Heart Development MED-202 Fall 2024 PDF

Heart Development MED-202 Histology/Embryology I Fall 2024 Annita Achilleos, PhD  Reading Material 1. Langman’s Medical Embryology: Chapter 13 be VERY selective 2. Ronald Dudek: Embryology 5th or 6th edition: Chapter 5 3. Lecture  Learning ob...

Heart Development MED-202 Histology/Embryology I Fall 2024 Annita Achilleos, PhD  Reading Material 1. Langman’s Medical Embryology: Chapter 13 be VERY selective 2. Ronald Dudek: Embryology 5th or 6th edition: Chapter 5 3. Lecture  Learning objectives Discuss the formation of the heart tube. Outline the formation of the aorticopulmonary and the atrial septa. Outline the formation of atrioventricular and interventricular septa. Outline examples of clinical correlations of heart development.  Week 3 – 8: The embryonic period Organogenesis Weeks 1 – 2 Weeks 3 – 8 Weeks 9 – birth GERMINAL PERIOD EMBRYONIC FETAL PERIOD PERIOD Conception – 12 weeks Weeks 13 - 26 Weeks 27 - birth FIRST TRIMESTER SECOND TRIMESTER THIRD TRIMESTER organogeneiss - most organs formed - till about week 10 about week 3 we have the formation of the 3 layers Organogenesis the heart is one of the first organs that forms for everything else to function it needs blood supply = from the heart Gastrulation Risk of birth Structural defect induction defects Functional defects  Development of the primitive heart tube Head Cardiogenic area form these 2 tubes Blood flow Endocardial Fusion into tubes primitive more 2D- but it will fold to become 3D heart tubes Primitive ventricle Primitive atrium the endocardial tubes due to the movement of the embryo (folding) the 2 tubes will come together, fuse and make the primitiva heart tubes in the embryoinic heart the blood comes from the bottom - its one hollow tube at this point the blood starts flowing Tail throught the heart 18 days 20 days 21 days 22 days cells that are destined to become heart cells Progenitor heart cells arise in the epiblast and migrate to the cardiogenic area (mesoderm) through the primitive streak. They form two cardiogenic cords that develop a lumen forming the endocardial tubes. Due to folding of the embryo, the endocardial tubes migrate together and fuse to form a single primitive heart tube.  The endocardial tubes fuse to form a single primitive heart tube Neural top of the embryo brain formed here Neural Neural tube tube tube Dorsal aorta Endocardial tubes Endocardial Wall of yolk sac tube Heart tube 20 days 22 days 24 days The primitive heart tube has five distinct regions We have the tube, but we alreasy have some defined part Blood flow 23 days 24 days 35 days Embryonic heart dilations Adult structure Truncus arteriosus Aorta and pulmonary trunk Bulbus cordis Smooth part of right and left ventricles Primitive ventricle Trabeculated part of right and left ventricles Primitive atrium Trabeculated part of right and left atria Sinus venosus Smooth part of right and left atria  Cardiac Looping The transformation of the straight embryonic heart tube into a helically wound loop Cardiac looping - important process- can end up with defects if it goes wrong Essential process in cardiac morphogenesis the heart tubes loop, the top part will become ventricles, it will turn to the right, loop at a certain way so that the atria, ventricles etc. end up in the posotion they are supposed to be cardiac looping to go from tubes to the 35 days https://www.youtube.com/watch?v=oNMdqBUsGoY  Clinical correlates: Dextrocardia if the looping goes wrong you can end up with dextrocardia The heart lies on the right side of the thorax instead of the left. - the heart looped to the left instead of the right Dextrocardia can: - be isolated (very rare) – no symptoms the only defect that happens - occur with situs inversus totalis (complete reversal of asymmetry in all organs) the problem is when it is asscoitaed with heterotaxy - be associated with heterotaxy (the position of only some organs is reversed) – occur with other heart defects (double outlet ventricle, endocardial cushion defect, pulmonary stenosis, single ventricle etc)  Formation of the cardiac septa: Separating the left and right atria it was a hollow tube, so know all the chambers are one hollow chamber, so we need to seperate them Formed by cell death Septum Septum Foramen secondum primum secondum whenever you see foramen - means hole Foramen Dorsal septum is tissue Foramen primum Septum need to have a hole between left and right atrium Septum endocardial secondum primum a signal that tells it to undergo cell death and that makes the hole primum cushion Foramen primum start at the top, proliferting the cells, making more and more of the cells, going down Septum Foramen Degenerating secondum secondum septum primum Foramen Foramen Septum post-natal the foramen ovale closes ovale ovale primum (closed) Septum secondum Cardiac septation takes place between 4 – 7 weeks of development The foramen ovale will eventually close in the first 6 – 12 months of life  Formation of the cardiac septa: Separating the left and right ventricles Endocardial cushion Muscular important to seperate the chambers during this process interventricular septum Ventricle septation: derives form the walls of the ventricle 1. Formation of the muscular septum (medial walls of the ventricles) 2. Formation of the membranous septum (by endocardial cushions) Clinical correlates: Atrial Septal Defects (ASD) − congenital heart abnormality (birth defect) − characterized by the presence of a hole in the atrial septum − accounts for 10 – 15% of congenital heart disease − 1 – 2 per 1000 live births − different degrees of severity depending on the size of the hole − small ASDs may close on their own during childhood − large ASDs need open heart surgery  Clinical correlates: Atrial Septal Defects (ASD) different categories - based on the process it effects 1. Ostium (foramen) secondum defects the one from the bottom diesnt form ordentlig - large opening between the left and right atria - due to: may have had too much cell death a. excessive cell death and resorption of the septum primum, or b. inadequate development of the septum secondum Clinical correlates: Atrial Septal Defects (ASD) the most severe - nothing was built - no wall was built 2. Common atrium - complete absence of the atrial septum - the most serious ASD - associated with other serious heart defects - needs open heart surgery early on  Clinical correlates: Atrial Septal Defects (ASD) 3. Patent foramen ovale - a flap-like opening between the right and left atria dont want the blood to go to the lungs so it bypasses and sends i t to the left atrium, there is no point in sending the blood to the lungs - due to incomplete fusion of the septum primum and septum secondum - not severe unless other heart defects are present soon after the baby is born, can take about 1 year to close - 25% prevalence have a patent foramen ovale - it is still open - but its not an issue - because its not an actual hole - its a flap and because of the pressure difference the flap closes  Clinical correlates: Atrial Septal Defects (ASD) 4. Premature closure of the foramen ovale - Very rare - Leads to massive hypertrophy of the right atrium and ventricle and underdevelopment of the left side - Death usually occurs shortly after birth Not compatible with life - rare but if it happens baby dies Interatrial septum (IAS) Stock et al., 2019, Cardiology in the young Formation of the aorticopulmonary septum (AP) DONT NEED DETAILS, BUT KNOW The AP separates the aorta from the pulmonary artery (trunk) seperate the 2 great vessels the aorta comes out from the left ventricle and the trunk comes out of the right ventricle To systemic To pulmonary circulation circulation Aorta Pulmonary trunk Aorta Pulmonary trunk so you twiat is and speerate it Aorticopulmonary septum  Clinical correlates: Transposition of the Great Arteries The two main arteries carrying blood out of the of the heart are switched in position, “transposed” Failure of the aorticopulmonary septum to form properly Typical heart Heart with transposition of the great arteries a problem because the aorta will take deoxygentated blood through the aorta to the rest of the bdoy Aorta Aorta (transposed) Pulmonary Pulmonary trunk Trunk (transposed)  Clinical correlates: Tetralogy of Fallot The most frequent abnormality of the conotruncal region (outflow track region) A combination of four heart congenital defects: a. Ventricular septal defect b. Overriding aorta c. Pulmonary stenosis stenosis - the walls are much thicker - narrowing- harder for the blood to go through d. Right ventricular hypertrophy this is a result of pulmonary stenosis Aorta Aorta Overriding aorta Pulmonary (b) Aorta trunk Pulmonary trunk Pulmonary Ventricular stenosis (c) septal defect (a) Right ventricular hypertrophy (d) The circulation before and after birth is different Fetal circulation Ductus arteriosus Pulmonary trunk Foramen ovale Inferior vena cava Text Ductus venosus Aorta Umbilical vein High Medium Umbilical Low arteries Placenta  The circulation before and after birth is different NEED TO KNOW Fetal circulation 1. The oxygen-poor blood from the fetus travels to the placenta via the two umbilical arteries (umbilical cord). Ductus arteriosus Pulmonary 2. When blood goes through the placenta it picks trunk Foramen up oxygen. ovale 3. The oxygen-rich blood returns to the fetus via Inferior vena the umbilical vein (umbilical cord). cava all the 3 ductus will close and become ligaments: Ductus venosus, ductus arteriousus, foramen ovale Ductus venosus Aorta 4. The returning oxygen-rich blood bypasses the fetal liver through the ductus venosus and enters Umbilical the right atrium. vein High Medium 5. The foramen ovale allows the blood to enter Umbilical Low the left atrium. arteries 6. Blood enters the left ventricle and aorta and to the rest of the fetal body. Placenta The circulation before and after birth is different NEED TO KNOW Fetal circulation 1. The oxygen-poor blood returning from the head in the right atrium passes to Ductus arteriosus the right ventricle. Pulmonary trunk Foramen ovale 2. From the right ventricle, the oxygen- poor blood bypasses the lungs and enters the descending aorta via the Inferior vena cava ductus arteriosus. Ductus venosus Aorta 3. The oxygen semi-poor blood goes to the lower half of the body. Umbilical vein High Medium Umbilical Low arteries Placenta  Prenatal circulation is used to bypass the organs that are not yet functional Connects the pulmonary artery to the aorta. Most of the blood coming from the right ventricle can bypass the lungs and pass directly Ductus back into the aorta and arteriosus fetal blood flow. Foramen ovale Passage of most of the blood from the placenta through the inferior vena cava directly across the Ductus right atrium into the left venosus atrium. Bypasses the liver carrying oxygenated blood from umbilical vein to inferior vena cava (regulates blood flow). Prenatal Postnatal  Circulatory changes at birth Ductus arteriosus 1. Closure of the umbilical arteries and gradual degeneration. 2. Closure of the umbilical vein and ductus venosus and gradual Foramen ovale degeneration. 3. Closure of the ductus arteriosus immediately after birth through the Ductus venosus release of bradykinin from the functioning lungs. 4. Closure of the foramen ovale (fusion Umbilical vein of the septa takes up to a year). Umbilical arteries  Summary 1. Development of bilateral cardiogenic cords as the first step towards heart development. 2. Development of endocardial tubes and fusion to form a single primitive heart tube. 3. Five-region compartmentalization of the heart and heart lopping (clinical correlates). 4. Formation of cardiac septa and associated clinical correlates. 5. Fetal (prenatal) blood circulation. 6. Comparison of prenatal and postnatal circulation. Thank you !