Histology Of The Respiratory System

Histology of the Respiratory System Ma. Minda Luz M. Manuguid, M.D.

The Respiratory Tract

The Respiratory Tract 

Conducting Portion - nasal passages, nasopharynx, larynx, trachea, bronchi, bronchioles *epithelium (mucosa):

pseudostratified columnar ciliated 

Respiratory Portion - respiratory

bronchioles, alveolar ducts, alveolar sacs, alveoli

*epithelium: simple squamous

Respiratory Epithelium

Nasal cavities 

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External nares - watery, filtering secretions & mucinous secretions vibrissae - large, short coarse hairs Nasal conchae/turbinates - superior, inferior, & middle plates of scalloped bone projecting into the nasal cavity - induce turbulent airflow to trap debris Extensive vascular bed - warms, cools, & moistens air

Nasal glands

Olfactory Epithelium 

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Olfactory epithelium - upper posterior portion of nasal cavities, just lateral to the nasal septum: Bowman’s glands - serous secretions moisten mucosa & bathe the olfactory cells Olfactory cells – bipolar neurons with very long nonmotile cilia; contain chemoreceptors; axons grouped into ‘fila olfactoria’ that penetrate the cribriform plate of the ethmoid bone to the olfactory lobe of the CNS Sustentacular cells – have apical microvilli

Respiratory & Olfactory Epithelium

Olfactory epithelium 

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Olfactory Cells (red arrow) - bipolar neurons that span the entire length of the epithelium, provide the sense of smell; nuclei can usually be found in the middle of the epithelium supportive Sustentacular cells (blue arrow) - provide mechanical and metabolic support to the olfactory cells; nuclei are usually the most superior ones, (closest to the lumen) . Basal Cells (green arrow) - cells that will give rise to

Nasopharynx 

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connects nasal cavities to the Larynx; abuts the oropharynx Epithelium is mostly pseudostratified columnar, with patches of stratified squamous, esp. in lower pharynx & epiglottis Pharyngeal tonsil (adenoid) – dorsomedial

Larynx  

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Glottis - laryngeal aperture Vocal folds/cords - folds of laryngeal mucosa on either side of the glottis: upper ventricular (false) & lower caudal (true) Laryngeal ventricles - deep recesses between cranial & caudal vocal folds Lining: stratified squamous on upper surface, epiglottis, & vocal folds; the rest -pseudostratified columnar ciliated

The Larynx

Larynx

Larynx 

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Hyoid bone - ‘caps’ the laryngeal body Epiglottis - ventral rim Laryngeal cartilages – hyaline & elastic Mucous glands especially abundant in the ventricular folds

Laryngeal cartilages 

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Thyroid cartilage - s -

anterior, large, broad, shield-like, hyaline cartilage Arytenoid – p - upper dorsal hyaline & elastic Corniculate – p - upper dorsal, elastic cartilage Cuneiform – p - form the rim of the larynx, elastic Cricoid – s - circular, hyaline, on top of trachea

Larynx: the Voice Box 

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The muscles inserting onto the outside wall can change the shape of the box, and in so doing change the tension and vibration frequencies of the vocal folds. Air being moved through from the depths of the respiratory system causes the vibration to occur. Overtones, harmonics, and other sounds are added by the echoes produced in the chest cavity, the tongue, the teeth, and the oral cavity.

Phonation involves distortion of the shape so that

the vocal folds at the cranial end vibrate at different rates and produce different tones.

Trachea 

Mucosa • Goblet cells - apical microvilli, apocrine secretion of mucin/mucus • Ciliated cells - numerous cilia • Short/basal cells - undifferentiated • Brush cells - apical microvilli (brush border): brush 1 cells- unusually long microvilli; brush 2 cellsshort microvilli • Small granule (APUD) cells catecholaminelike secretion • Free nerve endings • Mucous glands with serous demilunes

Trachea

Trachea 

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Lamina propria – areolar connective tissue, irregular weave of collagen & elastic fibers; many fibroblasts; also lymphocytes, plasma cells, macrophages, segmenters Elastic membrane – between mucosa & submucosa Submucosa – collagen, fibroblasts, blood vessels, lymphatics Cartilages – C-shaped hyaline cartilages; open

Bronchi 1° bronchi → 2° bronchi → bronchioles → terminal bronchioles → respiratory bronchioles  Lining - pseudostratified ciliated columnar with goblet cells, macrophages, fibroblasts  Mucous glands with myoepithelial cells  Irregular plates of hyaline cartilage  Smooth muscle fibers ***As one goes lower into the bronchial tree, the diameter of the lumen & thickness of the wall are progressively smaller; there is less cartilage, more smooth muscles; 

Bronchi

Bronchioles 

Bronchioles - simple columnar ciliated

epithelium; bronchiolar (Clara) cells; brush cells; few small granule cells; smooth muscle cells; fibroblasts; reticular, collagen & ↑elastic fibers; no cartilage 

Terminal bronchioles - simple cuboidal nonciliated

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epithelium;

Respiratory bronchioles - simple cuboidal

epithelium with cilia; bronchiolar cells; smooth muscles; fibroblasts; collagen fibers ***NO cartilage in walls of bronchioles <1 mm. in diameter ***Clara cells - domed apex with granules, basal RER, apical SER- secrete moistening fluid for

Bronchus & Bronchiole

Alveolar Ducts, Atria, & Sacs 

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Respiratory bronchiole → Alveolar ducts → Atria → Alveolar sacs → Alveoli Epithelium: - simple squamous (< 1µm thick) type I cells - great alveolar/septal/ type II cells – rounded or low cuboidal cells that protrude into alveolar spaces; contain multivesicular & multilamellar bodies (cytosomes); secrete surfactant (DPPC: DiPalmitoylPhosphatidylCholine); are also reserve cells – can produce more

Alveolar Ducts, Sacs, Alveoli

Alveolar Capillaries

Alveolar Cells

Alveolar Cells

Pulmonary Alveolar Macrophages

The Pleura 

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Visceral layer adherent to the outer surface of the lungs; simple squamous mesothelium; secretes pleural fluid Parietal layer outer layer; lined by mesothelium; separated from visceral layer by

The Pleura

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