Development of the Cardiovascular System PDF

Development of the cardiovascular system 1  Objectives At the end of this session students are able to: – Briefly discuss the embryonic origin of blood vessels and blood cells. – List the early embryonic vessels and trace the circulat...

Development of the cardiovascular system 1  Objectives At the end of this session students are able to: – Briefly discuss the embryonic origin of blood vessels and blood cells. – List the early embryonic vessels and trace the circulation of blood through these vessels. – Discuss the formation of the heart, beginning with the two early heart tubes. – Discuss fetal circulation. – Discuss the structural changes in the cardiovascular system at birth – Discuss lymphatic development 2  Introduction Circulatory system contain cardiovascular system and lymphatic system Cardiovascular system comprises heart, blood and blood vessels The cardiovascular system is the first major system to function in the embryo. The heart begins to beat at 22 to 23 days Blood flow begins during the fourth week and can be visualized by Doppler ultrasonography. 3  Introduction cont…… Early development of Heart and Blood vessels – Progenitor heart cells lie in the epiblast, to the cranial end of the primitive streak. – These cells migrate through the streak into the splanchnic layer of lateral plate mesoderm – To form a horseshoe-shaped cluster of cells called the primary heart field (PHF), cranial to the neural folds. – This region is known as the cardiogenic region; the intra embryonic (primitive body) cavity over it later develops into the pericardial cavity 4  The earliest sign of the heart is the appearance of paired endothelial strands called angioblast cords Which is in the cardiogenic mesoderm during the third week. An inductive influence from the anterior endoderm stimulates early formation of the heart. Angioblast cords Endocardial tubes Heart tubes 5  These cords canalize to form thin heart tubes. As a lateral embryonic folding occurs, the endocardial tubes approach each other and fuse to form a heart tube. Fusion of the heart tubes begins at the cranial end of the developing heart and extends caudally. 6  Introduction cont…… Cardiovascular system derived from: – Splanchnic mesoderm, which forms the primordium of the heart. – Extraembryonic mesoderm(umbilical vessels and blood cells) – Paraxial and lateral mesoderm near the otic placodes from which the internal ears develop. – Neural crest cells (endocardial derived cells) contribute for formation of endocardial cusion in the outflow of primitive heart 7  Introduction cont…… Vasculogenesis: – Formation of vascular cord from angioblast cells. Angiogenesis: – Budding and sprouting of new vessels from exisiting endothelial cords. Vascular intussusception: – Separation of exisiting vessel to generate additional vessels.  Primordial blood vessels cannot be distinguished structurally as arteries or veins,  But are named according to their future fates and relationship to the heart 9  Introduction cont…… Hematopoiesis: – Begins in the yolk sac and extra embryonic mesoderm. – Later shift to the liver where primary hematopoietic cells joined with, – Their second counter part derived from intraembryonic mesoderm. – Definitive hematopoietic stem cells are programed within the liver, – And they later colonize the bone marrow and other lymphatic organs. 11  DEVELOPMENT OF THE HEART Formation of the primitive heart. Looping of cardiac tube. Partition of the heart. 12  Development of heart cont….. The heart lie caudal to the oropharyngeal membrane. Mesenchymal cells in the cardiogenic area form two angioblastic cords. These cords become canalized to form two endothelial heart tubes. 13  During the lateral embryonic folding, the tubes fuse to form a single endothelial heart tube. – Fusion of the heart tubes begins at the cranial end of the developing heart and extends caudally The surrounding splanchnic mesoderm form the primitive myocardium 14  Development of heart cont….. Two Heart Tubes Formation of the Pericardial Cavity and Fusing of the Heart tubes 15  The endothelial tube becomes the lining of the heart, the endocardium The primitive myocardium becomes the muscular wall or myocardium. 18  Development of heart cont….. The visceral pericardium or epicardium is derived from mesothelial cells of the sinus venosus and spread over the myocardium On both pole of the primitive heart tube, there is cardiac progenitor cells from the surrounding mesoderm. The source of these cells is called secondary heart field. 19  Development of heart cont….. The tubular heart develops five zones: – Truncus arteriosus (T) – Bulbus cordis(B), – Ventricle,(V) – Atrium(A) – Sinus venosus (SV) Some would call these two together the primitive ventricle, with inlet and outlet portions 20  Formation of the Cardiac Loop The heart tube continues to elongate and bend on day 23. The cephalic portion: the tube bends ventrally, caudally, and to the right. The atrial (caudal) portion : shifts dorsocranially and to the left This bending is due to cell Note that the left ventricle will shape changes, which creates develop from the ventricle, and the cardiac loop. the right ventricle will develop from the bulbus cordis It is complete by day 28. 21  Changes in the primitive heart tube The sinus venosus – By the end of 4th week, the left sinus horn begun to be narrow. – As this occurs, the sinuatrial (SA) orifice moves to the right – and opens into primordial atrium that will become the adult right atrium 22 – So that, the right sinual horn enlarges and receive all the venous blood through SVC and IVC – Initially, the sinus venosus is a separate chamber of the heart – And opens into the dorsal wall of the right atrium 23  Changes in the primitive heart tube cont…… The sinus venosus cont…. – The left horn becomes the coronary sinus. – The right sinus horn becomes incorporated into the wall of the right atrium. 24  Because it is derived from the sinus venosus, The smooth part of the wall of the right atrium is called the sinus venarum. 25  Changes in the primitive heart tube cont…… The atrial portion: Contribute for the formation of the atrial system of the heart. 27  The atrioventricular junction remains narrow, and forms the atrioventricular canal Which connects the common atrium and the early embryonic ventricle 28  Changes in the primitive heart tube cont…… Fate of bulbus cordis: – Is narrow except for its proximal third. This portion will form the trabeculated part of the right ventricle – The mid-portion will form the outflow tracts of both ventricles. – The distal part of the bulbus, the truncus arteriosus, will form the roots and proximal portion of the aorta and pulmonary artery 29  Changes in the primitive heart tube cont…… Fate of bulbis cordis cont…. – The bulbus cordis is incorporated into the walls of the definitive ventricles: 1. In the right ventricle, the bulbus cordis is represented by the conus arteriosus (infundibulum), which gives origin to the pulmonary trunk. 30 2. In the left ventricle, the bulbus cordis forms the walls of the aortic vestibule, Which is the part of the ventricular cavity just inferior to the aortic valve. 31  Circulation Through the Primitive Heart The initial contractions of the heart are of myogenic origin. The muscle layers of the atrium and ventricle are continuous, Contractions of the heart occur in peristalsis like waves that begin in the sinus venosus At first, circulation through the primordial heart is an ebb-and-flow (rise and fall) type; 32  However, by the end of the 4th week, coordinated contractions of the heart result in unidirectional flow.  Blood enters the sinus venosus from the: Embryo through the common cardinal veins Developing placenta through the umbilical veins Umbilical vesicle through the vitelline veins 33  Blood from the sinus venosus enters the primordial atrium; flow from it is controlled by sinuatrial (SA) valves. The blood then passes through the atrioventricular canal into the primordial ventricle. 34  When the ventricle contracts, blood is pumped through the bulbus cordis and TA (truncus arteriosus) into the aortic sac, From which it is distributed to the pharyngeal arch arteries in the pharyngeal arches 35  The blood then passes into the dorsal aortas for distribution to; The embryo, umbilical vesicle, and placenta. 36  Partitioning of the Primitive Heart Endocardial cushions form on the dorsal and ventral walls of the atrioventricular canal. The atrioventricular endocardial cushions fuse, And dividing the atrioventricular canal into right and left atrioventricular canals. 37  These canals partially separate the primordial atrium from the primordial ventricle, And the endocardial cushions function as AV (Atrioventricular) valves 38  Partitioning of the Primitive Heart cont… The endocardial cushions develop from a specialized extracellular matrix or cardiac jelly. Inductive signals from the myocardium of the AV canal; Causes the inner endocardial cells undergoes epithelial- mesenchymal transformation, Which then invades the extracellular matrix. 39  The transformed endocardial cushions contribute to;  The formation of the valves  And the membranous septa of the heart. 40  At the end of the 4th week, the primordial atrium is divided into right and left atria by; The formation and modification as well as the fusion of two septa: The septum primum and septum secundum. 41  Partitioning of the Primitive Heart cont… The septum primum A thin crescent-shaped membrane. Grows toward the fusing endocardial cushions from the roof of the primordial atrium, Partially dividing the common atrium into right and left halves 42 Foramen primum Large opening between crescentic free edge of spetum primum and the endocardial cushions. Disappear when septum primum fuse with the cushions Serves as a shunt, enabling oxygenated blood to pass from the right to the left atrium. 43  Partitioning of the Primitive Heart cont… Before the foramen primum disappears, perforations appear in the central part of the septum primum to form foramen secundum. The foramen secundum ensures continued shunting of oxygenated blood from the right to the left atrium. 44  Septum secundum – Thick crescentic muscular fold, grows from the ventrocranial wall of the right atrium. – Overlaps the foramen secundum in the septum primum – The septum secundum forms an incomplete partition between the atria; consequently, an oval foramen 45  Initially, the cranial part of the septum primum attached to the roof of the left atrium, gradually disappears. The remaining part of the septum primum, attached to the fused endocardial cushions, Forms the flaplike valve of the oval foramen. 46  Partitioning of the Primitive Heart cont… Well oxygenated blood is shunted from the right atrium, Through the oval foramen to the left atrium when pressure rises Before Birth 47  Partitioning of the Primitive Heart cont….. Pressure in the left atrium rises due to blood return from the lungs. Septum primum is pressed against septum secondum permanatly, Closing the oval foramen forming the oval fossa After Birth 48  Partitioning of the Primitive Heart cont…. Prenatal (Before birth) – The foramen ovale allows the blood entering the right atrium from the inferior vena cava to pass into the left atrium. – And prevents the passage of blood in the opposite direction – Because, septum primum closes against septum secundum 49  Partitioning of the Primitive Heart cont….. Postnatal (After birth) The foramen ovale functionally closes due to higher pressure in the left atrium than the right. Approximately 3 months of age, the valve of the oval foramen fuses with the septum secundum, forming the oval fossa. 50 – When septum primum and septum secundum fuses; – Interatrial septum partition occurs between atria 51  Partitioning of the Primitive Heart cont…… Foramen Ovale: The oval foramen closes at birth Anatomical closure is due to adhesion of the septum primum (the valve of the foramen ovale) to the left margin of the septum secundum The septum primum forms the floor of the fossa ovalis The inferior edge of the septum secundum forms a rounded fold, the limbus fossae ovalis (anulus ovalis) 52  Partitioning of the Primitive Heart cont….. Interventricular (IV) septum – Muscular growth in the floor of the ventricle near its apex. – Later, there is active proliferation of myoblasts in the septum, which increase its size 53  Interventricular septum cont….. Until the 7th week, a crescent-shaped IV foramen formed between; The free edge of the IV septum and the fused endocardial cushions 54  Partitioning of the Primitive Heart cont….. Interventricular septum cont….. – Closure of the IV foramen and formation of the membranous part of the IV septum is; – The result of fusion of the tissues from three sources: 1. The right bulbar ridge, 2. The left bulbar ridge, and 3. The endocardial cushion. 55  Partitioning of the Primitive Heart cont….. Result of fusion of the septum: – The pulmonary trunk is communicate with the right ventricle – And the aorta communicates with the left ventricle 56  Partitioning of the Primitive Heart cont….. Partitioning of the Bulbus Cordis and Truncus Arteriosus The bulbar and truncal ridges are derived largely from neural crest mesenchyme. Neural crest cells migrate through the primordial pharynx and pharyngeal arches to reach the ridges. As this occurs, the bulbar and truncal ridges undergo a 180-degree spiraling. 57 Development and fate of veins associated with the heart 58 Development of veins cont…… Changes in the Sinus Venosus Initially, the sinus venosus opens into the center of the dorsal wall of the primordial atrium, And its right and left sinual horns are approximately the same size. 59  Progressive enlargement of the right sinus horn results from two left-to-right shunts of blood: A. The first shunt results from transformation of the vitelline and umbilical veins, B. The second shunt occurs when the anterior cardinal veins become connected by an anastomosis. 60  This communication, shunts blood from the left to the right anterior cardinal vein. So that, the shunt becomes the left brachiocephalic vein. The right anterior cardinal vein and the right common cardinal vein become the SVC. 61  By the end of the 4th week, the right sinual horn is clearly larger than the left sinus horn As this occurs, the sinuatrial (SA) orifice moves to the right And opens into the primordial atrium that will become the adult right atrium. 62  As the right sinual horn enlarges, it receives all the blood from the head and neck through the SVC And from the placenta and caudal regions of the body through the IVC. Initially, the sinus venosus is a separate chamber of the heart and opens into the dorsal wall of the right atrium. 63  The left horn becomes the coronary sinus, and the right sinus horn becomes incorporated into the wall of the right atrium Because it is derived from the sinus venosus, the smooth part of the wall of the right atrium is called the sinus venarum 64  Development of veins cont…… The veins develop from the three major venous circuits:- vitelline, umbilical and cardinal veins All of the three veins are initially bilateral 65  Development of veins cont…… General concept in the development of veins 1. The left side of the venous system degenerate and blood shunt from the left to the right side 2. New cardinal veins are developed as the old veins (classical cardinal veins) degenerate. 3. The formation of the liver and the mesonephric kidney has profound effects in redirecting blood flow 66  The Vitelline veins It give rise to liver sinusoides, portal system, and a portion of inferior vena cava. Arise from the capillary plexuses of the yolk sac 67  And form part of the vasculature of the developing gut and gut derivatives. The paired Vitelline vein empties to the SV of the primitive heart. 68  The Vitelline veins cont…… In relation to the developing liver in the septum transversum, The vitelline veins are divided into: A. Pre-hepatic part: forms anastomosis around the duodenum which later on gives rise to; The portal vein and superior mesentric vein. 69  Prominent left to right anastomosis remodeled to form splenic and inferior mesenteric veins. 70  The Vitelline veins cont…… Hepatic part: Interrupted by the liver cords, and forms an extensive vascular network called the hepatic sinusoides 71  Post-hepatic part: Left vein disappears Right vein forms the: Hepatic veins & Hepatic segment of inferior vena cava 72  Umbilical veins Initially, run on each side of the developing liver and drain into the sinus venosus As the liver grows, the right umbilical vein disappears in contrast to vitelline vein by the end of the embryonic period. 73  Umbilical veins cont…… The left umblical vein persists but loses its connection to SVC, because of the degeneration of the left horn of SVC. And anastomoses with the ductus venosus to reach IVC. 74  After birth:  The left umbilical vein obliterate to form – the ligamentum teres of the liver  The ductus venosus obliterate to form – the ligamentum venosum 75  Cardinal Veins Are responsible to drain the body of the embryo  The cranial part of the embryo is drained by paired anterior cardinal veins 76  The caudal part of the embryo is drained by paired posterior cardinal veins  The anterior & posterior cardinal veins join to form common cardinal veins,  Which drain into the sinus venosus 77  Cardinal Veins cont….. 1. Anterior Cardinal Veins (cranial, middle & caudal) – Become connected by an oblique anastomosis which shunts blood from left to the right – This anastomosing channel becomes the left brachiocephalic vein 78 A. Left anterior cardinal vein  Cranial part: becomes the left internal jugular vein  Caudal part: degenerates 79  Cardinal Veins cont….. B. Right anterior cardinal vein  Cranial part: (cranial to the 7th intersegmental vein)  Becomes the right internal jugular vein  Middle part: gives rise to the right brachiocephalic vein  Caudal part of right anterior cardinal vein and the right common cardinal vein form the superior vena cava 80  Cardinal Veins cont….. 2. Posterior Cardinal Veins – Drain the caudal part of the body of the embryo including; – The developing mesonephroi and largely disappear with this transitory kidneys. 81 – Caudally the two veins get connected by an anastomosing channel – That directs the blood from the left to the right vein. 82  Cardinal Veins cont….. Gradually the posterior cardinal veins are replaced by the two symmetrical new veins: A. Subcardinal & B. Supracardinal 83  Cardinal Veins cont….. As the sub cardinal veins are formed, Most of the posterior cardinal veins are degenerated except; In the caudal part and some cranial part. 84  The adult derivatives of the posterior cardinal veins are the:  Root of the azygos vein &  Common iliac veins 85  Subcardinal veins Appears before the supracardinal veins develop in the primitive nephrons and gonads area; And form venous system of this structure 86  Become connected: – To each other by the subcardinal anastomosis – With the posterior cardinal veins through the mesonephros – With supracardinal veins through subsupracardinal anastomosis 87  Subcardinal veins cont…… As the other venous system under go extensive remodeling and degeneration to shunt blood from left to right. The right subcardinal vein communicate with right vitelline vein to form the portion of IVC between the liver and kidney. 88  Adult derivatives of subcardinal veins are:  Stem of the left renal vein  Suprarenal veins  Gonadal veins  Prerenal segment of IVC 89  Supracardinal veins Last pair of veins to develop Appear lateral to the subcardinal veins Become connected at both ends, to the posterior cardinal veins 90  Cont… And drains the body wall via the segmental intercostal veins Get disrupted in the region of the kidney 91  Supracardinal veins cont…… Cranial to the kidney: – An anastomosis develops between the two veins shunting blood from the left to the right vein. 92 In the thoracic region  Anterior connection of the left vein with the posterior cardinal vein disappears And blood shunt to the right through medial connection to give rise to hemiazygos vein. 93 – The right supracardinal vein loses its connection to posterior cardinal vein – And make new anastomosis with superior vena cava to return to the heart. – Supracardinal vein then, is called azygos vein 94  Supracardinal veins cont…….. Caudal to the kidney: – Left vein degenerates – Right vein distally forms post-renal segment of IVC 95 Summery Vitilline vein……….drain the deoxygenated blood from the yolk sac 1. Umbilical vein…….return oxygenated blood from placenta 2. Cardinal veins ……..return deoxygenated blood from the rest of the body 96  Formation of the inferior vena cava The azygos vein CARDINAL VEINS system 97  Development of Inferior vena cava Sources of the four portion of IVC 1. Right vitelline vein gives rise to the terminal part of the IVC 2. The right subcardinal vein gives rise to a segment between liver and kidneys 3. Right supracardinal vein gives rise to an abdominal segment of IVC inferior to renal segment 4. Right and left posterior cardinal vein with their medial connection gives rise to sacral segment of IVC 98  Development of pulmonary veins They develop at the end of the 4th week Originate as midline structure within the caudal dorsal mesocardium; Which connect the developing lung with the dorsal of the developing common atrium 99 100 DEVELOPMENT OF THE ARTERIAL SYSTEM Pharyngeal Arch Arteries Dorsal Aorta Intersegmental artery Umbilical artery and Vitelline artery 101  Pharyngeal Arch Arteries The pharyngeal arch arteries arise from the aortic sac and terminate in the dorsal aortas. Initially, the paired dorsal aortas run through the entire length of the embryo. 102  Later, the caudal portions of the dorsal aortas fused at level of T4; to form a single lower thoracic/abdominal aorta. Of the remaining paired dorsal aortas, the right regresses and the left becomes the primordial aorta. 103  Fate of Aortic Arches Each pharyngeal arch has its aortic arch. There are 6 aortic arches that are connected ventrally to aortic sac and dorsally to dorsal aorta. A. First arch: Degenerates mostly leaving maxillary artery. 104 B. Second arch: Degenerates mostly leaving stapedial artery. 105 C. Third arch: Its ventral (proximal) part gives common carotid artery While the dorsal (distal) part gives internal carotid artery. External carotid artery begins as a new branch between proximal and distal parts of the 3rd arch. 106  Fate of Aortic Arches cont……. 4th aortic arch: – On the left side it forms part of the final aortic arch – While on the right side it forms part of the right subclavian artery. – N.B. Left subclavian artery are formed from the left 7th cervical intersegmental artery. 107 5th aortic arch: – Degenerate as the 5th pharyngeal arch. 108  Fate of Aortic Arches cont……. 6th aortic arch: Its ventral part form pulmonary artery which communicates with pulmonary trunk. 109  The dorsal part of the aortic arch remains in the left side as ductus arteriosus But in the right side, it degenerates. 110  Fate of Aortic Arches cont……. Part of dorsal aorta between 3rd& 4th arches disappears on both sides Aortic sac is divided into left and right parts: 111  – Left part forms proximal part of arch of aorta and becomes continuous with the Lt. 4th aortic arch – Right part forms innominate artery and becomes continuous with Rt. 3rd and 4th arches Part of Rt. dorsal aorta between Rt. 7th intersegmental a. and Lt. dorsal aorta disappears 112 Fate of Aortic Arches cont……. 113  CONGENITAL ANOMALIES 1. Double aortic arch: Due persistence of right dorsal aorta between rt. 7th cervical intersegmental artery and site of fusion. 2. Right aortic arch: Degeneration of left dorsal aorta and persistence of corresponding part of right dorsal aorta. 114 3. Coarctation of aorta: Narrowing of arch of aorta just distal to left subclavian artery. It could be pre- or post-ductal. 4. Abnormal origin of right subclavian artery: Arises from descending aorta and passes behind esophagus. 5. Interrupted aortic arch: Due to obliteration of left 4th aortic arch, Aorta supplies head while pulmonary artery supplies rest of body through ductus arteriosus. 115 Embryological Differences in the Course of Rt & Lt Recurrent laryngeal nerves 116 Cont…… 117 Cont…… 118  Dorsal Aortae and their Branches The dorsal aorta develops three groups of branches: 1. Postero-lateral branch 2. Lateral branch 3. Ventral branch 119  Dorsal Aortae and their Branches cont….. Dorsal intersegmental arteries: – Pass b/n and carry blood to the somites and their derivatives. 1. In the neck: join to form longitudinal arteries like vertebral and thyrocervical trunk of Subclavian artery from the 7th cervical intersegmental artery 2. In the thorax: posterior intercostal arteries. 3. In the lumbar region: lumbar arteries. 5th lumbar a. enlarge and form common iliac artery. 4. In sacral region: are small and dorsal aorta diminished and form median sacral a. 120  Dorsal Aortae and their Branches cont….. The aorta below the diaphragm 121  Dorsal Aortae and their Branches cont….. Lateral splanchnic arteries: – Supply intermediate mesoderm – In adults form renal, suprarenal, phrenic and gonadal arteries. Ventral splanchnic arteries: – Initially paired vitelline and umbilical arteries. – Fusion of 2 dorsal aortae form unpaired arteries run in dorsal mesentery. The remaining in the adults are celiac trunk, superior and inferior mesenteric arteries. 122  Dorsal Aortae and their Branches cont….. Ventral splanchnic arteries (The Vitelline Arteries) – The unpaired ventral branches of the dorsal aorta supply the umbilical vesicle (yolk sac), allantois, and chorion. – The vitelline arteries pass to the vesicle and later the primordial gut, which forms from the incorporated part of the umbilical vesicle. Fate – Only three vitelline arteries remain: celiac arterial trunk to foregut, superior mesenteric artery to midgut, and inferior mesenteric artery to hindgut. 123 Dorsal Aortae and their Branches cont….. 124  Dorsal Aortae and their Branches cont….. Ventral splanchnic arteries(umbilical arteries) – The paired umbilical arteries pass through the connecting stalk (primordial umbilical cord) – And become continuous with vessels in the chorion, the embryonic part of the placenta. – The umbilical arteries carry poorly oxygenated blood to the placenta. –Fate Proximal parts of the umbilical arteries become the internal iliac arteries and superior vesical arteries, whereas distal parts obliterate after birth and become the medial umbilical ligaments. 125 Ventral splanchnic arteries(umbilical arteries) cont….. 126  The Fetal Circulation The main features of the fetal circulation are: – Non-functioning lungs – Course of the blood from the placenta to the heart – Three shunts permitting the blood to bypass the liver and lungs: Foramen ovale Ductus venosus Ductus arteriosus 127 The fetal circulation cont……. 128  The fetal circulation cont……. – Well-oxygenated blood returns from the placenta in the umbilical vein – Half the blood from the placenta passes through the hepatic sinusoids – The remainder bypasses the liver and goes through the ductus venosus into the inferior vena cava – In the inferior vena cava, the oxygenated blood mixes with the deoxygenated blood arriving from the fetus – The blood flow through ductus venosus is regulated by a sphincter close to the umbilical vein 129  The fetal circulation cont……. The sphincter relaxes, more blood passes through the ductus venosus The sphincter contracts, more blood is diverted through the portal sinus to the portal vein and into the hepatic sinusoids There is a physiological sphincter that prevents overloading of the heart When venous flow in the umbilical vein is high, e.g., during uterine contractions 130  The fetal circulation cont……. After a short course in the inferior vena cava, the blood enters the right atrium of the heart The caudal vena cava contains poorly oxygenated blood from the lower limbs, abdomen, and pelvis The blood entering the right atrium is not a well oxygenated as that in the umbilical vein, but it is still well-oxygenated blood Blood from IVC is directed by the inferior border of the septum secundum called the crista dividens through foramen ovale into the left atrium 131  The fetal circulation cont……. Here it mixes with the deoxygenated blood returning from the lungs via the pulmonary veins From the left atrium, the blood passes into the left ventricle and leaves via the ascending aorta The arteries supplying the heart, head, neck, and upper limbs receive well-oxygenated blood 132  The fetal circulation cont……. The liver receives well oxygenated blood from the umbilical vein A small amount of well-oxygenated blood from the inferior vena cava remains in the right atrium This blood mixes with poorly oxygenated blood from the superior vena cava and coronary sinus and passes into the right ventricle This blood leaves via the pulmonary trunk Most of it passes through the ductus arteriosus into the aorta 133  The fetal circulation cont……. Because of the high pulmonary vascular resistance in fetal life 40-50 % of the blood in the descending aorta passes into the umbilical arteries And is returned to the placenta for reoxygenation The rest of the blood supplies the viscera and the inferior half of the body 134  SUMMARY OF FETAL CIRCULATION There is mixing of oxygenated and deoxygenated blood in the: I. Liver sinusoids II. Inferior vena cava III. Right atrium IV. Left atrium V. Descending aorta. 135  THE NEONATAL CIRCULATION  At birth, dramatic changes occur in the circulatory pattern.  The changes are initiated by baby’s first breath. – Fetal lungs begin to function – Placental circulation ceases – The three shunts that short-circuited the blood during the fetal life cease to function  The sphincter in the ductus venosus constricts so that all blood entering the liver passes through the hepatic sinusoids 136  The neonatal circulation cont……. Occlusion of the placental circulation causes fall of blood pressure in the inferior vena cava and right atrium Aeration of the lungs is associated with fall in pulmonary vascular resistance, increase in pulmonary blood flow, and a progressive thinning of the walls of the pulmonary arteries 137 The neonatal circulation cont……. 138  The neonatal circulation cont……. The infant’s lungs begin to function: – The lungs inflate, which tends to draw blood from the right ventricle. – Oxygenated blood from the lungs passes through pulmonary veins to left atrium. The increased pressure in the left atrium results in closure of the foramen ovale, effectively separating the two atria. – This also increases blood flow to the lungs as blood entering the right atrium can no longer bypass the right ventricle, which pumps it into the pulmonary artery and on to the lungs. 139  The neonatal circulation cont…….  The placental circulation ceases. – Umbilical vessels are no longer needed. They become obliterated – Occlusion of the placental circulation causes fall of blood pressure in the inferior vena cava and right atrium  The shunts stop to function: – Within a day or two of birth, the ductus arteriosus closes off, preventing blood from the aorta from entering the pulmonary artery – The ductus venosus closes off so that all blood entering the liver passes through the hepatic sinusoids. 140  Summary A. Circulatory routes during gestation and B. changes at birth 141 142  ANOMALIES OF THE HEART AND GREAT VESSELS Patent Ductus Arteriosus (PDA) – Associated with maternal rubella infection during early pregnancy – Failure of contraction of the muscular wall of the ductus arteriosus after birth is the primary cause of patency – Low oxygen content of the infant blood affect closure of the ductus arteriosus – PDA occurs in new born with respiratory difficulties due to deficiency of surfactant – PDA is common in infants born at high altitude – PDA occur in cardiac defects 143  ANOMALIES OF THE HEART AND GREAT VESSELS cont…. Ductus arteriosus is sensitive for: 1. Oxygen (high oxygen closes) 2. Brady kinin (released by lung at first inflation & make to close) 3. PGE2(produced by endothelial cell of ductus arteriosus in low oxygen to keep it open but decrease in high oxygen) 144 ANOMALIES OF THE HEART AND GREAT VESSELS cont…. Dextrocardia – If the heart tube bends to the left instead of to the right, the heart is displaced to the right and there is transposition; – The heart and its vessels are reversed left to right as in a mirror image 145  ANOMALIES OF THE HEART AND GREAT VESSELS cont…. Atrial Septal Defects(ASD) – Common congenital heart anomaly – Occurs more frequently in females than in males. – Most common form of ASD is patent oval foramen – Blood is shunted through the oval foramen into the left atrium and produces cyanosis (deficient oxygenation of blood) – There are four clinically significant types of ASD: ostium secundum defect, endocardial cushion defect with ostium primum defect, sinus 146  ANOMALIES OF THE HEART AND GREAT VESSELS cont…. Ventricular Septal Defects(VSD) – Most common type of CHD, accounting for approximately 25% of defects – Occur more frequently in males than in females – Occur in any part of the IV septum but membranous VSD is the most common type – Frequently, during the first year, 30% to 50% of small VSDs close spontaneously 147  ANOMALIES OF THE HEART AND GREAT VESSELS cont…. Cyanotic Cardiac Malformation – Tetralogy of Fallot 1. Dextro aorta (overriding aorta) 2. Pulmonary stenosis 3. Septal Defect (ASD) 4. Dilation & hypertrophy of the right ventricle 148 ANOMALIES OF THE HEART AND GREAT VESSELS cont…. Cyanotic Cardiac Malformation Eisenmanger Complex 1. Dextroaorta 2. IV septal defect 3. Right ventricular dilation with hypertrophy 149  Development of the lymphatic system Like blood vessels, lymphatic channels arise by vasculogenesis and angiogenesis from mesodermal precursors. By the end of 5th week, the jugular lymph sac developed 150  Development of the lymphatic system cont… There are six primary lymph sacs present at the end of the embryonic period – Two jugular lymph sacs near the junction of the subclavian veins with the anterior cardinal veins (the future internal jugular veins) – Two iliac lymph sacs near the junction of the iliac veins with the posterior cardinal veins – One retroperitoneal lymph sac in the root of the mesentery on the posterior abdominal wall – One chyle cistern (L. cisterna chyli) located 151 dorsal to the retroperitoneal lymph sac  Development of the lymphatic system cont… Lymphatic ducts: – First paired lymphatic ducts that empty at junction of internal jugular and subclavian vein at both sides. – Both ducts obliterate and definitive thoracic duct formed from: Caudal portion of the right duct The cranial portion of the left duct A median anstomosis 152  Development of the lymphatic system cont… Development of the Lymph Nodes: – Except for the superior part of the chyle cistern, the lymph sacs are transformed into groups of lymph nodes during the early fetal period 153 154