7. Embryology 2

Question 1

After how many weeks does the heart tube start contracting?

Answer 1

3 weeks

Question 2

What are the 3 septums that need to form?

Answer 2

Interatrial septum
Interventricular septum
Septation of ventricular outflow tract - pulmonary trunk and aorta

Question 3

What happens in septation step 1?

Answer 3

Endocardial cushions develop in atrioventricular region, connecting front to back
Divides the developing heart into right and left channels

Question 4

Describe atrial septation

Answer 4

Septum primum grows down towards the fused endocardial cushions
Ostium primum is hole present before septum primum rises with endocardial cushions
Before ostium primum closes, a second hole, the ostium secundum appears in the septum primum
Finally a second crescent shaped septum, the septum secundum grows, the hole in the septum secundum is the foramen ovale

Question 5

How does blood flow through the septum?

Answer 5

Pressure is higher in RA which forces the two septum apart so blood flows through
The foramen ovale and the ostium secundum are not in line

Question 6

What is the adult remnant of the foramen ovale?

Answer 6

Fossa ovalis

Question 7

Why is the inside of the left atrium more smooth compared to the right atrium?

Answer 7

Left atrium is developed from a vein

Question 8

What happens to the foramen ovale after birth?

Answer 8

Presssure in LA exceeds pressure in RA, septum primum is pushed against septum secundum

Question 9

What are the atrial septal defects?

Answer 9

Septum primum resorbed or too short
Septum secundum too small
Absence of septum secundum
Absence of both septum

Question 10

What is hypoplastic left heart syndrome?

Answer 10

Defect in development of mitral and aortic valves
Results in atresia, limited flow
Ostium secundum too small so right to left flow inadequate in utero
Left heart is underdeveloped

Question 11

What are the 2 components of ventricular septum?

Answer 11

Muscular

Membranous

Question 12

In which direction does the muscular portion of ventricular septum form?

Answer 12

Grows upwards towards the fused endocardial cushions

Question 13

What is the primary interventricular foramen?

Answer 13

Muscle portion flows up towards the endocardial cushions leaving a small gap which is the primary interventricular foramen

Question 14

How is the primary interventricular foramen closed?

Answer 14

Membranous portion of interventricular septum formed by connective tissue derived from endocardial cushions to fill the gap

Question 15

What happens during septation of the outflow tract?

Answer 15

Endocardial cushions also appear in the truncus arteriosus
As they grow towards each other they twist around each other
Form a spiral septum
Forms aorta and pulmonary trunk

Question 16

What can congenital birth defects be?

Answer 16

Structural abnormalities
Complete absence of a s
tructure

Question 17

What can cause congenital birth defects?

Answer 17

Genetic
Exposure to chemicals/drugs/infectious agents
Unexplained

Question 18

What is transposition of the great arteries?

Answer 18

Aorta rises from right ventricle
Pulmonary trunk arises from left ventricle
Causes cyanosis

Question 19

What is tetralogy of fallot?

Answer 19

Large ventricular septal defect
Overriding aorta
Right ventricular outflow tract obstruction (pulmonary vein stenosis)
Right ventricular hypertrophy 
Conotruncal septum formation defective