Embryology Heart and Fetal Circulation

Question 1

When does the primordial heart and vascular system appear?

Answer 1

week 3, 1st major system to develop

Question 2

When do cardiac progenitor cells derive? Where do they migrate to?

Answer 2

Lateral to primitive streak
Move towards cranium in the splanchnic layer of lateral plate of mesoderm→ cardiac myoblasts. Become surrounded by blood islands

Question 3

What is the cardiogenic field?

Answer 3

The islands untie and form a horse shoe shaped endothelial lined tube surrounded by myoblasts

Question 4

What forms the endocardial tube

Answer 4

Continous tub with inner endothelium kinin (future endocardium) and outer muscular layer (future myocardium) separate ny cardiac jelly

Question 5

When is the partying of the heart chambers complete?

Answer 5

Week 8

Question 6

During the portioning of the atrium, when mechanism allows R to L shunting of fetal blood?

Answer 6

In the first instance, the septum primum grows from the roof down towards the endocardial cushion, leave ing a space foramen primum.

Eventually the septum premium closes the foremen primum but a opening forms foramen secondum. A septum secundum grows which acts like a valve over the ovum secondum → foreman ovale

Question 7

When is the portioning of the ventricles complete?

Answer 7

The inter ventricular septum closes at week 7, after this the pulmonary artery communicate with the right ventricle and aorta with the left.

Question 8

What is the truncus arteriosis?

Answer 8

Aotra and pulmonary artery joined and drain both L&R ventricle

Question 9

When does the conducing tissue originate?

Answer 9

From the sinus venous, which is then incorporated by the right atrium.

Question 10

Name some environemental foctors that can cause heart defects.

Answer 10

ETOH
Rubella 
Thalidomide
Isotretinoin (vitamin A)
1st Trimester - high blood glucose and HTN

Question 11

ASDs - more likely to affect girls or boys

Answer 11

2 x more likely to affect females

Question 12

When is the incidence of patent foramen ovale?

Answer 12

25% - asymptomatic

Question 13

How well is Foramen Secundum ASD tolerate

Answer 13

Well in childhood, often develop PHTN in 3rd decade of life

Question 14

What is sinus venous ASD

Answer 14

Failure of incorporation of sinus venous into the R atrium.

Question 15

Are VSDs more are less common than ASDs? More common in boys or girls?

Answer 15

More common than ASDs

More common in boys

Question 16

What are can VSDs cause?

Answer 16

Dysponea
Pulmonary HTN
Heart failure

Question 17

What is the most common form of VSD. Prognosis?

Answer 17

Membranous VSD - failure of development of membranous part of IV septum. 30-50% close in 1st year of life.

Question 18

Where does the swiss cheese VSD develop?>

Answer 18

Muscle part of IV septum

Question 19

What type of VSD is commonly seen in Downs Syndrome. Why does it occur?

Answer 19

Atrioventricular septal defect (AVSD) - failure of fusion of endocardial cushions → large defect in heart. 20% downs

Question 20

What are the 4 features of tetralogy of fallot?

Answer 20

• Pulmonary stenosis
• Overrdiing aorta
• Ventricular hypertrophy
• VSD

Question 21

What happens in persistent truncus arteriosis?

Answer 21

Failure of division of truncus arteriosos aorta and pulmonary artery joined + VSD

Question 22

What is the most common cause of cyanotic heart disease of the newborn infant?

Answer 22

Transposition of the great vessels.

Has to be treated surgically

Question 23

What is the most common cause of sudden infant death syndrome in developed countries

Answer 23

Abnormality of the conducting system.

Question 24

Explain the fetal circulation

Answer 24

85% oxygenated blood enters through the umbilical vein.
Mostly bypasses the liver via the ductus venous which joins the inferior vena cava.
The inferior vena cava enters into the R atrium, passes through the forman ovale into the L atrium.
Then passes out L ventricle through the aorta.
Some blood still leaves the R side of heart via the pulmonary artery. Resistance in lungs s high so blood passes into the aorta via the ductus arteriosis.
Blood from aorta enters placenta via 2 x umbilical artier 58% oxygenated.

Question 25

When do the umbilical arteries close? What do they form?

Answer 25

Close within a few minutes of birth, obliteration takes 2-3 months. Form medial umbilical ligament. Proximal part stay patent - superior vesical artery

Question 26

When does the closure of the umbilical vein & ductus venous occur? What does it form?

Answer 26

Both close shortly after umbilical artery. After obliteration
umbilical vein → ligament teres hepatis (round ligament of liver) in lower margin of falciform ligament
Ductus venous → ligamentum venosum

Question 27

How does the closure of ductus arteriosis occur?

Answer 27

As the lungs are used they release bradykinin which causes muscular contractions around the ductus arteriosis, complete closure takes 1-3 months.

Ligament arteriosum

Question 28

What is the cause of cyanotic periods of the new born?

Answer 28

Oval foremen not completely fused, during crying there is R to L shunt.

Constant appoistion gradually leads to fusion of the 2 septum.