atomospheric (760 mm Hg) air what is Nitrogen

79% (doesnt change) 597 mmHg 

In atmospheric air what is O2

21% 159 mm Hg

In atmospheric air what is H2O

.5% 3.7 mmh Hg

In atmospheric air what is Co2

0.04% 0.3mmHg

Alveolar gas levels

Po2 of 100 mmmHg and Pco2 of 40 mmHg

differs from air due to mixing of inhaled and residual air

Arterial Blood Gasses

blood in systemic circuit arteries and arterioles carry blood to tissues

po2 of 95 mmHg and pco2 of 40 mmHg

Tissue Interstitial fluid gas levels

Po2 of 40 mmHg and Pco2 of 45 mm Hg in inactive tissue (at rest)

Po2 of less than 20 mm Hg in active tissue

Venous blood gas levels 

Blood in systematic circuit venules and veins returning blood from tissues 

Po2 of 40 mm Hg and Pco2 of 45 mm Hg 

Draw cycle of oxygen traveling/levels