Embryonic Development of the Heart

Developmental Timeline: Cardiogenic mesoderm and heart fields

Happen on Day 15-19

Development Timeline: Primitive Heart tube fuses( from 2 endocardial tubes) and first beat

Happen on day 21-22

Developmental Timeline: Tube defines 5 regions, Rightward looping

Happens day 22-28

Developmental Timeline: Chamber expansion, chambers/outflow tracts re-align into their adult spatial positions

Around weeks 4-5

Developmental Timeline: Septation and outflow division begins, endocardial cushions develop

Around weeks 5-8

Developmental Timeline: Functional closure of the fetal shunts

This happens at birth

1.Bottom- Venous inflow pole

Sinus venosus

2.

Primitive atrium

3.

Primitive ventricle

4.

Bulbus cordis

5. Top- Arterial outflow pole

Truncus arteriosus

Rightward looping- what happens to the RIGHT ventricle

It loops right and anteriorly

Righward looping- what happens to the LEFT ventricle

It loops left and posteriorly

Day 22

First heartbeat

First/Primary Heart Field (FHF)

forms much of the left ventricle and portions of the aorta

Second Heart Field (SHF)

adds cells to both poles of the heart tube; major contribution to right ventricle and outflow tract

What are endocardial cushions?

They are structures that develop within the cardiac jelly of the developing heart

Where do endocardial cushions come from?

Endocardial cells transform and migrate into cardiac jelly, forming the cushions.

What are endocardial cushions responsible for?

The superior and inferior AV cushions.

Perimembranous VSD

near the membranous septum; most
common morphologic region in many populations. (about 75% of
clinical VSD cases)

Muscular VSD

defect within trabecular muscular septum; may be
single or multiple.

Inlet VSD

associated with AV canal/endocardial cushion
abnormalities.

Outlet/subarterial VSD

related to conal/outflow septal
development and alignment.

Atrioventricular Septal Defect- AVSD

Strong association with trisomy 21(down syndrome), results from abnormal development of the AVS complex/endocardial cushions, it is a congetial heart condition where there are large holes in the center of the heart walls separating the chambers alongside, malformed heart valves

Ductus venosus (Fetal shunt)

directs oxygenated umbilical venous blood toward the IVC, partially bypassing the liver

Foramen ovale (Fetal shunt)

directs preferential right-to-left atrial flow toward the left atrium and systemic circulation

Ductus arteriosus (Fetal shunt)

connects pulmonary artery to descending aorta, bypassing the high-resistance fetal lungs

What is the function of the septum primum at the foramen ovale?

The septum primum acts like a flap valve over the foramen ovale during fetal development. The foramen ovale allows blood to flow from the right-atrium to the left atrium in the fetus. The septum primum acts as a one-way flap, allowing this right-to-left flow. It prevents blood from flowing backward from the left atrium to the right atrium.

Which layer does the cardiac development and cardiac progenitor cells occur?

It occurs primarily from the mesoderm germ layer, specifically the splanchnic (visceral) mesoderm

What is required for the final closer of the interventricular septum/foramen?

It requires the membranous part of the interventricular septum, which is formed with contribution from the endocardial cushions. The cushions close the hole.

Where do the six paired aortic arches come from?

The aortic sac and run through the pharyngeal arches to terminate in the left and right dorsal aortae.

4th Aortic arch

Left: part of the aortic arch, Right: part of the right subclavian artery

6th Aortic arch

becomes the pulmonary arteries and the ductus arteriosus on the left

What are the paired aortic arches?

are a series of embryonic arteries that form on the right and left sides of the developing embryo