Respiratory system PDF

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56.$Epiglottis$–$H&E$stain$ $ ! The%epiglottis%has%a%laryngeal$and$a$lingual$surface,%both%covered%by%stratified$ squamous$nonkeratinized$epithelium% o The%epithelium%of%the%laryngeal%side%is%distinctively%narrower%than%the% epithelium%on%the%oral%side% o Connective%tissue%papillae%are%only%present%on%the%lingual%surface% o On%the%posterior%surface%(laryngeal%surface),%near%the%base%of%the% epiglottis,%the%stratified% squamous%epithelium%transforms% into%ciliated$pseudostratified$ columnar$epithelium% (respiratory%epithelium)% o Taste$buds%are%also%present%on% the%posterior%side%(laryngeal% side)% ! Scattered%lymphocytes%are%often% observed%in%the%lamina%propria%beneath% the%epithelium% ! The%submucosa%is%characterized%by%the% presence%of%mixed%sero@mucous$glands% ! A%cartilage$(fibro@elastic$type)%supports%the%mucosa%and%submucosa% o The%cartilage%is%pitted%by%small$mucous$glands%and%often%perforated%by% excretory%ducts% o The%perichondrium%merges%with%the%submucosa%

% $ 17.$Larynx$–$human,$H&E$stain$ $ ! This%specimen%displays%a%frontal$section%of%a%median!sagitally%hemi!sected% larynx% ! At%this%level,%the%lamina%of%the%thyroid$cartilage$(hyaline$type)%represents%the% skeletal%frame%of%the%larynx%(from%25%years%of%age,%the%cartilage%may%calcify%or% ossify)% Marius'&'Stine'

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The%luminal%outline%shows%two%folds% projecting%into%the%laryngeal%cavity%–% the%vestibular$fold%(the%upper%one)% and%the%vocal$fold$(the%lower%one)% The%luminal%surface%above%the% vestibular%fold%borders%the%laryngeal$ vestibule% The%laterally%extending%recess%between% the%vestibular%and%vocal%folds%is%the% laryngeal$sinus%(laryngeal%ventricle)% The%cavum$subglotticum%(infraglottic% cavity)%is%the%part%of%the%laryngeal% lumen%below%the%vocal%fold% On%the%external%side%of%the%laryngeal% sinus,%the%thyroarytenoid$muscle%is% seen% Between%the%vestibule%and%the%thyroid% cartilage,%the%fibers%of%the% thyroepiglottic$muscle%can%be% identified% The%vocalis$muscle%(triangle!shaped% in%frontal%section)%is%closely%associated% with%the%vocal%ligament%and%the%upper% part%of%the%conus%elasticus%% % The%mucosa%(epithelium%+%lamina% propria):% o The%luminal%surface%of%the% larynx%is%covered%by%ciliated,$ pseudostratified$columnar$ epithelium$(respiratory% epithelium)% o The%exception%is%the%vocal$ folds,%which%are%lined%by% nonkeratinized$stratified$ squamous$epithelium% o The%lamina%propria%is%thin,%and% is%composed%of%loose,%cellular,% highly%vascular%connective% tissue% o The$lamina$propria$of$the%vocal$folds$is$denser,$less$cellular$and$ much$less$vascular%(which%explains%the%whitish%color)% % The%submucosa:% o The%submucosa%is%composed%of%extremely%loose$connective$tissue% containing%sero@mucous$glands% o Many%large%glands%in%the%wall%of%the%laryngeal%sinus%empty%their%secretory% product%over%the%vocal%folds,%which%are%devoid%of%submucosa%and%glands%

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o Dense$fibro@elastic$membranes%of%the% submucosa%support%the%mucosa%of%the% vestibule%and%the%subglotticum%(infraglottic% space)% o The%quadrangular%membrane%beneath%the% mucosa%in%the%vestibule%is%scarcely% identifiable%  Its%free%border%is%the%vestibular$ ligament,%located%in%the%vestibular% fold% o The%elastic%membrane%beneath%the%mucosa% of%the%infraglottic%cavity%is%called%the%conus%elasticus%  Its%free%thickened%border%is%the%vocal$ligament%in%the%vocal%fold% o The%thin%mucosa%over%the%vocal%folds%is%strongly%attached%to%the%vocal% ligament%without$intervening$submucosal$loose$connective$tissue$ % Edema'of'in'the'loose'connective'tissue'of'the'laryngeal'vestibule'is'life'threatening.'

% % 57.$Trachea$–$H&E$stain$ $ ! Cartilaginous$part:%a%C!shaped%framework%of% hyaline$cartilage%–%the%tracheal%rings% ! Membranous$part:$ o The%posterior%surface%of%the%trachea% o Unites%the%tracheal%rings%by%fibroelastic% ligaments%and%bundles%of%smooth$muscle$–$ the$trachealis$muscle% % ! Mucosa:% o Composed%of%pseudostratified,$ciliated$ columnar$epithelium%and%the%lamina$ propria%!%a%loose,%highly%cellular%and% vascular%connective%tissue%layer%rich%in% elastic%fibers%  The%deeper%part%of%the%lamina% propria%is%composed%of%a%condensed% fibroelastic%layer% o The%epithelium%has%a%thick$basement$ membrane%(20!30%μm)%that%appears% glassy,%lightly%stained,%and%is%composed%of% densely%packed%collagenous%fibers% o Mucus%secreting%goblet%cells%are%scattered% among%the%ciliated%cells% % ! Submucosa:% o Loose%connective%tissue%with%numerous% sero!mucous%glands%

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o Bands%of%smooth%muscle%cells%(trachealis$muscle)%are%seen%in%the% membranous%part% o The%perichondrium%of%the%hyaline%cartilage% merges%with%the%connective%tissue%of%the% submucosa% o Hyaline'cartilage'may'partially'ossify'with' age% % Adventitia:% o A%connective$tissue%layer%called%adventitia% invests%the%tracheal%cartilage%rings%and% trachealis%muscle% o Contains%blood%vessels,%nerves%and% lymphatics% o During%histological%procedure,%the%ends%of%the%C!shaped%cartilage%rings% may%be%displaced%into%the%membranous%part%

% % 58.$Lung$–$H&E$stain$ $ ! The%primary$bronchi%(mainstream%bronchi)%arise%from%the%trachea%and%contain% irregular%interconnected%cartilage$plates%arranged%around%the%entire% circumference%of%the%bronchial%wall% ! The%size%and%number%of%these%hyaline%cartilage%plates%decrease%along%the% branching%bronchi% ! Also%the%diameter%of%the%dividing%bronchi%gradually%diminishes%–%the%terminal$ bronchi%(tertiary/segmental%bronchi,%arising%from%the%secondary%bronchi)% display%diameters%less%than%5%mm% ! These%terminal%bronchi%divide,%giving%rise%to%bronchioles%with%diameters%less% than%1%mm% o Bronchioles$do$not$have$cartilage$support$ ! Each%of%the%bronchioles%enter%a%lobule,%and%branches%further%into%5!7%terminal$ bronchioles%% o Thin%connective%tissue%septae%separate%the%adjacent%pyramid!shaped% pulmonary%lobules% ! Each%terminal%bronchiole%subdivides%into%2!4%short,%thin!walled%respiratory$ bronchioles%accompanied%by%a%small%number%of%single%pouches%along%their%paths% called%alveoli% ! The%respiratory%bronchioles%continue,%subdividing%into%several%long%passages% called%alveolar$ducts% o These%ducts%display%dilated%portions%called%atria,%which%lead%into%two%or% more%clusters%of%alveoli,%called%alveolar$sacks% ! Respiratory%bronchioles,%alveolar%ducts%and%alveolar%sacks%all%display%alveoli% ! The%pulmonary$artery%branches%parallel%with%the%dichotomizing%(dividing%into% two%parts)%air%passage% ! Both%the%pulmonary$arteries$and$pulmonary$veins$have$thinner$walls$than% those%of%the%systematic%circulation% ! To%differentiate%between%arteries%and%veins%within%the%lungs:%arteries%and%bronchi% usually%run%together,%while%veins%are%situated%further%away%from%the%bronchi% Marius'&'Stine'

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Segmental%bronchus:% o Arise%from%secondary%bronchi%(lobar%bronchi)% o The%epithelium%of%the%segmental%bronchi%is%composed%of%pseudostratified$ ciliated$columnar$cells,%but% pseudostratification%and%goblet$ cell%numbers%are%less%than%those% in%the%trachea%or%in%the%primary% bronchi% o Beneath%the%epithelium%is%the%thin% lamina%propria% o A%smooth$muscle%layer%spirally% encircles%the%bronchus%lumen%at% the%mucosal!submucosal% boundary% o The%submucosal%loose%connective% tissue%contains%sero@mucous$ glands,%and%on%the%outer%aspect%of% the%submucosal%layer,%the%cartilage$framework%is%composed%of%isolated% cartilage%plates% o The%outermost%connective%tissue%layer%is%called%the%adventitia,%merging% with%the%submucosa%and%the%connective%tissue%of%adjacent%blood%vessels% and%nerves%% Bronchiole:% o They%arise%from%segmental%bronchi% o There%is%no$cartilaginous$support$ around$the$bronchioles% o They%are%devoid$of$glands% o The%lamina%propria%contains% mainly$smooth$muscle$and$ elastic$fibers%  The%proportion%of%smooth% muscle%is%the%largest%in%the% bronchiolar%walls% o The%epithelium%is%composed%of% simple$ciliated$columnar$cells% o After%death,%the%contraction%of%bronchiolar% muscle%cells%results%in%a%star@shaped$lumen% o They%divide%into%terminal%bronchioles% Respiratory%bronchiole:% o They%arise%from%terminal%bronchioles% o They%are%lined%with%simple$cuboidal$ epithelium% o The%lamina%propria%is%composed%of%a%small% amount%of%connective$tissue%and%some% smooth$muscle$cells%arranged%in%a%spiral% manner% o As%stated%above,%the%thin%walls%of%the% respiratory%bronchioles%contain%some%single% alveoli%

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Alveolar%ducts:% o These%are%long%passages%that%open%into%the% alveolar%sacs% o Only%the%small%aggregations%of%smooth$ muscle$cells%that%form%rings%around%the% alveolar%ducts,%and%the%openings%of%the% alveolar%sacs%can%be%seen%in%the%walls%of%the% alveolar%ducts%%

% % 60.$Lung$–$human,$toluidine$blue$(semithin$section,$illustrations$with$a$different$ stain)$ $ ! At%the%periphery%of%the%slide,%a%large%intrapulmonary% bronchus%is%present% o Its%epithelium%is%typical%pseudostratified%ciliated% columnar% o Among%the%columnar%epithelial%cells,%unicellular% glands%called%goblet$cells%(which%secrete%mucin)% can%be%observed% ! In%the%terminal%and%respiratory%bronchioles,%the%simple% epithelium%consists%of%low%columnar%to%cuboidal%cells% and%may%be%non!ciliated% % ! Alveolar%epithelium%consists%of%two%types%of%cells:% o Simple$squamous%type%I%alveolar%epithelial%cells,%called%type$I$ pneumocytes%  Type%I%pneumocytes%have%a%highly%attenuated%cytoplasm%covering% most%of%the%alveolar%surface%  Due%to%the%particularly% extensive%cytoplasm,%the% nuclear%region%is%rarely% visible% o Type%II%alveolar%epithelial%cells,% called%type$II$pneumocytes$(great$ alveolar$cells)$  These%cells%are%round%in% shape,%displaying%large% round%nuclei%and%vacuolated% cytoplasm%  They%are%easily%recognized% since%their%foamy$ cytoplasm%with%rounded% luminal%surfaces%project%into% the%alveolar%lumen%  The%type%II%pneumocytes%greatly%outnumber%the%type%I% pneumocytes%(approximately%75%–%90%%%of%the%alveolar%epithelial% cells%are%type%II%pneumocytes)%

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These%cells%are%primarily%responsible%for%the%secretion%of% pulmonary$surfactant% Around%the%alveoli,%terminal%branches%of%pulmonary% arteries%form%the%richest%capillary%bed%of%the%human% body% The%capillary$endothelial$lining%is%particularly%thin% where%it%is%in%contact%with%the%alveolar%epithelium% o The%endothelial%and%alveolar%extremely%thin% cytoplasm%and%their%fused%supporting%basal% laminae%form%the%blood!air%barrier%% The%interalveolar$septum%is%a%minute%space%between% the%walls%of%adjacent%alveoli% The%septa%may%contain%only%a%continuous%capillary,%or%it% may%be%wider,%containing%a%capillary,%thin%collagen%fibers% (type%III),%elastic%fibers,%macrophages,%fibroblasts% and/or%myofibroblasts% Alveolar$macrophages%are%located%either%in%the%interalveolar%septa%or%on%the% luminal%surfaces%of%pneumocytes% o The%macrophages%exhibit%an%irregular% shape%and%are%large%in%size%(15!35%µm)%and% may%be%easily%recognized%since%the%engulfed% carbon%and%dust%particles%stain%them%dark% It%is%extremely%difficult%to%differentiate%type%I% alveolar%cells%and%endothelial%cells%using%a%light% microscope%

% % 59.$Lung$–$monkey,$Resorcin$fuchsin$ % ! Resorcin%fuchsin%stains%the%elastic%fibers%deep%blue%while%Orcein%stains%a%brown% color% ! Under%the%epithelium,%broad%longitudinal%bundles$of$elastic$fibers%follow%the% course%of%the%branching%respiratory%tree% ! The%proportion%of%elastic%fibers%increases%towards%the%periphery%of%the%bronchial% tree% ! In%the%alveolar%well,%a%rich$elastic$network$surrounds%the%lining%epithelium% ! At%the%rim%of%alveolar%and%atrial%(distal%terminations%of%alveolar%ducts)%openings,% the%elastic%and%fine%reticular%fibers%form%an%elastic$and%supporting$ring% ! The%larger%pulmonary%arteries%display%a%well!developed%internal$elastic$ membrane$and%a%less%prominent%external%elastic%membrane% ! The%smaller%pulmonary%arteries%contain%only%internal%elastic%membrane,%while% the%pulmonary%veins%have%neither%internal%nor%external%elastic%membranes% % % 61.$Fetal$lung$–$human,$H&E$stain$ $ ! The%specimen%has%been%taken%from%a%seven!month!old%fetus%at%the%early$alveolar$ phase$of%lung%development%

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The%alveolar%distension%(balloon%effect,%due%to%aspiration%of% amniotic%fluid)%is%still%minimal% The%glandular$appearance$of%fetal%lung%tissue%makes%it% difficult%to%recognize%it% o Therefore,%the%entire%slide%must%be%actively%studied% to%find%the%lung!specific%structure:%hyaline$cartilage$ which%cannot%be%found%in%glands% The%fetal%segmental%pulmonary$artery%has%a%thick$ muscular$wall$ o In%fetal%life,%the%pulmonary%arterial%pressure%is%high,% forcing%blood%from%the%right%ventricle%through%the% ductus%arteriosus%into%the%systemic%circulation% o After%birth,%by%the%third%postnatal%day,%the%pulmonary%arteries%enlarge%and% their%muscularis%tunica%media%becomes%thin% Alveolar%epithelial%cells%do%not%differentiate%into%type%I%and%type%II%pneumocytes% until%late%pregnancy% Secretion%of%surfactant%begins%in%the%7th%month%of% gestation% o Surfactant%is%produced%by%type%II%pneumocytes% and%reduces%surface%tension%throughout%the% lungs%

' *Immaturity*of*the*lungs:** ! The*most*common*cause*of*neonatal*respiratory* distress*syndrome*and*hyaline*membrane*disease* ! The*fundamental*defect*is*a*deficiency*of*pulmonary* surfactant*resulting*in*lung*collapse*with*each* successful*breath*

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