1. Cardiovascular System
Development of
Cardiovascular System
Department of Histology and Embryology
Medical college in Three Gorges University

2. 1.Establishment of the Cardiogenic Field
The heart (like all blood vessels ) is mesodermal in origin. The mesoderm is constitutes the cardiogenic field (area). It is closely related to the pericardial cavity and heart tube.

6. Heart tube
Cardiogenic area

7. As a result of growth of the brain and
cephalic folding of the embryo, the buccopharyngeal membrane is pulled for-
ward, while the heart and pericardial cavity move first to the cervical region and finally to the thorax.

8. Before the folding:pericardial cavity (dorsal)
Heart tube(ventral)
After the folding: heart tube (dorsal )
pericardial cavity(ventral)

10. Thus the heart tube consists of three layers: (a) the endocardium, forming the internal endothelial lining of the heart;
(b) the myocardium, forming the muscular
wall;
(c) the epicardium or visceral pericardium, covering the outside of the tube.

11. The heart is at first seen in the form of right and left endothelial heart tubes that soon fuse with each other. The single tube thus formed shows a series of dilations.These are :
(1) Bulbus cordis.
(2) Ventricle(primitive ventricle)
(3) Atrium (primitive atrium)
(4) Sinus venosus

12. Exterior of the Heart
U-shaped Bulbo-ventricular loop
S-shaped(atrium and sinus venosus come to lie behind and above the ventricle)

16. Atrioventricular canal: The ventricle and atrium are connected by a narrow.
The bulbus cordis lies at the arterial end of the heart.
the conus: proximal part
truncus arteriosus: is continuous distally with the aortic sac. (distal part )

17. The sinus venosus lies at the venous end of the heart
The sinus venosus lies at the venous end of the heart.It has right and left horns.one vitelline vein (from the yolk sac ),one umbilical vein (from the placenta ) and one common cardinal vein (from the body wall ) join each horn of the sinus venosus.

18. The fate of five dilatation:
Truncus arteriosus(T)
Bulbus cordis (B)
Primitive ventricle(PV)
Aorta
Pulmonary trunk
Smooth part of right ventricle
( cornus arteriosus)
Smooth part of left ventricle
(aortic vestibule)
Trabeculated part of right ventricle
Trabeculated part of left ventricle

19. Primitive atrium(PA) Sinus venosus Trabeculated part of right atrium
Trabeculated part of left atrium
Primitive atrium(PA)
Smooth part of right atrium
Coronary sinus
Oblique vein of left atrium
Sinus venosus

20. 2. Formation of the Cardiac Septa
The Atrioventricular (AV) septum
Atrial septum
Interventricular septum
Aorticopulmonary septum

21. SEPTUM FORMATION IN THE ATRIOVENTRICULAR CANAL:
The Atrioventricular (AV) septum divides the AV canal into the right AV canal and left AV canal.
Formation: The dorsal and ventral AV cushion fuse to form the AV septum.
Clinical correlations:
Unventricular heart
Tricuspid atresia

22. Inferior and superior

24. SEPTUM FORMATION IN THE COMMON ATRIUM
(A)At the end of the fourth week, a sickle-shaped crest grows from the roof of the common atrium into the lumen. This crest is the first portion of the septum primum. The two limbs of this septum extend toward the endocardial cushions in the atrioventricular canal.

25. The opening between the lower rim of the septum primum and the endocardial cushions is the ostium primum. It is obliterated (closed)when the septum primun fused with the AV septum.

28. (c ) Before closure is complete, however,
cell death produces perforations in the upper
portion of the septum primum. Coalescence of these perforations forms the ostium secundum, ensuring free blood flow from the right to the left primitive atrium.

30. (D) At the beginning of fifth week,a new crescent-shaped fold appears in the right of the septum primum . This new fold, the septum secundum, never forms a complete partition in the atrial cavity. Its anterior limb extends downward to the septum in the atrioventricular canal.

31. (E) The opening left by the septum secundum is called the oval foramen (foramen ovale), the remaining part of the septum primum ( the upper part of the septum primum gradually disappears) becomes the valve of the oval foramen.
It is a valvular aperture that allows blood to flow from right to left, but not from left to right.

35. After birth, when lung circulation begins and pressure in the left atrium increases, the valve of the oval foramen is pressed against the septum secundum, obliterating the oval foramen and separating the right and left atria.

37. Clinical correlations: Heart defects involving the atrial septum are called atrial septum defects(ASDs)
(1) Foramen secundum defect is caused by excessive resorption of the septum of the septum primum, septum secundum,or both.

39. (2)Premature closure of foramen ovale is the closure of the foramen ovale during prenatal life. This results is hypertrophy of the right side of the heart and underdevelopment of the left side.

40. SEPTUM FORMATION IN THE VENTRICLES

41. Formation:
(1) The muscular interventricular septum develops in the floor of the ventricle it grows toward the AV cushions but stops short leaving the interventricle foramen.
(2)The membranous IV septum forms by the fusion of three components: the right bulbar ridge,left bulbar ridge, and AV cushions. This fusion closes the IV foramen.

48. CLINICAL CORRELATES
Ventricular septal defect (VSD) involving the membranous portion of the septum is the most common congenital cardiac malformation, occurring as an isolated condition in l2/10,000 births.

50. SEPTUM FORMATION IN THE TRUNCUS ARTERIOSUS AND CONUS CORDIS
Aortucopulmonary (AP) septum: The AP septum divides the truncus arteriosus into the aorta and pulmonary trunk.
(1)Formation: Pairs of opposing ridges, in the the truncal and bulbar ridges which grow in a spiral fashion and fuse to form the AP septum. (not straight )

51. Left truncus ridge
Right truncus ridge
Left bulbar ridge

55. Clinical corralations:
(1)Persistent truncus arteriosus
(2) D-Transposition of the great vessels (complete):

56. (3)Tetralogy of Fallot,
Four cardiovascular alterations:
(a) a narrow right ventricle outflow region, a pulmonary infundibular stenosis
(b)a large defect of the ventricular septum
(c) an overriding aorta that arises directly above the septal defect.
(d) hypertrophy of the right ventricular wall because of higher Pressure on the right side

58. III: the carotid arteries IV:right----subclavian artery
Aortic arches I
II:
III: the carotid arteries
IV:right----subclavian artery
left -----the arch of the aorta
V: disappeared
VI :pulmonary artery,( the left is connected to the aorta through the ductus arteriosus during the fetal life)
disappeared

59. Circulation Before and After Birth:
Fetal Circulation:
The circulation in the fetus is essentially the same as in the adult except for the following:
(1) The source of oxygenated blood is not the lung but the placenta
(2)Oxygenated blood from the placenta comes to the fetus through the umbilical vein, which joins the left branch of the portal vein.

60. the greater part of this blood passes direct to the inferior vena cava through the ductus venosus.
(3)Most of the blood in the right atrium flow into the left atrium through the foramen ovale
(4) Only a small portion of the pulmonary trunk reaches the lungs, the greater part is short-circulation by the ductus arteriosus into the aorta.

61. Changes in the circulation at Birth:
(1)Closure of the umbilical arteries
(2) Closure of the lumen of the umbilical veins and the ductus venosus
(3) Closure of the ductus arteriosus, so that all blood from the right ventricle now goes to the lungs.
(4)The valve of the foramen ovale is occluded.

62. The vessels that are occluded soon after birth are, in due course, replaced by fibrous tissue, and form the following ligaments:
Vessels Remant
Umbilical arteries Medial umblical ligaments
Left umbilical vein ligamentum teres of the liver
Ductus venosus ligamentum venosum
Ductus arteriosus ligmentum arteriosum