Human Physiology, 14th edition (2016)

Respiratory Physiology 549

Figure 16.20 The relationship between

alveoli and blood vessels. The extensive area

of contact between the pulmonary capillaries and

the alveoli allows for rapid exchange of gases

between the air and blood.

Alveoli

Alveolar sac

Alveolar duct

Pulmonary

arteriole

Pulmonary

venule

Capillary network

on surface of alveolus

Blood

flow Pulmonary venule

Pulmonary

arteriole

Bronchiole

Terminal bronchiole

Respiratory bronchiole

Figure 16.21 Blood gas measurements using the P^ O 2 electrode. ( a ) The electrical current generated by the oxygen
electrode is calibrated so that the needle of the blood gas machine points to the P^ O 2 of the gas with which the fluid is in equilibrium.
( b ) Once standardized in this way, the electrode can be inserted into a fluid such as blood, and the P^ O 2 of this solution can be measured.

152 100

Calibrate to PO 2 of gas

Blood-gas machine

Total pressure = 760 mmHg

% O 2 = 20%

PO 2 = 152 mmHg

Certified gas cylinder

Dissolved

O 2

Dissolved

O 2

O 2 electrode

Arterial blood

sample

First step: Calibration of

O 2 electrode

Second step: Measurement of

arterial PO 2

Equilibrium

e– e–

(a) (b)