Respiratory System - Part 2

Alveolar Structure

bronchiole

alveolar sac

capillary network

● Alveolar walls are very thin

● Alveoli are moist

● Hundreds of millions of alveoli

● Sac shape increases surface area

● Covered in a dense network of capillaries

Alveoli facilitate gas exchange in a number of ways:

In lungs, gas exchange occurs between alveoli and capillary network

Alveolar Structure

● Alveolar walls are very thin

● Alveoli are moist

● Hundreds of millions of alveoli

● Sac shape increases surface area

● Covered in a dense network of capillaries

Alveoli facilitate gas exchange in a number of ways:

In lungs, gas exchange occurs between alveoli and capillary network

Structure of Hemoglobin

heme group

Transporting Respiratory GasesRed blood cells (RBCs) contains about 250 million hemoglobin molecules, each of which can bind four O2 molecules

Transporting Respiratory GasesHemoglobin also transports some CO2 , although most is converted to bicarbonate ions and dissolves into blood stream

9% in plasma

27% as carboaminhemoglobin

64% as bicarbonate ions

Dalton’s law of partial pressure states that overall pressure that a mixture of gas exerts is sum of pressures exerted by each gas (partial pressure) in mixture

Movement of O2 and CO2 is dictated by their partial pressures

Gas Exchange

atmospheric partial pressure

of O2 (PO2)

atmospheric pressure

% O2 content in atmX=

101 kPa 21.01 %X=

= 21.2 kPa

Gas Exchange

tissue

capillaries

alveoli

atmosphere

0.0 5.5 11.0 16.5 22.0

21.2

13.3

5.3

5.0oxygen

PO2 (kPa)

O2 moves from alveoli into capillaries

For O2 to diffuse from alveoli into RBC there must be a PO2 gradient

O2 moves from capillaries into tissue

Dalton’s law of partial pressure states that overall pressure that a mixture of gas exerts is sum of pressures exerted by each gas (partial pressure) in mixture

Movement of O2 and CO2 is dictated by their partial pressures

O2capillary

oxygenated RBC

deoxygenated RBC

alveolus

interstitial fluid

Gas Exchange

alveolar PO2 = 13.3 kPa

capillary PO2 = 5.0 kPa

Diffusion of O2 out of alveoli turns hemoglobin into oxyhemoglobin

O2

CO2capillary

oxygenated RBC

deoxygenated RBC

interstitial fluid

alveolus

Gas Exchange

Higher PCO2 in bloodstream causes CO2 to diffuse into alveoli

alveolar PCO2 = 5.0 kPa

capillary PCO2 = 6.0 kPa

CO2

Diffusion of O2 out of alveoli turns hemoglobin into oxyhemoglobin