--- module: 086-01 language: en chapter: 86 title: "Organogenesis, Congenital Anomalies, and Teratology" module_title: "Cardiovascular and respiratory organogenesis, fetal shunts, and congenital mechanisms" source_sha256: 9ca814733ca5a2512b145fbaca156694132985022cc9035fd6e0035cbb850763 --- # Cardiovascular and respiratory organogenesis ## Heart tube formation and looping ### First to function: diffusion cannot support the embryo ### Cardiogenic mesoderm cranial to oropharyngeal membrane ### Folding brings paired regions ventrally together #### Endothelial tubes fuse into primitive heart tube #### Splanchnic mesoderm forms myocardium #### Cardiac jelly separates myocardium and endocardium ### Epicardium spreads from proepicardial tissue ### Sinus venosus to truncus arteriosus, inflow to outflow ### Beats in fourth week, before septation ### Rightward bulboventricular loop #### Ventricles ventrocaudal, atria dorsocranial #### Sets position, not chamber identity #### Abnormal looping gives discordant connections ## Venous inflow and atrial remodelling ### Right horn enlarges into sinus venarum ### Left horn becomes coronary sinus and oblique vein ### Crista terminalis marks smooth-trabeculated junction ### Pulmonary veins form smooth posterior left atrium #### Anomalous drainage into systemic veins #### Obstruction and mixing set presentation ## Atrial septation and foramen ovale ### Septum primum leaves ostium primum ### Perforations coalesce as ostium secundum ### Septum secundum on right leaves foramen ovale ### Septum primum flap allows right-to-left flow ### Birth: rising left-atrial pressure closes flap #### Incomplete fusion: probe-patent foramen ovale #### True septal defect: deficient tissue, sustained shunt ## Cushions, ventricular septum, and valves ### Cushions: matrix swelling, endothelial-mesenchymal transition #### Divide atrioventricular canal, form leaflets #### Cushion defects: septal defects plus valve anomalies ### Muscular septum grows up from ventricular floor ### Membranous part closes interventricular foramen #### Defects most often membranous #### Large left-to-right shunt, pulmonary vascular disease ##### Eventual shunt reversal ### Valves from excavated swellings and cushions #### Cusp number, fusion, or matrix errors #### Stenosis or regurgitation may appear years later ## Outflow tract and conotruncal anomalies ### Neural-crest ridges spiral into aorticopulmonary septum ### Migration or rotation defects #### Persistent truncus, interrupted arch, double outlet ### Tetralogy: anterior outflow septum displacement #### Outflow obstruction, septal defect, overriding aorta #### Secondary right-ventricular hypertrophy ### Transposition: failed spiralling #### Parallel circuits need mixing to survive ## Arch, venous, and coronary vessels ### Third arch: common and proximal internal carotid ### Left fourth: aortic arch; right fourth: subclavian ### Sixth: pulmonary arteries; left distal is ductus ### Coarctation narrows aorta near ductal region ### Vascular rings compress trachea and oesophagus ### Vitelline veins: sinusoids, portal system, caval part ### Cardinal remodelling explains venous variants ### Coronary stems must enter correct sinuses #### Between great vessels or from pulmonary artery ## Airway budding and larynx ### Respiratory diverticulum from ventral foregut, week four ### Tracheoesophageal folds separate the tubes #### Oesophageal atresia with distal fistula #### Polyhydramnios, choking, gastric distension ### Larynx from fourth and sixth arches, vagal supply ### Failed recanalisation: webs or atresia ## Lung branching and maturation ### Endoderm epithelium, splanchnic mesoderm wall ### Epithelial-mesenchymal signals drive branching ### Pseudoglandular: airways branch, no gas exchange ### Canalicular: vessels, respiratory bronchioles ### Saccular: thin epithelium near capillaries ### Alveolarisation continues into childhood ### Surfactant from type two pneumocytes #### Deficiency: atelectasis, low compliance #### Antenatal glucocorticoids accelerate maturation ## Lung growth and diaphragm ### Needs space, fluid, movement, vessels, branching ### Oligohydramnios or absent urine: hypoplasia ### Posterolateral diaphragmatic hernia compresses lung #### Hypoplasia and pulmonary hypertension #### Severity follows lung, not hole size ## Flow-path reasoning ### Connect, separate, remodel, mature ### Ask which flow path failed