Heart embryology

Question 1

Explain the formation of the heart tube.

Answer 1

1. epiblast cells migrate through prim. streak into splanchnic mesoderm → formation of Primary heart field
2. endoderm induces blood island formation
3. unite → cardiogenic area + dorsal aorta
4. angioblastic cords originating from splanchnic mesoderm → canalize to endocardial tubes
5. splanchnic mesoderm facing the endoderm forms myoepicardial mantles (secrete cardiac jelly)
6. folding: flexion, rolling

Question 2

What are the effects of flexion of the embryo w/r/t the heart?

Answer 2

heart primordium moves into final position

Question 3

What are the effects of rolling of the embryo w/r/t the heart?

Answer 3

• heart tubes fuse
• intraembryonic coeloms fuse → pericardial cavity

Question 4

What are the derivatives of splanchnic mesoderm?

Answer 4

• endocardial tubes → endocardium
• myoepicardial mantles → myocardium, epicardium

Question 5

What is a derivative of the intraembryonic coelom?

Answer 5

pericardial cavity

Question 6

What is a derivative of the somatic mesoderm?

Answer 6

parietal layer of pericardium

_{cf. formation of body cavities}

Question 7

Explain the folding of the heart tube.

Acronym?

Answer 7

Elves Love Singing In Very Different Valleys

1. heart tube Elongates → dilations/constrictions
2. heart bends upon itself → bulboventricular Loop
3. changes in Sinus venosus → enlargement of right sinus horn + movement to right
4. sinus venosus becomes Incorporated into prim. atrium
5. outgrowth of right atrium forms prim. pulm. Vein
6. Differentiation of prim. pulm. v. → 4 pulmonary vv.
7. Valve formation in SA orifice

Question 8

Why does the heart tube bend upon itself?

Answer 8

bc fixed at

• venous end by pharnygeal arches
• arterial end septum transversum

Question 9

What does the sinus venosus form during the process of bending of the heart tube?

Answer 9

right + left sinus horn

Question 10

What forms when the dorsal mesocardium degenerates centrally during the process of bending of the heart tube?

Answer 10

transverse pericardial sinus

Question 11

What are final derivatives of the bulbus cordis?

Answer 11

• conus cordis = outflow tracts → conus arteriosus, vestibulum aortae
• contributes to formation of trabeculated part of right ventricle

Question 12

What are later derivatives of the primordial ventricle?

Answer 12

• inflow part of right ventricle
• left ventricle

Question 13

What does the left sinus horn eventually form?

Answer 13

sinus coronarius

Question 14

What does the sinus venosus form as it is incorporated into the right atrium?

Answer 14

sinus venarum cavarum

Question 15

Explain the partitioning of the AV canal and the atria.

Answer 15

Cute Furry Troublesome 2 Primates Forget Secret Diapers Sent Secretly Over Vacation

→ secret-related things always refer to “secundum”

1. invasion of mesenchyme on dorsal/ventral sides of AV canal → endocardial Cushions
2. Fusion → left/right AV canals
3. epithelial-mesenchymal Transformation of cushions
4. septum Primum grows towards endoc. cushions, eventually foramen Primum forms = comm. site btw atria
5. perforations form in septum primum → Foramen Secundum
6. foramen primum Disappears
7. Septum Secundum grows adjacent to septum primum in right atrium → overlaps foramen secundum
8. formation of foramen Ovale
9. cranial part of septum primum disappears → flaplike Valve of foramen ovale

Question 16

What are later derivatives of endocardial cushions?

Answer 16

• AV valves
• aortic/pulmonary channels
• membraneous part of IV septum

Question 17

How do the outflow channels of the ventricles form?

Answer 17

happens during incorporation of bulbus cordis into ventricle

1. neural crest cells form bulbar/truncal ridges in bulbus cordis
2. 270° spiraling
3. ridges fuse → spiral aorticopulmonary septum
4. hook arises from sup. edge → isolates pulm. trunk

Question 18

Explain the partitioning of the ventricles.

Answer 18

1. dilation of ventricles → muscular part of IV Septum forms on floor of prim. ventricle
2. active proliferation of myoblasts → septum increases in size until IV foramen forms btw the endocardial cushions + IV septum
3. fusion of bulbar ridges and endocardial cushions → membraneous part of IV septum
4. membr. part of IV septum fuses with spiral aorticopulmonary septum → full seperation

Question 19

How do you call the process when structures form from the walls of the ventricles?

Which structures form?

Answer 19

cavitation → trabeculae carnae, mm. papillares, chordae tendinae

Question 20

Explain the fate of the left and right venous valve resp.

Answer 20

• both: dorsocranial fusion of valves → septum spurium
• left venous valve + septum spurium fuse and contribute to formation of interatrial septum
• right venous valve:
  
  • sup. portion forms crista terminalis
  • inf. portion forms Eustachian, Thebesian valve

Question 21

Explain the formation of the conducting system.

Acronym?

Answer 21

FiNES HelP

1. cardiac myocytes in sinus venosus region Fire faster than in other regions
2. formation of AV/SA Nodes as sinus venosus is incorporated
3. cardiac skeleton develops → Electrical Seperation of atria/ventricles
4. bundle of HIS forms at AV junction
5. Purkinje fibers develop from already contractile myocytes within the myocardium