Structures of the Respiratory System (Continued) Bronchi and Lungs Pages 440-445

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 © 2015 Pearson Education, Inc.

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

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 © 2015 Pearson Education, Inc.

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 © 2015 Pearson Education, Inc.

(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.

(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.

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) © 2015 Pearson Education, Inc.

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

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.

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