Histology of the respiratory system

Objectives

Discuss the microscopic features of Nasal cavity.

Discuss the microscopic features of Epiglottis.

Discuss the microscopic features of Larynx.

Discuss the microscopic features of Trachea.

Discuss the microscopic features of lung.

Respiratory system

LungConducting portion

Intrapulmonary bronchi Bronchioles Terminal bronchioles

Respiratory portion Respiratory bronchioles Alveolar ducts Alveoli

Airways – conducting portionBronchi (extra

pulmonary)TracheaLarynxPharynx (naso – oro –

laringo-)Nasal cavity/mouth –

paranasal sinuses

Function To provide O2To eliminate CO2 from cellsBy respirationBreathing/ventilation (in – out - lung)External respiration (CO2-O2 exchange - in

blood) – respiratory portion - lungTransport of gases – to cellsInternal respiration (CO2-O2 exchange- in the

vicinity of cells)

Breathing/ventilation

Thoracic cage: parietal – visceral pleura lung – pleural cavity – thin film - serous lubricant

Muscles: inter costal – scalenus –abdominal, etc. Diaphragm Elastic – collagen fibers – lung via conducting portion – function

As conduit/ airways/transportFilter clean moistened - warm

Nasal cavity

Walls - bordersnasal septum - bone - cartilageBony wall - ala nasi – cartilageOpenings:

Nares/nostrils – anterior Choanae – posterior

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Nasal cavity Anterior portion – vestibule: vibrissae – skin - sebaceous +

sweat glands

Posterior aspect – nasal fossae: resp ep - conchae (sup, mid, inf), olfactory region, Kiesselbach area: arterial plexuses and venous sinuses bleeding

Nasal Cavity

Keratinized stratified squamous epithelium

Non Keratinized stratified squamous epithelium

Pseudostratified ciliated columnar epithelium with

goblet cells

Olfactory Epithelium

Lamina Propria

Mucous GlandsSerous GlandsVenous SinusesMucoperiosteum or Mucoperichondrium

Secretions of nasal mucosa- Bactericides - Lysozymes

Nasal Cavity

Olfactory regionRoof-nasal cavity, superior aspect-nasal septum,

concha superiorOlfactory epithelium - yellow

Olfactory cells- bipolar neuron: dendrite end - olfactory vesicle – olfactory cilia – odor receptor

Sustentacular cells, basal cells source: Gartner

Lamina propria Bowman’s gland - serousCapillary plexus

Olfactory Epithelium

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Paranasal sinuses

Frontal-maxillary-ethmoid-sphenoidParanasal sinuses - nasal cavityMucosa ≈ posterior nasal cavity

Respiratory epithelium

Lamina propria Seromucous gland Lymphoid tissue

Periosteum

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Pharynx (naso-oro-laringo)

MucosaRespiratory epitheliumStratified squamous epitheliumLamina propria – loose-dense irreguler CT

VascularizedSeromucous glandLymphoid tissue – posterior: pharyngeal tonsil

Skeletal muscle-epimysium

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Larynx – voice box Additional function:

PhonationPrevent food/drinks – respiratory system

Tube : cartilage (hyaline, elastic) – ligaments – skeletal muscles (intrinsic-extrinsic)Epiglottis – elastic cartilage

Stratified squamous non keratinized epithelium Pseudostratified (respiratory epithelium)

Vestibular fold – false vocal cord (superior)Vocal fold - true vocal cord (inferior) - stratified squamous

Vocalis muscle vocal ligament – regular dense elastic CT

Trachea–extrapulmonary bronchusMucosa

Respiratory epithelium – pseudostratified ciliated columnar epithelium: goblet, cilated columnar, basal, brush, serous, DNES cells

L propria – loose fibroelastic-mucous, seromucous gl-lymphoid tissue

--elastic laminaSubmucosa-dense irreg. fibroelastic CT, mucous-

seromucous gl- lymphoid tissueAdventitia – fibroelastic CT - C ring hyaline cartilage (p

cartilaginea) – fibrous CT – smooth muscle (p. membranacea)

Trachea Epithelium

Lamina propria

Submucosa

Adventitia

C shape cartilage

Trachea

Trachea

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Terminal Bronchiole

Lung

Respiratory Bronchiole

Lung Intrapulmonary bronchus

(2ndary -3tiary: lobe – broncho pulmonary segment)Mucosa –folded app

Respiratory epithelium L propria – fibroelastic-

seromucous gl-lymphoid nodules

--Smooth muscles-spiral

Submucosa-seromucous gl-lymphoid nodules

Adventitia – plates of cartilage (hyaline)

BronchiolesMucosa

Pseudostratified columnar epithelium- goblet cells ciliated simple columnar ciliated cuboidal (with Clara cells)

Lamina propria No glands Elastic fibers

Smooth muscles – helical loose meshwork – surrounded by fibroelastic CT

Lung

Terminal bronchiolesMost distal conducting

portionCiliated simple cuboidal

epithelium with Clara cellsLamina propria –

fibroelastic CTSmooth muscle cellsAdventitia-elastic fibers

Terminal Bronchiole

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Alveolar walls & Alveolar cells

Lung

Respiratory brochiolesSimilar – terminal br.Wall – alveoli – gas exchange

Alveolar ductWall ≈ alveoli ends into alveolar sac

Alveolar sacCluster of alveoliOpen – common space -atrium

Alveolar cells

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Alveolus Small air sac - gas exchange Between alveoli – interalveolar septum – alveolar pores

Connective tissue: elastic, reticular (coll III) – lymphoid tissue Macrophages, fibroblast, myofibroblast, mast cells

Continuous capillary bed (from pulmonary artery vein)Both side

Type I pneumocytes/alveolar cells - squamous alveolar cells) – tight junction – basal lamina – very thin region permeable to gasses

Type II pneumocytes/alveolar cells - great alveolar cell – septal cells – surfactant – surface tension↓ ≠ collapse

Alveolus Alveolar macrophages

Monocytes Migrate – through pneumocytes I

lumen alveolus phagocytose surfactant, particulate matter (dust, bacteria) dust cells bronchy – cilia–swallowed/ expectorated

Migrate back - connective tissue - interpulmonary septum lymph vessel

Alveolar pores of Kohn8-60 µmRim: fusion cell membrane

– two pneumocytes I – both side - interalveolar septum

In alveolar septum air communication between alveoli

Function: equalize air pressure

Blood gas barrier

Gas exchange – thinnest region – interalveolar septum: alveolar lumen – bloodSurfactantPneumocyte I – thin regionFused basal laminaeEndothelial cell – continuous capillary

Defense mechanism

Vibrissae – filter large particlesMucus – trap smaller particlesCough reflex – expectorationAlveolar macrophages – phagocytoseLymphoid tissue – specific immune response

Pleura

Mesothelial cellsConnective tissue

Pleural effusion - fluidHaemothorax - bloodPneumothorax - airPleuritis - infection

Clinical correlation Normal

Smooth muscle-bronchioles – para sympathetic Inpiration – relax Expiration-end –contract

Asthmaprolonged contraction –

expiration Lumen << – wheezing, dyspnea Hypersecretion goblet cell,

mucus/serous glSteroids, Β2-agonist -relax

Premature infant surfactant << - respiratory

distress syndromeSynthetic surfactantGlucocorticoid

maturation of pneumocyte II Emphysema

Longterm exposure- cigarette smoke ≈ inh – antitrypsin >< elastase – dust cells – elastic fiber destructed

Source of pictures

Norton NS. Netter’s head and neck anatomy for dentistry. Philadelphia; Saunders:2007.

Gartner LP, Hiatt JL. Color textbook of Histology, 2nd ed. Philadelphia; Saunders:2001

Thank you