Development of

Cardiovascular System

Department of Histology and Embryology Medical college in Three Gorges University

• 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.

1.Establishment of the Cardiogenic Field

Cardiogenic area

Heart tube

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.

• Before the folding:pericardial cavity (dorsal)

Heart tube(ventral)

After the folding: heart tube (dorsal )

pericardial cavity(ventral)

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.

• 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

U-shaped Bulbo-ventricular loop

S-shaped(atrium and sinus venosus come to lie behind and above the ventricle)

Exterior of the Heart

• 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 )

• 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.

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)

The fate of five dilatation:

Trabeculated part of right ventricle

Trabeculated part of left ventricle

• Primitive atrium(PA)

Smooth part of right atrium

Coronary sinus

Oblique vein of left atrium

Trabeculated part of right atrium

Trabeculated part of left atrium

Sinus venosus

• 2. Formation of the Cardiac Septa

• The Atrioventricular (AV) septum

• Atrial septum

• Interventricular septum

• Aorticopulmonary septum

• 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

Inferior and superior

• SEPTUM FORMATION IN THE COMMON ATRIUM

Formation:

(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.

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.

(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.

(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.

(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.

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.

• 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.

• (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.

• SEPTUM FORMATION IN THE VENTRICLES

• 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.

• 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.

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 )

Left truncus ridgeRight truncus ridge

Left bulbar ridge

• Clinical corralations:

(1)Persistent truncus arteriosus

(2) D-Transposition of the great vessels (complete):

(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

• 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)

Aortic arches

disappeared

• 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.

• 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.

• 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.

•

• 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