cardiovascular system embryology ppt pptx

embryology of cardiovascular system

1. HEART DEVELOPMENT

2. By day 18, the lateral mesoderm has somatopleure and splanchnopleure components The splanchnopleure gives rise to almost all of the heart components. These early endocardial cells separate from the mesoderm to create paired heart tubes.

3. At the end of the second week, embryonic nutrition is obtained from the maternal blood by diffusion through the extraembryonic coelom and umbilical vesicle. At the beginning of the third week, blood vessel formation begins in the extraembryonic mesoderm of the umbilical vesicle, connecting stalk, and chorion. Embryonic blood vessels begin to develop approximately 2 days later.

4. The early formation of the cardiovascular system is correlated with the urgent need for blood vessels to bring oxygen and nourishment to the embryo from the maternal circulation through the placenta. During the third week, a primordial( the first formed ) uteroplacental circulation develops

5. Primordial Cardiovascular System The heart and great vessels form from mesenchymal cells in the cardiogenic area Paired, endocardial heart tubes , develop during the third week and fuse to form a primordial heart tube . The tubular heart joins with blood vessels in the embryo, connecting the stalk, chorion, and umbilical vesicle to form a primordial cardiovascular system . By the end of the third week, the blood is circulating, and the heart begins to beat on the 21st or 22nd day .

6. Mesodermal cells from the primitive streak migrate to form bilateral paired strands of the primary heart field . Cardiac progenitor cells from the pharyngeal mesoderm are constituted as the second heart field , which is located medial to the first heart field.

7. The primordial myocardium , is formed from splanchnic mesoderm surrounding the pericardial cavity . At this stage, the developing heart is composed of a thin endothelial tube, separated from a thick myocardium by a gelatinous matrix of connective tissue, cardiac jelly.

8. The endothelial tube become endocardium The visceral pericardium from sinus venosus and spread over the myocardium The remainder of the right ventricle and outflow tract are derived from the secondary heart field (SHF), which also contributes cells to formation of the atria at the caudal end of the heart.

9. FORMATION OF THE HEART TUBE The heart is the first functional organ to develop. It develops from splanchnic mesoderm (cardiogenic area), cranial to the developing mouth and nervous system. It lies ventral to the developing pericardial sac. The heart primordium is first evident at 18 days (as an angioplasty cords which soon canalize to form the 2 heart tubes). After completion of the head fold, the developing heart tubes lie in the ventral aspect of the embryo and dorsal to the developing pericardial sac. After lateral folding of the embryo: The 2 heart tubes fuse together to form a single endocardial heart tube. It begins to beat at 22 to 23 days .

10. Blood flow begins during the beginning of 4 th week (22 or 23 day) and can be visualized by Ultrasound Doppler.

11. Development of the Heart tube After lateral folding of the embryo, the 2 heart tubes approach each other and fuse in a craniocaudal direction to form a single endocardial heart tube within the pericardial sac.

12. What is the fate of the Heart Tube ? The heart tube grows faster than the pericardial sac, so it shows 5 dilations separated by constrictions. These are: Sinus Venosus. Truncus Arteriosus. Bulbus Cordis. Common Ventricle. Common Atrium. The endocardial heart tube has 2 ends : 1. Venous end; Sinus Venosus . 2. Arterial end; Truncus arteriosus.

13. U-SHAPED HEART TUBE Bulbus cordis and ventricle grow faster than the other chambers. So the heart bends upon itself, forming what is called: The U-shaped heart tube, or ( Bulboventricular loop ). Bulboventricular loop

14. Loop formation Or S-Shaped Heart Tube With further development the hear t tube bends , u pon itself : SO, t he atrium and sinus venosus be come dorsal to the truncus arteriosus, bulbus cordis, and ventricle. By this stage the sinus venosus has developed into a body and 2 lateral expansions, called the 2 horns ( right and left horns).

15. Veins Associated With Heart Development Each horn of the sinus venosus receives 3 veins: 1.Common cardinal. 2.Vitelline. 3.Umbilical. Cardinal vein from the fetal body. Vitelline from the yolk sac. Umbilical from the placenta.

16. 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 .

17. Right Atrium The right horn of the sinus venosus forms the smooth posterior part of the right atrium. Rough Trabeculated anterior part of the right atrium is derived from the primitive or primordial common atrium. These two parts are demarcated by the crista terminalis internally and sulcus terminalis externally.

18. Rough Trabeculated part: derived from the primitive or common primordial atrium. The smooth part: derived from the absorbed part of the Pulmonary Veins . Left Atrium

19. Partitioning of Primordial Heart Partitioning of: 1- Atrioventricular canal. 2- Common atrium. 3- Common ventricle. 4- Bulbus cordis. 5- Truncus Arteriosus. It begins by the middle of 4 th week. It is completed by the end of 5 th week .

20. Partitioning of the atrioventricular canal Two anterior and posterior (ventral & dorsal) subendocardial cushions are formed on walls of the AV canal. The AV subendocardial cushions approach each other and fuse together to form the septum intermedium. Dividing the AV canal into right & left canals. These canals partially connect the primordial atrium and primordial ventricle.

21. Partition of the common atrium Septum Primum A sickle- shaped septum grows from the roof of the common atrium towards the septum intermedium. So the common atrium is divides into right & left halves.

22. Ostium Primum At first the two ends of the septum primum reach to the growing subendocardial cushions before its central part. So the septum primum bounds a foramen called ostium primum. It serves as a shunt, enabling the oxygenated blood to pass from right atrium to left atrium. The ostium primum become smaller and disappears as the septum primum completely fused with subendocardial cushions (septum intermedium) to form the interatrial septum.

23. Septum Secundum The upper part of septum primum that is attached to the roof of the common atrium shows gradual resorption forming an opening called ostium secundum . Another septum descends on the right side of the septum primum called septum secundum . It forms an incomplete partition between the two atria. Consequently a valvular foramen forms, (foramen ovale ).

24. At birth when the lungs inflated and pulmonary circulation begins the pressure in the left atrium increases and exceeds that of the right atrium. So the two septae oppose each other. Its site is represented by the Fossa Ovalis. The septum primum forms the floor of the fossa ovalis. The septum secondum forms the margin of the fossa ovalis which is called the limbus ovalis or (annulus) ovalis. Fate of foramen Ovale

25. Partitioning of Primordial Ventricle Muscular part of the interventricular septum Division of the primordial ventricle is first indicated by a median muscular ridge, the primordial interventricular septum . It is a thick crescentic fold which has a concave upper free edge. This septum bounds a temporary connection between the 2 ventricles called interventricular foramen, (IVF).

26. Interventricular Septum Membranous part of IV septum: It is derived from: 1- A tissue extension from the right side of the endocardial cushion. 2- A orticopulmonary septum. 3- Thick muscular part of IV septum.

27. Spiral Aorticopulmonary Septum A spiral septum develops in the Truncus arteriosus dividing it into aorta and pulmonary trunk . So, now the pulmonary artery joins the right ventricle while the aorta joins the left ventricle.

28. BULBUS CORDIS The bulbus cordis forms the smooth upper part of the two ventricles . Right Ventricle : Conus Arteriosus or (Infundibulum ) which leads to the pulmonary trunk. Left ventricle: Aortic Vestibule leading to ascending aorta.

29. Blood cells develop from specialized endothelial cells ( hemangiogenic epithelium) of vessels as they grow on the umbilical vesicle and allantois At the end of the third week and later in specialized sites along the dorsal aorta. Blood formation (hematogenesis) does not begin in the embryo until the fifth week. It occurs first along the aorta and then in various parts of the embryonic mesenchyme, Mainly the liver and later in the spleen, bone marrow, and lymph nodes. Fetal and adult erythrocytes are derived from hematopoietic progenitor cell

30. B,  Dorsal view of the embryo exposed by removing the amnion (approximately 20  days)

31. Diagram of the primordial cardiovascular system in an embryo of approximately 21 days, viewed from the left  side.  Observe the transitory stage of the paired symmetric vessels.  Each heart tube continues dorsally into a dorsal aorta that passes  caudally

32. The heart tube remains attached to the dorsal side of the pericardial cavity by the dorsal mesocardium that is derived from the SHF No ventral mesocardium is ever formed. the dorsal mesocardium disappears, creating the transverse pericardial sinus, which connects both sides of the pericardial cavity. The heart is now suspended in the cavity by blood vessels at its cranial and caudal poles

33. FORMATION OF THE CARDIAC LOOP The heart tube continuous to elongate as cells are added from the SHF to its cranial end. This lengthening process is essential for normal formation of part of the right ventricle and the outflow tract and for the looping process.

34. The cephalic portion of the tube bends ventrally, caudally, and to the right and the atrial (caudal) portion shifts dorsocranially and to the left. This bending, creates the cardiac loop. While the cardiac loop is forming, local expansions become visible throughout the length of the tube. The atrial portion, initially a paired structure outside the pericardial cavity, forms a common atrium and is incorporated into the pericardial cavity The atrioventricular junction remains narrow and forms the atrioventricular canal, which connects the common atrium and the early embryonic ventricle.

35. The midportion, the conus cordis, will form the outflow tracts of both ventricles. The distal part of the bulbus, the truncus arteriosus, will form the roots and proximal portion o f the aorta and pulmonary artery The junction between the ventricle and the bulbus cordis, externally indicated by the bulboventricular sulcus remains narrow. Thus, the cardiac tube is organized by regions along its craniocaudal axis from the conotruncus to the right ventricle to the left ventricle

36. With obliteration of the right umbilical vein and the left vitelline vein during the fifth week, the left sinus horn rapidly loses its importance When the left common cardinal vein is obliterated at 10 weeks, all that remains of the left sinus horn is the oblique vein of the left atrium and the coronary sinus

37. VASCULAR DEVELOPMENT Blood vessel development occurs by two mechanisms: Vasculogenesis in which vessels arise by coalescence(union) o f angioblasts and Angiogenesis whereby vessels sprout from existing vessels. The major vessels, including the dorsal aorta and cardinal veins , are formed by vasculogenesis . The remainder of the vascular system then forms by angiogenesis. The entire system is patterned by guidance cues involving vascular endothelial growth factor (VEGF) and other growth factors

38. Arterial System Aortic Arches When pharyngeal arches form during the fourth and fifth weeks of development, each arch receives its own cranial nerve and its own artery . These arteries, the aortic arches, arise from the aortic sac, the most distal part of the truncus arteriosus. The aortic arches are embedded in mesenchyme of the pharyngeal arches and terminate in the right and left dorsal aortae. (In the region of the arches, the dorsal aortae remain paired, but caudal to this region, they fuse to form a single vessel.)

39. The pharyngeal arches and their vessels appear in a cranial-to-caudal sequence, so that they are not all present simultaneously. The aortic sac contributes a branch to each new arch as it forms, giving rise to a total of five pairs of arteries. (The fifth arch either never forms or forms incompletely and then regresses

40. Division of the truncus arteriosus by the aorticopulmonary septum divides the outflow channel of the heart into the ventral aorta and the pulmonary trunk. The aortic sac then forms right and left horns, which subsequently give rise to the brachiocephalic artery and the proximal segment of the aortic arch, respectively.

41. The first aortic arch has disappeared, although a small portion persists to form the maxillary artery. Similarly, the second aortic arch soon disappears , remaining portions of this arch are the hyoid and stapedial arteries. The third arch is large; the fourth and sixth arches are in the process of formation. Even though the sixth arch is not completed, the primitive pulmonary artery is already present as a major branch

42. The third aortic arch forms the common carotid artery and the first part of the internal carotid artery. The remainder of the internal carotid is formed by the cranial portion of the dorsal aorta. The external carotid artery is a sprout of the third aortic arch.

43. The fourth aortic arch persists on both sides, but its ultimate fate is different on the right and left sides. On the left, it forms part of the arch of the aorta, between the left common carotid and the left subclavian arteries. On the right, it forms the most proximal segment of the right subclavian artery, the distal part of which is formed by a portion of the right dorsal aorta and the seventh intersegmental artery.

44. The fifth aortic arch either never forms or forms incompletely and then regresses. The sixth aortic arch, also known as the pulmonary arch, gives off' an important branch that grows toward the developing lung bud. On the right side, the proximal part becomes the proximal segment of the right pulmonary artery. The distal portion of this arch loses its connection with the dorsal aorta and disappears. On the left, the distal part persists during intrauterine life as the ductus arteriosas .

45. A number of other changes occur along with alterations in the aortic arch system: (1) the dorsal aorta between the entrance of the third and fourth arches, known as the carotid duct, is obliterated (2) the right dorsal aorta disappears between the origin of the seventh intersegmental artery and the junction with the left dorsal aorta (3) cephalic folding, growth of the forebrain, and elongation of the neck push the heart into the thoracic cavity. Hence, the carotid and brachiocephalic arteries elongate considerably

46. As a further result of this caudal shift, the left subclavian artery, distally fix ed in the arm bud, shifts its point of origin from the aorta at the level of the seventh intersegmental artery to an increasingly higher point until it comes close to the origin of the left common carotid artery ; and as a result of the caudal shift of the heart and the disappearance o f various portions of the aortic arches, the course of the recurrent laryngeal nerves becomes different on the right and left sides.

47. When the heart descends, the LRLNs hook around the sixth aortic arches and ascend again to the larynx, which accounts for their recurrent course. On the right, when the distal part of the sixth aortic arch and the fifth aortic arch disappear, the recurrent laryngeal nerve moves up and hooks around the right subclavian artery. On the left, the nerve does not move up because the distal part of the sixth aortic arch persists as the ductus arteriosus, which later forms the ligamentum arteriosum

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49. Vitelline and Umbilical Arteries The vitelline arteries, initially a number of paired vessels supplying the yolk sac, gradually fuse and form the arteries in the dorsal mesentery of the gut. In the adult, they are represented by the celiac and superior mesenteric arteries. The inferior mesenteric arteries are derived from the umbilical arteries. These three vessels supply derivatives of the foregut, midgut, and hindgut, respectively

50. The umbilical arteries, initially paired ventral branches of the dorsal aorta, course to the placenta in close association with the allantois . During the fourth week, however, each artery acquires a secondary connection with the dorsal branch of the aorta, the common iliac artery, and loses its earliest origin. After birth, the proximal portions o f the umbilical arteries persist as the internal iliac and superior vesical arteries, and the distal parts are obliterated to form the medial umbilical ligaments.

51. Venous System In the fifth week, three pairs o f major veins can be distinguished: (1) the vitelline veins, or omphalomesenteric veins, carrying blood from the yolk sac to the sinus venosus; (2) the umbilical veins, originating in the chorionic villi and carrying oxygenated blood to the embryo; and (3) the cardinal veins, draining the body of the embryo proper

52. DEVELOPMENT OF THE SINUS VENOSUS In the middle of the fourth week, the sinus venosus receives venous blood from the right and left sinus horns . Each horn receives blood from three important veins: (1) the vitelline or the omphalomesenteric vein, (2) the umbilical vein, and (3) the common cardinal vein. At first, communication between the sinus and the atrium is wide. Soon, however, the entrance of the sinus shifts to the right This shift is caused primarily by left-to-right shunts of blood , which occur in the venous system during the fourth and fifth weeks of development.

53. Vitelline Veins Before entering the sinus venosus they form a plexus around the duodenum and pass through the septum transversum. The liver cords growing into the septum interrupt the course of the veins, and an extensive vascular network, the hepatic sinusoids, forms . The left vitelline vein regresses, and the right vitelline vein forms most of the hepatic portal system as well as a portion of the inferior vena cava (IVC).

54. With reduction of the left sinus horn, blood from the left side of the liver is rechanneled toward the right, resulting in an enlargement of the right vitelline vein (right hepatocardiac channel). Ultimately, the right hepatocardiac channel forms the hepatocardiac portion of the inferior vena cava. The proximal part of the left vitelline vein disappears

55. The anastomotic network around the duodenum develops into a single vessel, the portal vein . The superior mesenteric vein, which drains the primary intestinal loop, derives from the right vitelline vein. The distal portion o f the left vitelline vein also disappears .

56. Umbilical Veins Initially, the umbilical veins pass on each side of the liver, but some connect to the hepatic sinusoids. The proximal part of both umbilical veins and the remainder of the right umbilical vein then disappear, so that the left vein is the only one to carry blood from the placenta to the liver . With the increase of the placental circulation, a direct communication forms between the left umbilical vein and t he right hepatocardiac channel, the ductus venosus

57. This vessel bypasses the sinusoidal plexus o f the liver. After birth, the left umbilical vein and ductus venosus are obliterated and form the ligamentum teres hepatis and ligamentum venosum, respectively.

58. Cardinal Veins Initially, the cardinal veins form the main venous drainage system of the embryo. This system consists of the anterior cardinal veins, which drain the cephalic part of the embryo, and the posterior cardinal veins, which drain the rest of the embryo. The anterior and posterior veins join before entering the sinus horn and form the short common cardinal veins. During the fourth week, the cardinal veins form a symmetrical system

59. During the fifth to the seventh weeks, a number of additional veins are formed: (1) the subcardinal veins, which mainly drain the kidneys (2) the sacrocardinal veins, which drain the lower extremities; and (3) the supracardinal veins, which drain the body wall by way of the intercostal veins, taking over the functions of the posterior cardinal veins

60. Formation of the vena cava system is characterized by the appearance of anastomoses between left and right in such a manner that the blood from the left is channeled to the right side.

61. Development of Inferior Vena Cava occur when blood, returning from the caudal part of the embryo, is shifted from the left to the right side of the body. The IVC is composed of four main segments: ● A hepatic segment derived from the hepatic vein (proximal part of the right vitelline vein) and hepatic sinusoids ● A prerenal segment derived from the right subcardinal vein ● A renal segment derived from the subcardinal – supracardinal anastomosis ● A postrenal segment derived from the right supracardinal vein

62. The anastomosis between the anterior cardinal veins develops into the left brachiocephalic vein Most of the blood from the left side of the head and the left upper extremity is then channeled to the right. The terminal portion of the left posterior cardinal vein entering into the left brachiocephalic vein is retained as a small vessel, the left superior intercostal vein This vessel receives blood from the second and third intercostal spaces.

63. The superior vena cava is formed by the right common cardinal vein and the proximal portion of the right anterior cardinal vein. The anterior cardinal veins provide the primary venous drainage of the head during the fourth week of development and ultimately form the internal jugular veins

64. The anastomosis between the subcardinal veins forms the left renal vein. When this communication has been established, the left subcardinal vein disappears, and only its distal portion remains as the left gonadal vein.

65. Hence, the right subcardinal vein becomes the main drainage channel and develops into the renal segment of the inferior vena cava.

66. The anastomosis between the sacrocardinal veins forms the left common iliac vein The right sacrocardinal vein becomes the sacrocardinal segment of the inferior vena cava. When the renal segment of the inferior vena cava connects with the hepatic segment, which is derived from the right vitelline vein, the inferior vena cava, consisting of hepatic, renal, and sacrocardinal segments, is complete

67. With obliteration of the major portion of the posterior cardinal veins, the supracardinal veins assume a greater role in draining the body wall. The 4th to 11th right intercostal veins empty into the right supracardinal vein, which together with a portion of the posterior cardinal vein forms the azygos vein On the left, the 4th to 7th intercostal veins enter into the left supracardinal vein, and the left supracardinal vein, then known as the hemiazygos vein, empties into the azygos vein

68. Development of Cardiac Valves When partitioning of the truncus arteriosus is nearly completed, the semilunar valves begin to develop from three swellings of subendocardial tissue around the orifices of the aorta and pulmonary trunk. Cardiac precursor neural crest cells also contribute to this tissue. These swellings are hollowed out and reshaped to form three thin-walled cusps The AV valves (tricuspid and mitral valves) develop similarly from localized proliferations of tissue around the AV canals The atrioventricular valves are formed from  a complex arrangement of an annulus and leaflets, supported by a subvalvar apparatus that is composed of tendinous cords and papillary muscles . Although much has been said and written about their development, the exact nature of the process has yet to be fully clarified

69. Development of Spleen and Tonsils The spleen develops from an aggregation of mesenchymal cells in the dorsal mesogastrium . The palatine tonsils develop from the endoderm of the second pair of pharyngeal pouches and nearby mesenchyme. The tubal tonsils develop from aggregations of lymph nodules around the pharyngeal openings of the pharyngotympanic tubes. The pharyngeal tonsils (adenoids) develop from an aggregation of lymph nodules in the wall of the nasopharynx. The lingual tonsil lymph develops from an aggregation of lymph nodules in the root of the tongue. Lymph nodules also develop in the mucosa of the respiratory and alimentary systems.

70. Atrial Septal Defects (ASD) Absence of septum primum and septum secundum, leads to common atrium. Absence of Septum Secundum

71. Excessive resorption of septum primum (ASD) Patent foramen ovale ( ASD)

72. VENTRICULAR SEPTAL DEFECT (VSD) Roger’s disease Absence of the membranous part of the interventricular septum. Usually accompanied by other cardiac defects .

73. TETRALOGY OF FALLOT Fallot’s Tetralogy: 1-VSD. 2- Pulmonary stenosis. 3-Overriding of the aorta 4- Right ventricular hypertrophy.

74. TETRALOGY OF FALLOT Blue Baby

75. (TGA) TRANSPOSITION OF GREAT ARTERIES TGA is due to abnormal rotation or malformation of the aorticopulmonary septum. So the right ventricle joins the aorta, while the left ventricle joins the pulmonary artery. One of the most common cause of cyanotic heart disease in the newborn. Often associated with ASD or VSD or PDA. Blue Baby

76. Persistent Truncus Arteriosus It is due to failure of the development of the aorticopulmonary (spiral) septum. It is usually accompanied with VSD.

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