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� Includes : - the lung
- a system of tube
� Divided into 2 principal regions :
- conducting portion :
nasal cavity, nasopharynx, larynx, trachea,
bronchi, bronchioles & terminal bronchioles
- rerspiratory portion :
respiratory bronchioles, alveolar ducts, alveoli
(alveoli : the greater part of the lung)
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The main divisions of the
respiratory tract. The natural
proportions of these structures
have been altered for clarity; the
respiratory bronchiole, for
example, is in reality a short
transitional structure.
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RESPIRATORY EPITHELIUM
� Ciliated Pseudostratified Columnar Epithelium
� 5 types of cell :
1. ciliated columnar epithelium
2. mucous goblet cells
3. brush cells
4. basal cells
5. small granule cells
Photomicrograph illustrating the main components of the
respiratory epithelium. Pararosaniline—toluidine blue (PT)
stain. High magnification.
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NASAL CAVITY
� Consists of : - vestibule (external)
- nasal fossae (internal)
VESTIBULE
� Is the most anterior and dilated portion of nasal cavity
� Numerous sebaceous & sweat glands, vibrisae
� Within the vestibule � keratinized (-) �respiratory epithelium before entering the nasal fossae
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NASAL FOSSAE
� Conchae :
- superior : specialized olfactory epithelium
- middle respiratory
- inferior epithelium
� The olfactory epithelium �olfactory chemoreceptor located
� Ciliated Pseudostratified Columnar Epithelium
� 3 types of cells :
1. supporting cells
2. basal cells
3. olfactory cellsOlfactory mucosa showing the 3 cell types (supporting,
olfactory, and basal) and a Bowman’s gland.
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PARANASAL SINUSES
� Closed cavities in the : frontal, maxillary, ethmoid, sphenoid bones
� Lined with a thinner respiratory epithelium, few goblet cells
� Communicate with nasal cavity through small openings
� Mucous product � drain in to the nasal passages by ciliated epithelial cells
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NASOPHARYNX
� First part of the pharynx
� Lined with respiratory epithelium
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LARYNX
� Connects the pharynx to the trachea
� The larger cartilge : hyaline cartilage
� The smaller cartilage : elastic cartilage
� Cartilage participate in producing sounds for phonation
� Below the epiglottis : - false vocal sound
- true vocal sound
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TRACHEA� Mucosa :
- Ciliated Pseudostratified Columnar Epithelium
with goblet cells
- Lamina propria
� Sub mucosa : loose connective tissue
� Hyaline cartilage : 16-20 C-shaped rings
� Smooth muscle fibers
� Adventisia (fibrosa)
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Section of trachea showing the respiratory epithelium with goblet cells and columnar ciliated cells. Also shown are serous glands in the lamina propria and hyaline cartilage. The mucous fluid produced by the goblet cells and by the glands forms a layer that permits the ciliary movement to propel foreign particles out of the respiratory system. PT stain. Medium magnification.
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Light photomicrograph of the trachea in a monkey (´270).
There are numerous cilia (Ci) as well as goblet cells (GC) in
the epithelium. Also observe the mucous glands (MG) in the
subepithelial connective tissue and the hyaline C-ring (HC)
in the adventitia. L, lumen; PC, perichondrium.
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BRONCHIAL TREE
TRACHEA
BRONKUS PRIMER BRONKUS PRIMER
ka : 3 CAB. BRONKUS ki : 2 CAB. BRONKUS
BRONKIOLUS
BRONCHIOLUS TERMINALIS
BRONCHIOLUS RESPIRATORIUS
DUCTUS ALVEOLARIS
ALVEOLUS ALVEOLUS
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BRONCHUS� Ф ± 5 mm
� Mucosa : similar to the mucosa of the trachea (Ciliated Pseudostratified Columnar Epithelium)
� The bronchial cartilage are more irregular shape
� Larger bronchi : cartilage rings completely encircle the lumen
� Smaller bronchi : cartilage rings are replaced with isolated plates or islands of hyaline cartilage
� Lamina propria : smooth muscle layer, rich in elastic fiber, abundance of mucous & serous gland � ducts � bronchial lumen
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� PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
� CARTILAGE
� MUSCULARIS
� ADIPOSE TISSUE
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Hyaline cartilage
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BRONCHIOLES
� Ф ≤ 5 mm
� Mucosa : - cartilage & glands (-)
- scattered goblet cells
TERMINAL BRONCHIOLES
RESPIRATORY BRONCHIOLES
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TERMINAL BRONCHIOLES
� Ciliated Pseudostratified Columnar Epithelium �Ciliated Simple Columnar Epithelium � Ciliated Simple Cuboidal Epithelium
� Clara cells :
- (-) cilia
- (+) secretory granules in their apex
- secrete protein � protect the bronchiolar lining
against oxidative pollutants and inflamation
- lamina propria : smooth muscle, elastic fiber
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Clara cells in the epithelium of a terminal
bronchiole. These cells show secretory
granules and a bulging apical cytoplasm. PT
stain. High magnification.
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RESPIRATORY BRONCHIOLES
� Transition between conducting and respiratory
� Mucosa : identical to the terminal bronchioles, except their walls are interrupted by numerous sacklike alveoli � proceeding distally � alveoli »
� Ciliated Cuboidal Epithelium & Clara cells
� Smooth muscle and elastic fiber
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Section of a terminal bronchiole with a small portion of a respiratory bronchiole continuous with an alveolar
duct and many alveoli. PT stain. Low magnification.
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ALVEOLAR DUCTS
� Proceeding distally � the number of alveolar openings » � alveolar ducts
� Alveolar duct & alveoli lined with squamous cells
� Lamina propria : smooth muscle � disappears at the distal ends of alveolar ducts
� Alveolar ducts � atria that communicate with alveolar sacs
� Elastic fiber : - enable the alveoli to expand
- contract passively with expiration
� Reticular fibers :
- prevent overdistention
- prevent damage to the delicate capillaries and thin alveolar septa
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Transition of a terminal bronchiole into an alveolar duct (arrow). Note the
Clara cells (arrowheads). PT stain. Medium magnification.
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ALVEOLUS
� Sacklike evaginations of the respiratory bronchioles, alveolar ducts, alveolar sacks
� Resemble small pockets that are open on one side similar to the honeycombs of a beehive
� Exchange of O2 and CO2 between air & blood
� Each wall lies between 2 alveoli � interalveolar septum
� An interalveolar septum consists of 2 thin squamous epithelial layers :
- type I cells = squamous alveolar cells
- type II cells = surfactant cells
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TYPE I CELLS
� Line the alveolar surface
� Cells are so thin (25nm)
� Desmosomal & occluding junctions � prevent leackage of tissue fluid into alveolar air space
� To provide a barrier minimal thickness that is readily permeable to gases
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TYPE II CELLS
� Interspersed among the type I cells
� Desmosomal and occluding junctions
� Divided by mitosis �replace type I & II pupolation
� Exhibit a characteristic vesicular or foamy cytoplasm, by presence of lamellar bodies
� Lamellar bodies � pulmomary surfactant � alveolar surface tension ↓
� Without surfactant � alveoli collaps (expiration)
� Surfactant appears in the last week of gestation
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Secretion of surfactant by a type II cell. Surfactant is a protein-lipid complex synthesized in the rough
endoplasmic reticulum and Golgi complex and stored in the lamellar bodies. It is continuously secreted by
means of exocytosis (arrows) and forms an overlying monomolecular film of lipid covering an underlying
aqueous hypophase. Occluding junctions around the margins of the epithelial cells prevent leakage of tissue
fluid into the alveolar lumen.
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LUNG MACROPHAGE
� = alveolar macrophage = dust cells
� Found in the anterior of the interalveolar septum, often seen on the surface of the alveolus
� The alveolar macrophage never passed through the epithelial lining �that scavenge the outer surface of the epithelium � carried to the pharynx � swallowed
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ALVEOLAR PORES
� To connect neighboring alveoli
� Equalize air pressure in the alveoli
� Promote the collateral circulation of air when a bronchiole is obstructed
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BLOOD AND LYMPH CIRCULATIONBlood and lymph
circulation in a pulmonary
lobule. Both vessels and
bronchi are enlarged out
of proportion in this
drawing. In the
interlobular septum, only
one vein (on the left) and
one lymphatic vessel (on
the right) are shown,
although both actually
coexist in both regions. At
the lower left, an
enlargement of the pleura
shows its mesothelial
lining. (Modified and
reproduced, with
permission, from Ham AW:
Histology, 6th ed.
Lippincott, 1969.)
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