Histology of Respiratory System~ dr.Mirna by : Dr. EzyanRespiratory System Respiratory system consist of the paired lungs & the series of air passages that lead to & from the lungs. the RS devided into 2 principal region:1. Conduction portion2. Respiratory portion Conducting portion consist of : nasal cav, nasopharynx, larynx, trachea, pair of main bronchi, broncioles. Respiratory portion consist of: respiratory bronchioles, alveolar duct, alveolar sac, alveoli.Air passing through the respiratory passagesmust be conditioned before reaching theterminal respiratory units. Its include: warming, moistening & removal of particulate materials.

Nasal Cavities Paired chambers separated by a bony & cartilaginous septum. Each chamber communicates ant with ext environment through nares & post with nasopharynx through choanae. Divided into 3 regions :- vestibule - respiratory segm. - Olfactory segm.

Vestibule of the Nasal Cavity Lined with stratified squamous epith. Contains : stiff hairs, vibrissae entrap large particulate. Posteriorly stratified sguamous epith become thinner & transition to the pseudostratified epith that characterizes the respiratory segment sebaceous glands are absent.

Respiratory segment of NC

Constitutes most of the volume of NC Lined with ciliated pseudostratified columnar epith. Nasal septum medial wall of resp segm is smooth but lateral wall (conchae) is bony projection. Conchae plays a dual role : increase surface area & cause turbulence in airflow to allow more efficient conditioning of inspired air. The Epithelium of RS is composed of 5 cell types : Ciliated cells: covering the surface of epith Goblet cells: synthesize & secrete mucus.The mucus & other secr are move toward the pharynx by means of coordinated sweeping movements of cilia normally swallowed Brush cells: has blunt microvilli. Small granule cells: contain secretory granules Basal cells: steam cell from which other cell types arise.Epithelium of RS of NC is essentially same as the epithelium lining most of the parts that follow in theconducting system.

Olfactory Segment of NC

The epithelium is thicker than the nonsensory epith & it serves as the receptor for smell. Its consists of :- Olfactory cells: bipolar neurons that span the thickness of the epithelium.- Supporting or sustentacular cells: columnar cells with apical microvilli. - Basal cells: steam cells from which the olfactory &supporting cell differentiate.- Brush cells Lamina propria directly contiguous with periosteum. Contains numerous blood & lymphatic vessels, nerves & olfactory (bowmans gland).

Paranasal Sinuses PS are air filled spaces in the bones of the walls of the nasal cavity. Lined by respiratory epithelium with numerous goblet cells. Named for the bone which they are found, i.e, ethmoid, frontal, sphenoid & maxillar. Mucus produced in the sinuses is swept into nasal cav by coordinated cilliary movement.Larynx Irregular tube that connects pharyng to trachea. Within lam propria lie a number of laringeal cartilages. Larger cartilages are hyaline, smaller cartilage are elastic. Function of the cartilages :- Maintainance an open airways- prevent swallowed food/fluid from entering trachea - participate in producing sounds for phonation.Larynx

Epiglottis Mikr : devided into : - Pars Lingualis : stratified squamous ephit. - Pars Laringealis : respiratory ephitelium Lamina propria : seromucous gland Elastic cartilage located in the middle.Vocal cords Located in the post of epiglottis. Devided into : - cranial fold false focal cord: resp epith, gland ++, have no intrinsic musc so do not modulate in phonation. - caudal fold true focal cord : stratified squamous epith serves to protect the mucosa from abrasion caused by the rapidly moving air stream, has no gland, have intrinsic & extrinsic musc.

Trachea

A short, flexible, air tube (2,5 cm in diameter & 10 cm long) Its wall assists in conditioning inspired air. Divided into 2 main bronchi. The wall consist of 4 definable layers :- mucosa: composed of ciliated, pseudostratified epith & an elastic fiber rich lamina propria. - submucosa: composed of slightly denser conn tissue than the lamina propria.- cartilaginous layer: composed of C shaped hyaline cartilages.- Adventitia Tracheal epithelium is similar to resp epith. Ciliated columnar cells, goblet cells & basal cells principales cells types in tracheal epith. Brush cells, small granule cells in small number. C-shaped hyaline cartilage to prevent collapse of tracheal lumen, particularly during expiration. Fibroelastic tissue & smooth muscle (trachealis muscle) also present.

Bronchi

The wall of bronchus have 5 layers :- Mucosa: pseudostratified epithelium, height of cells decrease as the bronchus decrease in diameter.- Muscularis:continous layer of smooth muscles in the larger bronchi.- Submucosa:contain gland & adiposed tissue.- cartilage layer:become smaller as bronchial diameter diminishes.- Adventitia

Bronchioles

Air conducting ducts that measure 1 mm or less. Cartilage plates & glands are not present in bronchioles. Epithelium: pseudostratified ciliated columnar epithelium transform into simple cilliated columnar and become cuboidal epithelium as the duct narrow. Goblet cells still present in the largest bronchioles but disappear in terminal bronchioles. Respiratory bronchioles contains both ciliated cells & clara cells but distally clara cells predominant.

Alveoli

Alveoli are the actual sites of gas exchange between the air & the blood. Each adult lung has about 150-250 million alveoli, their combined internal surface area is 75 m2. Each alveolus is a thin wall polyhendral chambers 0,2 mm in diameter. Alveolar duct : elongated airways, almost have no walls only alveoli as their peripheral boundary. Rings of smooth muscles are present in the interalveolar septa. Alveolar sac: spaces surrounded by clusters of alveoli. Usually occur at termination of an alveolar duct. Alveolar epithelium is composed of type I & type II alveolar cells & occasional brush cells. Type I alveolar cells are extremely thin squamous cells that line most (95%) of the surface of the alveoli. Joint to another cell by occluding juntions. Type II alveolar cells/ septal cell are secretory cells. Cover only 5 % of alveolar air surface. Rich in the mixture of phospholipids, neutral lipids & proteins that secreted by exocytosis to form surface-active agent surfactant Brush cells: only few in number serve as receptors that monitoring air quality in the lung.