CVS S3 - Early development of the heart

Question 1

How does lateral folding of the embryo contribute to development of the CVS?

Answer 1

Creates primitive heart tube from two endocardial tubes

Question 2

How does cephalocaudal folding of the embryo contribute to development of the CVS?

Answer 2

Moves the heart tube into the thoracic region

Question 3

What is looping?

Answer 3

Continued elongation of the primitive heart tube results in bending

Question 4

What happens to the cephalic end of the primitive heart tube during looping?

Answer 4

Moves ventrally, caudally and to the right

Question 5

What happened to the caudal part of the primitive heart tube during looping?

Answer 5

Moves dorsally, cephalic ally and to the left

Question 6

What are the main purposes of looping?

Answer 6

• Optimises space available within pericardial cavity
• Puts primordial of right ventricle closest to outflow tract
• Puts primordial of left ventricle closest to inflow tract
• Atrium closest to bulbus cordis dorsal

Question 7

List the parts of the primitive heart tube in descending order?

Answer 7

Aortic roots 
Truncus arteriosus
Bulbus cordis
Ventricle
Atrium
Sinus venosus

Question 8

What occurs to the right and left horns of the sinus venosus?

Answer 8

• Left sinus horn recedes

- Right sinus horn is absorbed by the enlarging right atrium

Question 9

What structures make up the developing right atrium?

Answer 9

• Most of the primitive atrium

- Sinus venosus

Question 10

What structures make the left atrium?

Answer 10

• Small part of primitive atria

- Absorbs proximal parts of primitive veins

Question 11

How are the transverse and oblique sinuses formed?

Answer 11

Transverse - formed during looping of the primitive heart tube

Oblique - formed as left atrium expands absorbing the pulmonary veins

Question 12

What is the purpose of the ductus arteriosus?

Answer 12

Vessel that connects the pulmonary trunk to the aorta in gestation enabling fetal circulation to bypass the lungs

Question 13

Describe the process of atrial septation

Answer 13

• Septum primum grows downwards from roof of primitive atrium towards fused endocardial cushions
• Ostium primum present before septum primum reaches the fused endocardial cushions
• Ostium secundum forms before closing in septum primum by programmed cell death
• Second crescent shaped septum secundum grows
• Hole in septum secundum is the foramen ovale

Question 14

Describe the process of ventricular septation

Answer 14

• Muscular portion of interventricular septum grows upwards towards fused endocardial cushions
• Small gap left is the primary interventricular foramen
• Membranous portion closes gap
• Connective tissue derived from the endocardial cushions grow downwards

Question 15

What is the purpose of the conotruncal septum and how is it formed?

Answer 15

• Separates the outflow tract of the heart into pulmonary arteries and aorta
• Formed when endocardial cushions appear in the truncus arteriosus
• Cushions grow towards each other
• Twist and form a spiral septum

Question 16

What is the fate of the sinus venosus?

Answer 16

Makes up the right atrium (except for the left horn which regresses)

Question 17

What is the fate of the primitive atrium?

Answer 17

Auricles of definitive atria

Question 18

What is the fate of the primitive ventricles

Answer 18

Left ventricle

Question 19

What are the three fetal shunts and what are their functions?

Answer 19

Foramen ovale - between the right and left atrium
Ductus arteriosus - between pulmonary artery and aorta
Ductus venosus - between placenta and inferior vena cava

Question 20

What are the fates of the fetal shunts?

Answer 20

Forman ovale - Fossa ovalis
Ductus arteriosus - Ligamentum arteriosum
Ductus venosus - Ligamentum venosum

Question 21

What is the fate of the bulbus cordis?

Answer 21

Proximal 1/3 - right ventricle
Conus cordis - outflow tract of left and right ventricle
Truncus arteriosus - roots, proximal aorta and pulmonary trunk

Question 22

What are the three fetal shunts and where are they?

Answer 22

Foramen ovale - between the right and left atrium
Ductus arteriosus - between pulmonary artery and aorta
Ductus venosus - between placenta and inferior vena cava

Question 23

What causes the closure of the foramen ovale?

Answer 23

• After birth in the left atrium exceeds the pressure in the right atrium
• Septum primum is pushed up against the septum second
• Fossa ovalis is formed

Question 25

Describe the process that occurs after birth to close the fetal shunts

Answer 25

• Respiration begins
• Pressure in lungs decreases - more blood returns to the left side of the heart
• Left atrial pressure increases
• Foramen ovale closes
• Ductus arteriosus contracts
• Placental support is removed so ductus venosus closes