I- Respiratory system Is divided into: 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.

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

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

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.

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

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

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

Intrapulmonary bronchus

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.

Bronchiole

Clara 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 epith.

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.

Respiratory bronchioles Have the same structure as terminal bronchioles but, They have alveoli through them gas exchange takes place. They terminate in an alveolar ducts.

Terminal bronchiole

Alveolar ducts Alveolar 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.

Alveolus 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.

Lining 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.

B-Type II pneumocytes B-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.

Type I &Type II pneumocytes

Pneumocyte type II

EM of Pneumocyte II

The 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.

Blood-Air barrier

Blood-Air Barrier

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.

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.

Alveolar macrophages (dust 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.

Lung

Pleura Pleura Is 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

PRACTICAL SLIDES

Trachea

Lung