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Lecture 9Respiratory physiology
B Nursing II HUB228 2022
Dept. Medical Biosciences
University of the Western Cape
, Respiratory physiology
The process of respiration involves 3 integrated steps:
1. Pulmonary ventilation (breathing)
– physical movement of air into and out of the lungs
– requires pressure gradients to exist between the outside of the
body and the alveoli
2. Gas exchange
– involves gas diffusion, i) across the respiratory membrane
(between alveolar air & alveolar capillaries) and ii) across
capillary cell membranes between blood & other tissues
3. Gas transport
– transport of O2 & CO2 in the blood between the alveolar
capillaries and the capillary beds in other tissues
, 1. Pulmonary ventilation
Pulmonary ventilation = the physical movement of air into
and out of the respiratory tract
Please revise from HUB128:
1. Inspiration (inhalation)
2. Expiration (exhalation)
3. Boyle’s law (P = 1/V)
www.biology.eku.edu
4. Muscles of respiration
Two other aspects of pulmonary ventilation
1. Pressure and volume changes during the respiratory cycle
2. Lung volumes and lung capacities
, 1. Pulmonary ventilation
1. Pressure and volume changes during the respiratory cycle
1.1) Intrapulmonary pressure changes
= air pressure inside the lung alveoli
a) at the end of inspiration and expiration,
when there is no movement of air, the
intrapulmonary pressure is equal to
atmospheric pressure, change in
pressure = 0 mmHg
b) during inspiration (quiet breathing)
pressure in alveoli decrease to -1
mmHg, which is sufficient to suck in
about 500 ml of air into the lungs during
the 2 second period of inspiration
c) during expiration (quiet breathing)
pressure in alveoli increase to +1
mmHg, which forces 500 ml of air out
of the lungs during the 2-3 seconds of
expiration
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