Pages 445-448
•
Gas exchange occurs via diffusion
– Oxygen enters the blood
– Carbon dioxide enters the alveoli
•
Alveolar macrophages (“dust cells”) protect:
– pick up bacteria, carbon particles, and other
debris
•
Surfactant (a lipid-protein molecule) coats
gas-exposed alveolar surfaces to prevent
“sticking” and collapse during expiration
© 2015 Pearson Education, Inc.
Red blood cell
Capillary
Endothelial cell
nucleus
Alveolar pores
Capillary
Macrophage
Nucleus of
squamous
epithelial cell
Respiratory
membrane
Alveoli (gasfilled air
spaces)
Red blood
cell in
capillary
Surfactantsecreting cell
Squamous
epithelial cell
of alveolar wall
O2
CO2
Alveolus
Alveolar epithelium
Fused basement
membranes
Capillary endothelium
Pulmonary ventilation
1.
•
air into and out of the lungs (breathing)
External respiration
2.
•
gas exchange between pulmonary blood and alveoli
 Oxygen into blood; Carbon dioxide out of blood
Respiratory gas transport
3.
•
O2 and CO2 transported in the bloodstream
Internal respiration
4.
•
gas exchange between blood tissue cells
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
air flows into lungs
◦ Diaphragm and external intercostal muscles contract
 The size of the thoracic cavity increases
◦ External air is pulled into the lungs as a result of:
 Increase in intrapulmonary volume
 Decrease in gas pressure
© 2015 Pearson Education, Inc.
Changes in anterior-posterior and
superior-inferior dimensions
Ribs elevated
as external
intercostals
contract
External
intercostal
muscles
Changes in lateral
dimensions
Full inspiration
(External
intercostals contract)
Diaphragm moves
inferiorly during
contraction
(a) Inspiration: Air (gases) flows into the lungs
Pressure relative
to atmospheric pressure
+2
+1
Inspiration
Expiration
Intrapulmonary
pressure
0
−1
−2
(a)
Volume of
breath
Volume (L)
0.5
0
−0.5
(b)

air flows out of lungs
◦ Muscles relax
 Decrease in intrapulmonary volume
 Increase in gas pressure
◦ passive process; affected by lung elasticity
◦ Forced expiration occurs mostly by contraction of
internal intercostal muscles to depress the rib cage
© 2015 Pearson Education, Inc.
Changes in anterior-posterior and
superior-inferior dimensions
Changes in lateral
dimensions
Ribs depressed
as external
intercostals relax
External
intercostal
muscles
Diaphragm moves
superiorly as
it relaxes
(b) Expiration: Air (gases) flows out of the lungs
Expiration
(External
intercostals relax)
Pressure relative
to atmospheric pressure
+2
+1
Inspiration
Expiration
Intrapulmonary
pressure
0
−1
−2
(a)
Volume of
breath
Volume (L)
0.5
0
−0.5
(b)
•
intrapleural pressure - pressure within the
pleural space is always negative
– keeps lungs from collapsing
– Atelectasis is collapsed lung due to:
• Pneumothorax- the presence of air in the intrapleural
space due to disruption of the fluid bond between the
pleural layers
• Can be caused by impact/injury/infection
© 2015 Pearson Education, Inc.