Embryological development of the heart

Question 1

When does the circulatory system begin to form?

Answer 1

Begins to develop and function by 4th week.

Question 2

What is the difference between the adult and foetal cardiovascular system?

Answer 2

1. The placenta is a low resistance, high flow pathway and site of gasm nutrient and waste exchange.
2. Lungs not breathing air, fluid filled, high resistance.
3. Two right ot left shunts of blood (foramen ovale and ductus arteriosus).
4. RV and LV act in parallel - both pump into the systemic circulation (RV via ductus arteriosus, a right to left shunt).

Question 3

Umbilic cord

Answer 3

Contains:

• Umbilical arteries: which carry embryonic/foetal blood to the placenta. From internal iliac aa.
• Umbilical veins: returning embryonic/foetal bloof to the embryo/foetus. To liver and ductus venosus.

Foetal and maternal blood fo not mix, but exchange gases, nutrients and wastes.

Question 4

Foramen ovale

Answer 4

In interatrial septum.

Oxygenated blood from IVC directed by valve of IVC from RA through foramen ovale to LA.

Question 5

Ductus arteriosus

Answer 5

Blood from pulmonary trunk to aorta, just past L subclavian a.

Question 6

From which layer of the embryo does the CVS develop?

Answer 6

Almost entirely from mesoderm.

Question 7

Overview of timeline of heart development

Answer 7

Late 3rd - early 4th week: cardiogenic field in mesoderm forms paired endocardial tubes, which fuse in midline as the embryo folds to form heart tube, which begins to beat.

4th week: heart tube folds into a shape that resembles adult heart (ventricle anterior, atrium posterior).

5th - 8th weeks: septa, valves develop, separating heart into 4 chambers.

9th week: mature foetal form achieved.

Question 8

Segments of the heart tube (4th week)

Answer 8

• (veins)
• Sinus venosus (caudal end of heart)
• Primitive atrium
• Primitive ventricle
• Bulbus cordis (cranial end of heart)
  
  • Caudal part of bulbus cordis
  • Conus cordis
  • Truncus arteriosus
• (arteries)

Question 9

Adult derivative of sinus venosus

Answer 9

Part of right atrium, coronary sinus

Question 10

Origin of left atrium

Answer 10

Most from pulmonary veins

Question 11

Embryological derivative of primative atrium

Answer 11

Right and left auricles.

Question 12

Embryological derivature of primative ventricle

Answer 12

Most of left ventricle, part of right ventricle.

Question 13

Embryological derivature of bulbus cordis

Answer 13

Caudal part - most of right ventricle.

Conus cordis - outflow tracts of ventricles.

Truncus arteriosus - pulmonary trunk, ascending aorta.

Question 14

Formation of cardiac loop.

Answer 14

4th week.

• Bulbus cordis (cranial end) moves ventrally, caudally and to the right.
• Atrium (caudal end) moves dorsally, cranially and to the left.
• Atrial and venous ends approximate.

Question 15

Dextrocardia

Answer 15

Heart tube rotates in opposite direction, resulting in mirrow image of normal (heart moves on right side).

Isolated dextrocardia often associated with transposition of the great vessels.

Question 16

Situs inversus

Answer 16

All thoracic and abdominal organs mirrow image of normal - usually normal functioning.

Question 17

Division of the heart tube into chambers

Answer 17

Single heart tube becomes chambered heart in the 5th - 8th weeks

• Atrioventricular valves separates atria from ventricles
• Interatrial septum - separates RA adn LA
• Interventircular septum - separates RV and LV

Question 18

Interatrial septum formation

Answer 18

Septum primum

• Foramen (osteium) primum
• Foreamen (ostium secundrym)

Septum secundum forms definitive interatrial septum.

Question 19

Foramen ovale

Answer 19

Opening in septum secundum between RA dn LA; septum primum serves as a one-way valve. Blood from IVC directed by valve of IVC in RA through foramen ovale to LA.

Question 20

Atrial septal defects

Answer 20

Septum primum or secundum defects can lead to patent foramen ovale (stays open) after birth. This results in shunt of blood from higher to lower pressure side after birth (LA to RA).

Question 21

Atrioventricular canal and outflowo tract realignment

Answer 21

1. Primitive atrium opens into primitive ventricle (future LV) via atrioventricular (AV) canal.
2. Caudal bulbus cordus (future RV) to conus cordis (outflow tract) to truncus arteriosus (future aorta and pulmonary artery)
3. AV canal moves to the right and outflow tract to left - so centred on LV/RV

Question 22

Interventricular septum formation

Answer 22

The interventricular septum divides primitive ventricle and caudal bulbus cordis into LV and RV.

• Muscular interventricular septum: grows cranially from near the apex - largest part of septum.
• Endocardial cushions help form membranous interventricular septum (near AV valves).

Question 23

Ventricular septal defects

Answer 23

Most common

Question 24

Development of AV valves

Answer 24

Endocardial cushions (EcC): swellings of subendocardial mesenchyme atrioventricular (AV) canal region.

4: right, left, superior/anterior, inferior/posterior

Divide AV canal into right and left AV canals

From the AV valves and the membranous IV septum.

Question 25

Persistent common AV canal

Answer 25

Separate right and left atrioventricular valves do not form, due to endocardial cushion problems.

Atrial and ventricular septal defects occur with this abnormality.

Question 26

Division of conus arteriosus and truncus arteriosus

Answer 26

Conotruncal cushions (also called bulbar ridges) and endocardial cushions contribute.

Form conotruncal septum which separates:

• Conus cordis into RV and LV outflow tracts
• Truncus arteriosus into pulmonary trunk and ascending aorta

Question 27

Aortic and pulmonary valve development

Answer 27

Formed by conotruncal cushions.

Question 28

Endocardial and conotruncal cushion problems

Answer 28

Incorrect development of endocardial and conotruncal cushions can lead to a variety of problems such as:

• Transposition of the great vessels
• Persistent truncus arteriosus with VSD
• Tetralogy of the flalot
• Stenotic valves

Question 29

Transposition of the great arteries (TGA)

Answer 29

• Left ventricle to pulmonary trunk
• Right ventricle to aorta

Question 30

Persistent truncus arteriosus with VSD

Answer 30

Common pulmonary trunk/ascending aorta

Mixing of pulmonary and systemic circulations

Question 31

Tetralogy of fallot

Answer 31

• VSD
• Pulmonary stenosis, usually below the valve (RB outflow tract) narrowing
• Overriding aorta (emerges from LV and RV)
• Right ventricular hypertrophy

Question 32

Changes in the heart at birth

Answer 32

• Circulatory system adapts quickly at birtht o changes (separation from blacenta, bretahing starts)
• Air enters lungs, pulmonary resistance drops, greater flow, greater venous return to LA, greater pressure in LA vs RA.
• Foramen ovale closes - fossa ovalis

Question 33

Changes in the circulatory system at birth

Answer 33

• Umbilic aa close, become medial umbilic ligaments
• Umbilical v close, becomes ligamentum teres hepatis (round ligament of liver)
• Ductus venosus closes, becomes ligamentum venosum
• Ductus arteriosus closes over days, becomes ligamentum arteriosus.

Question 34

Patent ductus arteriosus

Answer 34

Left to right shunt after birth (aorta to pulmonary trunk)