Heart Embryology

Question 1

When does the heart begin to develop

Answer 1

Begins when embryo folds in the 4th week of embryonic development
Begin to develop cells in mesoderm that have the capability to develop into cardiovascular system
Space opens up to give pericardial cavity
Either side of the midline, there are two blood islands which when folded together form blood cells

Question 2

Outline the structure of the primitive heart vessel

Answer 2

Primitive heart vessel a modified vessel with an inlet and outlet with no chambers and valves 
Sinus venosus
Atrium
Ventricle
Bulbus cordis
Truncus arteriosus 
Aortic roots

Question 3

How does cardiac looping occur

Answer 3

Cardiac looping - ensures the tissues inside the primitive heart tube are aligned with each other
Ventricle enlarges the most, while atrium moves posteriorly
Confinement in pericardial cavity drives process until heart fills sac
Tube elongates, runs out of room, and twists and folds up

Question 4

Relate the anatomy of the adult heart to embryonic structures

Answer 4

Right atrium develops from most of the primitive atrium
Consumes some of the sinus venosus
Receives venous drainage from the body and the heart
Left atrium develops from a small portion of the primitive atrium
Mainly absorbs proximal parts of pulmonary vein

Question 5

What does the 4th arched vessel develop into

Answer 5

R = proximal part of R subclavian artery
L = arch of aorta

Question 6

What does the 6th arched vessel develop into

Answer 6

R = right pulmonary artery
L = left pulmonary artery and ductus arteriosus

Question 7

Understand the principles of fetal circulation

Answer 7

Circulation delivers oxygen and nutrients and removes CO2 from placenta
However has to immediately switch to a mature circulation after birth to link with the lungs
Shunts are required, which need to be reversible at birth

Question 8

Outline the three shunts in embryonic development

Answer 8

Shunts around liver (ductus venosus) into inferior vena cava and enters right atrium
Shunts blood from right atrium to into left atrium and left ventricle to pump around blood (foramen ovale)
Shunt between pulmonary trunk and aorta (ductus arteriosus)
Some blood enters right ventricle to ensure normal development of ventricle
To ensure development of lungs, this blood bypasses lungs
With the first breath, shunts are closed and placenta support removed
Spasm occurs to increase oxygen pressure to close shunts

Question 9

Outline the process of inter-atrial septation

Answer 9

Endocardium cushions grow a wedge of tissue from primitive atrium down to endocardium cushion
Builds a wall to create two atrium but need passage from right to left (ostium primum) - first hole
A second hole appears (ostium secundum) to continue free communication
Second septum grows a crescent shaped wedge with a hole which does not line up
Pressure on the right side will be higher and will find its way though both holes by pushing two wedges apart to maintain shunt
With the first breathe, left atrium pressure higher which pushes wedges together so blood cannot pass

Question 10

Outline the process of inter-ventricular septation

Answer 10

Ventricular septum has 2 components - muscular and membranous
Muscular protein forms most of the septum and grows upwards towards the endocardial cushions
Leaves a tiny gap called the primary interventricular foramen
Membranous portion formed by connective tissue derived from endocardial cushions to fill gap

Question 11

Outline the process of septation of the outflow tract

Answer 11

Endocardial cushions also appear in the trunchus arteriosus

As they grow towards each other, they twist around each other to form a spiral septum