CVS 5 - Development Of The Heart

Question 1

What is the estimated worldwide incidence of congenital heart defects?

Answer 1

Around 1% (most common birth defect)

Question 2

Give some causes of congenital birth defects

Answer 2

• genetic
• exposure to chemicals/drugs/infectious agents
• can arise ‘de novo’

Question 3

Why are some heart defects only apparent after the child is born?

Answer 3

Because the foetus has a different circulatory route to the newborn, so defects may not impact the foetal circulation.

Question 4

What falls within the classification of a ‘heart defect’?

Answer 4

• structural defect or chambers or vasculature
• obstruction
• communication between pulmonary and systemic circulations

Question 5

What does the foetal heart look like before folding?

Answer 5

One long tube (basically a modified blood vessel) with an inlet and outlet but no valves

Question 6

Briefly describe the act of ‘looping’ of the primitive heart tube

Answer 6

• tube elongates and runs out of room in the pericardial sac

- twists and folds up in a regular and predictable way

Question 7

What does the right atrium develop from?

Answer 7

Most of the primitive atrium and the sinus venosus

Question 8

What does the right atrium receive?

Answer 8

Venous drainage from the body and the heart

Question 9

What does the left atrium develop from?

Answer 9

A small portion of the primitive atrium and absorbs proximal parts of pulmonary veins

Question 10

What does the left atrium receive?

Answer 10

Oxygenated blood from lungs

Question 11

Why does a foetus require shunts in its heart?

Answer 11

The lungs do not work before birth, so these must be bypassed by circulation

Question 12

Why must the liver be bypassed in foetal circulation?

Answer 12

It is very metabolically active and could consume all the oxygenated blood before it was able to reach the rest of the body

Question 13

What are the three shunts in the foetal heart?

Answer 13

• ductus venosus
• foramen ovale
• ductus arteriosus

Question 14

What is the name given to the early arterial system which begins as a bilaterally symmetrical system of arched vessels?

Answer 14

The aortic arches

Question 15

What does the 4th aortic arch become?

Answer 15

Part of subclavian artery and arch of aorta

Question 16

What does the sixth arch become?

Answer 16

The left and right pulmonary arteries, ad ductus arteriosus

Question 17

How is the foramen ovale constructed?

Answer 17

• septum primum forms (this is a flap that partially blocks passage of blood)
• ostium secundum forms (this is a hole in the septum primum)
• septum secundum forms (a second flap with a hole in it)

Question 18

How is the foremen oval closed after birth?

Answer 18

Pressure in the left atrium becomes higher than in the right atrium leading to the septum primum being pushed against the septum secundum. They fuse and form a barrier.

Question 19

Give some examples of ways an atrial septal defect can be caused

Answer 19

• excessive resolution of septum primum
• short septum primum
• absence of septum secundum
• absence of both septum secundum and septum primum

Question 20

What is hypoplastic left heart syndrome?

Answer 20

This occurs when the left ventricle is underdeveloped, resulting in atresia and limited flow

Question 21

What are the two components of the ventricular septum?

Answer 21

Muscular and membranous

Question 22

What is the primary interventricular foramen?

Answer 22

A small gap between the ventricles that is closed by the interventricular septum

Question 23

What effect would transposition of the great arteries have on the appearance of the baby?

Answer 23

The baby would have cyanosis

Question 24

What is the tetralogy of Fallot?

Answer 24

1) pulmonary stenosis
2) ventricular septal defect
3) right ventricular hypertrophy
4) over-riding aorta