2. Embryology - early development of CVS

Question 1

Importance of cardiogenic field

Answer 1

where the heart, blood vessels + blood cells develop

Question 2

Where is the position of the cardiogenic field?

Answer 2

lies at cranial end (head) before folding

cardiogenic field is only termed before folding

Question 3

how does the cardiogenic field appear?

Answer 3

overlying mesoderm from gastrulation develop into myoblasts (muscle cells) and blood islands
as a horseshoe shape cephalo / cranial

Question 4

Lateral folding

Answer 4

creates heart tube:
brings the 2 endocardio tubes to the midline
fuse together to form primitive heart tube

Question 5

cephalocaudal folding

Answer 5

brings the heart tube into the thoracic region

Question 6

what structure is the primitive heart tube an how does it receive blood?

Answer 6

linear at first, receives blood through the sinus venosus from the caudal (tail) pole

Question 7

where is the outflow of blood in the primitive heart tube

Answer 7

(in) sinus venosus –> (out) aortic roots

Question 8

name the segments of the primitive heart tube

Answer 8

sinus venosus –> primitive atrium –> primitive ventricle –> bulbus cordis –> truncus arteriosus –> aortic roots

Question 9

why is looping of the primitive heart tube important?

Answer 9

the pericardial sac doesn’t increase in size, the in order for the heart to develop, it must loop to fill the space of the pericardial sac in order to be able to enlarge

Question 10

what happens to the cephalic / cranial end during looping?

Answer 10

ventral, caudal, right

front, down, right

Question 11

what happens to the caudal region during looping?

Answer 11

dorsal, cranial, left

back, up, left

Question 12

What does looping achieve?

Answer 12

inflow + outflow both cranial (head)
inflow behind outflow (aortic arch in front of vena cava)
atrium communicates with ventricle via atrioventricular canal (1st division between atrium + ventricle)
transverse pericardium sinus (insert fingers - aortic arch + pulmonary trunk in front, vena cava behind (outflow))

Question 13

in terms of the components of the primitive heart tube, what is achieved through looping?

Answer 13

sinus venosus + primitive atrium above and behind truncus arteriosus, primitive ventricle and bulbis cordis
arteries in front of veins

Question 14

development of sinus venosus

Answer 14

right + left sinus horns (part of sinus venosus) start off the same size
venous return shifts to the right hand side, so left sinus horn starts to recede
the right sinus horn is absorbed by the enlarging right atrium

Question 15

what is the function of the sinus venosus?

Answer 15

embryo collect blood from placenta (connects foetus to uterine wall), yolk sac (source of nutrients, umbilical cord) + body

Question 16

development of the right atrium

Answer 16

from most of the primitive atrium
absorbs right horn of sinus venosus
receives venous drainage (deoxy) from body (venae cava) & heart (coronary sinus (opposite of coronary artery - collect blood from myocardium to RA)

Question 17

development of the left atrium

Answer 17

from small portion of primitive atrium
sprout pulmonary vein (oxygenated blood: lungs –> LA)
absorbs proximal parts of pulmonary vein + first 4 branches
receives oxygenated blood from lungs (to rest of body - aorta)

Question 18

what is the oblique sinus and how does it form?

Answer 18

the ‘cul-de-sac’ under the heart

formed when left atrium expands + absorbs pulmonary veins

Question 19

why is fetal circulation important & what does it achieve?

Answer 19

lungs are non-functional (not yet developed), so bypass lungs
receives oxygenated blood from mother via placenta + umbilical vein (OXY)
returns to placenta via umbilical arteries (DEOXY)

Question 20

name 2 arteries that carry deoxygenated blood and 2 veins that carry oxygenated blood

Answer 20

arteries: pulmonary artery + umbilical artery (DEOXY)
veins: pulmonary vein + umbilical vein (OXY)

Question 21

what is the early arterial system?

Answer 21

bilaterally symmetrical systems of arched vessels

Question 22

how does bilateral symmetrical system turn into major arteries?

Answer 22

through extensive remodelling to create major arteries leaving the heart

Question 23

what is the right + left 4th aortic arch derivative?

Answer 23

right: proximal part of right subclavian artery
left: arch of aorta

Question 24

what are the L + R derivatives of the 6th aortic arch?

Answer 24

Right: right pulmonary artery (RA –> lungs)
left: left pulmonary artery & ductus areriosus (connect pulmonary artery –> descending aorta)

Question 25

How does the primitive heart tube form?

Answer 25

through cardiogenic field from gastulation (formation of 3 germ layers)

Question 26

significance of aortic arch 5

Answer 26

no derivative in humans - non existant

Question 27

what are recurrent laryngeal nerves

Answer 27

each aortic arch has corresponding nerve

and the recurrent laryngeal nerves are the ones corresponding to the 6th aortic arch

Question 28

nerve corresponding to 6th aortic arch (left + right)

Answer 28

recurrent laryngeal nerve
right recurrent laryngeal nerve descends to: T1-T2
left recurrent laryngeal nerve descends to: T4-T5

Question 29

what are the factors affecting the course of the nerve on the right & left hand side

Answer 29

1. caudal (tail) shift of developing heart & expansion of developing neck region
2. require foetal shunt between pulmonary trunk & aorta

Question 30

After looping, what is produced and what isn’t?

Answer 30

atrioventricular canal links atrium & ventricle

don’t yet have 2 pumps in configuration

Question 31

what shunts the pulmonary trunk to the aorta

Answer 31

ductus arteriosus