Session 2 - Early development of the heart

Question 1

What is the cardiogenic field?

Answer 1

-An undifferentiated area within an embryo from which the heart, vessels and blood cells arise from

Question 2

Where is the primitive heart tube after lateral folding?

Answer 2

-Initially suspended in the pericardial cavity by a membrane, membrane breaks down and primitive heart tube is free within the cavity

Question 3

What is the effect of cephalocaudal folding on the heart tube?

Answer 3

-Relocates the primitive heart tube, within the pericardial cavity, to the correct anatomical location

Question 4

At what point in the pregnancy does the primitive heart tube form?

Answer 4

-Approx. day 25

Question 5

Describe the primitive heart tube initially

Answer 5

-Linear pulsatile sturcture consisting of sinus venosus, primitive atrium, primitive ventricle, bulbus cordis, truncus arteriosus and aortic roots

Question 6

Where, initially, is the inflow of the primitive heart tube?

Answer 6

-At the caudal end -> sinus venosus

Question 7

Where, initially, is the outflow of the primitive heart tube?

Answer 7

-At the cranial end -> throughout the aortic roots

Question 8

In what direction is bloodflow through the primitive heart tube?

Answer 8

-From caudal to cranial

Question 9

Why does the primitive heart tube need to develop from its original linear structure?

Answer 9

-The linear structure is sufficient to supply the embryo at first, but as the embryo develops, the primitive heart tube needs to change to meet demand

Question 10

Why is looping a key developmental event?

Answer 10

-Ensures septation of chambers and outflow tract -Development of transverse sinus -Optimises space for growth

Question 11

What is looping of the primitive heart tube?

Answer 11

-Continued elongation of the primitive heart tube results in the tube bending and folding upon itself -The primitive ventricle pushes ventrally, caudally and right -The primitive atrium pushes dorsally, cranially and left

Question 12

When does looping occur?

Answer 12

-Approximately day 23-day 28

Question 13

What does looping achieve?

Answer 13

-Primordium of right ventricle closest to its outflow -Primordium of LV closest to its inflow -Atrium dorsal to bulbis cordis (inflow dorsal to outflow) -Both inflow and outflow are cranial

Question 14

What does the development of the transverse sinus ensure?

Answer 14

-The great arteries are in front of the great veins

Question 15

What is the atrioventricular canal?

Answer 15

-A constriction between the primitive atrium and the primitive ventricle which is the first division between the two zones

Question 16

What is the purpose of the atrioventricular canal?

Answer 16

-Allows communication between the atria and ventricles -Contributes to the asymmetrical development of the heart, allowing the ventricles to enlarge more than the atria

Question 17

When is the oblique sinus formed?

Answer 17

-During formation of the left atrium when the LA absorbs the pulmonary veins and expands

Question 18

What happens to the sinus venosus during atrial development?

Answer 18

-As venous return shifts to the right side of the heart, the left horn of sinus venosus recedes and the right atrium absorbs the right sinus horn

Question 19

Where does the right atria develop from?

Answer 19

-Most of the primitive atrium and the right sinus horn

Question 20

Where does the left atrium develop from?

Answer 20

-A small portion of the primitive atrium but mostly from pulmonary veins

Question 21

Describe development of the left atrium

Answer 21

-LA sprouts pulmonary veins which branches into 4 veins -LA absorbs the proximal portions of these branches and expands to form complete LA

Question 22

Name the shunts in the feotal system

Answer 22

-Ductus arteriosus -Ductus venosus -Foramen ovale

Question 23

What is the function of ductus arteriosus?

Answer 23

-Shunt blood from the pulmonary trunk to aorta in order to bypass the lungs

Question 24

What is the function of ductus venosus?

Answer 24

-A shunt from umbilical vein to inferior vena cava to bypass the liver, as it is the first organ to be reached, and it is a very demanding one which would use all the oxygen and nutrients

Question 25

What is the function of foramen ovale?

Answer 25

-A shunt from the RA to the LA in order to bypass the right heart as it is not needed

Question 26

Why is there a ductus arteriosus if the right heart is bypassed?

Answer 26

-Because a small amount of blood does pass into the right ventricle in order to support its development and the development of the lungs

Question 27

Why does blood pass through the ductus arteriosus instead of continuing to the lungs?

Answer 27

-The resistance in the lungs is very high as they are collapsed, so flows through DA where pressure is lower

Question 28

What are the aortic arches?

Answer 28

-A bilateral system of arched vessels, connected to the primitive heart, which undergo extensive remodelling to create the major arteries leaving the heart

Question 29

What are the derivatives of the 4th aortic arch?

Answer 29

-Right -> right subclavian artery -Left -> arch of aorta

Question 30

What are the derivatives of the 6th aortic arch?

Answer 30

-R-> Right pulmonary artery -L->Left pulmonary artery and ductus arteriosus

Question 31

Which arch does the recurrent laryngeal nerve correspond to?

Answer 31

-6th

Question 32

What is the function of the recurrent laryngeal nerve?

Answer 32

-Innervate the intrinsic muscles of the larynx

Question 33

Where do the left and right recurrent laryngeal nerve loop?

Answer 33

-Left loops around aorta as it is hooked around the ductus arteriosus -Right loops around the right subclavian artery due to remodelling of the arches

Question 34

What happens to the cardiogenic field to produce the primitive heart tube?

Answer 34

-Pair of endocardial tubes form in the cardiogenic field by week 3 -Lateral folding of the embryo results in fusion of the endocardial tubes at the midline, forming the primitive heart tube