1. Structures of the Respiratory System (Continued)
Bronchi and Lungs
Pages

2. Main (Primary) Bronchi
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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3. Nasal cavity Oral cavity Nostril Pharynx Larynx Trachea Left main
Figure 13.1 The major respiratory organs shown in relation to surrounding structures.
Nasal cavity
Oral cavity
Nostril
Pharynx
Larynx
Trachea
Left main
(primary)
bronchus
Right main
(primary)
bronchus
Left lung
Right lung
Diaphragm

4. Lungs 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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5. Membranous layers of the Lungs
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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6. (in pericardial cavity of mediastinum)
Figure 13.4a Anatomical relationships of organs in the thoracic cavity.
Intercostal muscle
Rib
Parietal pleura
Pleural cavity
Trachea
Lung
Visceral pleura
Thymus
Apex of lung
Right superior lobe
Left superior lobe
Horizontal fissure
Oblique fissure
Right middle lobe
Left inferior lobe
Oblique fissure
Right inferior lobe
Heart
(in pericardial cavity
of mediastinum)
Diaphragm
Base of lung
(a)
Anterior view. The lungs flank mediastinal structures laterally.

7. (in posterior mediastinum) Vertebra
Figure 13.4b Anatomical relationships of organs in the thoracic cavity.
Posterior
Esophagus
(in posterior mediastinum)
Vertebra
Root of lung at hilum
Left main bronchus
Right lung
Left pulmonary artery
Parietal pleura
Left pulmonary vein
Visceral pleura
Left lung
Pleural cavity
Thoracic wall
Pulmonary trunk
Pericardial
membranes
Heart (in mediastinum)
Anterior mediastinum
Sternum
Anterior
(b)
Transverse section through the thorax, viewed from above.

8. Bronchial (Respiratory) Tree Divisions
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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9. The Respiratory Zone includes: Respiratory bronchioles Alveolar ducts> Alveolar sacs> Alveoli (air sacs)
Alveolar duct
Alveoli
Respiratory
bronchioles
Alveolar duct
Terminal
bronchiole
Alveolar
sac
(a)
Diagrammatic view of respiratory
bronchioles, alveolar ducts, and alveoli
This is the only site of gas exchange

10. The Respiratory Membrane
The lungs are mostly air spaces; the rest is the stroma, mostly elastic connective tissue
Alveoli:
Inner walls lined with a squamous epithelial layer
Pulmonary capillaries cover external surfaces
Respiratory membrane (air-blood barrier)
one side is air, and the other side is flowing blood
Formed by alveolar and capillary walls
Alveolar pores connect neighboring air sacs
© 2015 Pearson Education, Inc.

12. Figure 13.6 Anatomy of the respiratory membrane (air-blood barrier).
Red blood cell
Capillary
Endothelial cell
nucleus
Alveolar pores O2
Capillary
CO2
Macrophage
Alveolus
Nucleus of
squamous
epithelial cell
Respiratory
membrane
Alveolar epithelium
Fused basement
membranes
Capillary endothelium
Alveoli (gas-
filled air
spaces)
Red blood
cell in
capillary
Surfactant-
secreting cell
Squamous
epithelial cell
of alveolar wall