CVS Embryology PDF

EMBRYOLOGY OF THE CVS  INTRODUCTION The cardiovascular system begins development at around the 10th day after fertilization. The heart is the first functional organ to develop, with the heart beat able to be heard on sonography by around the 6th week. FORMATION OF THE PRIM...

EMBRYOLOGY OF THE CVS  INTRODUCTION The cardiovascular system begins development at around the 10th day after fertilization. The heart is the first functional organ to develop, with the heart beat able to be heard on sonography by around the 6th week. FORMATION OF THE PRIMITIVE HEART TUBE At the start of its development, the cardiovascular system exists as two regions near the cranial end of the embryo. These regions are called cardiogenic fields They are derived from the mesoderm Specifically, lateral splanchnic mesoderm… FORMATION OF THE PRIMITIVE HEART TUBE (CONT’D) The cardiogenic fields consist of blood islands These areas (blood islands) develop further and fuse to form two tubes, which are called endocardial tubes, one on each side of the embryo.  FORMATION OF THE PRIMITIVE HEART TUBE (CONT’D) In the fourth week of development the embryo begins to fold Folding of the embryo put the heart tissue in the correct position to form the primitive heart tube surrounded by the pericardial sac. The embryo folds in two directions: a. Cephalo-caudal folding brings the cardiogenic f ields from the cranial end towards the centre of the embryo to sit in thoracic region where the heart will be. b. Lateral folding fuses the two lateral sides of the embryo. This brings to two cardiogenic f ie lds into the midline so they can fuse and form the primitive heart tube. FORMATION OF This primitive heart tube is formed at around day 25 of THE PRIMITIVE gestation. It is divided into six parts: Aortic roots HEART TUBE Form the arteries of the aortic arch (CONT’D) Truncus arteriosus Involved in the formation of the pulmonary trunk and aorta (outflow from the heart) Bulbus cordis Involved in the formation of the pulmonary trunk and aorta (outflow from the heart) Primitive ventricle Forms the ventricles Primitive atrium Forms the atria Sinus venosus Forms part of the right atrium and vena cava  CARDIAC LOOPING As the heart tube elongates during its growth, it outgrows the pericardial sac that originally surrounded it. Primary and secondary loops When folding is finished, the primitive ventricle is sitting at the bottom of the cavity, with the primitive atrium behind it DEVELOPMENT OF THE RIGHT ATRIUM The right atrium develops from most of the primitive atrium, and part of the sinus venosus. The primitive heart tube receives blood from the sinus venosus via the sinus horns. The right sinus horn is partially absorbed by the primitive atrium as it grows, forms the superior and inferior vena cava. The left sinus horn becomes the coronary sinus  DEVELOPMENT OF THE LEFT ATRIUM The left atrium develops from a small part of the primitive atrium, and the proximal portions of the pulmonary veins. The pulmonary veins begin as a single vein entering the left atrium. It develops from four branches which are absorbed into the developing left atrium. The part of the mature left atrium that came from the primitive atrium is trabeculated – the auricle The part derived from the pulmonary veins (which makes up most of the future right atrium) is smooth.  DEVELOPMENT OF THE LEFT ATRIUM The proximal parts of the pulmonary veins become absorbed into the wall of the left atrium. The contribution of the pulmonary veins is shown in blue, and the primitive left atrium is shown in pink  PARTITIONING OF THE ATRIA Endocardial cushions develop in the dorsal and ventral aspects of the developing heart. Act as target for the developing septum. Sequence 1. Septum primum 2. Ostium primum 3. Ostium secundum 4. Septum secundum 5. Ostium of septum secondum 6. Formation of foramen ovale PARTITIONING OF THE ATRIA PARTITIONING OF THE Takes place in two steps VENTRICLE Formation of the muscular portion – primary interventricular foramen Formation of the membranous portion  SEPTATION OF THE OUTFLOW TRACT The bulbus cordis and truncus arteriosus form one tube allowing outflow from the heart. Splitting of the common tube form the aorta and pulmonary trunk. 2 lines of proliferations of neural crest cells appear on the inner walls of the outflow tract. The 2 lines of cells spiral around and grow towards each to form the aorticopulmonary septum This forms the aorta and pulmonary trunk.  SEPTATION OF THE OUTFLOW TRACT
(AORTA & PULMONARY TRUNK)  FORMATION OF THE GREAT VESSELS Head and neck vessels arise from the truncus arteriosus as aortic arches. There are five pairs of arches, numbered I, II, III, IV, VI (arch V doesn’t form in humans, so there are 5 arches numbered between 1-6 without a number 5). Arches and truncus arteriosus form the large arteries.  FUTHER ARTERIAL DEVELOPMENT In the rest of the body, the arterial patterns develop mainly from the right and left dorsal aortae. The right and left dorsal aortae fuse to form the dorsal aorta, which then sprouts posterolateral arteries, lateral arteries, and ventral arteries (vitelline and umbilical). 14 
FATE OF SINUS VENOSUS The right horn of the sinus venosus forms the smooth posterior wall of the right atrium. The left horn and the body of the sinus venosus atrophy and form the coronary sinus. The left common cardinal vein forms the oblique vein of the left atrium.  DEVELOPMENT OF THE VENOUS VASCULATURE Each horn of the sinus venosus receives 3 veins: Cardinal vein from the fetal body. 1.Common cardinal Vitelline from the yolk sac. 2.Vitelline Umbilical from the placenta. 3.Umbilical  EMBRYONIC & ADULT VENOUS VASCULATURE Embryonic Adult Vitelline veins Right and left Portion of the IVC,a hepatic veins and sinusoids, ductus venosus, portal vein, inferior mesenteric vein, superior mesenteric vein, splenic vein Umbilical veins Right Degenerates early in fetal life Left Ligamentum teres Cardinal veins Anterior SVC, internal jugular veins Posterior Portion of IVC, common iliac veins Subcardinal Portion of IVC, renal veins, gonadal veins Supracardinal Portion of IVC, intercostal veins, hemiazygos vein, azygos vein Development of the vitelline and umbilical veind during the (A) 4th , (B) 5th weeks, (C) second and (D) third months. In (A) and (B) note the plexus around the duodenum, formation of the hepatic sinusoid, and initiation of left-to-right shunts between the vitelline veins. In (C) and (D) note formation of the ductus venosus, portal vein, and hepatic portion of the inferior vena cava. The splenic and superior mesenteric veins enter the portal vein (Sadler 2010).  FETAL CIRCULATION 1. Umbilical vein 2. IVC DV 3. RA FO LA (Pulmonary bypass). 4. LV AORTA 5. Blood that doesn’t pass through the FO enters the RV and it’s pumped into the pulmonary trunk to fetal systemic circulation via the DA  CIRCULATION AFTER BIRTH a. The ductus arteriosus closes - Ligamentum arteriosum b. The oval foramen closes - Foramen ovale fuses with septum secundum to form solid interatrial septum. c. The umbilical vein closes - Ligamentum teres hepatis. d. The ductus venosus closes - Ligamentum venosum e. The umbilical arteries close - The medial umbilical ligaments FETAL AND NEWBORN HEART  CONGENITAL HEART DEFECTS Congenital heart defects are divided into two categories: a. Cyanotic defects – newborns will present with central cyanosis due the mixing of oxygenated and deoxygenated blood in the heart causing reduced pO2 of systemic blood. E.g. Tetralogy of Fallot and transposition of the great arteries. b. Acyanotic defects – the pO2 of blood in the systemic circulation is maintained. E.g. atrial septal defects and coarctation of the aorta.  ACYANOTIC CONGENITAL HEART DEFECTS
PATENT DUCTUS ARTERIOSUS (PDA) Patent Ductus Arteriosus (PDA) is an acyanotic heart defect where the ductus arteriosus remains open, allowing blood under higher pressure in the aorta to flow into the pulmonary artery, leading to a higher afterload for the right ventricle which can eventually result in right-sided heart failure.  ATRIAL SEPTAL DEFECT (ASD) Caused by underdevelopment of the septum primum or secundum, resulting in a hole in the atrial septum. This allows blood in the left atrium to flow into the right atrium. The increased volume in the right atrium leads to a higher volume of blood being pumped around the pulmonary circulation. If left untreated, this will cause damage to the vasculature and fibrosis of the arteries in the lungs. This makes the arteries less distensible which increases resistance to blood flow and results in pulmonary hypertension. VENTRICULAR SEPTAL DEFECT (VSD) The membranous portion of the septum fails to develop properly, primary IV foramen remains open. Blood in the LV will flow into the RV Will cause pulmonary hypertension and right sided heart failure. ATRIOVENTRICULAR SEPTAL DEFECT Caused by failure of the endocardial cushions to develop properly. Results in a hole in the middle of the heart with one common atrioventricular valve, instead of a mitral and a pulmonary valve. Common in Down’s syndrome.  COARCTATION OF THE AORTA Coarctation of the aorta is a congenital narrowing of part of the aorta that can cause high blood pressure upstream and weak pulses and cramping in the legs downstream. The location of the narrowing determines whether there is a radial-femoral delay(after the 3 branches of aorta) or radial-radial delay (between the brachiocephalic trunk and left subclavian) A patient with coarctation of the aorta will present with radio-femoral delay, strong radial pulses, and weak or absent femoral pulses.  CYANOTIC HEART DEFECTS
TRANSPOSITION OF THE GREAT ARTERIES The aorticopulmonary septum forms, but does not spiral, therefore when the baby is born the aorta arises from the right ventricle, and the pulmonary trunk arises from the left ventricle. This is a neonatal emergency and prostaglandins must be given to the baby quickly in order to maintain the PDA and allow some oxygenated blood into the systemic circulation until surgery can be performed.  TETRALOGY OF FALLOT Pulmonary Stenosis – the pulmonary artery or the pulmonary valve is narrowed, so less blood can enter. Overriding Aorta – aorta is large and situated right next to the VSD so most of the blood in the heart flows through it. Ventricular Septal Defect – allows blood from the right ventricle which cannot be pumped through the stenosed pulmonary artery/valve to move into the left ventricle and be pumped around the body via the aorta. Hypertrophy of the Right Ventricle – in an attempt to generate more force to pump the blood through the stenosis into the pulmonary artery. "As we conclude our journey through the development of the cardiovascular system, always remember to follow your heart – but don't forget to take your notes with you!"