Lecture 6- Embryology

Question 1

What is aetiology?

Answer 1

The cause of a disease or condition

Question 2

Main event in third week of development?

Answer 2

Gastrulation

Question 3

Main event in fourth week of development?

Answer 3

Folding

Question 4

What i the cardiogenic field?

Answer 4

Group of cells that will develop into whole cardiovascular system

Question 5

What is the effect of lateral and cephalocaudal folding?

Answer 5

Lateral creates the heart tube

Cephalocaudal brings the tube into the thoracic region

Question 6

When does heart begin to beat?

Answer 6

Day 25 of gestation

Question 7

What is the problem with vital organs eg the heart developing early?

Answer 7

Woman may not be aware that she is pregnant

Question 8

What must happen to the primitive heart tube?

Answer 8

It must be remodelled in order to supply both the pulmonary and systemic circulations

Question 9

Primitive heart tube structures?

Answer 9

Sinus venosus- atrium- ventricle- bulbous cordis- truancy’s arteriosus- aortic roots

Question 10

What drives looping of the primitive heart tube?

Answer 10

Constraints on size caused by the pericardial sac

Question 11

How does looping result in the formation of the transverse pericardial sinus?

Answer 11

Looping causes atria to be pushed up above and behind the ventricles. The gap between the aorta and superior vena cava forms the transverse pericardial sinus

Question 12

How does the sinus venosus develop?

Answer 12

Initially left and right sinus horns equal in size. Venous return shifts to the right and so the left sinus horn recedes. Right atrium enlarges and absorbed right sinus horn which becomes part of right atrial wall

Question 13

How does right atrium develop?

Answer 13

Develops from primitive atrium and uses sinus venosus to make part of its wall. Receives systemic venous drainage and venous drainage from heart through coronary sinus.

Question 14

How does left atrium develop?

Answer 14

Primitive atrium contributes a small amount. A pulmonary vein is sprouted and is absorbed to help form left atrial wall. Eventually end up with entrances for four pulmonary veins.

Question 15

What is the oblique sinus and its relevance to development?

Answer 15

The cul de sac of the pericardial sac found at the cranial end of the heart. The cul de sac is created through the left atrium absorbing the pulmonary veins which creates the “dead end” at the top of the pericardial sac and this can be felt by putting your hand underneath the heart

Question 16

Why re shunts required in the foetus?

Answer 16

Lungs aren’t used so blood needs to be moved directly from right atrium to left atrium.

Shunts also need to be reversible at birth

Question 17

What are the three foetal shunts?

Answer 17

Ductus venosus

Ductus arteriosus

Fossa ovale

Question 18

What happens with the circulatory shunts?

Answer 18

Ductus venosus brings blood from placenta to inferior vena cava.

Blood enters right atrium.

Some blood goes from right atrium to right ventricle and from there to the pulmonary trunk and to the aorta through the ductus arteriosus bypassing the lungs. This happens as its important that the right ventricle is used to prevent it from wasting.

Most of blood goes straight from right atrium to the left atrium through the fossa ovale.

Question 19

What does the fossa ovale become?

Answer 19

Fossa ovalis

Question 20

What causes the shunts to close?

Answer 20

Fossa ovale- on breathing pressure is increased in left atrium which closes the shunt.

Ductus arteriosus- increase in oxygen is sensed and DA contracts and regents blood going through it

Ductus venosus- placental support is removed so ductus venosus closes as no more blood is passing through it

Question 21

What is patent ductus arteriosus?

Answer 21

Congenital heart defect where ductus arteriosus doesnt close properly. This means that the aorta and pulmonary artery remain connected and blood will shunt from the left to the right side of the heart.

This is most commonly seen in prematurity

Question 22

Which aortic arch derivatives are particularly important?

Answer 22

4th arch
RHS- proximal part of R subclavian A

LHS- arch of aorta

6th arch “pulmonary arch”
RHS- R pulmonary artery
LHS- left pulmonary artery and ductus arteriosus