embryology of the respiratory system - uwi...

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EMBRYOLOGY EMBRYOLOGY OFOFOF OF

THE THE RESPIRATORYRESPIRATORYRESPIRATORY RESPIRATORY

SYSTEMSYSTEM

Formation of Embryonic DiskFormation of Embryonic Disk(first three weeks)(first three weeks)

Gastrulation

15 daysy

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Formation of Embryonic DiskFormation of Embryonic Disk(first three weeks)(first three weeks)

Implantation of Implantation of blastocystblastocyst–– ExocoelomicExocoelomic cavitycavity–– Inner cell massInner cell massInner cell massInner cell mass

Formation of amniotic cavity inside inner cell massFormation of amniotic cavity inside inner cell massFormation of primary yolk sac cavity inside Formation of primary yolk sac cavity inside exocoelomicexocoelomic cavitycavity

–– Formation of Formation of bilaminarbilaminar embryonic disc between amniotic embryonic disc between amniotic cavity & yolk saccavity & yolk sac

EpiblastEpiblast Layer (amniotic cells Layer (amniotic cells -- epiblastsepiblasts) ) –– Future EctodermFuture EctodermHypoblast Layer (primary yolk sac cells) Hypoblast Layer (primary yolk sac cells) –– Future EndodermFuture Endoderm

–– GastrulationGastrulation::GastrulationGastrulation: : Formation of primitive streak & groove on surface of Formation of primitive streak & groove on surface of EpiblastEpiblastMigration of Migration of EpiblastEpiblast cells to Hypoblast & formation of Endodermcells to Hypoblast & formation of EndodermFormation of Formation of IntraembryonicIntraembryonic Mesoderm between Ectoderm & Mesoderm between Ectoderm & Endoderm from Endoderm from EpiblastEpiblast cellscellsFormation of the Ectoderm from cells remaining in Formation of the Ectoderm from cells remaining in EpiblastEpiblast

–– Formation of Formation of TrilaminarTrilaminar EnbryonicEnbryonic Disc between amniotic Disc between amniotic cavity & yolk sac cavity & yolk sac

ESTABLISHMENT of GENERAL BODY ESTABLISHMENT of GENERAL BODY FORM FORM

((at the beginning of the fourth week)at the beginning of the fourth week)FoldingFolding of theof the flatflat trilaminartrilaminar embryonicembryonicFoldingFolding of the of the flat flat trilaminartrilaminar embryonic embryonic diskdisk into a into a cylindricalcylindrical embryo.embryo.–– Longitudinal Folding in the Median Plane:Longitudinal Folding in the Median Plane:

Cranial and caudal foldingCranial and caudal folding–– Transverse Folding in Horizontal Plane:Transverse Folding in Horizontal Plane:Transverse Folding in Horizontal Plane: Transverse Folding in Horizontal Plane:

Right and left lateral to medial folding. Right and left lateral to medial folding.

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Trilaminar Embryonic Disk Trilaminar Embryonic Disk (3 weeks)(3 weeks)

Trilaminar Embryonic Disk (3 weeks)Trilaminar Embryonic Disk (3 weeks)

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Folding in Median & Horizontal Plane Folding in Median & Horizontal Plane (4(4thth week)week)

Folding in Median & Horizontal Plane Folding in Median & Horizontal Plane (4(4thth week)week)

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OropharyngealOropharyngeal membrane (ruptures at 24 days)membrane (ruptures at 24 days)

CloacalCloacal Membrane (Membrane (ruptures at the end of 7ruptures at the end of 7thth weekweek))

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DEVELOPMENT OF THE FACEDEVELOPMENT OF THE FACE((from fourth to eighth weeksfrom fourth to eighth weeks))

DEVELOPMENT OF THE PRIMITIVE DEVELOPMENT OF THE PRIMITIVE MOUTH MOUTH –– STOMODEUM STOMODEUM (beginning (beginning f 4f 4thth k)k)of 4of 4thth week) week)

Rupture of Rupture of oropharyngealoropharyngeal; membrane (24; membrane (24thth day)day)

DEVELOPMENT OF THE NASAL DEVELOPMENT OF THE NASAL CAVITYCAVITY ((from the end of 4from the end of 4thth weekweek))

R t fR t f ll b (6b (6thth k)k)Rupture of Rupture of oronasaloronasal membrane (6membrane (6thth week)week)Development of Development of paranasalparanasal air air sinusessinuses from from deverticulideverticuli of nasal of nasal walls during late fetal life & after birthwalls during late fetal life & after birth

DEVELOPMENT OF THE PRIMITIVE MOUTH DEVELOPMENT OF THE PRIMITIVE MOUTH (STOMODEUM)(STOMODEUM)

It develops from five facial primordia:It develops from five facial primordia:––Frontonasal prominenceFrontonasal prominencepp

It constitutes cranial boundaryIt constitutes cranial boundary––Paired maxillary prominencesPaired maxillary prominences

They form lateral boundariesThey form lateral boundaries––Paired mandibular prominencesPaired mandibular prominences––Paired mandibular prominencesPaired mandibular prominences

They constitute caudal boundaryThey constitute caudal boundary

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Stomodeum & Nasal Stomodeum & Nasal PlacodesPlacodes

Stomodeum

DEVELOPMENT OF THE NASAL CAVITYDEVELOPMENT OF THE NASAL CAVITYNasal Nasal placodesplacodes (bilateral right & left oval thickenings of surface (bilateral right & left oval thickenings of surface

ectoderm) develop on each side of inferior part of ectoderm) develop on each side of inferior part of frontonasalfrontonasalprominence by the end of the fourth week.prominence by the end of the fourth week.HorseshoeHorseshoe--shaped elevations at margins of theseshaped elevations at margins of these placodesplacodes areareHorseshoeHorseshoe--shaped elevations at margins of these shaped elevations at margins of these placodesplacodes are are formedformed

Medial & lateral sides of each elevation (surrounding one Medial & lateral sides of each elevation (surrounding one placodeplacode) are called ) are called as as Medial & Lateral Nasal ProminencesMedial & Lateral Nasal Prominences respectively respectively

Nasal Nasal placodesplacodes now lie in depressions called now lie in depressions called Nasal PitsNasal PitsProgressive deepening of nasal pits form Progressive deepening of nasal pits form Nasal SacsNasal Sacs

Medial & Lateral Nasal Prominence form a boundary of Medial & Lateral Nasal Prominence form a boundary of NarisNarisNasal sacs are separated from oral cavity by Nasal sacs are separated from oral cavity by oronasaloronasalp y yp y ymembrane, which ruptures during the sixth weekmembrane, which ruptures during the sixth week

This forms primitive This forms primitive choanaechoanae, which lie posterior to primitive palate, which lie posterior to primitive palateAfter secondary palate develops, After secondary palate develops, choanaechoanae lie at junction of nasal cavity and lie at junction of nasal cavity and nasopharynxnasopharynx

Nasal septum, incisive bone & central part of upper lip develop Nasal septum, incisive bone & central part of upper lip develop from merged medial nasal prominences.from merged medial nasal prominences.

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Formation of Nasal PlacodesFormation of Nasal Placodes

Formation of Nasal Pits & SacsFormation of Nasal Pits & Sacs

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Boundaries of Right Nasal PitBoundaries of Right Nasal Pit

Merging of Medial Nasal ProminencesMerging of Medial Nasal Prominences

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Formation of Nasal ProminencesFormation of Nasal Prominences

Beginning of Merging of Medial Nasal ProminencesBeginning of Merging of Medial Nasal Prominences

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Merging of Medial Nasal Prominences is CompletedMerging of Medial Nasal Prominences is Completed

Derivatives of Merged Medial Nasal ProminencesDerivatives of Merged Medial Nasal Prominences

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Development of Nasal CavityDevelopment of Nasal Cavity

Components of Inferior Nasal Wall in AdultComponents of Inferior Nasal Wall in AdultView from Oral Cavity

Secondary Palate

Interpalatine suture

or Incisive bone(primary palate)

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Congenital Anomalies of Middle Face Area:Congenital Anomalies of Middle Face Area:Oblique cleft of the face (persistent nasolacrimal Oblique cleft of the face (persistent nasolacrimal grove)grove)–– It connect mouth to medial palpebral angle of the orbitIt connect mouth to medial palpebral angle of the orbit

N l i l d t i tN l i l d t i t–– Nasolacrimal duct is present as open groveNasolacrimal duct is present as open groveIt results from failure of fusion of lateral nasal and maxillary It results from failure of fusion of lateral nasal and maxillary prominencesprominences

Cleft upper lip, superior alveolar arch and palateCleft upper lip, superior alveolar arch and palate–– It results from failure of fusion of medial nasal and maxillary It results from failure of fusion of medial nasal and maxillary

prominencesprominencesThey could be unilateral or bilateralThey could be unilateral or bilateral

Bilateral Oblique Cleft of the FaceBilateral Oblique Cleft of the Face

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Unilateral Cleft Upper Lip, Superior Alveolar Arch & PalateUnilateral Cleft Upper Lip, Superior Alveolar Arch & Palate

Right

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Bilateral Cleft Upper Lip, Superior Alveolar Arch & PalateBilateral Cleft Upper Lip, Superior Alveolar Arch & Palate

After Orthopedic Correction

Remaining Bilateral Cleft Palate in AdultRemaining Bilateral Cleft Palate in Adult

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DEVELOPMENT OF THE DEVELOPMENT OF THE BRANCHIAL APPARATUS BRANCHIAL APPARATUS (arches, pouches, grooves, (arches, pouches, grooves,

membranes)membranes)membranes)membranes)Branchial archesBranchial arches (from 1 to 6) develop (from 1 to 6) develop early in week 4 as neural crest cells early in week 4 as neural crest cells migrate through the mesenchyme to the migrate through the mesenchyme to the f t h d d k i f if t h d d k i f ifuture head and neck region, forming future head and neck region, forming elevations of mesoderm on each side of elevations of mesoderm on each side of the primitive pharynx.the primitive pharynx.

BRANCHIAL APPARATUS BRANCHIAL APPARATUS INCLUDES:INCLUDES:

Branchial archesBranchial archesBranchial archesBranchial archesBranchial groovesBranchial groovesBranchial pouches Branchial pouches Branchial membranesBranchial membranes

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A Typical Branchial Arch Contains:A Typical Branchial Arch Contains:An aortic archAn aortic arch

Derivatives of branchial arch arteriesDerivatives of branchial arch arteriesA cartilaginous roadA cartilaginous road

Derivatives of branchial arch cartilagesDerivatives of branchial arch cartilagesA nerveA nerve

Derivatives of branchial arch nervesDerivatives of branchial arch nervesDerivatives of branchial arch nervesDerivatives of branchial arch nervesA muscular componentA muscular component

Derivatives of branchial arch musclesDerivatives of branchial arch muscles

Development of Branchial ApparatusDevelopment of Branchial Apparatus

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FURTHER DEVELOPMENT OF FURTHER DEVELOPMENT OF THE BRANCHIAL THE BRANCHIAL

APPARATUS AND ITS APPARATUS AND ITS DERIVATIVESDERIVATIVES

DEVELOPMENT OF THE DEVELOPMENT OF THE LARYNX, TRACHEA, LARYNX, TRACHEA, BRONCHIAL TREE, LUNGS AND BRONCHIAL TREE, LUNGS AND PLEURAPLEURA

Development of Lower Airway & LungsDevelopment of Lower Airway & LungsThe lower airway and lungs develop as an outgrowth The lower airway and lungs develop as an outgrowth from the primitive gut. from the primitive gut. A laryngotracheal diverticulum buds out from the A laryngotracheal diverticulum buds out from the primitive pharynx about the fourth weekprimitive pharynx about the fourth weekprimitive pharynx about the fourth week.primitive pharynx about the fourth week.–– Its blind end forms the lung bud.Its blind end forms the lung bud.

The tracheoesophageal septum separates the The tracheoesophageal septum separates the growing lung bud from the esophagus.growing lung bud from the esophagus.The lung bud continues to elongate and branch into The lung bud continues to elongate and branch into bronchial buds, secondary bronchi etc. bronchial buds, secondary bronchi etc.

About 24 orders of branches are eventually formed, with the last few About 24 orders of branches are eventually formed, with the last few y ,y ,being formed after birth. being formed after birth.

The endoderm of the lung bud gives rise to the The endoderm of the lung bud gives rise to the epithelium and glands of the lower airwayepithelium and glands of the lower airway. . The mesenchyme, that surrounds the bud, gives rise The mesenchyme, that surrounds the bud, gives rise to connective tissue, cartilage, muscle, vessels & to connective tissue, cartilage, muscle, vessels & pleurae. pleurae.

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Scheme of Development of Lower Airway & LungsScheme of Development of Lower Airway & Lungs

Scheme of Development of Lower Airway & LungsScheme of Development of Lower Airway & Lungs

Lung BronchialBud

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View of Developing Lower Airway & Lung BudView of Developing Lower Airway & Lung Bud

Development of Laryngeal InletDevelopment of Laryngeal Inlet

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Development of Trachea & Lung BudsDevelopment of Trachea & Lung Buds

Separation of Trachea from EsophagusSeparation of Trachea from Esophagus

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CONGENITAL ABNORMALITIES OF TRACHEA:CONGENITAL ABNORMALITIES OF TRACHEA:Tracheoesophageal Fistula (Common):Tracheoesophageal Fistula (Common):

Communication connecting trachea & esophagus that Communication connecting trachea & esophagus that occurs in every 2500 birthsoccurs in every 2500 births

It has four main varieties:It has four main varieties:1. Superior portion of esophagus ends blindly 1. Superior portion of esophagus ends blindly (esophageal atresia), inferior portion joins trachea near its (esophageal atresia), inferior portion joins trachea near its bifurcation (most common bifurcation (most common –– 90%)90%)2. Esophagus has communication with trachea near its 2. Esophagus has communication with trachea near its bifurcationbifurcation3. Upper end of esophagus has communication with 3. Upper end of esophagus has communication with trachea near its bifurcation, whereas the lower portion trachea near its bifurcation, whereas the lower portion ends blindlyends blindlyends blindlyends blindly4. Upper end of esophagus has communication with 4. Upper end of esophagus has communication with trachea, whereas the lower portion of esophagus also has trachea, whereas the lower portion of esophagus also has communication with trachea near its bifurcationcommunication with trachea near its bifurcation

Tracheal Stenosis (narrowing) and Atresia (closure)Tracheal Stenosis (narrowing) and Atresia (closure)Tracheal diverticulumTracheal diverticulum

Tracheoesophageal Fistula Tracheoesophageal Fistula -- 11

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Development of LungsDevelopment of Lungs

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Development of Lung Buds: 41Development of Lung Buds: 41--45 days45 days

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Development of Lungs: 13 weeksDevelopment of Lungs: 13 weeks

Posterior View

Adult Lungs Adult Lungs –– Front ViewFront ViewNot SmokerNot Smoker SmokerSmoker

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PeriodsPeriods of Lung Developmentof Lung Development

Pseudoglandular period (5 Pseudoglandular period (5 –– 17 17 weeks)weeks)))Canalicular period (16 Canalicular period (16 –– 25 weeks)25 weeks)Terminal sac period (24 weeks to Terminal sac period (24 weeks to birth)birth)Alveolar period (late fetal period to 8 Alveolar period (late fetal period to 8 years after birth)years after birth)

PeriodsPeriods of Lung Developmentof Lung DevelopmentFrom 5From 5--17 weeks the branching forms the 17 weeks the branching forms the bronchi and terminal bronchioles. bronchi and terminal bronchioles. From 17From 17--24 weeks the diameter of the tube 24 weeks the diameter of the tube increases and respiratory bronchioles and increases and respiratory bronchioles and alveolar ducts develop. alveolar ducts develop. At 25 weeks the alveolar sacs give rise to At 25 weeks the alveolar sacs give rise to primitive alveoli with cuboidal epithelium. By 26 primitive alveoli with cuboidal epithelium. By 26 weeks the alveoli have become vascularizedweeks the alveoli have become vascularizedweeks the alveoli have become vascularized. weeks the alveoli have become vascularized. By this stage the production of surfactant has By this stage the production of surfactant has begun and the fetus might survive if born begun and the fetus might survive if born prematurely. prematurely.

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PeriodsPeriods of Lung Developmentof Lung Development

Pseudoglandular Pseudoglandular (5(5--17 w)17 w) & Canalicular & Canalicular (16(16––25 w)25 w) PeriodsPeriods

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Canalicular Canalicular (16(16––25 w)25 w) & Terminal Sac & Terminal Sac (24w to birth)(24w to birth) PeriodsPeriods

PeriodsPeriods of Lung Developmentof Lung DevelopmentBarriers to survival born by 26 week are the Barriers to survival born by 26 week are the small surface area available for gas exchange, small surface area available for gas exchange, lack of adequate development of the pulmonary lack of adequate development of the pulmonary vasculature and insufficient surfactant vasculature and insufficient surfactant production. production. The lung must develop further however before it The lung must develop further however before it is mature.is mature.This process of maturation continues for aboutThis process of maturation continues for aboutThis process of maturation continues for about This process of maturation continues for about eight years, as the number of alveoli increase.eight years, as the number of alveoli increase.

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Developed Respiratory SystemDeveloped Respiratory System

CONGENITAL ABNORMALITIES:CONGENITAL ABNORMALITIES:INFANT RESPIRATORY DISTRESS INFANT RESPIRATORY DISTRESS SYNDROME (IRDS)SYNDROME (IRDS): : ( )( )–– Also calledAlso called Hyaline Membrane DiseaseHyaline Membrane DiseaseCongenital Lung CystsCongenital Lung CystsAgenesis of Lungs or one LungAgenesis of Lungs or one LungL H l iL H l iLung HypoplasiaLung HypoplasiaAccessory LungAccessory LungLobe of Azygos VeinLobe of Azygos Vein

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Features of Respiratory Distress SyndromeFeatures of Respiratory Distress SyndromeInfants born premature with weights of up to 1.5 kg Infants born premature with weights of up to 1.5 kg show RDSshow RDSTheir surfactant producing cells (type II pneumocytes Their surfactant producing cells (type II pneumocytes & Clara cells) are not properly developed& Clara cells) are not properly developedDeficiency of pulmonary surfactantDeficiency of pulmonary surfactant

In absence of surfactant alveoli tend to collapse during exhalationIn absence of surfactant alveoli tend to collapse during exhalation

Lungs are under inflated, alveoli contain a fluid of high Lungs are under inflated, alveoli contain a fluid of high protein content that resembles a hyaline (glassy) protein content that resembles a hyaline (glassy) membranemembraneProlonged intrauterine asphyxia may also produceProlonged intrauterine asphyxia may also produceProlonged intrauterine asphyxia may also produce Prolonged intrauterine asphyxia may also produce irreversible changes in type II alveolar cells irreversible changes in type II alveolar cells (responsible for surfactant production)(responsible for surfactant production)Infants develop rapid, labored breathingInfants develop rapid, labored breathing

Infants must inhale each time with extra force to reopen alveoli on Infants must inhale each time with extra force to reopen alveoli on next breath and they rapidly becomes exhaustednext breath and they rapidly becomes exhausted

DEVELOPMENT OF THE DEVELOPMENT OF THE PLEURA AND PLEURAL PLEURA AND PLEURAL

CAVITIESCAVITIESCAVITIESCAVITIESPleural cavities develop from the Pleural cavities develop from the Intraembryonic Intraembryonic CoelomCoelom–– Right pleural cavity forms from Right PericardioRight pleural cavity forms from Right Pericardio--Peritoneal Peritoneal

CanalCanal–– Left pleural cavity forms from Left PericardioLeft pleural cavity forms from Left Pericardio--Peritoneal Peritoneal

CanalCanalPleurae develop from the Lateral Mesoderm of Three Pleurae develop from the Lateral Mesoderm of Three Laminar Embryonic DiscLaminar Embryonic Disc–– Parietal Pleura Parietal Pleura –– from Somatopleurefrom Somatopleure–– Visceral Pleura Visceral Pleura –– from Splanchnopleurefrom Splanchnopleure

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3 Somite Embryo of 21 Days3 Somite Embryo of 21 Days

Position of Intraembryonic CoelomPosition of Intraembryonic Coelom

Intraembryonic Coelom

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Development of Pleural CavitiesDevelopment of Pleural Cavities

Development of Pleural CavitiesDevelopment of Pleural Cavities

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Development of DiaphragmDevelopment of DiaphragmDiaphragm develops from 4 sources:Diaphragm develops from 4 sources:

1) Septum Transversum1) Septum Transversum––1) Septum Transversum1) Septum Transversum––2) Pleuroperitoneal Membranes2) Pleuroperitoneal Membranes––3) Dorsal Mesentery of Esophagus3) Dorsal Mesentery of Esophagus––4) Body Wall4) Body Wall) y) y

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Diaphragmatic HerniasDiaphragmatic Hernias

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FETAL CIRCULATION: FETAL CIRCULATION: Oxygenated Blood Oxygenated Blood

Oxygenated Blood from Placenta Oxygenated Blood from Placenta Umbilical vein Umbilical vein Branch of Hepatic Portal VeinBranch of Hepatic Portal Vein DuctusDuctus venosusvenosusBranch of Hepatic Portal Vein Branch of Hepatic Portal Vein DuctusDuctus venosusvenosusInferior Vena Cava (Mixture with Venous blood) Inferior Vena Cava (Mixture with Venous blood) Right atrium Right atrium Foramen Foramen OvaleOvaleLeft atrium Left atrium Left ventricle Left ventricle Aorta Aorta –– Mixture with Venous blood from Pulmonary trunkMixture with Venous blood from Pulmonary trunk

Systemic circulation Systemic circulation Umbilical artery Umbilical artery Placenta Placenta

FETAL CIRCULATION: FETAL CIRCULATION: Deoxygenated BloodDeoxygenated Blood

Venous blood from Superior Vena Cava Venous blood from Superior Vena Cava Right atrium Right atrium Right ventricleRight ventricleRight ventricle Right ventricle Pulmonary trunk Pulmonary trunk Left pulmonary artery Left pulmonary artery DuctusDuctus arteriosusarteriosusLeft end of aortic archLeft end of aortic archLeft end of aortic arch Left end of aortic arch Descending aorta: Mixture with Arterial blood Descending aorta: Mixture with Arterial blood Umbilical artery Umbilical artery Placenta Placenta

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Prenatal circulationPrenatal circulation

Aeration of Lung at BirthAeration of Lung at BirthLungs at birth are half filled with amniotic Lungs at birth are half filled with amniotic fluid because breathing movements occur fluid because breathing movements occur before birthbefore birth to cause aspiration of amnioticto cause aspiration of amnioticbefore birthbefore birth to cause aspiration of amniotic to cause aspiration of amniotic fluid into the lungs fluid into the lungs Fluid in lungs is cleared by three routes:Fluid in lungs is cleared by three routes:–– Through mouth and nose by pressure on Through mouth and nose by pressure on

thorax during deliverythorax during deliverythorax during deliverythorax during delivery–– Into pulmonary capillaries and blood vesselsInto pulmonary capillaries and blood vessels–– Into lymphatic capillaries and vesselsInto lymphatic capillaries and vessels

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CHANGES THAT OCCUR AFTER BIRTHCHANGES THAT OCCUR AFTER BIRTHAfter birth, the circulation of fetal blood through the After birth, the circulation of fetal blood through the placenta ceases: placenta ceases: –– Delivery of oxygenated blood to fetus via umbilical vein Delivery of oxygenated blood to fetus via umbilical vein

ceases ceases –– The sphincter of ductus venosus constricts so all bloodThe sphincter of ductus venosus constricts so all bloodThe sphincter of ductus venosus constricts so all blood The sphincter of ductus venosus constricts so all blood

entering the liver passes through the hepatic sinusoidsentering the liver passes through the hepatic sinusoids–– Fall of blood pressure in the IVC and right atrium occur Fall of blood pressure in the IVC and right atrium occur –– Hypoxia of all tissues is increasing Hypoxia of all tissues is increasing –– Respiratory centers of the brain stem are stimulated by Respiratory centers of the brain stem are stimulated by

carbon dioxide carbon dioxide –– Inspiratory muscles contract, thoracic cage is expandedInspiratory muscles contract, thoracic cage is expandedp y g pp y g p–– Expansion of the lungs and Expansion of the lungs and First BreathFirst Breath takes placetakes place–– Inspired air enters respiratory passageways, pushes the Inspired air enters respiratory passageways, pushes the

contained fluids out of the way and inflates the contained fluids out of the way and inflates the bronchial and respiratory treesbronchial and respiratory trees

–– Infant’s lungs begin to function and newborn infant Infant’s lungs begin to function and newborn infant utters a loud cryutters a loud cry

CHANGES THAT OCCUR AFTER BIRTHCHANGES THAT OCCUR AFTER BIRTHFall in pulmonary vascular resistanceFall in pulmonary vascular resistanceDuctus arteriosus constrictsDuctus arteriosus constrictsIncrease in pulmonary blood flowIncrease in pulmonary blood flowIncrease in pulmonary blood flowIncrease in pulmonary blood flowLeft atrium pressure becomes higher than in Left atrium pressure becomes higher than in right atriumright atriumValve of oval foramen is pressed against Valve of oval foramen is pressed against septum secondumseptum secondumppForamen ovale closesForamen ovale closes

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Postnatal circulationPostnatal circulation

embryology of the respiratory system - uwi...

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