Heart Development

Question 1

What does the secondary heart field produce?

Answer 1

• forms right ventricle and outflow tract
• cells of this field are derived from pharyngeal mesoderm and cam form either cardiac or skeletal muscle
• cells express Hand-2 -> absence results in absence of righ ventricle

Question 2

What does the proepicardium form?

Answer 2

• forms epicardium
• forms interstitial cells and vasculature smooth muscle
• gives rise to coronary vasculature

Question 3

What forms in late third week? What is it guided by? What are some characteristics?

Answer 3

• primary myocardium
• guided by Tbx-2
• slow growth, slow impulse conduction, slow contraction, ability to undergo spontaneous depolarization

Question 4

Describe how the cardiac tube loops.

Answer 4

• composed mostly of cells from primary heart field
• incorporates cells from secondary heart field
• undergoes dextran looping
• first asymmetric embryonic structure to appear
• atrial and ventricular chamber bulges appear on outer surface of loop and at inflow end -> chamber myocardium

Question 5

What is chamber myocardium guided by? What it’s characteristics?

Answer 5

• guided by Tbx-5

- fast growth, high impulse conduction, strong contraction, low ability to undergo spontaneous depolarization

Question 6

What are some characteristics of early symmetrical heart tube? (Primary myocardium)

Answer 6

• slow growth slow impulse conduction
• slow contraction
• ability to undergo spontaneous depolarization
• development guided by transcription factor Tbx-2

Question 7

WHat are the characteristics of the chamber asymmetrical heart tube?

Answer 7

• bulges representing the ventricular and atrial chambers appear as the heart tube loops
• development of ventricular chamber guided by TF Tbx-5
• high proliferative capacity
• high conduction velocity
• low capacity to generate spontaneous impulses

Question 8

What is the result of cardiac looping?

Answer 8

• S shaped heart
• original caudal inflow part (atrium) is now dorsal to outflow part of heart
• outflow part of heart = bulbus cordis, leads to aortic sac and aortic arch system
• internal septum begins to divide ventricle
• later an internal septum will begin to divide antrum

Question 9

What are the different parts of the bulbus cordis?

Answer 9

• broader proximal part of bulbus cordis -> conus arteriosus

- narrower distal part of bulbus cordis -> truncus arteriosus

Question 10

What is the AV partitioning derived from?

Answer 10

• derived from thickening of cardiac jelly

- endocardial cells transform into mesenchymal cells and migrate into the existing cardiac jelly

Question 11

What thickening so form for the AV septum?

Answer 11

• AV cushions

- endocardial cushions

Question 12

What are the AV cushions?

Answer 12

-two cushions meet in middle and form two channels between the single atrium and the single ventricle

-these early cushions serve as primitive valves but probably do not contribute to the final valves
_final valves come from endocardial invaginations

Question 13

What are primary heart fields?

Answer 13

• aka heart crescent
• forms left ventricle and the atria
• most primitive component of the mammalian heart

-more anterior cells are not exposed to TA and assume the default ventricular identity
+cells here express Hand-1, absence results in defective left ventricle

-more posterior cells are exposed to high gradient of RA and assume an atrial identity

Question 14

When does atrial partitioning happen?

Answer 14

-during 5th week

Question 15

What are the components of the atrial partition?

Answer 15

• interatrial septum primum

- interatrial septum secundum

Question 16

How does the interatrial septum primum grow?

Answer 16

• downward growth from cephalic wall of single atrium to endocardial cushion
• separates the atrium into left and right chambers

Question 17

How does the septum secundum form?

Answer 17

-forms to the right of the septum primum and grows from dorsal to the ventral part of the atrium

Question 18

What the three openings in the atrial wall?

Answer 18

• interatrial foramen primum
• interatrial foramen secundum
• foramen ovale

Question 19

What is the interatrial foramen primum?

Answer 19

• space between the leading edge of septum primum and the endocardial cushion
• right to left atrial shunt

Question 20

What is the interatrial secundum?

Answer 20

• forms at the cephalic end of the septum primum through apoptosis
• continues the right to left atrial shunt after the foramen primum closes with the fusion of the septum primum with the endocardial cushion

Question 21

What is the foramen ovale?

Answer 21

• space formed within the septum secundum

- right to left atrial shunt

Question 22

When does ventricle partitioning begin?

Answer 22

-during the fifth week

Question 23

What are the components of the ventricular partition?

Answer 23

• thick interventricular septum growing from apex of ventricular loop toward atrial endocardial cushions
• interventricular foramen

Question 24

What is the interventricular foramen?

Answer 24

• transitory opening between the future right ventricle and the future left ventricle
• becomes obliterated as the septum fuses with the endocardial cushions

Question 25

What is the outflow tract initially made of?

Answer 25

-bulbus cordis
+divided into the conus arteriosus and the truncus arteriosus

• proximal region (conus) is derived from secondary heart field
• distal region (truncus) is derived from neural crest

Question 26

How does the outflow tract partition form?-

Answer 26

• partitioning begins with growth of two opposing truncoconal ridges into the lumen
• ridges meet in the middle ad completely divide the lumen into two separate passageways
• the final septum forms a spiral path which V creates the spiral pattern of the ascending aorta with the pulmonary trunk in the final heart pattern