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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.