Development_of_the_Heart_and_great_vessels.pdf

Development of the Heart and Great vessels Fraser Chisholm [email protected] https://www.latimes.com/entertainment-arts/movies/story/2020-06-17/ultimate-summer-movie-showdown-finding-nemo Learning Outcomes After this lecture, time spent in the dissecting room, and further private study you sh...

Development of the Heart and Great vessels Fraser Chisholm [email protected] https://www.latimes.com/entertainment-arts/movies/story/2020-06-17/ultimate-summer-movie-showdown-finding-nemo Learning Outcomes After this lecture, time spent in the dissecting room, and further private study you should be able to: • Describe the normal development of the chambers and valves of the heart • Describe the formation of the foramen ovale and the changes that occur at the time of birth that lead to the formation of the fossa ovalis • Discuss how the complex development of the heart can lead to congenital abnormalities • Describe what is meant by patent ductus arteriosus • Describe what is meant by patent foramen ovale • Describe the complex organisation of the aortic arches and how it relates to the position of the recurrent laryngeal nerves • Discuss major congenital defects in the heart (ASD, Patent FO, VSD,) and major vessels (Tetralogy of Fallot, Transposition of the great vessels, Patent ductus arteriosus Coarctation of aorta) 2 Summary 1. Formation of the heart (endocardial) tube 2. Folding and looping of the heart tube 3. Partitioning of the common AV canal 4. Formation of papillary muscles, chorda tendinea and AV valves 5. Formation of the interventricular septum 6. Formation of the interatrial septum 7. Spiral partitioning of the conus cordis and truncus arteriosus CONCURRENT, NOT SEQUENTIAL Larsen’s Human Embryology New York, 1998, Churchill Livingstone 3 Heart Defects (8 in 1,000) • Causes - genetic and teratogenic • Effects depend on timing of exposure • Defects will often be multifactorial – Rubella virus, social drugs, thalidomide, insulin-dependant diabetes, hypertension – Genetic syndromes such as Downs, DiGeorge, trisomy 18 • Craniofacial abnormalities are linked to cardiac malformation (neural crest cells) 4 Formation of Endocardial Tube • Initial nourishment and oxygenation via diffusion • Growth necessitates circulatory system • Heart is first functional organ in the embryo – day 22-25 • Around day 17 – splanchnic lateral plate mesoderm produces • Angiogenic cells • Heamangioblasts • Blood islands • Form Primary Heart field 5 Formation of endocardial tube 2 - lateral folding • Day 18 – endothelial lined tubes surrounded by myocytes • Other blood island form paired dorsal aorta 18 days 17 days • Day 20 – Two sides of the horseshoe fuse to form single heart tube • Ventral to gut tube • Separated from somatic lateral plate mesoderm by pericardial cavity. 20 days 6 Slightly different image 7 Formation of Endocardial tube 2 - crainiocaudal folding • Heart moves inferiorly form superior to oropharyngeal membrane into future thorax 18 days 20 days 21 days 22 days 8 Primary heart tube • Day 22 Myocardial cells infiltrate cardiac jelly • Begin contraction and electrical activity Day 22 9 10 Evolution intervention 11 12 You are nothing more than a jumped up fish Human Fish 21/10/2023 https://schoolbag.info/biology/living/194.html 13 The heart tube 1aa AS • 1st Aortic arch • Aortic sac • Bulbous cordis • BC Outflow tract • Conus cordis • Truncus arteriosus • Primitive Ventricle PV • Primitive Atrium PA SV CV UV VV • Sinus Venosus • Cardinal Veins • Umbilical veins • Vitelline Veins 14 15 Folding of the heart tube - days 22-24 16 https://www.youtube.com/watch?v=oNMdqBUsGoY 17 Folding complete – day 28 Left medial view Anterior view • Formation of trabeculae in primitive ventricle • → LV • And in proximal 1/3 of BC • → RV 18 Remodelling of Ventricle wall • Erosion and remodelling in the ventricular wall leads to • trabeculae • Beginning of septation • AV valves (more later) Day 30 19 Fate of the Sinus Venosus 20 Septation of Common AV canal • • • • Endocardial cushion cells from neural crest Dorsal and ventral cushions meet, forming left and right AV canals Forming a definitive atrioventricular septum Left and right endocardial cushions contribute to fibrous ring around AV canals (Dorsal) Day 23-35 21 Ventricular Septation • Muscular growth forms the inferior part of AV septum • Stops at about 7 weeks Day 34-35 • Superior part derived from endocardial cushions • Membranous part • Completed by about 8 weeks (more on this later) 22 AV valves • Erosion and remodelling of Ventricle and BC led to trabeculae • Also leads to formation of AV Valves • Dense mesenchymal tissue- derived from Endocardial cushions • Muscular tissue regresses leaving fibrous valves, dense connective tissue chordae and papillary muscles • All lined with endothelium 23 Ventral view Atrial septation • Separation but must maintain pulmonary bypass • Day 26 - 33 a depression appears in roof of common Atrium and a ridge approaches the AV canal – Septum Primum • Under its lower free edge is Ostium Primum • As Septum primum approaches Endocardial cushions, apoptosis forms – Ostium Secundum Medial view 24 Atrial Septation • Day 33-37 A second septum forms – Septum secundum • Crescentic growth never entirely complete • Free space – Foramen Ovale • Septum primum forms Valve of foramen ovale newborn newborn 25 Pulmonary vein • As septum primum is forming, a protrusion form the dorsal mesocardium follows it into the heart. • In the mesenchyme is the primitive pulmonary vein • Pulmonary vein is incorporated into the wall of the Left Atrium • It send two branches to each lung, but atrial growth eventually incorporates all four branches in the wall • These branches meet with developing venous plexuses near developing lungs 26 Septation of the outflow tracts Superior inferior • week – single ventricular outflow • Conolotruncal ridges (cushions) begin to form • Grow distally and spiral • When the two conus swellings have fused, the septum divides the conus into an 5th – anterolateral portion (the outflow tract of the right ventricle) and a – posteromedial portion (the outflow tract of the left ventricle) 7 weeks 27 Semilunar valves • Left and right swelling in the wall and one on either side of the fused conotruncal ridges 28 Aortic Arches 29 Aortic arches • Starting in the 4th week, Pharyngeal arches develop each has its own pair of arteries from the aortic sac 1st AA • 5 arches develop cranial to caudally over the next 3-4 weeks – Numbered 1- • Each arch terminates in the paired dorsal aorta 30 • As embryo grows more arches develop • Intersegmental arteries grow out supplying surrounding tissues 1st aa 2nd aa 4 weeks 6 weeks 31 • 4th week: 1st arch has regressed, second is going • 3rd and fourth well developed 3rd aa 4th aa • Longitudinal connections between intersegmental arteries 1-7 form and extend cranially 32 • • • • Week 5-6 arches 1 and 2 gone 6th arch present DA degenerates between 3 and 4 7th intersegmental artery grows out to the upper limb bud 3rd aa 4th aa 6th aa • Longitudinal artery extends up to brain – Vertebral arteries • 3rd becomes Common and Internal carotid arteries 7th Intersegmental Artery 33 • 6-7 weeks Right dorsal aorta degenerates • 1-6 intersegmental arteries degenerate • 7th intersegmental becomes subclavian ( diff on right • Pulmonary trunk septation • 6 Arch send branches to Lungs – pulmonary arteries 3rd aa 4th aa 6th aa 7th Intersegmental Artery 34 35 36 Fates of Embryological Structures Embryo Adult Sinus venosus (sinus venarum) Right atrium, smooth part Sinus Venosus Right Horn – Superior Vena Cava Left Horn – Coronary sinus Primitive Atrium Right and Left Atria Pulmonary Veins Left atrium – smooth part Primitive Ventricle Left Ventricle Bulbus cordis: Proximal 1/3 Right Ventricle Bulbus cordis: middle 1/3 (conus cordis) Infundibulum (RV) and Aortic vestibule (LV) Bulbus cordis: distal 1/3 (truncus arteriosus) Proximal Aorta and Pulmonary trunk Endocardial cushions AV valves, Membranous IV septum, lower IA septum, Spiral septum 37 Fates of Embryological Structures Aortic Arch Right Left Aortic sac Proximal Aortic arch and proximal brachiocephalic trunk 1st and 2nd Arteries in the head and neck (just wait till MD4001) 3rd Right common carotid Proximal Internal carotid Left common carotid Proximal Internal carotid 4th Right Proximal subclavian Aortic arch - middle 5th ? ? 6th Right Pulmonary artery Left Pulmonary artery Ductus arteriosus 7th Intersegmental artery Right Distal subclavian Left subclavian Dorsal aorta Right subclavian Descending aorta 38 Congenital conditions Condition Embryology and cause Patent foramen ovale Foramen ovale is a defect on septum secundum, which is connected with ostium secundum (on septum primum). • Caused by failure of fusion of either. Patent ductus arteriosus Ductus arteriosus is the connection between 6th aortic arch and left dorsal aorta. After full development, it extends between pulmonary trunk and aorta (distal to the origin of left subclavian artery) • No clear cause; Chromosomal abnormalities, prematurity, low birth weight, prostaglandins, high altitude and low atmospheric oxygen tension, hypoxia Atrial septal defect (ASD) (Ostium primum defect is a form of ASD) IA septum is formed by septum primum and septum secundum • Caused by failure of proper development of septum secundum • or failure of closure of ostium primum • Excessive Resorption of Septum Primum • Absence of the Septum Secundum 39 Congenital conditions Condition Embryology and cause Ventricular septal defect (VSD) (most common congenital heart defect) IV septum is derived from endocardial cushion (membranous) and walls of primordial ventricle and bulbus cordis (muscular) • Caused by a defect either in membranous (more common) or muscular portion of IV septum • or failure of fusion of membranous or muscular portions Tetralogy of Fallot (VSD, pulmonary artery stenosis, deviation of the aortic origin to the right (overriding aorta), hypertrophy of RV) • Caused by unequal division of conus cordis with resultant anterior displacement (malalignment) of the aorticopulmonary septum Transposition of the great vessels • Caused by failure of the aorticopulmonary (conotruncal) septum to spiral Coarctation of aorta (narrowing of • No clear cause; contraction of ductus arteriosus the aorta, usually distal to the origin of the left subclavian artery from the arch of aorta) 40 Sources of figures and Images • • • • • • • • DAFFNER: Daffner & Hartman. Clinical Radiology. The Essentials ,4th Ed, 2014 © Lippincott Williams & Wilkins. DRAKE: Drake et al. Gray’s Atlas of Anatomy 2nd Ed, 2018 © Elsevier. GILROY: Gilroy et al. Atlas of Anatomy 2nd Ed, 2012 © Thieme KELLEY: Kelly&Petersen. Sectional Anatomy for Imaging Professionals, 3rd Edition, 2013 © Mosby, Elsevier Inc MOORE: Moore et al. Clinically Oriented Anatomy 8th Ed, 2018 © Wolters Kluver. NETTER: Hansen. Netter's Clinical Anatomy, 3rd Edition, 2014 © Saunders, Elsevier Inc SOBOTTA: Putz&Pabst. Sobotta Atlas of Human Anatomy, 14th Edition, 2006 © Urban and Fischer Verlag, Elsevier Inc Langman’s Medical Embryology, Sadler, Lippincott Williams and Wilkins 11th Ed 2010 41