Histology of Respiratory Tract

Dr. Sama ul Haque Dr. SafaaHistology of Respiratory TractObjectivesDifferentiate between the olfactory and nasal mucosa.Discuss the microscopic structure of larynx. Describe the microscopic structure of trachea and lungs.Differentiate between the terminal and respiratory bronchioles. Explain alveolar cells.Respiratory SystemThis consists of the lungs and the air passages that lead to and form the lungs. The air passages branch as they enter the lungs to finally form alveoli. This system has 3 functions: 1.Air conduction; 2.Air filtration; 3.Gas exchange (respiration).

Air passages consist of: A conducting portion A respiratory portionConducting portion1.Nasal cavities; 2.Nasopharynx and oropharynx; 3.Larynx; 4.Trachea; 5.Paired primary bronchi. Bronchi within the lungs branch extensively to form bronchioles. The terminal bronchioles form the last part of the conducting system.

The respiratory portion is the part of the tract where gaseous exchange takes place and includes: 1.Respiratory bronchioles; 2.Alveolar ducts; 3.Alveolar sacs; 4.Alveoli.

Respiratory EpitheliumThe typical respiratory epithelium consists of 5 cell types: 1.Ciliated cells; 2.Goblet cells; 3.Brush cells (have short blunt microvilli); 4.Small granule cells (contain secretory granules); 5.Basal cells (stem cells).

Nasal CavityKeratinized stratified squamous epithelium Non Keratinized stratified squamous epitheliumPseudostratified ciliated columnar epithelium with goblet cellsOlfactory Epithelium

Nasal CavityNasal Cavity formed of:1.Vestibule. 2.Respiratory segment. 3.Olfactory segmentVestibule: Keratinized stratified squamous epithelium Non Keratinized stratified squamous Contains vibrissae (fine hair), sebaceous glands and sweat glands

Nasal CavityRespiratory segment - Respiratory Epithelium - Lamina PropriaOlfactory segment - Olfactory Epithelium: i. Olfactory cells (bipolar neurons) ii. Basal cells iii. Supportive cells - Lamina Propria

Nasal Cavity

Lamina Propria

Mucous GlandsSerous GlandsVenous SinusesMucoperiosteum or Mucoperichondrium

Secretions of nasal mucosa- Bactericides - Lysozymes

Olfactory Epithelium

NasopharynxMucosaRespiratory EpitheliumStratified Squamous EpitheliumLamina PropriaElastic TissueMucus Gland

LarynxMucosaFalse vocal cords: Pseudostratified ciliated columnar epithelium True vocal cords: Non Keratinized stratified squamous epitheliumIntrinsic MusclesCartilages- Larger Laryngeal Cartilages (Hyaline)

LarynxEpiglottisMucosaAnteriorly (Lingual mucosa):Non Keratinized stratified squamous epitheliumPosteriorly: (Laryngeal mucosa):Pseudostratified ciliated columnar epithelium

Elastic Cartilage

EpiglottisTrachea MucosaPseudostratified ciliated columnar epitheliumLamina propiaSub mucosaConnective TissueSeromucous bronchial Glands

Hyaline Cartilage

Adventitia

Trachea

Trachea

LungBronchiMucosa; Pseudostratified ciliated columnar epitheliumLamina propiaMuscularis; Submucosa;Connective TissueSeromucous GlandsCartilage layer; Adventitia. Connective Tissue

At 1 mm diameter, the cartilage plates disappear and it becomes a bronchiole.

Respiratory Bronchioles

Alveolar Ducts

And

Alveoli

Intrapulmonary Bronchus

Terminal Bronchiole

Respiratory BronchioleSimple cuboidal epitheliumAlveolar CellsAlveolar Epithelial Cells (Type I Pneumocyte)Type II PneumocyteInteralveolar Pores Alveolar Macrophages (dust cells)Alveolar Surfactant

Alveolar walls & Alveolar cells

Alveolar walls & Alveolar cellsRespiratory Membrane It is the area where gas exchange occurs. It is formed of:Alveolar Epithelium.

Fused basement membranes of the alveolar epithelium and the capillary endothelium.

Capillary Endothelium.

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