Dr. Sami Zaqout IUG

The

Respiratory

System

Dr. Sami Zaqout IUG

Respiratory System Divisions

Conducting portion

Nasal cavity

Nasopharynx

Larynx

Trachea

Bronchi

Bronchioles

Terminal bronchioles

Respiratory portion

Respiratory bronchioles

Alveolar ducts

Alveoli

Dr. Sami Zaqout IUG

Respiratory

Epithelium

Ciliated

Columnar

Cells

Mucous

Goblet

Cells

Brush

Cells

Basal

Short

Cells

Small

Granule

Cell

Ciliated pseudostratified columnar epithelium

Dr. Sami Zaqout IUG

Ciliated Columnar Cells

Most abundant type.

Each cell has about 300 cilia on its apical surface.

Beneath the cilia, in addition to basal bodies, are numerous small mitochondria that supply adenosine triphosphate (ATP) for ciliary beating.

Dr. Sami Zaqout IUG

Mucous Goblet Cells

The next most

abundant cells in the

respiratory epithelium.

The apical portion of

these cells contains

the mucous droplets

composed of

glycoproteins.

Dr. Sami Zaqout IUG

Brush Cells

Have numerous

microvilli on their

apical surface.

Have afferent nerve

endings on their basal

surfaces and are

considered to be

sensory receptors.

Dr. Sami Zaqout IUG

Basal (Short) Cells

Small rounded cells that

lie on the basal lamina

but do not extend to the

luminal surface of the

epithelium.

These cells are believed

to be generative stem

cells that undergo mitosis

and subsequently

differentiate into the other

cell types.

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Small Granule Cell

Resembles a basal cell

except that it possesses

numerous granules with

dense cores.

Histochemical studies

reveal that these cells

constitute a population of

cells of the diffuse

neuroendocrine system

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Note

From the nasal cavity through the larynx,

portions of the epithelium are stratified

squamous.

This type of epithelium is evident in regions

exposed to direct airflow or physical abrasion:

Oropharynx

Epiglottis

Vocal folds

It provides more protection from attrition than

does typical respiratory epithelium.

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Nasal Cavity

Vestibule

Around the inner surface of the nares are numerous sebaceous and sweat glands, in addition to the thick short hairs, or vibrissae, that filter out large particles from the inspired air.

Within the vestibule, the epithelium loses its keratinized nature and undergoes a transition into typical respiratory epithelium before entering the nasal fossae.

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Nasal Cavity

Nasal Fossae

The middle and inferior projections are covered with respiratory epithelium.

The superior conchae are covered with a specialized olfactory epithelium.

Within the lamina propria of the conchae are large venous plexuses known as swell bodies.

Nasal cavity has a rich vascular system with a complex organization.

Dr. Sami Zaqout IUG

Olfactory Epithelium

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Conditioning of Air

A major function of the conducting portion

is to condition the inspired air.

Before it enters the lungs, inspired air is

cleansed, moistened, and warmed.

Vibrissae

Mucus

Superficial vascular network

Dr. Sami Zaqout IUG

Paranasal Sinuses

They are lined with a

thinner respiratory

epithelium that

contains few goblet

cells.

The lamina propria

contains only a few

small glands and is

continuous with the

underlying periosteum.

Dr. Sami Zaqout IUG

Nasopharynx

It is lined with

respiratory epithelium

in the portion that is in

contact with the soft

palate .

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Larynx

Laryngeal cartilages

hyaline elastic

thyroid

cricoid

most of arytenoids

epiglottis

corniculate

tips of the arytenoids

cuneiform

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Epiglottis

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Vocal Cords

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Trachea

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Bronchial Tree

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Bronchi

The mucosa of the bronchi is structurally similar to the mucosa of the trachea.

The bronchial cartilages are more irregular in shape than those found in the trachea.

The lamina propria has a smooth muscle layer.

The lamina propria is rich in elastic fibers and contains an abundance of mucous and serous glands.

Dr. Sami Zaqout IUG

Bronchi

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Bronchi

Numerous lymphocytes

are found both within the

lamina propria and

among the epithelial cells.

Lymphatic nodules are

present and are

particularly numerous at

the branching points of

the bronchial tree.

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Bronchioles

Intralobular airways with diameters of 5 mm or less.

Have neither cartilage nor glands in their mucosa.

There are only scattered goblet cells within the epithelium of the initial segments.

The epithelium is: Ciliated pseudostratified columnar

Ciliated simple columnar

Ciliated simple cuboidal

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Bronchioles

Bronchiolar lamina propria is composed largely

of smooth muscle and elastic fibers.

The musculature of both the bronchi and the

bronchioles is under the control of the vagus

nerve and the sympathetic nervous system.

Stimulation of the vagus nerve decreases the diameter

of these structures.

Sympathetic stimulation produces the opposite effect.

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Terminal Bronchioles

The epithelium of terminal

bronchioles also contains

Clara cells:

Devoid of cilia.

Have secretory granules

in their apex.

Known to secrete

proteins that protect the

bronchiolar lining against

oxidative pollutants and

inflammation.

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Respiratory Bronchioles

Their walls are interrupted by numerous saclike alveoli where gas exchange occurs.

Portions of the respiratory bronchioles are lined with ciliated cuboidal epithelial cells and Clara cells.

But at the rim of the alveolar openings the bronchiolar epithelium becomes continuous with the squamous alveolar lining cells.

Dr. Sami Zaqout IUG

Alveolar Ducts

Both the alveolar ducts and the alveoli are lined with extremely attenuated squamous alveolar cells.

In the lamina propria surrounding the rim of the alveoli is a network of smooth muscle cells.

A rich matrix of elastic and reticular fibers provides the only support of the duct and its alveoli.

Dr. Sami Zaqout IUG

Alveoli

Alveoli are saclike

evaginations about 200

µm in diameter of the

Respiratory bronchioles

Alveolar ducts

Alveolar sacs

Within these cuplike

structures, O2 and CO2

are exchanged between

the air and the blood.

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The Structure of The Alveolar Walls

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Blood-Air Barrier

The surface lining and cytoplasm of the alveolar cells

The fused basal laminae of the closely apposed alveolar and endothelial cells

The cytoplasm of the endothelial cells.

The total thickness of these layers varies from 0.1 to 1.5 µm.

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Capillary Endothelial Cells

Extremely thin and can be easily confused with type I alveolar epithelial cells.

The endothelial lining of the capillaries is continuous and not fenestrated.

Clustering of the nuclei and other organelles allows the remaining areas of the cell to become extremely thin.

The most prominent feature of the cytoplasm in the flattened portions of the cell is numerous pinocytotic vesicles.

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Type I Cells, or Squamous Alveolar Cells

Extremely attenuated cells that line the alveolar surfaces.

Make up 97% of the alveolar surfaces.

The cytoplasm in the thin portion contains abundant pinocytotic vesicles, which may play a role in the turnover of surfactant and the removal of small particulate contaminants from the outer surface.

The main role of these cells is to provide a barrier of minimal thickness that is readily permeable to gases.

Dr. Sami Zaqout IUG

Type II Cells

Rounded cells that are usually found in groups of two or three

They divide by mitosis to replace their own population and also the type I population.

They exhibit a characteristic vesicular or foamy cytoplasm.

Vesicles are caused by the presence of lamellar bodies

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Type II Cells

The lamellar bodies give rise to a material that spreads over the alveolar surfaces, providing an extracellular alveolar coating, pulmonary surfactant, that lowers alveolar surface tension.

The surfactant layer consists of an aqueous, proteinaceous hypophase covered with a monomolecular phospholipid film that is primarily composed of dipalmitoyl phosphatidylcholine and phosphatidylglycerol.

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Lung Macrophages - Dust Cells

Found in the interior of the

interalveolar septum and

are often seen on the

surface of the alveolus.

The alveolar macrophages

that scavenge the outer

surface of the epithelium

within the surfactant layer

are carried to the pharynx.

Dr. Sami Zaqout IUG

Alveolar Pores

Connect neighboring

alveoli.

These pores equalize

air pressure in the

alveoli and promote the

collateral circulation of

air when a bronchiole is

obstructed.

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Pulmonary Blood and Lymphatic Vessels

Circulation in the

lungs includes:

Nutrient (systemic)

Functional (pulmonary)

Lymphatic networks

include:

Deep network

Superficial network

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Pleura

The pleura is the serous membrane covering the lung.

It consists of two layers:

Parietal

Visceral

Both membranes are composed of mesothelial cells resting on a fine connective tissue layer that contains collagen and elastic fibers.

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Respiratory Movements

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Defense Mechanisms

Particles larger than 10 µm are retained in the nasal passages

Particles of 2-10 µm are trapped by the mucus-coated ciliated epithelium.

The cough reflex can eliminate these particles by expectoration or swallowing.

Smaller particles are removed by alveolar macrophages.

BALT (bronchus-associated lymphatic tissue).

Dr. Sami Zaqout IUG

Tumors of the Lung

The incidence of lung tumors is higher in men but is increasing in women.

Squamous cell carcinoma is related to the effects of cigarette smoking on the bronchial and bronchiolar epithelial lining.

Chronic smoking induces the transformation of the respiratory epithelium into a stratified squamous epithelium.

Dr. Sami Zaqout IUG