Embryology

Question 1

What one of the three germ layers creates the heart?

Answer 1

Mesoderm

Question 2

When does folding ensure the cardiogenic field is in the right place?

Answer 2

4th week

Question 3

What are blood islands?

Answer 3

A primitive tissue - Beginning of blood vessels and blood tissue

Question 4

What effect does literal folding have?

Answer 4

It creates a heart tube

Question 5

What effect does cephalocaudal folding have?

Answer 5

Brings the heart tube into the thoracic region

Question 6

When does the heart begin to beat?

Answer 6

22 days after fertilisation - first system to function

Question 7

What must occur to the primitive heart tube for it to become an adult heart?

Answer 7

The primitive heart tube must divide to create four chambres.

The inflow and outflow vessles must be remodelled. This will create a configuration of vessles retuning blood from the systemic circulation and the great vessels and taking blood away from the heart.

Question 8

What are the names of the different zones of the primitive hart tube?

Answer 8

Question 9

What happens in cardiac looping?

Answer 9

• Tube elongates
• Runs out of room
• Twists and folds up
• Places the inflow and outflow in correct orientation with each other.

Question 10

What is the percardial sinus?

Answer 10

A gap between pulmonary trunk and aorta

Question 11

How does the sinus venosis (venous inlet) develop?

Answer 11

At the start, the left and right sinus horns are the same size.

Venous retun then shifts to the right hand side which causes the left sinus to recede.

The right sinus horm is absorbed by enlarging the right atruim.

Question 12

What does the right atria develop from?

Answer 12

Most of the primitive atrium

Sinus venosis

Receives venous drainage from the body (venae cava) and the heart (coronary sinus)

Question 13

What does the left atrium develop from?

Answer 13

A SMALL portion of the primitive atrium

Absorbs the porximal parts of the pulmonary veins.

Recieves oxygenated blood from the lungs

Question 14

How does the oblique sinus form?

Answer 14

Oblique pericardial sinus forms as the left atrium expands absorbing the pulmonary veins.

Question 15

How is foetal circulation different to mature circulation?

Answer 15

Foetus:

• Lungs not work
• Oxygenation and removal of CO2 occurs at the placenta.
• So shuts are required to maintain foetal life.
• Shunts MUST be reversible at birth.

Question 16

Where is there the highest pO2 in foetus?

Answer 16

Umbilicus

Question 17

How does blood circulate in the foetus?

Answer 17

Question 18

What are the names of foetal shunts?

Answer 18

• Foramen ovale - takes blood from right atrium to left atrium
• Ductus Venosus - takes blood from pulmonary trunk to aorta (bipass lungs)
• Ductus Arteriosus - Takes blod from placenta to IVC.

Question 19

How does foetal circulation become adult circulation?

Answer 19

• Respiration starts
• Left Atrium pressure increases and foramen ovale closes
• Ductus Arteriosus contracts.
• Placental support removed
• Ductus Venosus closes. (No flow through umbilical vein)

Question 20

What are aortic arches?

Answer 20

Early arterial system begins as a bilaterally symmetrical system of arched vessels.

These arched vessles undergo entensive remodelling to create the major arteries leaving the heart.

Question 21

What aortic arches are important? Why?

Answer 21

4th:

Right = proximal part of Right subclavian artery

Left = arch of aorta

6th:

Right = right pulmonary artery

Left = Left pulmonary artery and ductus arteriosus

Question 22

How are aortic arches remodelled?

Answer 22

As the heart “descends” the nerve hooks around the 6th aortic arch and it “turns back on itself”

The left recurrent (goes back on itslef) laryngeal nerve becomes hooked around the shunt between the pulmonary trunk and the aorta.

Question 23

PDA?

Answer 23

Patent Ductus Arteriosus

DA should normally contract with first breach but it doesn’t.

So, persistence communication between the descending aorta and the pulmonary artery.

Failure of physiological closure. Blood will shunt from aorta to right (high to low pressure).

Question 24

What three things get separated in septation?

Answer 24

Interatrial septum (atria get separated)

Interventricular septum (ventricles get separated)

Septation of ventricular outflow tract (pulmonary trunk and aorta)

Question 25

How does the inter-atrial septum form?

Answer 25

There is already a narrowing but, endocardial cushions form in the atrioventricular region. It divides the developing heart into left and right channels

Question 26

How does atrial sepation occur?

Answer 26

Division of the common atrium formation of two septa with three “holes” **Septum primum** grows form towards the fused endocardial cushions. Th **optimum primula** is the hole present before the septum proimum fuses with the endocardial cushions. Before optimum primum closes, a second hole, the **optimum secundum**, appears in the septum premium. Finally, a second crescent shaped septum, the **septum secundum** grows. The hole in the septum secundum is the **foramen ovale**. This process is only complex as they need to maintain the flow from right to left.

Question 27

How does arrangement of atrium septum allow flow?

Answer 27

Pressure in RA higher than LA. This means blood moves through foramen ovale and then ostium secundum into LA from RA.

Question 28

Give a summary of atrial septation.

Answer 28

Both left and right atria components derived from the primitive atrium (i.e. auricles) The right atrium absorbs the sinus venosus The left atrium sprouts the pulmonary vein then grows to absorb it and its first 4 branches. Interatrial septum forms to divide the chamber into left ad right chambers. The fossa ovalis is the adult remnant of the shunt used in utero to by-pass the lungs.

Question 29

How does the atrial septum close?

Answer 29

Septum premium is pushed against septum secundum because the pressure in the LA become larger than that in the RA.

Question 30

What could result in an atrial septal defect?

Answer 30

Ostium secundum defect - * If septum premium is resorbed or too short. * If septum secundum is too smal.

Question 31

What is hypoplastic left heart syndrome?

Answer 31

Exact cause is unknown... Defect in development of mitral and aortic valves -resulting in atresia and limited flow. Ostium secundum is too small therefore right to left flowis inadequate in Utero. “Use it or loose it” -means the left heart is underdeveloped.

Question 32

What occurs in ventricular septation?

Answer 32

Starting with a single ventricular chamber Ventricular septum forms which has 2 components: - Muscular - Membranous Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions. It forms a small gap, the 1st interventricular foramen. The membranous portion of the interventricular septum is formed by connective tissue derived from endocardial cushions to "fill the gap."

Question 33

What is the most common ventricular septal defect?

Answer 33

Most commonly, the membranous portion fails to obliterate the small hole between the two ventricles.

Question 34

How do the outflows then get separated?

Answer 34

Endocardial cushions appear in the truncus arteriosus (Grow in the lumen). As they grow towards each other, they twist around each other and form a spiral septum.

Question 35

What can congenital birth defects be?

Answer 35

Structural abnormalities (not form properly) Complete absence of a structure.

Question 36

What could the causes of congenital birth defects be?

Answer 36

* Genetic * Exposure to chemical / drugs / infectious agents * Unexplained.

Question 37

When do congenital heart defects occur?

Answer 37

Congenital heart defects occur when there is... - A structural defect of the chambers - A structural defect of the vasculature These is an obstruction Communication between pulmonary and systemic circulation. Additional complexity due to the differing circulatory needs of the foetus as compared to the newborn (mature).

Question 38

Describe the transposition of the great arteries

Answer 38

Aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle. -Cyanosis will occur Likely to relate to the development of the aortic and pulmonary valves which need to be carefully positions to ensure normal “pluming”

Question 39

What is tetralogy of Fallot?

Answer 39

Large ventricular septal defect Overring aorta Right ventricular outflow tract obstruction Right ventricular hypertrophy Conotruncal septum formation defective (neural crest cells are important)