Cardiovascular system-Embryology .pdf

‫ﺑﺳم ﷲ اﻟرﺣﻣن اﻟرﺣﯾم‬ ‫‪1‬‬  Embryology Cardiovascular System 2  Septum Formation in the Atrioventricular Canal Initially, the atrioventricular canal gives access only to the primitive left ventricle and is separated from the bulbus cordis by the bulbo (cono) ventricular...

‫ﺑﺳم ﷲ اﻟرﺣﻣن اﻟرﺣﯾم‬ ‫‪1‬‬  Embryology Cardiovascular System 2  Septum Formation in the Atrioventricular Canal Initially, the atrioventricular canal gives access only to the primitive left ventricle and is separated from the bulbus cordis by the bulbo (cono) ventricular flange. Since the atrioventricular canal enlarges to the right, blood passing through the atrioventricular orifice now has direct access to the primitive left and the primitive right ventricle  Septum Formation in the Atrioventricular Canal Two mesenchymal cushions, the atrioventricular endocardial cushions, appear at the anterior and posterior borders of the atrioventricular canal. Two lateral atrioventricular cushions appear on the right and left borders of the canal. The anterior and posterior cushions, in the meantime, project further into the lumen and fuse, resulting in a complete division of the canal into right and left atrioventricular orifices by the end of the fifth week. ‫‪26‬ا‬  Endocardial cushions Divide the atrioventricular canal into a right and left orifice. Close the ostium primum. Form the membranous portion of the interventricular septum. Form the normal mitral and tricuspid valves. 6  Failure of endocardial cushions to fuse cause Persistent atrioventricular canal Atrial septal defect. Ventriculal septal defect. Abnormal valve leaflets in the single atrioventricular orifice. 7 8  Septum Formation in the Truncus Arteriosus and Conus Cordis During the fifth week, right superior and left inferior truncus swellings appear. The right superior truncus swelling grows distally and to the left, and the left inferior truncus swelling grows distally and to the right. The swellings twist around each other, foreshadowing the spiral course of the future septum.  Septum Formation in the Truncus Arteriosus and Conus Cordis After complete fusion, the ridges form the aorticopulmonary septum, dividing the truncus into an aortic and a pulmonary channel. Other two swellings, The conus swellings appear and grow toward each other and distally to unite with the truncus septum. When the two conus swellings have fused, the septum divides the conus into an anterolateral portion (the outflow tract of the right ventricle) and a posteromedial portion (the outflow tract of the left ventricle.  Neural crest cells Contribute to endocardial cushion formation in both the conus cordis and truncus arteriosus. Abnormal migration, proliferation, or differentiation of these cells results in congenital malformations in this region, such as a. Tetralogy of Fallot. b. Pulmonary stenoses. c. Persistent truncus arteriosus. d. Transposition of the great vessels. Since neural crest cells also contribute to craniofacial development, it is not uncommon to see facial and cardiac abnormalities in the same individual Abnormality of the conotruncal region Abnormalities cause Tetralogy of Fallot Unequal division of the conus resulting from anterior displacement of the conotruncal septum Persistent truncus Failure of the conotruncal ridges to arteriosus fuse and to descend toward the ventricles Transposition of the Failure of the conotruncal septum great vessels to follow its normal spiral course and runs straight down  Septum Formation in the Ventricles By the end of the fourth week, the two primitive ventricles begin to expand. This is accomplished by continuous growth of the myocardium on the outside and continuous diverticulation and trabecula formation on the inside. The medial walls of the expanding ventricles become apposed and gradually merge, forming the muscular interventricular septum  Septum Formation in the Ventricles The interventricular foramen is closed by the conus septum and the inferior endocardial cushion which forms the membranous part of the interventricular septum  Ventricular septal defects (VSDs) The most common congenital cardiac malformation Most (80%) occur in the muscular region of the septum and resolve as the child grows. Membranous ventricular septal defects (VSDs) usually represent a more serious defect. Aortic Arches A number of other changes occur along with alterations in the aortic arch system The dorsal aorta between the entrance of the third and fourth arches, known as the carotid duct, is obliterated The right dorsal aorta disappears between the origin of the seventh intersegmental artery and the junction with the left dorsal aorta The carotid and brachiocephalic arteries elongate considerably. As a result of the caudal shift of the heart and the disappearance of various portions of the aortic arches, the course of the recurrent laryngeal nerves becomes different on the right and left sides. Derivatives of the Aortic Arches  Fetal Circulation About 80% of oxygenated blood from the placenta returns to the fetus by the umbilical vein. Most of this blood flows through the ductus venosus directly into the inferior vena cava to the liver. A smaller amount enters the liver sinusoids and mixes with blood from the portal circulation. A sphincter mechanism in the ductus venosus, close to the entrance of the umbilical vein, regulates flow of umbilical blood through the liver sinusoids. This sphincter closes when a uterine contraction renders the venous return too high, preventing a sudden overloading of the heart.  Fetal Circulation After a short course in the inferior vena cava, where placental blood mixes with deoxygenated blood returning from the lower limbs, it enters the right atrium. Here it is guided toward the oval foramen by the valve of the inferior vena cava, and most of the blood passes directly into the left atrium.  Fetal Circulation A small amount is prevented from doing so by the lower edge of the septum secundum, the crista dividens, and remains in the right atrium. Here it mixes with desaturated blood returning from the head and arms by the superior vena cava. From the left atrium, where it mixes with a small amount of desaturated blood returning from the lungs, blood enters the left ventricle and ascending aorta. Since the coronary and carotid arteries are the first branches of the ascending aorta, the heart musculature and the brain are supplied with well-oxygenated blood.  Fetal Circulation Desaturated blood from the superior vena cava flows by way of the right ventricle into the pulmonary trunk. During fetal life, resistance in the pulmonary vessels is high, such that most of this blood passes directly through the ductus arteriosus into the descending aorta, where it mixes with blood from the proximal aorta. After coursing through the descending aorta, blood flows toward the placenta by way of the two umbilical arteries. The oxygen saturation in the umbilical arteries is approximately 58%.  The following changes occur in the vascular system after birth Closure of the umbilical arteries. Distal parts of the umbilical arteries form the medial umbilical ligaments. Closure of the umbilical vein and ductus venosus the umbilical vein forms the ligamentum teres hepatis. The ductus venosus forms the ligamentum venosum.  The following changes occur in the vascular system after birth Closure of the ductus arteriosus forms the ligamentum arteriosum. Closure of the oval foramen is caused by an increased pressure in the left atrium, combined with a decrease in pressure on the right side. The first breath presses the septum primum against the septum secundum. Constant apposition gradually leads to fusion of the two septa in about 1 year forming fossa ovalis Thanks