Microstructure of respiratory system Dr. Ashraf Hussain

Function of Respiratory System Gets air into and out of the body and allows gas exchange Olfaction Phonation Conducting portion –Nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles –Warms, moistens air Respiratory portion –Respiratory bronchioles, alveolar ducts, alveoli –Gas exchange occurs

Respiratory tree  trachea  main bronchus  lobar bronchus  segmental bronchus  conducting bronchiole  terminal bronchiole  respiratory bronchiole  alveolar duct  alveolar sac  alveolus

The human respiratory tree may consist of up to 28 generations

Layers of Wall Mucosa –Epithelium –Lamina propria (loose CT) –Smooth muscle Submucosa –Dense irregular CT –Glands often present Adventitia

Respiratory Epithelium In the conducting portion: –Ciliated columnar cells 30% –Mucous goblet cells 30% –Basal cells 30% –Generative stem cells that replace other cells --Brush cells (microvilli) 5% Sensory receptor cells –Small granule cell 5% Produce biogenic amines (catecholamines, serotinin, calcitonin) paracrine cells

Surface of Respiratory Mucosa Ciliated cell Goblet cell Brush cell

Small Granule Cell Electron micrograph of a cell of the diffuse neuroendocrine system. Note the accumulation of secretory granules (arrows) in the basal region of the cell. The Golgi complex seen in the upper part of the micrograph shows some secretory granules.

Immotile Cilia Syndrome A disorder that causes infertility in men and chronic respiratory tract infections in both sexes Immobility of cilia and flagella Deficiency of dynein

Smokers Alert

Smokers alert! Proportion of ciliated cells to goblet cells is altered to aid in clearing the increased particulate and gaseous pollutants Reduction in ciliated cells--- decreased movement of the mucous layer---- congestion of small airways

Respiratory epithelium Ciliated pseudostratified columnar epithelium Ciliated columnar cells Mucous goblet cells Brush cells (microvilli on their apical surface) Basal (short) cells Small granule cells (population of diffuse neuro endocrine system)

Stratified squamous epithelium Regions exposed to direct airflow or physical abrasions (e.g., oropharynx, epiglottis, vocal folds) It provides more protection from attrition than does typical respiratory epithelium

Nasal cavity Vestibule----sebaceous and sweat glands, Vibrissae—thick short hairs Nasal fossae– shelf like projections (conchae) Superior conchae covered with specialized olfactory epithelium Other two conchae covered by respiratory epithelium

Nasal Passage Turbinates

Nasal Cavity Vestibule (outer nasal area) –Keratinized epithelium transitions to respiratory –Short hairs filter Nasal Fossae –Chonchae Respiratory epith (pseudostratified squamous) Swell bodies; extensive venous system for countercurrent flow to warm air. Olfactory epithelium of superior choncha

Nasal Mucosa E – Epithelium M – Mucous glands of lamina propria S – Serous glands of lamina propria V – Thin walled venules

Sinuses

Epithelium Lining of Sinus Thinner respiratory epithelium that contains few goblet cells.

Epiglottis: stratifified squamous epithelium False vocal cords: respiratory epithelium True vocal cords: stratified squamous epithelium

Respiratory Structures

Trachea Lined with typical respiratory mucosa “C”shaped rings of hyaline cartilage

Bronchiole Neither cartilage nor glands in mucosa Scattered goblet cells within the epithelium Pseudostratified columnar epithelium, which decreases in height and complexity to become ciliated simple columnar or cuboidal epithelium in smaller terminal bronchioles Terminal bronchioles contain Clara Cells

Functions of Clara cells Produce one of the components of surfactant Act as reserve cells, i.e. they are able to divide, differentiate and replace other damaged cell types Contain enzyme systems which can detoxify noxious substances

Transition of terminal bronchioles into alveolar ducts