Embryology: Atrial Septation And Development

Question 0

First portion of the septum primum comes from:

Answer 0

Sickle shaped crest that grows from the roof of the common atria

Question 1

Paired atria at day 27-28

Answer 1

Fuse together to form a common atria

Question 2

Septum primum extends which direction?

Answer 2

Down towards the endocardial cushions of the AV canal

Does not connect to the cushions, leaves a space called the ostium primum

Question 3

How does the ostium primum close?

Answer 3

Endocardial tissues cpg row along the septum primum and close it
Before closure, apoptosis creates perforations in the upper part of the septum primum (forms ostium secundum, allowing blood shunt from right to left)

Question 4

Formation of an ostium primum ASD

Answer 4

If there is a small residual hole at the endocardial cushion after fusion with the septum primum

Question 5

Formation of the septum secundum

Answer 5

Lumen of RA expands, creating a new crest shaped fold

Question 6

Formation of the foramen ovals

Answer 6

Septum secundum extends downward to septum in AV canal and overlaps with ostium secundum
Remaining hole btwn Septum secundum and ostium secundum is foramen ovale (blood can now enter LA)