1) Endocardium - forms the internal endothelial lining of the heart

2) Myocardium - forming the muscular wall

3) Epicardium (visceral pericardium) - covering the outside of the tube

1) wider proximal third which forms the trabeculated part of the right ventricle

2) conus cordis which forms the outflow tracts of both ventricles

3) truncus arteriosus which forms the roots and proximal portion of the aorta and pulmonary artery

Septum primum grows from the roof of the common atrium into the lumen

The lumen of the right atrium expands and the septum secundum appears - it does not form a complete partition in the atrial cavity

The opening left by the septum secundum is the oval foramen

The oval foramen is essential before birth because this how placental blood passes through (at this time RA pressure is higher than LA pressure)

1) Ostium secundum is characterized by a large opening between the left and right atria

Caused by

a) excessive cell death and resorption of the septum primum

or

b) inadequate development of the septum secundum

2) cor triloculare biventriculare is complete absence of the atrial septum and it is always associated with serious defects elsewhere in the heart

Tricuspid atresia, which involves obliteration of the right atrioventricular orifice, is characterized by the absnece or fusion of the tricuspid valves

It is always assoc. with

a) patency of the oval foramen

b) ventricular septal defect

c) underdevelopment of the right ventricle

d) hypertrophy of the left ventricle

* At the end of the fourth week, two mesenchymal cushions, the atrioventricular endocardial cushions appear at the superior and inferior borders of the atrioventricular canal

*two lateral atrioventricular cushions appear on the right and left borders of the canal

*the superior and inferior cushions prokect into lumen and fuse, resulting in a complete division of the canal into right and left atrioventricular orifices

* truncus swellings (cushions) that lie on opposing sides grow towards the aortic sac and twist around each other and fuse to form the aorticopulmonary septum which divides the truncus into an aortic and pulmonary channel

*similar conus swellings grow towards each other and fuse, dividing the septum into the outflow tract of the right ventricle and the outflow tract of the left ventricle

*the medial walls of expanding ventricles become apposed and gradually merge, forming the muscular interventricular septum

*the interventricular foramen, above the muscular portion of the interventricular septum, shrinks on completion of the conus septum

*outgrowth from the inferior endocardial cushion closes the foramen

*complete closure of the interventricular foramen forms the membranous part of the interventricular septum

*when partitioning of the truncus is almost complete, primordia of the semilunar valves become visible as small tubercles found on the main truncus swellings

*one of each pair is assigned to the pulmonary and aortic channels

*a third tubercle appears in both channels opposite the fused truncus swellings

*gradually the tubercles hollow out at their upper surface, forming the semilunar valves

*the most frequently occuring abnormality of the conotruncal region

*due to an unequal division of the conus resulting from anterior displacement of the conotruncal septum

four problems

a) a narrow right ventricular outflow region - pulmonary infundibular stenosis

b) large defect of the interventricular septum

c) an overriding aorta that arises directly above the septal defect

d) hypertrophy of the right ventricular wall

cyanosis (blue skin due to deoxygenated blood) at rest is indicative of this disorder

*results when the conotruncal ridges fail to fuse and to descend toward the ventricles

*this causes the pulmonary artery to arise some distance above the origin of the undivided truncus

*always accompanied by a defective interventricular spetum

*the undivided truncus overrides both ventricles and receives blood from both sides

*occurs when the conotruncal septum fails to follow its normal spiral course and runs straight down

*results in the aorta originating from the right ventricle and the pulmonary artery originating from the left ventricle

*sometimes assoc. with a defect in the membranous interventricular septum

 * usually accompanied by an open ductus arteriosus

*the trunk of the pulmonary artery is atretic

*the patent oval foramen then forms the only outlet for blood from the right side of the heart

*the ductus arteriosus, always patent, is the only access route to the pulmonary circulation

*complete fusion of the semilunar aortic valves

*the aorta, left ventricle, and left atrium are markedly underdeveloped

*usually accompanied by an open ductus arterious, which delivertsblood into the aorta

first arch - maxillary arteries

second arch - hyoid and stapedial arteries

third arch - common carotid artery and first part of the internal carotid artery

fourth arch

a)left side - arch of the aorta from the left common carotid to the left subclavian arteries

b)right side - proximal portion of right subclavian artery

fifth arch - does not lead to anything

sixth arch (pulmonary arch)

a) left side - left pulmonary artery and ductus arteriosus

b) right side - right pulmonary artery

*arteries in the abdomen

celiac

superior mesenteric

inferior mesenteric

internal iliac

superior vesical arteries

NOTE - u. artery takes blood from the fetus to the mother

*the aortic lumen below the origin of the left subclavain artery is significantly narrowed

*preductal type - ductus arteriousus persists

*postductal type- the channel is usu. obliterated

*caudal part of the body is supplied by hypertrophied intercostal and internal thoracic arteries

hepatocardiac portion of the inferior vena cava

portal vein

superior mesenteric vein

after birth 

1) left umbilical vein obliterated to form ligamentum teres hepatis

2)ductus venosus obliterated to form ligamentum venosum

NOTE - U. vein takes blood from the mother to the fetus

left brachiocephalic vein

left superior intercostal vein

superior vena cava

left renal vein

left gonadal vein

renal segment of the inferior vena cava

left common iliac vein

azygos vein

hemiazygos vein