Embryology

Question 1

What are the demands of the developing embryo lead to a cardiovascular system?

Answer 1

First major system
Rapidly growing so needs to form a system to help with nutritional and oxygen demands, accompanying a reduction in nutritional support provided by yolk sac

Question 2

What occurs in the 3rd week of gestation?

Answer 2

Primordial heart and vascular system begin to develop

Question 3

What happens during Day 21-23?

Answer 3

Heart starts to beat

Question 4

What occurs in the 4th week of gestation?

Answer 4

Blood flow begins in the embryo

Important for structural remodelling

Question 5

What occurs in the first 1-2 weeks?

Answer 5

Cardiac lineage establishment

Question 6

Where does most of the CV system derive from in the trilaminar disc?

Answer 6

(Blood cells)- mesoderm

Question 7

Describe the formation of heart fields

Answer 7

Cardiac progenitors in primitive streak
Cardiogenic precursors in mesoderm
Crescent shaped heart field (two fields join to make one U)

Question 8

What happens at the start of the 4th week?

Answer 8

Formation of primary heart tube

Question 9

Describe the formation of the primary heart tube

Answer 9

Lateral folding of the embryo in the midline (from cranial to caudal) brings the heart fields together
Endocardial tubes form

Question 10

How does the primary heart tube develop?

Answer 10

Pericardial cavity, cardiac jelly, myocardium, dorsal mesocardium, dorsal aorta

Question 11

What happens to the endocardial tubes?

Answer 11

Fuse together to form arterial and venous ends of the heart

Question 12

What are the main components of the primary heart tube?

Answer 12

Myocardium
Cardiac jelly
Endocardium

Question 13

Describe the myocardium

Answer 13

Walls of the heart- formed from mesoderm containing myocardial progenitor cells

Question 14

Describe the cardiac jelly

Answer 14

Separates the myocardium from the cardiac tube

Question 15

Describe the endocardium

Answer 15

Inner lining of the heart

Question 16

What happens near the end of week 4?

Answer 16

Cardiac tube elongation and cardiac looping

Question 17

Where does the source of blood flowing into the sinus venosus of the heart come from?

Answer 17

Vitelline veins- returning poorly oxygenated blood from the yolk sac
Umbilical veins- carrying oxygenated blood from the chorionic sac
Common cardinal veins- returning poorly oxygenated blood from the embryo itself to the heart

Question 18

What occurs as the heart elongates and loops?

Answer 18

The primitive atria are displaced dorsally and cranially
The primitive ventricles are displaced caudally with the left ventricle towards the left and the right ventricle towards the right

Question 19

What happens in the 5th week?

Answer 19

Cardiac septation until 8th week

Question 20

How does septation in the ventricles occur?

Answer 20

Dorsal and ventral atrioventricular endocardial cushions- thickenings in the wall of the heart that develop into septa by fusing
Interventricular septum grows upwards to separate left and right ventricles, eventually joining to the endocardial cushions at around week 8

Question 21

What is the process of cardiac septation in the atria?

Answer 21

Septum primum forms and grows downwards
Foramen primum space is formed
Foramen secundum forms in septum primum
Septum secundum begins to form

Question 22

What is the hole in the right atria called?

Answer 22

Crista terminalis

Question 23

Describe foetal blood circulation in the heart

Answer 23

Foetal lungs not yet functional, so oxygen-rich blood from chorionic sac/placenta enters RA and goes directly into LA (right to left shunt)

Question 24

What hole in the atrial septa permits oxygen-rich blood to move from RA to LA?

Answer 24

Foramen Ovale

Question 25

How does the right to left shunt work?

Answer 25

Right atrium at higher pressure than left atrium so septum primum (valve of foreamen ovale) opens

Question 26

What happens to the right to left shunt after birth?

Answer 26

Higher pressure in atrium so septum primum shuts, foramen ovale becomes oval fossa (closed)

Question 27

Name the foetal remnants of adult heart anatomy

Answer 27

Fossa ovalis- foramen ovale Ligamentum arteriosum- ductus arteriosus Ligamentum venosum- ductus venosus Ligamentum teres (hepatis)- umbilical vein

Question 28

Describe congenital heart defects

Answer 28

6-8/1000 births Leading cause of neonatal morbidity Can be caused by genetic or environmental factors Variable severity

Question 29

Describe septal defects

Answer 29

Most common form is patent foramen ovale Abnormal resorption of septum primum during formation of foramen secundum Results in short septum primum and therefore foramen ovale is still open after birth

Question 30

Describe other types of CHD

Answer 30

Transposition of the great arteries- rare but very serious, pulmonary artery and aorta swapped over Truncus arteriosus- rare but very serious, pulmonary artery and aorta don't develop and remain as single vessel Patent ductus arteriosus- connection between pulmonary artery and aorta in the foetus (remains open after birth)