Embryology

Question 1

what are blood islands

Answer 1

groups of cells that have the capacity to develop into blood cells and bloods vessels

Question 2

where is the cardiogenic region located

Answer 2

in the splanchic mesoderm at the cranial end

Question 3

what happens to the endocardial tubes during folding

Answer 3

the pairs of tubes (one at either side of the trilaminar disk) fuse together to form the primitive heart tube

Question 4

what is the primitive heart tube

Answer 4

a modified blood vessel which contracts to allow the flow of blood

Question 5

what are the zones that make up the primitive heart tube

Answer 5

aortic roots, truncus arteriosus, bulbus cordis, ventricles, atrium and sinus venosus

Question 6

why does cardiac looping occur

Answer 6

the primitive heart tube grows and elongates so it runs out of room in the pericardial sac so must fold

Question 7

what does the right atrium develop from

Answer 7

primitive atrium and the sinus venosus

Question 8

what does the left atrium develop from

Answer 8

a small amount of the primitive atrium and the pulmonary veins

Question 9

why are the walls of the left atrium smoother than that of the right

Answer 9

the right atrium is made up of mostly primitive atrium which is trabeculated whereas the pulmonary veins which mostly make up the left is smooth

Question 10

what happens to the position of the atria during cardia looping

Answer 10

they are pushed up from the most caudal part to toward the head

Question 11

what does the right 4th arched vessel develop into

Answer 11

the right subclavian artery

Question 12

what does the left 4th arched vessel develop into

Answer 12

the arch of the aorta

Question 13

what does right 6th arched vessel develop into

Answer 13

right pulmonary artery

Question 14

what does the left side of the 6th arched vessel develop into

Answer 14

left pulmonary artery and the ductus arteriosus

Question 15

what happens to the arched vessels which are of no use

Answer 15

they disappear

Question 16

what nerve supplies the 6th arched vessel

Answer 16

left recurrent laryngeal nerve

Question 17

what 3 shunts are found in the fetal heart

Answer 17

ductus venosus, ductus arteriosus and foremen ovale

Question 18

what does the ductus venosus do

Answer 18

bypasses blood from the liver as it is very metabolically active

Question 19

what does the ductus arteriosus do

Answer 19

allows blood to flow from the pulmonary trunk into the aorta to bypass the lungs

Question 20

why must blood bypass the lungs

Answer 20

as blood may damage the developing lungs and also it is not oxygenating the blood as this is done at the placenta

Question 21

what does the foremen ovale do

Answer 21

allows the passage of blood from the right to left atrium to bypass the right ventricle

Question 22

what cells develop into the endocardial cushions

Answer 22

neural crest cells

Question 23

how is the foremen ovale formed

Answer 23

1. the septum primum grows from the roof of the primitive atrium towards the endocardial cushion leaving a crescent shaped gap called the ostium primum to allow blood flow
2. before the septum primum fully forms, apoptosis occurs to give a hole called the ostium secundum
3. the septum secundum forms and apoptosis also occurs to form another hole but lower down

Question 24

how does the foremen ovale close

Answer 24

at birth the pressure in the LA exceeds that of the RA pushing the septum primum against the septum secundum to close the shunt

Question 25

what causes the closure of the ductus venosus

Answer 25

the removal of the placenta support

Question 26

how are the ventricles separated

Answer 26

1. a muscle portion forms upwards from the endocardial cushions at the bottom but leaves a small gap called the primary intraventricular foramen
2. a membranous portion then forms from connective tissue derived from endocardial cushion

Question 27

how does septation of the outflow tract occur

Answer 27

endocardial cushions in the truncus arteriosus grow and twist around eachother forming a spiral septum