Cardiac Embryology

Question 1

In what direction does the heart rotate during embryological development/

Answer 1

Left

Question 2

Label the structures on the diagram

Answer 2

Question 3

Where do blood vessels develop?

At what stage of development is this embryo?

What do the umbilical vessels communicate with?

Label the blood vessels on the diagram

Answer 3

In the extraembryonic mesoderm

Week 3

Umbilical vessels communicate with:

• Developing fetal circulation
• Developing placenta

Question 4

Label the features on the cardiac mesoderm

At what stage of development is this embryo?

What are angiogenic cell clusters?

Answer 4

Angiogenic cell clusters are collections of angiogenic cells which are developing into blood vessels.

• Form paired angiogenic cords
• Cords canalise to form paired endochondral heart tubes

Embryo in image is in week 3 of development

Question 5

When does the embyronic heart begin beating?

When does blood flow begin?

Answer 5

Heart starts beating day 22-23

Blood flow begins week 4

Question 6

What is the role of neural crest cells?

Answer 6

Neural crest cells from the developing brain and spinal cord migrate away from the developing central nervous system.

Involved in the development of parts of the heart

Question 7

Label the structures on the embryonic disc

Where is the heart tube?

Answer 7

Question 8

What occurs during longitudinal folding?

Answer 8

The brain, mouth and heart are moved into ‘adult’ position:

• The brain develops quickly and pushes itself above the mouth region

Question 9

What does the septum transversum become?

Answer 9

Fibrous pericardium and part of diaphragm

Question 10

What happens to the paired heart tubes during lateral folding?

Answer 10

They are brought together and fuse in the midline to form a large singular tube

Venous inflow enters and flows through the tube into the aortic arches

Question 11

Where do the aortic arches sit?

Answer 11

Pharyngeal arches

Question 12

What anchors the developing heart tube to the future diaphragm (septum transversum)

Label the developing structures on the diagram

Answer 12

Vitelline veins

Question 13

What do the dilations of the heart tube become?

Label them on the diagram

Answer 13

Bulbus cordis

• = aortic vestibule of left ventricle
• = conus arteriosis of left ventricle

Truncus arteriosus

• = Ascending aorta
• = Pulmonary truk

Ventricle

• = trabecular walls of left and right ventricles

Atrium

• = auricles/pectinate walls of left and right atria

Sinus venosus

• = Coronary sinus
• = Smooth wall of right atrium

Question 14

How does the heart tube split to form right and left sides of the heart?

Answer 14

• Endocardial cushion develops and grows into a septum separating the heart tube into 2 sections longitudinally

Question 15

What develops from the future left atrium section of the heart tube?

Answer 15

Pulmonary veins

Question 16

Where are the rough atrial walls derived from embryologically?

What are the smooth walls formed from?

Answer 16

Rough atrial walls: embryological atrium

Right smooth atrial wall: right horn of the venous sinus

Left smooth atrial wall: formed from its growth into the pulmonary veins

Question 17

What causes the heart tube to fold?

Describe this process

Answer 17

Folds due to the fixed position of the aortic arches and venous input.

• Bulbus cordis grows quickly and moves infero-anteriorly to the right

Question 18

Describe the vascular shunts in the embryonic heart

Answer 18

Right to left shunts exist to bypass the lungs which are not fully developed.

Shunt between right and left atria

Shunt between pulmonary trunk and aorta

Question 19

How does dextrocardia occur?

What is it?

Answer 19

Dextrocardia= adult heart on the right side instead of left.

Occurs when bulbus cordis folds to the left and ventricles form to the right

Question 20

How are the developing atria connected to the ventricles?

Answer 20

Via the atrioventricular canal

Question 21

Where do the bicuspid and mitral valves grow?

Answer 21

Within the atroventricular canal

Question 22

How is the atrioventricular canal separated?

Answer 22

By endocardial cushions that grow from anterior to posterior and meet in the middle to separate right and left AV canals

Question 23

How does atrial septation occur?

Answer 23

1. Septum primum develops and grows towards endocardial cushion.
2. Before it reaches the cushion, holes form (foramen secondum)- this maintains right to left shunt.
3. Muscular septum secondum then grows towards cushion
4. This forms the foramen ovale through which blood is shunted right to left.

Question 24

Describe the pressure differences in the right and left sides of the heart in utero compared to a neonate.

Why is there a difference?

Answer 24

In utero:

• High pressure right side of heart
• Lower pressure in left side of heart
• Due to:
  
  • Lungs filled with fluid
  • High pulmonary vascular resistance
  • More blood is entering the right atrium than the left
  • Blood shunted through foramen ovale

Post-natal:

• Lower right sided pressure than left
• Due to:
  
  • Lungs drained and functional
  • Low pulmonary vascular resistance
  • Greater pulmonary blood flow
  • More blood in left atrium
  • Valve of foramen ovale closes on first breath

Question 25

When do tissues of the foramen ovale fuse? What is it called when they don't properly fuse? When can this be a problem? How can this defect be detected?

Answer 25

Usually fuse several months after birth Failure to properly fuse = probe-patient foramen ovale Can become a problem in situations where right sided heart pressure increases over left- for example during the valsalva manouvre * Increases possibility of TIA and stroke (clots in the right side can be pushed over to the left and enter the systemic circulation) Microbubble test is used to detect defects (ultrasound)

Question 26

Where can atrial septal defects form? Are they always symptomatic?

Answer 26

* In the septum/foramen primum * In the septum/foramen secondum * In the endocardial cushion Some symptomatic, some not Some close during growth without the need for surgical intervention

Question 27

In what direction would the blood be shunted in an atrial septal defect after birth? Why is a small atrial septal defect not a cyanotic congenital cardiac defect?

Answer 27

Left to right (pressure in left side higher after birth than right) Cyanosis woud not occur as blood shunted would be re-circulated around the lungs

Question 28

How does ventricular septation occur?

Answer 28

Ventricular septum grows towards endocardial cushion from ventricular floor- remains incomplete in upper region Completed in the upper (cranial) region by membranous downgrowth of bulbar ridges and endocardial cushion. * Membranous tissue also separates the aorta and pulmonary trunk

Question 29

Where do ventricular septal defects most commonly occur?

Answer 29

In the membranous part of the septum

Question 30

How is the ventricular outflow separated (into aorta and pulmonary trunk)? At what stage of embryological development does this occur?

Answer 30

Membranous septum forms in truncus arteriosis and bulbus cordis which spirals (spiral septum) due to the turbulent flow of blood. Grows down to meet the muscular part of the ventricular septum

Question 31

What would be the result of a failure of bulbar ridge formation?

Answer 31

_Failure of bulbar ridge formation_ * Ventricular septal defect AND * Common arterial outflow * Results in mixing of oxygenated and deoxygenated blood as both right and left ventricles pump blood into the aorta and pulmonary trunk * Cyanosis

Question 32

What would be the result of unequal separation of aorta and pulmonary trunk by the spiral septum?

Answer 32

Can result in small pulmonary trunk which increases vascular resistance (may cause cyanosis) * This leads to right ventricular hypertrophy OR a small aorta (aortic stenosis) These conditions often accompanied by ventricular septal defects

Question 33

What is transposition of the great vessels?

Answer 33

Congenital heart defect producing 2 isolated circulations (right ventricle pumps into the aorta and the left ventricle pumps blood into the pulmonary trunk) Often accompanied by ventricular septal defects which are beneficial in this case. Patent ductus arteriosus can also help to mix blood

Question 34

What is tetralogy of fallot?

Answer 34

Multiple congenital cardiac defects occuring together: * Pulmonary stenosis * Right ventricular hypertrophy * Ventricular septal defect * Over-riding aorta (aorta receives blood from left and right ventricles) Caused by failure of formation of the ventricular septum, unequal separation of the aorta and pulmonary trunk Cyanotic condition

Question 35

Name some cyanotic congenital cardiac defects

Answer 35

* Tetralogy of fallot * Transposition of great vessels * Truncus arteriosus defects * Critical pulmonary stenosis

Question 36

Name some non-cyanotic cardiac defects

Answer 36

* Atrial septal defect * Ventricular septal defect * Patent ductus arteriosus