Respiratory System Organs Nose Nasal Cavity Pharynx Larynx

Respiratory System: Organs • • • Nose Nasal Cavity Pharynx Larynx Trachea Bronchi & their divisions • Lungs

Respiratory system Is divided into: I-Conducting portion (transports, filters, moistens Iand 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-Respiratory portion ( has alveoli- the sites of IIgas exchange): Is formed of respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli.

Parts of respiratory system

Nasal cavity 1 -Anterior portion: portion or vestibule, is lined with skin (sweat &sebaceous glands) and vibrissae. 2 -Posterior portion: portion is lined with respiratory mucosa (except olfactory area) Is formed of: respiratory epithelium and vascular lamina propria rich in seromucous glands, lymphoid nodules, mast cells and plasma cells. It has three conchae (superior, middle and inferior)

Nasal Mucosa

Olfactory region of the nasal cavity It covers the roof of the nasal cavity, superior aspect of the nasal septum and the superior concha. It is formed of olfactory mucosa (olfactory epithelium and lamina propria). Olfactory epithelium comprises three types of cells: 1 -Olfactory cells. 2 -Sustentacular cells. 3 -Basal cells.

Olfactory mucosa

Olfactory mucosa

Para-nasal sinuses & nasal septum

Paranasal sinuses They are mucoperiosteum-lined spaces in ethmoid, sphenoid, frontal and maxillary bones. They communicate with the nasal cavity and have same lining. Pharynx Is subdivided into: a-Nasopharynx (lined with respiratory mucosa and has pharyngeal tonsil) b -Oral pharynx (lined with non-keratinized stratified squamous epthelium) c -Laryngeal pharynx (lined with respiratory mucosa)

Larynx Is located between pharynx and trachea(4 cm in length and 4 cm in diameter). It is responsible for phonation and prevent the entry of solids into the respiratory system during swallowing. It is reinforced by hyaline cartilage (thyroid, cricoid and arytenoids) and elastic cartilage (epiglottis, corniculate and cuneiform) Larynx has 2 pairs of shelf-like folds: A-superiorly B-Inferiorly vestibular folds. vocal folds

Epiglottis

The epiglottis • It is leaf like structure. It covers the upper end of larynx to prevent the entrance of food to respiratory passage. • It is formed of elastic cartilage that surrounded with respiratory epithelium EEXCEPT its superior (anterior or dorsal) surface and the upper part of the (inferior or ventral) posterior surface that are covered with non-keratinized st. sq. epith.

Vestibular folds &Vocal cords *Vestibular folds are immovable. They are surrounded with respiratory epith. The lamina propria composed of loose C. T, houses seromucous glands, adipose cells and lymphoid elements. *Vocal cords: are formed of dense regular elastic C. T, vocal ligament, skeletal (intrinsic) muscle and covered with non-keratinized st. sq. epith.

Trachea

Trachea • It is formed of: • 1. Mucosa, composed of: * Lining epith. • a-Respiratory epith(col. ciliated) • b-Basal cells. • c-Brush cells. • d-Serous cells. • e-DNES (defuse neuro-endocrine cells). • Lamina propria: fibroelastic C. T. contains lymphoid elements, mucous, serous glands and elastic lamina.

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: 3. Adventitia is composed of fibero-elastic C. T. and C-rings of hyaline cartilage.

Bronchial tree • It begins at the bifurcation of the trachea. • It is composed of: 1. Extrapulmonary or 1 ry bronchi. 2. Intrapulmonary (2 ry &3 ry) bronchi. 3. Bronchioles. 4. Terminal bronchioles. 5. Respiratory bronchioles.

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 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.

Bronchioles. • Are less than 1 mm in diameter. • Have no cartilage. • Have Clara cells. • Large bronchioles are lined with simple columnar ciliated epithelium and 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 r. ER. • Are secretory cells, (glycoprotein and surfactant-like material) • Have abundant s. ER. • 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. 5 mm). • 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 • 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 pneumocytes : *Line about 95% of alveolar surface. *Highly attenuated squamous cells. *Have thin cytoplasm that contain few mitochondria, few r. ER and a modest Golgi apparatus. *Have occluding junctions. *have well developed basal lamina.

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 r. ER, 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

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