Transcript Structures of the Respiratory System (Continued) and

Bronchi and Lungs
Pages 440-454


Formed by division of the trachea
Each bronchus enters the lung at the hilum
(medial depression)
◦ then subdivide into smaller and smaller branches
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Nasal cavity
Nostril
Oral cavity
Pharynx
Larynx
Trachea
Right main
(primary)
bronchus
Left main
(primary)
bronchus
Left lung
Right lung
Diaphragm
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
Occupy most of the thoracic cavity
Each lung is divided into lobes by fissures
 Left lung—two lobes
 Right lung—three lobes
◦ Connective tissue lines the fissures
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•
Serous membrane (“serosa”) covers the outer
surface of the lungs; 2-layer membrane:
– Pulmonary (visceral) pleura covers the lung surface
– Parietal pleura lines the walls of the thoracic cavity
•
Pleural (serous) fluid fills the area between
layers
– Allows gliding and decreases friction during
breathing
•
Pleural space lies between the layers
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Intercostal muscle
Rib
Trachea
Parietal pleura
Pleural cavity
Visceral pleura
Lung
Thymus
Apex of lung
Right superior lobe
Horizontal fissure
Right middle lobe
Oblique fissure
Right inferior lobe
Heart
(in pericardial cavity
of mediastinum)
Diaphragm
Base of lung
Left superior lobe
Oblique fissure
Left inferior lobe
(a) Anterior view. The lungs flank mediastinal structures laterally.
Vertebra
Posterior
Esophagus
(in posterior mediastinum)
Root of lung at hilum
• Left main bronchus
• Left pulmonary artery
• Left pulmonary vein
Right lung
Parietal pleura
Visceral pleura
Left lung
Pleural cavity
Thoracic wall
Pulmonary trunk
Pericardial
membranes
Sternum
Heart (in mediastinum)
Anterior mediastinum
Anterior
(b) Transverse section through the thorax, viewed from above.

All have reinforcing cartilage in their walls
◦ Exception are the smallest branches

Hierarchy of branches:
◦ Bronchi
 Primary (largest)
 Secondary
 Tertiary
◦ Bronchioles
◦ Terminal bronchioles (smallest)
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Alveolar duct
Respiratory
bronchioles
Terminal
bronchiole
(a) Diagrammatic view of respiratory
bronchioles, alveolar ducts, and alveoli
This is the only site of gas exchange
Alveoli
Alveolar duct
Alveolar
sac
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The lungs are mostly air spaces; the rest is
the stroma, mostly elastic connective tissue
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Alveoli:

Respiratory membrane (air-blood barrier)
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Alveolar pores connect neighboring air sacs
◦ Inner walls lined with a squamous epithelial layer
◦ Pulmonary capillaries cover external surfaces
◦ one side is air, and the other side is flowing
blood
◦ Formed by alveolar and capillary walls
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•
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
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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
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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
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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
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