3. Development of heart part 1.pdf

Development of the heart (part 1) Dr. Nora Helal Department of human Anatomy and Embryology Faculty of Medicine Mansoura National University, Egypt  Intended Learning Outcomes (ILOs) 1. Describe external changes of the heart tube and t...

Development of the heart (part 1) Dr. Nora Helal Department of human Anatomy and Embryology Faculty of Medicine Mansoura National University, Egypt  Intended Learning Outcomes (ILOs) 1. Describe external changes of the heart tube and their related congenital anomalies. 2. Identify development the derivatives of sinus venosus. 3. Describe development of atrioventricular canal and its related congenital anomalies. 4. Describe the development and anomalies of atria and inter-atrial septum.  Agenda 1. Describe external changes of the heart tube and their related congenital anomalies? 2. Identify development the derivatives of sinus venosus? 3. Describe development of atrioventricular canal and its related congenital anomalies? 4. Describe the development and anomalies of atria and inter-atrial septum?  Development of the Heart Time: At the beginning of the 4th week. Origin: 2 sources: Angioblastic cells. Myo-epicardial mantle. Steps: The heart starts as 2 heart tubes. The 2 tubes fuse with each other to form a single tube. This tube has 2 ends: ✓ Venous end: where the blood enters the heart. ✓ Arterial end: where the blood leaves the heart.  Development of the Heart A constriction appears in the heart tube dividing it into 2 parts: o Primitive atrium. o Primitive ventricle. Another 2 constrictions appear in the primitive ventricle dividing it into 3 chambers: o Primitive ventricle. o Bulbus cordis. o Truncus arteriosus. Another dilatation appears in the primitive atrium called sinus venosus. Now the heart tube is formed of 5 dilatations from cranial to caudal: Truncus arteriosus. Bulbus cordis Primitve ventricle Primitive atrium Sinus venosus At this stage the heart tube is connected to the esophagus by a dorsal mesocardium.  Development of the Heart ▪ Elongation of the heart tube results in its folding to become U-shaped. ▪ The dorsal mesocardium becomes absorbed giving a passage between the arterial and the venous ends of the heart called transverse Sinus of pericardium.  Development of the Heart ▪ Further elongation of the heart tube to become S-shaped and consists of: Ventral limb: the truncus arteriosus and the bulbus cordis. Transverse limb: the primitive ventricle. Dorsal limb: the primitive atrium and the sinus venosus.  Sinus venosus Development of sinus venosus: The sinus venosus lies in the mesoderm of septum transversum (future diaphragm). At an early stage it is formed of: ▪ Body: which opens in the primitive atrium by Sino-Atrial orifice which lies transversely. ▪ 2 horns (right and left): each horn receives 3 veins: Vitelline vein: carries un-oxygenated blood from the yolk sac. Umbilical vein: carries oxygenated blood from the placenta. Common cardinal vein: ✓ Carries un-oxygenated blood from the body wall. ✓ It is formed by union of anterior and posterior cardinal veins.  Sinus venosus Development of sinus venosus: The sinus venosus lies in the mesoderm of septum transversum (future diaphragm). At an early stage it is formed of: ▪ Body: which opens in the primitive atrium by Sino-Atrial orifice which lies transversely. ▪ 2 horns (right and left): each horn receives 3 veins: Vitelline vein: carries un-oxygenated blood from the yolk sac. Umbilical vein: carries oxygenated blood from the placenta. Common cardinal vein: ✓ Carries un-oxygenated blood from the body wall. ✓ It is formed by union of anterior and posterior cardinal veins.  Sinus venosus Development of sinus venosus: The sinus venosus lies in the mesoderm of septum transversum (future diaphragm). At an early stage it is formed of: ▪ Body: which opens in the primitive atrium by Sino-Atrial orifice which lies transversely. ▪ 2 horns (right and left): each horn receives 3 veins: Vitelline vein: carries un-oxygenated blood from the yolk sac. Umbilical vein: carries oxygenated blood from the placenta. Common cardinal vein: ✓ Carries un-oxygenated blood from the body wall. ✓ It is formed by union of anterior and posterior cardinal veins.  Sinus venosus Later on: the blood reaching the right horn exceeds that of the left due to: Presence of transverse anastomosis between the left and right anterior cardinal veins with shift of blood from left to right. Development of the liver on the right side. This results in: The right horn becomes larger than the left. The Sino-Atrial orifice becomes vertical and guarded by 2 valves (right & left venous valves). Liver  Sinus venosus Fate of sinus venosus: The right horn: forms the smooth posterior part of right atrium. The left horn &the body: form the coronary sinus. The Sino-Atrial valves: ▪ The upper end of the right and left valves: fuse together to form Septum Spurium. ▪ The left venous valve: forms part of inter-atrial septum. ▪ The right venous valve: The upper 1/3 with the septum spurium: gives the crista terminalis. The middle 1/3: will give the valve of inferior vena cava. The lower 1/3: will give the valve of the coronary sinus.  Sinus venosus Fate of sinus venosus: The right horn: forms the smooth posterior part of right atrium. The left horn &the body: form the coronary sinus. The Sino-Atrial valves: ▪ The upper end of the right and left valves: fuse together to form Septum Spurium. ▪ The left venous valve: forms part of inter-atrial septum. ▪ The right venous valve: The upper 1/3 with the septum spurium: gives the crista terminalis. The middle 1/3: will give the valve of inferior vena cava. The lower 1/3: will give the valve of the coronary sinus.  Anomalies in position of the heart Dextrocardia: Cause: the heart tube bends to the opposite direction. Features: ▪ The heart is displaced to the right. ▪ The heart chambers are reversed as in mirror image. Situs inversus: Cause: genetic factor. Features: all body organs are reversed. Ectopia cordis: Cause: failure of formation of thoracic wall. Features: ▪ The sternum is separated into 2 halves. ▪ The pericardium is opened. ▪ Partial or complete exposure of the heart.  Atrio-Ventricular canal Division of A-V canal: ▪ At the end of the 4th week: dorsal (superior) and ventral (inferior) endocardial cushions appear in the A-V canal. ▪ The 2 cushions grow and fuse together to form septum intermedium which divides the A-V canal into right and left halves. Fate of A-V canal ▪ The upper part: forms part of the corresponding atrium (Rt and Lt). ▪ The lower half: forms part of the corresponding ventricle (Rt and Lt). ▪ The septum intermedium: shares in the formation of inter-atrial septum and membranous part of the inter-ventricular septum. Septum intermedium  Anomalies of Atrio-Ventricular canal Mitral Stenosis A. Persistent A-V canal: Persistent atrioventricular canal &/or Cause: failure of development of septum intermedium. Tricuspid regurgitation Features: ▪ There is a single channel between the 2 atria and the 2 ventricles. ▪ It is potential cyanotic heart disease. B. Unequal division of A-V canal: 1. Mitral Stenosis &/or tricuspid regurgitation: Cause: deviation of septum intermedium to the left. Features: narrow mitral orifice and wide tricuspid. There is ASD and VSD. 2. Tricuspid Stenosis &/or mitral regurgitation: Cause: deviation of septum intermedium to the right. Features: narrow tricuspid orifice and wide mitral. There is ASD and VSD. Tricuspid Stenosis &/or Mitral regurgitation  Anomalies of Atrio-ventricular canal 3. Mitral Atresia: 4. Tricuspid Atresia: Cause: complete fusion of the cusps of mitral valve. Cause: complete fusion of the cusps of tricuspid valve. Features: small left ventricle and large right ventricle. Features: small right ventricle and large left ventricle.  Development of Inter-Atrial Septum Septum Primum: ▪ Appears at the end of the 4th week as a sickle- shaped septum extending from the roof of the primitive atrium towards the septum intermedium. ▪ The opening between the septum primum and intermedium is called foramen primum. ▪ The septum primum gradually fuses with the septum intermedium closing the foramen primum. ▪ The upper end of the septum primum breaks down forming foramen secundum.  Development of Inter-Atrial Septum Septum Secundum: ▪ Extends downwards from the roof of the primitive atrium. ▪ Lies on the right side of septum primum. ▪ Has crescentic lower border. ▪ Doesn’t fuse with the septum intermedium. ▪ Overlaps the foramen secundum which now called foramen ovale.  Development of Inter-Atrial Septum Fate of foramen ovale: after birth the septum primum and secundum fuse together resulting in: ▪ The septum primum: will form the fossa ovalis. ▪ The lower edge of septum secundum: will form the annulus ovalis. Annulus ovalis Development of Inter-Atrial Septum  Embryological origin of Inter-Atrial Septum, right & left atria Embryological origin of inter-atrial septum: 2 1. Septum primum. 3 2. Septum secundum. 1 3. Septum intermedium. 4 4. Left venous valve of sino-atrial orifice. 5. Some cells of neural crest. 5  Embryological origin of Inter-Atrial Septum, right & left atria Embryological origin of right atrium: 1. The right ½ of the primitive atrium (gives the rough part). 2. The upper part of the right ½ of A-v canal. 3. Right horn of sinus venosus (gives the smooth part). 2 4. Septum spurium and upper 1/3 of right venous valve give the crista terminalis. 5. Right venous valve gives the valves of IVC (middle 1/3) and 1 coronary sinus (lower 1/3). 4 5 3  Embryological origin of Inter-Atrial Septum, right & left atria Embryological origin of left atrium: 1. The left ½ of the primitive atrium (gives the rough part). 2. The upper part of the left ½ of A-V canal. 3. Absorption of the root and 1st division of the pulmonary vein (gives the smooth part and results in 4 openings for the pulmonary veins in the left atrium). 3 2 1  Congenital anomalies of inter-atrial septum Atrial Septal defects (ASD) 1. Tri-locular (bi-ventricular) heart: 2. Persistent foramen primum 3. Persistent foramen secundum Cause: failure of development of inter-atrial (Patent ostium primum): (Patent ostium secundum): septum. Cause: failure of fusion between the septum Cause: Features: primum and intermedium. ▪ Excess destruction of septum primum. ▪ The heart is formed of one atrium and 2 Features: ▪ Failure of development of septum secundum. Features: ventricles. ▪ There is opening in the lower part of inter- ▪ There is opening in the upper part of inter-atrial atrial septum. septum. ▪ The most common form of ASD.  Congenital anomalies of inter-atrial septum Foramen ovale Defects 1. Patent foramen ovale: 2. Probe patent foramen ovale: 3. Premature closure of foramen ovale: Cause: failure of fusion between septum primum and Cause: failure of complete fusion between secundum. septum primum and secundum. Cause: fusion between septum primum and Features: Features: secundum during intra-uterine life. ▪ There is an opening between the right and ▪ Present in 20-30% of people. left atria. ▪ No symptoms. Features: leads to intra-uterine fetal death. ▪ Blood passes from right to left during ▪ There is a very narrow passage between crying or exercise due to increased venous septum primum and secundum which pressure). allow a probe to pass and not the blood.