Embryology

Question 1

Initial formation of the heart - what is happening in the third week

Answer 1

the heart begins as a pair of cords
Cords hollow out to become tubes
Tubes come together in the midline and fuse to form a single tube late in 3rd week.

Question 2

When does heart begin to beat

Answer 2

After fusion - in the 4th week

Question 3

Four distinct regions that the heart develops into

Answer 3

1. Sinus venosus
2. The atrium
3. The ventricle
4. The trunctus arteriosus

Question 4

4 elements that divide the atria, ventricles and trunctus arteriosus

Answer 4

1. Endocardial cushions
2. Interventricular septum
3. Aorticopulmonary (spiral) septum
4. Interatrial septum

Question 5

Folding of tube -4 results

Answer 5

• folds so
  a) atria become located superiorly and posteriorly
  b) ventricles end up inferior to the atria and great vessels
  c) great vessles located superiorly and somewhat anteriorly
  d) interventricular septum, interatrial septum, spiral septum all meet at the endocardial cushions

Question 6

Two components of interventricular setptum

Answer 6

1. muscular interventricular septum forms most of the structure
2. Membranous interventricular septum

Question 7

Membranous interventricular septum -location

Answer 7

-small region located at the top of the interventricular septum

Question 8

Membranous interventricular septum - origin

Answer 8

-from cells that migrate from the inferior edge of the spiral septum, the endocardial cushions and the muscular interventricular septum

Question 9

Function of spiral septum

Answer 9

Spirals down the truncus arteriosus

Divides it in half in such manner that the two vessels are twisted around each other

Question 10

Fusion of spiral septum

Answer 10

The lower edge of the spiral septum fuses with the endocardial cushions and the interventricular septum

Question 11

Formation of interatrial septum - components

Answer 11

Formed from the septum primum and septum secundum

Question 12

How does oxygenated blood flow in the fetal circulation

Answer 12

• lungs are not functional therefore flows into the RA from the placenta
• does so by going through holes in the developing atrial septa (3 openings = foramen (ostium) primum, foramen (ostium) secundum, foramen ovale)

Question 13

Formation of foramen primum

Answer 13

Septum primum grows towards endocardial cushions

When septum primum fuses with endocardial cushions it is obliterated

Question 14

Formation of foramen secundum

Answer 14

Before the foramen primum closes the superior part of the septum primum breaks down and leaves a second opening for blood to pass from right –> left

Question 15

Formation of foramen ovale

Answer 15

1. Septum secundum grows from the superior pat of the atrium on the right hand side of the septum primum
2. Septum secundum grows towards the endocardial cushions bit does not reach them - comes done far enouh to cover the foramen secundum but blood can still flow right to left by pushing septum primum aside = opening pathway = foramen ovale

Question 16

Fate of sinus venosus

Answer 16

As right atrium grows the right side of the sinus venosus becomes incorporated into it (becoming the smooth walled portion of the RA = sinus venarum)
The left side of the sinus venosus forms the coronary sinus

Question 17

Origin of pulmonary veins/ left atrium

Answer 17

1. Pulmonary veins Originate from small vessels that gradually form one vessel that finds its way back to the left atrium
2. As the left atrium grows it incorporates the pulmonary veins into the wal;
3. The embryonic atrium forms the rough walled atrial appendage. The smooth walled portion of the left atrium is formed from the incorporated pulmonary veins

Question 18

Ductus arteriosus - function

Answer 18

Shunt that passes blood from the pulmonary circuit to the systemic circut (between pulmonary artery and aorta)
-allows most of blood being pumped out of RV to bypass the inactive lungs

Question 19

Fate of ductus arteriosus

Answer 19

Closes shortly after birth and leaves a remnant = the ligamentum arteriosum in adults