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DEVELOPMENT > Development of the heart and its conduction system > Flashcards

Development of the heart and its conduction system Flashcards

1
Q

What are the 3 germ layers the embryo has already formed shortly after gastrulation?

A

The endoderm, ectoderm and mesoderm

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2
Q

What are the 2 ‘fields’ the heart forms from, which make a simple crescent shape in the flat disc of the embryo?

A

The first heart field and the second heart field.

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3
Q

From what germ layer do the FHF and SHF originate?

A

The mesoderm

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4
Q

What does the simple crescent develop into, and what does this consist of?

A

The simple crescent develops into a tube with the outflow tract at the top and a venous pole at the bottom, connected by the primary heart tube.

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5
Q

What happens to the primary heart tube as it develops?

A

It balloons out to form the right and left ventricles and atria

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6
Q

What happens to proepicardial cells of the proepicardial organ?

A

They migrate from the proepicardial organ to surround the heart and give rise to the coronary vasculature

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7
Q

What are the cells above the outflow tract?

A

CNCCs- cardiac neural crest cells- which migrate to the circumpharyngeal ridge to contribute to the 3rd, 4th and 6th pharyngeal arches

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8
Q

Where does the proepicardial region arise?

A

As an outgrowth of the coelomic mesothelium at the ventrocaudal base of the developing heart

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9
Q

In what weeks post-conception does heart development occur?

A

Weeks 3-10

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10
Q

What type of cells derive the cardiac crescent?

A

Mesodermal cells

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11
Q

What lines the lumen of the crescent-shaped tube of myocardium that is the origin of the heart?

A

A single cell layer of endocardium

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12
Q

What will the medial part of the crescent become?

A

The medial part of the crescent expands to form the left ventricle.

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13
Q

What controls the direction of looping of the heart tube as it elongates and bends?

A

Genetics

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14
Q

What is dextrocardia?

A

A rare congenital heart condition in which your heart points towards the right side of your chest instead of the left side

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15
Q

How does the heart tube elongate?

A

Cells from the second heart field are added at both the outflow and inflow ends

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16
Q

What cells make outflow cushions

A

Neural crest cells

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17
Q

Where do epicardium cells come from?

A

The pro-epicardial organ

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18
Q

What’s the name of the process by which the tube is divided into chambers?

A

Partitioning

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19
Q

What does the single layer of epithelium lining the myocardium of the simple heart tube secrete?

A

Cardiac jelly (mesenchymal tissue)

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20
Q

Where is cardiac jelly found?

A

The space between the myocardium and the endocardium

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21
Q

In the outflow tract region, neural crest cells migrate into the cardiac jelly to do what 3 things?

A

Separate the pulmonary artery and aorta
Form outflow cushions
Form valves in the heart

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22
Q

Describe the surfaces of the 4 chambers of the heart once they’ve formed

A

The atria have a smooth surface, while the ventricular chambers have a honeycombed appearance known as trabeculation

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23
Q

What is atrioventricular septation?

A

The forming of a septum between the atria and ventricles

24
Q

What is atrial septation?

A

The forming of a septum between the left and right atria

25
Q

What is ventricular septation?

A

The forming of a septum between the left and right ventricles

26
Q

What is outflow tract septation?

A

The forming of a septum to separate the pulmonary artery from the aorta

27
Q

What are the 2 things that can divide the heart?

A

Cushions

Muscular walls

28
Q

What are the 2 types of cushions?

A

Atrioventricular cushions

Outflow tube cushions

29
Q

What are 3 possible consequences of cushion formation problems?

A

Valve formation defects
Stenosis
Atresia defects

30
Q

How does AV cushion formation occur?

A

Cardiac jelly is secreted by the myocardium. Endocardial cells undergo epithelial-mesenchymal transition. Epithelial cells separate from their neighbours, become migratory and migrate from the epithelial layer to the cardiac jelly layer and populate the jelly

31
Q

What septa are formed from muscular walls?

A

The primary and secondary interatrial septa and the interventricular septum

32
Q

What is pulmonary atresia?

A

A congenital heart defect that’s normally diagnosed soon after birth and involves incorrect formation of the pulmonary valve

33
Q

Name a condition in which AVSDs are common

A

Down’s syndrome

34
Q

When the primary inertial septum grows down to fuse with the AV cushions, what happens to the trailing edge?

A

The trailing edge of the primary septum breaks down to form a hole called ostium secundum or foramen ovale, which allows blood to continue to flow from the right to left atrium

35
Q

What does the septum secundum grow down to form?

A

A flap valve which allows communication between the right and left sides of the heart in foetal circulation

36
Q

What causes the flap valve to close and foramen ovale to seal shut after birth?

A

An increase in left atrial pressure

37
Q

Name 3 atrial septal defects

A

Persistent foramen ovale
Ostium primum ASD
Ostium secundum ASD

38
Q

When does an ostium primum ASD occur?

A

When the atrial septum near the AV valves has a communication between the 2 atria, causing a left to right shunt

39
Q

What causes an ostium secundum ASD?

A

When there’s a hole in the centre of the atrial septum that allows blood to mix and the heart works less efficiently as a result

40
Q

Why does ASD lead to left to right shunting?

A

The pressure is higher in the left side of the heart than the right, leading to an acyanotic defect

41
Q

What % of ventricular septal defects are perimembranous?

A

75%

42
Q

What are 25% of ventricular septal defects?

A

Muscular

43
Q

Are VSDs cyanotic or acyanotic?

A

VSDs are acyanotic

44
Q

What 2 conditions does a left-to-right shunt cause?

A

Pulmonary hypertension and right heart hypertrophy

45
Q

Describe septation of the outflow tract in 3 steps

A

A single tube is separated into the aorta and pulmonary artery.
2 cushions spiral through the trunks arteriosus.
There’s a complex remodelling at each end of the tube

46
Q

Name 3 initial properties of pharyngeal arch arteries

A

Paired
Symmetrical
Formed sequentially

47
Q

What’s the order of formation of the pairs of pharyngeal arch arteries?

A

The 1st pair, then the 2nd pair, then the 3rd pair, then the 4th pair, then the 6th pair

48
Q

Which pairs contribute to the heart?

A

Pairs 3, 4 and 6 form part of the aortic arch

49
Q

Describe the formation of the outflow tract in 4 steps

A

Spiralling cushions separate the aorta and pulmonary artery
Neural crest cells contribute to the AP septum
Complex remodelling of the aortic arches
Proximal cushions fuse with the IVS and AVS to separate the 2 ventricles

50
Q

What can unequal division of the OFT cause?

A

Atrial or pulmonary stenosis

51
Q

What can happen without spiralling of cushions through the common arterial trunk?

A

Transposition of the great arteries

52
Q

What is transposition of the great arteries?

A

The aorta is connected to the right side and the pulmonary artery to the left side, which is a cyanotic defect that Cana be lethal

53
Q

What are the 4 characteristic features of tetralogy of Fallot?

A

VSD
Pulmonary stenosis
Right ventricular hypertrophy
Overriding aorta

54
Q

What does tetralogy of Fallot cause?

A

Right to left shunt, which leads to cyanosis.

55
Q

How can cyanosis be recovered from in a patient with tetralogy of Fallot?

A

Squatting, as this increases peripheral arterial resistance and causes a left to right shunt which increases pulmonary blood flow

56
Q

What tissue does conduction tissue originate from?

A

Myocardium (not nerves)

57
Q

What causes variations in conduction properties?

A

Differences in ion channel and connexin expression

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