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Respiratory system Is divided into: I I - - Conducting portion: (transports, filters, moistens and warms the inspired air): Is formed of nasal cavity, nasopharynx, larynx, trachea, primary bronchi, secondary bronchi (lobar), tertiary bronchi (segmental), bronchioles, and terminal bronchioles.

Bronchial Tree

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Respiratory systemIs divided into:II- - Conducting portion: (transports, filters, moistens and warms the inspired air): Is formed of nasal cavity, nasopharynx, larynx, trachea, primary bronchi, secondary bronchi (lobar), tertiary bronchi (segmental), bronchioles, and terminal bronchioles.

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IIII- - Respiratory portion: ( has alveoli- the sites of gas exchange): Is formed of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.

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Bronchial Tree Begins at the bifurcation

of the trachea Is composed of:

Extrapulmonary Part: Primary (main) bronchi.

Intrapulmonary Part: that includes: Secondary (lobar)

bronchi Tertiary (segmental)

bronchi Bronchioles Terminal bronchioles Respiratory bronchioles. Alveolar Ducts and sacs Alveoli

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Trachea• It is formed of:• 1.Mucosa,1.Mucosa, composed of:* Lining epith.Lining epith.• a-Respiratory epith.• b-Basal cells.• c-Brush cells.• d-Serous cells.• e-DNES (defuse neuro-endocrine cells).• Lamina propriaLamina propria: fibroelastic C.T.contains

lymphoid elements, mucous, serous glands and elastic lamina.

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2.Submucosa: 2.Submucosa: is composed of dense irregular fibero-elastic C.T. containing mucous and seromucous glands. It contains lymphoid elements and bl. Vessels.3.Adventitia3.Adventitia:is composed of fibero-elastic C.T.and C-rings of hyaline cartilage.

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General Characters of Bronchial Tree

Progressive decrease in: Size (diameter) Amount of cartilage. Number of glands and goblet cells The height of epithelial cells.

Progressive increase in: Amount of smooth muscle Amount of elastic tissue

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Primary bronchiPrimary bronchi are identical in structure to trachea (but smaller).Intrapulmonary bronchiIntrapulmonary bronchi have irregular plates of hyaline cartilage (in lieu of C-ring), which completely surrounds the lumen of intrapulmonary bronchi.

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Intrapulmonary bronchus

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Bronchioles.Bronchioles.• Are less than 1mm in diameter.

• Have no cartilage.

• Have Clara cells.

• Large bronchioles are lined with simple columnar ciliated epithelium with few goblet cells.

• Small bronchioles are lined with simple cuboidal ciliated epith.without goblet cells.

• Lamina propria has NO glands.

• Are surrounded by helically oriented smooth muscle layers that surrounded by elastic fibers.

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Clara cellsClara cells• Are columnar cells with dome shaped

apices.• Have microvilli.• Have abundant rER.• Are secretory cells,

(glycoprotein and surfactant-like material) • Have abundant sER.• Can degrade toxins in the inhaled air.• Can divide to regenerate the bronchiolar


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Terminal Bronchioles.Terminal Bronchioles.• Are the smallest and most distal region of

the conducting portion (less than o.5mm).• Are lined by Clara cells and partially ciliated

cuboidal cells.• Lamina propria is formed of fibro-elastic

C.T.• Have one or two layers of smooth muscle.• Elastic fibers radiate from the adventitia.• They give rise to respiratory bronchioles.

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Respiratory bronchiolesRespiratory bronchioles

• Have the same structure as terminal bronchioles but,

• They have alveoli through them gas exchange takes place.

• They terminate in an alveolar ducts.

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Terminal bronchiole

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Alveolar ductsAlveolar ducts

• Do not have walls of their own, but are lined with extremely attenuated squamous alveolar cells.

• They end with two or more small clusters of alveoli (alveolar sac).

• The opening of each alveolus to the alveolar duct is controlled by a single smooth muscle cell, embedded in type III collagen.

• Fine elastic fibers ramify from the alveolar ducts and sacs.

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AlveolusAlveolus• Is a small outpouching of respiratory

bronchiole, alveolar ducts and alveolar sacs.• Is the structural and functional unit of

respiratory system.• Contiguous alveoli communicate through an

alveolar pore of Kohn (equilibrate air pressure).• Interalveolar septum is occupied by extensive

continuous blood capillaries and C.T. rich in elastic and type III collagen.

• Opening of alveoli associated with alveolar sacs are devoid of smooth muscle cells, instead there are elastic and reticular fibers.

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Lining of the alveoliLining of the alveoli

• A-Type I pneumocytesA-Type I pneumocytes : *Line about 95% of alveolar surface.

*Highly attenuated squamous cells.

*Have thin cytoplasm that contain few mitochondria, few rER and a modest Golgi apparatus.

*Have occluding junctions.

*have well developed basal lamina.

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B-Type II pneumocytesB-Type II pneumocytes*occupy 5% of the alveolar surface.*Are cuboidal cells.*Form occluding junctions with type I alveolar cells.*Occupy most of the alveolar septa.*Have basal lamina.*Have apical microvilli.*Have central nuclei.*Have abundant rER, well developed Golgi apparatus and mitochondria.*Have membrane-bound lamellar bodies.*Secrete pulmonary surfactant (phospholipids and proteins) and undergo mitosis.

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Type I &Type II pneumocytes

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Pneumocyte type IIPneumocyte type II

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EM of Pneumocyte II

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The surfactantThe surfactant

• Is secreted by exocytosis from type II alveolar cells into the lumen of the alveolus.

• Decrease surface tension of the alveoli thus prevent their collapse.

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Blood-Air barrier

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Blood-Air Barrier

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EM of Blood-Gas Barrier

*Pneumocytes type I and surfactant.

*Fused basal lamina of type I pneumocytes and endothelial cells of the capillary.

*Endothelial cells of the continuous capillaries.

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Interalveolar Septum

• Lies between the alveoli• Contains extensive

continuous blood capillaries, Dust cells, macrophages and CT rich in elastic and type III collagen

• Contiguous alveoli communicate through an alveolar pore of Kohn to equilibrate air pressure.

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Alveolar macrophages (dust Alveolar macrophages (dust cells)cells)

• Are monocytes in the pulmonary interstitium.

• Migrate between type I alveolar cells, and enter the alveoli.

• Phagocytose dust and bacteria.

• Migrate to bronchi to the pharynx or into lymph vessels.

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PleuraPleuraIs formed of two layers:Parietal and visceral.

It is formed of simple squamous mesothelium. The two layers are separated by serous of fluid. The visceral layer has sub-epithelium loose C.T that extends in lung tissue

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