Heart Embryology

Question 1

when does the development of the heart start?

Answer 1

2-3 weeks

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Question 2

Where does the development of the heart start?

Answer 2

in the head end of the mesoderm called the cardiogenic area - in response to the cells from the endoderm

Question 3

how does development start?

Answer 3

endoderm signals to the mesoderm cardiogenic area to form two cardiogenic tubes

cardiogenic chords then form holes within them and form the endocardial tubes

endocardial tubes then fuse together to form the primitive heart tube at 22 days

Question 4

what does the primitive heart tube contain

Answer 4

From most inferiorly to superiorly - 
the venous sinuses 
the primitive atria (below ventricle)
the primitve ventricles 
the bulbus cordis 
the truncus arteriorsus

Question 5

what do each part of the heart do?

Answer 5

the venous sinuses form the posterior part of the heart - they form the cornary sinus and the SA node
PRIMITIVE ATRIA forms the left and right atrium anteriorly
PRIMITIVE VENTRICLE forms the left ventricle
BULBUS CORDIS forms the right ventricle
TRUNCUS ARTERIOSUS forms the pulmonary trunk and the aorta

Question 6

How does the heart tube become the heart at 2-5 weeks?

Answer 6

Folding andd looping into a U shape and then a S shape at day 23 and the forming the heart.
The bulbus cordis and the primitive ventricle (both form right and left ventricles) develop first and the fastest. they then come to their positions at day 28

Question 7

Development of sinus venousus

Answer 7

the left horn of the sinus venousus becomes redundant and disappears at week 5.
the right horn starts to form the right atrium
the sinoatrial orrifice then comes together to form septa spurium and the venous valves (right and left) come together and fuse with the setum spurium.
the fusion of the valves inferiorly disappears and forms the coronary sinus and the vena cava valve (inferior)

Question 8

what are endocardial cushions?

Answer 8

masses of tissues that grow upwards and towards the septum (across a chamber) to form partitions (septums)

Question 9

Why does the heart not allow complete partition of the chambers?

Answer 9

regions failing to grow because to allow shunting of the blood from the right to the left atria in order to bypass unfunctioning lungs

Question 10

Describe the division of the atria

Answer 10

The septum primum develops at the top of the heart and then mves downwards toeards the endocardial cushions - the endocardial cushion comes upwards in order to close the ostium primum formed in between the septum primum and the endocardial cushion (ostium primum is a hole)

The septum secundum starts to develop as well as the ostium secundum at the septum primum superiorly. the ostium secundum remains and is called the FORMAEN OVALI which closes up after birth due to high pressure in the left atrium.

Question 11

The formation of the atrioventricular canal

Answer 11

at the end of week 4 the atrial is connected to the ventricle through one canal (common atria and common ventricle)

the endocardial cushions from superiorly of the canal and inferiorly of the canal start to extend towards each other and then fuse to form the right and left atrioventriclular orrifice.

the right and loeft atrioventricle orrficice now have mesenchymal tissues surrounding it which are called then become mesenchymal extensions and form into valves - the tricuspid and the bicuspid valve.

Question 12

The outflow of the Left ventricle goes through

Answer 12

aorta

Question 13

the outflow of the right ventricle goes through

Answer 13

pulmonary trunk

Question 14

How is the truncus arteriosus divided into the right and the left parts?

Answer 14

the swellings within the right truncus moves upwards and outwards and attaches on the left. the left inferior truncus swells upwards and outwards and attaches to the right. these swellings fuse and form the aorticopulmonary septum.
more swellings form within the cornus cordis walls and fuse with the aoritco pulmonary septum - divide the outflow between the right and left pulmonary septum

Question 15

when do the semilunar valves form?

Answer 15

just before the finishing of the formation of the aorticopulmonary septum - aorta and pulomary trunk

Question 16

Septal formations in the ventricles?

Answer 16

the endocardial cushions start moving upwards from the bottom of the ventricles to the interventriclar septum and fuse upwards and are eventually closed off.

Question 17

partitioning of the canals and the chambers occur in what week?

Answer 17

end of 5th

Question 18

valves formation occurs in what week?

Answer 18

5-8 (atrioventricular)

5-9 (semilunar)

Question 19

Development of the conducting system?

Answer 19

the pacemaker at first (SA) is placed on the bottom left hand side of the heart tube.
The pacemaker then moves to the sinus venosus where it moves upto the right atrium and is situated near the superior vena cava.

Question 20

what makes up the atrioventricular node (2 types of cells)

Answer 20

atrioventricular canal and the sinus venosus cells of the left sinus venosus.

Question 21

4 types of cardiac defects?

Answer 21

abnormality in cardiac looping
atrial septal defects
defects in the atrioventricular canal
ventricular septal defects.

Question 22

abnormality in cardiac looping

Answer 22

heart loops towards the left instead of right
therefore heart becomes positioned towards the right instead of left - called DEXTACARDIA
- causes all organs to be asymetrical - SITUS INTERVERSUS
- causes only some organs to be randomly placed - HETRAXATY
usually have other heatt defects too.

Question 23

atrial septal defects

Answer 23

6/10,000 - 2:1 women than men.
abnormalities in the complete closure of the atrium
completely open - common atria (cor trioculare biventriculare)
partially open - patent fossa ovali. Causes hypertrophy of the right atrium and ventricle.

Question 24

defects in the atrioventricular canal:

Answer 24

incomplete fusion of the endocardial cushions (usually form a cross like septa) or incomplete closure of the ostium primum.

Question 25

ventircular septal defects

Answer 25

more common 12-10,000
abnormal partioning of the truncus arteriosus.
1.2-1.7 more blood flows in the pulmonary artry than normal as the blood shunts from left to right.