The Aortic Arches and The Foetal Circulation Alfred Cuschieri Department of Anatomy University of Malta The Aortic Arches 1st • Connect the outflow tract of 2nd the heart to paired dorsal 3rd 4th aortae. 6th • Lie in the branchial arches and supply them. Outflow tract • Develop in cranio-caudal sequence. • They are labelled 1 to 6 but the fifth branchial arch fails to develop. Dorsal aortae Changes in Aortic Arches 4th week: 5th week 1st arch Maxillary artery 2nd arch Stapedial artery 6th week 3rd arch Subclavian artery loses connection with aortae 4th arch Asymmetric development 6th arch 4th and 6th Aortic Arches Develop Asymmetrically Right 4th arch Left 4th arch Atrophies Aorta Right subclavian artery Left subclavian artery -2ndry outgrowth -2ndry outgrowth Right 6th arch Left 6th arch atrophies Ductus arteriosus Right pulmonary artery Left pulmonary artery ndry -2ndry outgrowth -2 outgrowth The foetal circulation 4. The ductus arteriosus Upper ½ shunts most of the blood from 3. In the right atrium, blood Of body pulmonary trunk to the aorta from IVC is directed mainly to Pulmonary foramen ovale, and from the circulation SVC to the AV opening Liver 5. The lungs are collapsed 2. ….it is shunted via the shutting off most of the ductus venosus into the pulmonary circulation inferior vena cava 1. Oxygenated blood in 6. The left ventricle pumps Placenta umbilical vein is under all the blood into the aorta, increased pressure due to to supply the body and uterine contractions on Lower ½ placenta. placenta … Of body The foetal circulation has three shunts Upper ½ Of body Pulmonary •Inter-atrial foramen circulation (Right to left atrium) Liver •Ductus arteriosus •Ductus venosus (Pulmonary trunk to aorta) (Umbilical vein to IVC) Placenta Lower ½ Of body Upper ½ Of body Pulmonary circulation Liver Placenta Lower ½ Of body.