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In The Name of AllahIn The Name of Allah
The Most Powerful And MostThe Most Powerful And Most
MercifulMerciful
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Never Try to Suppress Opinions That YouNever Try to Suppress Opinions That You
Think Dangerous of, Because You Do So,Think Dangerous of, Because You Do So,
The Opinions Will Suppress You.The Opinions Will Suppress You.
(Bernarnd(Bernarnd
Russell)Russell)
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SequenceSequence
Respiratory BronchiolesRespiratory Bronchioles
Alveolar DuctsAlveolar Ducts
AlveoliAlveoli
Respiratory CorrelationsRespiratory Correlations
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Respiratory Bronchioles
Epithelium
Alveoli
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EpitheliumThe respiratory bronchioles are lined with
ciliated cuboidal epithelium.
The bronchiolar epithelium becomes continuouswith the squamous alveolar lining cells.
The cuboidal cells lose their cilia towards the
distal part of the respiratory bronchioles.
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Alveoli of The Respiratory
Bronchioles Alveoli are characteristic of the respiratory portion
of the respiratory tract
Alveoli are the sites for gaseous exchange
Alveoli interrupt the epithelium of the respiratorybronchioles at the intervals
Proceeding distally along the respiratorybronchioles, the alveoli greatly increase in number.
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Alveolar DuctsAlveolar Ducts
AlveoliAlveoli
AtriaAtria
Supporting StructuresSupporting Structures
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Alveoli of The Alveolar DuctAlveoli of The Alveolar Duct
The Alveolar ducts are solely composedThe Alveolar ducts are solely composed
of alveoliof alveoli
Alveoli are lined with extremelyAlveoli are lined with extremely
attenuated squamous alveolar cells.attenuated squamous alveolar cells.
The rim of the alveoli is surrounded by aThe rim of the alveoli is surrounded by a
network of smooth muscle cells.network of smooth muscle cells.
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AtriaAtria
Atria represent the expanded altar ofAtria represent the expanded altar of
Alveolar SacsAlveolar Sacs
Each Atria communicates with twoEach Atria communicates with twoAlveolar Sacs.Alveolar Sacs.
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Supporting StructuresSupporting Structures
Elastic and Reticular Fibers.Elastic and Reticular Fibers.
Elastic fibers enable the alveoli to expandElastic fibers enable the alveoli to expand
with inspiration and to contract passivelywith inspiration and to contract passivelywith expiration.with expiration.
Reticular fibers serve as a support thatReticular fibers serve as a support thatprevents overdistention and damage to theprevents overdistention and damage to the
delicate capillaries and thin alveolar septa.delicate capillaries and thin alveolar septa.
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Alveoli-The Functional Unit ofRespiratory System
Introduction
Interalveolar Septum
Blood-Air Barrier
Supporting Structures
Type I Alveolar Cells
Type II Alveolar Cells
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Introduction
Alveoli are saclike evaginations (about200 um in diameter) of the respiratory
bronchioles, alveolar ducts, andalveolar sacs.
They resemble small pockets open onone side, similar to the honeycombs ofa beehive.
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Interalveolar Septum
The alveolar wall lying between two neighboringalveoli is called Interalveolar Septum.
Interalveolar Septum consists of two thin
squamous epithelial layers and the interveningmeshwork of capillaries, elastic an reticularfibers, and connective tissue matrix and cells.
Interalveolar Septa contain the richest capillary
network in the body.
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Blood-Air Barrier
The Blood-Air Barrier consists of thesurface lining and the cytoplasm ofthe alveolar cells, the fused basal
lamina of the closely apposed alveolarand endothelial cells, and thecytoplasm of the endothelial cells.
Total thickness varies from 0.1 and 0.5um.
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Supporting Structures
The supporting structures within theinteralveolar septum and include a meshwork ofreticular and elastic fibers.
The fibers support the capillary networkThey are arranged to permit the expansion and
contraction of the interalveolar septum.
They also contain leukocytes, macrophages and
fibroblasts.
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Type I Cells
Type I cells, or squamous alveolar cells,are extremely attentuated cells that linethe alveolar surfaces.
They make up 97% of the total cells
The orgenelles are collected around thenucleus leaving space for diffusion ofgases in the periphries.
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Type II Cells
Type II cells are rounded cells found alongthe alveolar walls.
They exhibit a characteristic vesicular or
foamy cytoplasm with lamellar bodies.Lamellar bodies are responsible for the
formation of pulmonary surfactants.
Type II cells divide by mitosis to replace bothtypes of populations in the alveolar walls.