CARDIAC EMBRYOLOGY & FETAL CIRCULATION

Presenter Dr Virbhan BalaiModerator- Dr Y.K Arora

The heart is mesodermal in origin.Its formed from splanchnopleuric mesoderm.The mesoderm constitute the cardiogenic areaIts closely related to pericardial cavity

(derived from intraembroyonic coelom).

Establishment of the heart fields

BMP2 & 4 in mesoderm

WNT inhibition (from “Anterior” Visceral Endoderm) in anterior mesoderm

BMP2,4+/Wnt- expression pattern specifies cardiac tissue (evidenced by expression of NKX-2.5, aka tinman)

Retinoic acid (RA) and other factors determine the cranio-caudal axis of heart primordia

• Primary heart field: left ventricle• Posterior segment of primary heart field:

atria• Secondary heart field: right ventricle &

outflow tract• EXOGENOUS RETINOIDS CAN INTERFERE

WITH THIS PROCESS!

Carlson fig 17-17

Embryonic disc-relation ship of pericardial cavity to other structure

Embryonic disc showing neural plate and related structures

Formation of heart tube

Relation ship of heart tube to pericardial cavity;A. Before formation of head

fold.B. After formation of head

fold. C. C & D shows the process

of invagination of the pericardial cavity by single heart tube.

Repositioning the cardiogenic field(mammals)

The heart is first seen in the form of right and left endothelial heart tubes.

Soon fuse with each otherSingle tube thus formed shows a series of

dilation.Bulbus cordisVentricleAtrium Sinus venosus

Fusing cardiac primordia

“conotruncus”(outflow tract)

future ventricles

future atria

septum transversum(liver & diaphragm primordium)

21 days 22 days

Bulbus cordis is divisible into three parts-Proximal one third is dilated- no sp nameMiddle one third-CONUSDistal one third-TRUNCUS ARTERIOSUS

Arterial & venous end of heart tube

Fate of various parts of heart tube

Prior to the completion of looping, heart shows primitive chambers (bulbous cordis, ventricles and atria, and sinus venosus) and the regions of

separation between them (atrioventricular and bulboventricular sulcus). Human Age: 25 days View

Atrioventricular sulcus

Bulboventricular sulcus

The truncus arteriosus carries blood out of the heart into the aortic sac and subsequently into the aortic arch vessels. The conus cordis is a major contributor to

the right ventricle

Folding and rotation of heart tube

• Ventricle moves ventrally and to right

• Atrium moves dorsally and to left

bulbus cordis

truncus arteriosus

aortic roots

ventricle

atrium

sinus venosus

22 days 23 days 24 days Langman’s fig 12-6

Heart tube-loops to right sideCephalic portion bends

Ventral CaudalRight

Bulboventricular sulcusProximal tube expands-

Primitive ventricles

Distal(smaller)Bulbus cordis

Formation of atria

The sinus venosus and primitive atrial chamber are at first connected by a wide opening.

Gradually the opening become narrows & shift to right.

Finally it becomes a narrow slit.The slit has right and left margin called right

and left venous valve.

Cranially these structure fuse to form a structure called septum spurium.

The A-V canal divide into right and left halvesTwo thickening, A-V cushion appear on its

dorsal and ventral walls.They grow toward each other and fuseThe fused cushion forms septum

intermedium

Changes in sinu-atrial orifice

A.V canal division into right & left

Formation of interatrial septum

The atrial chamber undergoes division into right and left halves by formation of two septae which later fuse.

The septum primum- arise from the roof of right atrium-grows towards AV canal (ultimately fuse with septum intermedium)

The septum secundum- grows down from the roof the atrial chamber, to the right of atrial chamber.

Development of right atrium

Main part of RA is derived from the right half of primitive atrium

The sinus venosus is absorbed into the RA by great enlargment of sinuatrial orifice

Right half of AV canal is also absorbed into RA

Left horn of sinus venosus remain very small. It become part of the coronary sinus

The right common cardinal vein becomes part of SVCThe right vitelline vein forms the terminal parts of

IVCThe right margin of the the original sinuatrial orifice

(i.e rt venous valve) expands greately and divide into three parts-Crista terminalisValve of IVCValve of cornary sinus

Incorporation of sinus venosus into RA

Fate of right & left venous valves- The right venous valve expands greately and

forms crista terminalis, valve of IVC & the valve of CS.

The left venous valve remain small and fuse with IAS

Fate of right & left venous valves

Development of LA

The left atrium is derived from-Left half of primitive atrial chamberLeft half of atrio-ventricular canalAbsorbed proximal parts of pulmonary veins

Absorption of pulmonary veins

Absorption of pulmonary veins into the LAAt first only one vein from the lungs enter the

atriumThe proximal part of vein is gradually absorbed

and is incorporated into the wall of the atrium.As a result of continued absorption of

tributeries, four vein (two right & two left) finally open into atrium.

Absorption of pulmonary veins

Development of ventricle

Fate of bulbus cordisBulbus cordis is divisible into three partsThe proximal one third-merge with the cavity

of primitive right ventricleThe CONUS- forms the outflow tracts

(smooth parts) of both right and left ventricles.Distal (TRUNCUS ARTERIOSUS)-

A spiral septum appears within the truncus arteriosus and subdivides into the ascending aorta and the pulmonary trunk.

It is formed by union of right superior and left inferior truncus swellings or cushions.

Two parts of ventricular chamber

Part ‘1’ is derived from the proximla one third of bulbus cordis and primitive ventricle, while part ‘2’ is from CONUS.

Formation of IVS

Interventricular septum grows upwards from the floor of the bulbo-ventricular cavity and divide the lower dilated part of this cavity into right and left halves.

It meets the fused AV cushions (septum intermedium) and partly fuse with them.

On the ext heart surface formation of IVS correspond with bulbo-ventricular sulcus.

Two ridge, right and left bulbar ridges arise in the wall of the bulbo-ventricular cavity(in the part der from conus).

These ridges grow towards each other and fuse to form bulbar septum.

The bulbar septum grows downward towards IVS but doesnot quiet reach it.

The gap b/w upper edge of IVS & lower edge of BS is filled by proliferation of tissue from AV cushions.

Formation of AV valvesDependent on AV cushions and ventricular myocardium…

Moore & Persaud fig 13-19

Exterior of the heart

A. Heart tube suspended by mesocardium B. Appearance of hole in mesocardium C. Disappearance of mesocardium resulting in

formation of transverse sinus of pericardiumD. B to D gradual freeing of heart tube from

septum transversum and folding of heart tube

Stages in the establishment of ext. form of heart

Retrogression of left horn of sinus venosus

THE ARTERIES

The greater part of first and second arch arteries disappear.

In adult life first arch artery is represented by the maxillary artery.

The second arch artery persist for some part of fetal life as the stapedial artery; it contribute to formation of ECA.

Fifth arch artery also disappearsThe aortic sac is therefore connected only to

third, fourth and sixth arches.The portion off the dorsal aorta b/w the

attachment of third and fourth arch arteries (DUCTUS CAROTICUS), disappears on both sides.

Relation of first aortic arch to heart tube before and after fusion of heart tube

ventral view of heart (35 days),Note the aortic arches arising from aortic sac and terminate in the dorsal aortae.

Fate of aortic archs-disappearance of 1st,2nd and 5th arches

Disappearance of ductus caroticus, part of rt dorsal aorta and part of rt 6th arch

Changes in the aortic arch pattern (AS,1,2,3,5)

5th arch fails to form

2nd arch mostly disappears• stapedial a. • (hyoid a.?)

3rd arch:• common carotid a.• part of internal carotid a.• internal and external

carotid aa. sprout from 3rd arch

Aortic Sac (AS):• proximal part of aortic arch• brachiocephalic a.

1st arch mostly disappears• maxillary a.• (part of external carotid a.?)

Aortic sac

Changes in the aortic arch pattern (4)

4th arch on left:– arch of aorta

(from left common carotid a. to left subclavian a. only)

4th arch on right:– proximal segment of right

subclavian a. (rest of subclavian a. from 7th intersegmental a. and R dorsal aorta)

Changes in the aortic arch pattern (6)

(6th arch = pulmonary arch)6th arch on left:– left pulmonary artery– distal segment persists as ductus arteriosus

6th arch on right:– right pulmonary artery– distal segment regresses

Aortic Arch Anomalies

(A) Double aortic archabnormal persistence of right distal segment~1:1000 incidence –often assoc. with dysphagia and/or dyspnea

(B) Right aortic archabnormal persistence of right distal segment & regression of left distal segment~1:1000 incidence –usually asymptomatic

(C) Aberrant right subclavian (from aortic arch)

(abnormal regression of right proximal segment & persistence of right distal segment) ~1:100 incidence –often assoc. with dysphagia and/or dyspnea; also, R radial pulse may be weak

normallyregresses

normallypersists

normallypersists

Carlson fig 17-42

Adult derivatives of truncus arteriosus,aortic sac and aortic arch

FETAL CIRCULATION

The circulation of fetus is essentially same as in the adult except-

The source of oxygenated blood is not lungs but placenta

Oxygenated blood from placenta comes to fetus through umbilical vein

Oxygen reach blood reaching the RA through IVC is directed through foramen ovale

Circulation in the human adult

Fetal circulation

Changes in circulation at birth

Umbilical arteries occlude Umbilical veins and ductus venosus occludeDuctus arteriosus is occludedThe pulmonary vessel increase in sizeForamen ovale closes: LA pressure> RA pr.

The vessel that are occluded soon after birth are, in due course, replaced by fibrous tissue, and form the following ligamnets:

Vessel Remnant Umbilical arteries Medial umbilical ligaments

Left umbilical vein Ligamentum teres of the liver

Ductus venosus Ligamentum venosum

Ductus arteriosus Ligamentum arteriosum

Time table-