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Histology / Embryology Unit 3 > Cardiovascular Development > Flashcards

Cardiovascular Development Flashcards

1
Q

How are the endocardial tubes formed and what are their splits?

A

In the splanchnic mesoderm in the cardiogenic plate, two longitudinal angioblastic cell clusters form ventrolateral to the neural plate. They will canalize to become the two endocardial tubes
Divisions:
1. Lateral endocardial tube
2. Dorsal aorta

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2
Q

How is the dorsal aorta made? (outflow tract)

A

This outflow tract is connected to the dorsal aorta endocardial tube before folding begins

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3
Q

What do the endocardial tubes become as a result of folding?

A

Lateral: two tubes fuse ventrally (lateral folding) to form primitive heart tube in thoracic region (cephalic folding)
Dorsal aorta: Head folding forms the first aortic arch

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4
Q

How is the inflow tract of the heart made? What vessels contribute?

A

Sinus venosus - receives blood from three pairs of vessels:

  1. Common cardinal
  2. Vitelline
  3. Umbilical
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5
Q

What is the precursor to the pulmonary artery / aorta?

A

Truncus arteriosus

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6
Q

What is the precursor to the right ventricle?

A

Bulbus cordis

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7
Q

What is the precursor to the left ventricle?

A

Primitive ventricle

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8
Q

What two layers does the splanchnic mesoderm differentiate into after the heart tubes are formed?

A
  1. Myoepicardial mantle -> becomes myocardium

2. Cardiac jelly

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9
Q

What is cardiac jelly?

A

An acellular matrix composed of GAGs and matrix proteins, separates myocardium from heart tube

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10
Q

What are the functions of the cardiac jelly?

A
  1. Serves as a substrate for cell migration in cardiac septation and valve formation
  2. Accumulates to form endocardial cushions at AV junction and in outflow tract
  3. Stimulates endothelial cells to come to this cushion matrix, and become mesenchyme which will form fibrous mitral and tricuspid valves.
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11
Q

What forms the endocardium and the serous epicardium?

A

Endocardium - endothelial heart tube

Epicardium - dorsal mesocardium which surrounds the heart tube as it bulges into the pericardial cavity

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12
Q

How does the heart tube become suspended in the pericardial cavity?

A

It is pinched off from dorsal mesocardium, a derivative of foregut splanchnic mesoderm. The heart tube will be left hanging cranially be the dorsal aorta and caudally by the vitelloumbilical veins when the dorsal mesocardium ruptures

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13
Q

What forms the transverse pericardial sinus?

A

It’s formed by the space behind the heart tube and the wall of the visceral pericardium, as the dorsal mesocardium ruptures and leaves room.

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14
Q

What happens during cardiac looping of the heart tube? What is this the first of?

A

Future right ventricle, bulbus cordis, pushes out to the right, forming the bulboventricular loop. Primitive atrium moves cranially to become cranial and dorsal to both ventricles. Both ventricles will move caudally.

This is the first asymmetrical structure to appear in the body, probably due to asymmetrical distribution of actin bundles + cardiac jelly

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15
Q

What constrains the cardiac tube at the sinus venosus?

A

The septum transversum

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16
Q

Where does nodal tissue for the conduction system develop? Where are its two spots?

A

Develops in sinus venosus
SA node - entry of SVC
AV node - right A-V orifice

The bundle of His appears in the ventricular septae at this point

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17
Q

What are the paired dorsal aorta and where do they unite?

A

The truncus arteriosis opens into the aortic sac, from which the aortic arches give rise to paired dorsal aorta. They will be formed in paraxial mesoderm, but ultimately unite behind the heart to the level of LV4 (where the common iliac is)

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18
Q

What does vitelline circulation do and what does it correspond to in the adult?

A

Arteries arise from dorsal aorta and bring blood to yolk sac and future gut (in the midgut).
Correspond to celiac, superior, and inferior mesenteric arteries.
Blood returns to the heart via the vitelline veins, which will form the portal and hepatic veins of the portal system!

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19
Q

What does umbilical circulation correspond to?

A

Arteries arise from dorsal aorta and conduct 50% of cardiac output to the placenta. Oxygenated blood returns to heart via the umbilical vein

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20
Q

What is the general circulation of the embryo?

A

Blood distributed by dorsal intersegmental branches of dorsal aorta to neural tube + somites. Lateral segmental arteries to developing kidneys + gonads.

Blood returns to heart via anterior + posterior cardinal veins, which becomes the common cardinal vein to empty into the sinus venosus

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21
Q

How does the sinus venosus shift?

A

Overtime, it moves to the right more and is called the sinoatrial orifice (SA), until it communicates only with the right atrium.

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22
Q

What happens to the left horn of the sinus venosus?

A

It gets smaller, while the right one enlarges. In time, the left horn (receiving blood from common cardinal, vitelline, and umbilical veins) will become the coronary sinus, and they will all dump into the right atrium.

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23
Q

What is the sinus venarum?

A

The smooth-walled portion of the right atrium to the left of crista terminalis, which is formed by the incorporated sinus venosus

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24
Q

What does the right venous valve of the SA orifice make?

A

The crista terminalis (division between smooth and muscular), valve of IVC, and valve of coronary sinus

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25
Q

What does the original embryonic right atrium become?

A

The pectinate auricular appendage, to the right of crista terminalis. Contains the pectinate muscles

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26
Q

What does the primitive pulmonary vein become? What does the embryonic left atrium become?

A

Pulmonary vein - becomes smooth-walled part of definitive atrium
Embryonic left atrium - auricular appendage which is rough

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27
Q

What happens to the single A-V canal?

A

The endocardial cushions made form cardiac jelly form on the dorsal and ventral walls, approaching one another, and fuse to make the single canal into a left and right A-V canal

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28
Q

What is the function of adherons produced by myocardial cells? Where does this happen?

A

They accumulate in endocardial cushion tissue and induce the overlying endothelium to become mesenchymal cells which will form the mitral and tricuspid valves

This EMT occurs in bulbus cordis (primitive right ventricle), but not primitive atrium / ventricle

29
Q

What originally divides the primitive atrium in two?

A

The formation of the interatrial septum, which is forming due to the endocardial cushions which are moving dorsally towards the atrium (behind the ventricles)

30
Q

What are septum primum and foramen primum?

A

Septum primum - first structure, growing from roof of atrium towards endocardial cushions
Foramen primum - the shrinking opening between the lower edge of septum primum and the A-V cushions. It is obliterated when septum primum fuses with foramen primum

31
Q

Where does foramen secundum appear and why?

A

Before the free edge of septum primum fuses to terminate foramen primum, foramen secundum forms as perforations in the proximal part of the septum primum.

  • > it is in the septum primum
  • > avoids loading of pulmonary circulation, blood can flow freely from right to left atrium
32
Q

What is septum secundum?

A

A new septum which forms to the right of septum primum, and will overlap the foramen secundum which is inside septum primum.

33
Q

What is the space between the lower edge of the septum secundum and the fused A-V cushions called?

A

Foramen ovale

34
Q

What part of the septum primum persists and what is this called?

A

Part which is proximal to foramen secundum disappears. Distal part connected to the A-V cushion persists as the valve of foramen ovale.

This will become the floor of fossa ovalis in postnatal life

35
Q

What forms the limbus of fossa ovalis?

A

The overlapping edges of septum primum and septum secundum

36
Q

What is the interventricular foramen?

A

The muscular interventricular septum results as the ventricles dilate / grow, but the IV septum never reaches the fused A-V cushions, which leaves the foramen between the two ventricles.

37
Q

What closes the interventricular foramen?

A

The growth of the membranous part of the IV septum. It is derived from A-V cushion tissue that fuses with the aortico-pulmonary septum and muscular interventricular septum.

38
Q

What results from cavitation of the ventricular walls?

A

Formation of trabeculae carneae, papillary muscles, and chordae tendineae

39
Q

What forms the aortico-pulmonary septum?

A

Neural crest mesenchyme which divides the bulbus cordis and truncus arteriosus. This will also form the membranous IV. “Truncoconal swellings”

Its spiral nature leads to the twisting of the pulmonary trunk with respect of aorta

40
Q

What is the function of neural crest cells in the outflow channel of the heart?

A

Forms tunica media of aorta + pulmonary trunk, and contributes connective tissue to leaflets of aorta + pulmonary valves at the base of bulbus cordis

41
Q

What does the bulbus cordis form?

A

proximal part: trabeculated right ventricle

distal part: conus arteriosus in right + aortic vestibule in the left ventricle

42
Q

What forms the trabeculated left ventricle?

A

Primitive ventricle

43
Q

What do the left and right anterior cardinal veins become?

A

They anastomose, the left ACV below the anastomosis disappears. Superior to their anastomosis they are right and left brachiocephalic veins, inferior to the right is a small segment which is the superior vena cava.

44
Q

What happens to the posterior cardinal veins?

A

They largely disappear - the terminal portion of the right posterior cardinal vein will persist as the azygos vein which enters the superior vena cava

45
Q

What forms the IVC between the liver and the sinus venosus?

A

the right vitelline vein

46
Q

What percentage of blood from the left umbilical vein bypasses the liver of the fetus? What structure does it use to bypass this?

A

80%, the remainder circulates through the liver and returns to the IVC through the hepatic veins.

Bypasses via the ductus venosus, which will become the ligamentum venosum

47
Q

What is the 1.25 rule?

A

There are six aortic arches on each side. The first two start to regress as the later arches form, and the 5th is absent often and regresses completely, not contributing to any vascular structure.

1,2,5 are the arches which regress

48
Q

What do aortic arches 1-3 become?

A
  1. Mostly disappear, maxillary arteries
  2. Mostly disappear, stapedial arteries,
  3. Common carotid and proximal part of internal carotid
49
Q

What does aortic arch 4 become?

A

Left 4th: Arch of aorta

Right 4th: Proximal part of right subclavian artery (distal part is from right dorsal aorta and 7th intersegmental

50
Q

What does the aortic 6th arch become on right and left?

A

Gives branches to lungs, becomes pulmonary arteries (since we’re arising from the outflow tract)
On the right: distal part of 6th arch disappears
On the left: Persists as ductus arteriosus, then ligamentum arteriosum

51
Q

Where does most of the blood reaching the pulmonary trunk in fetal circulation go and why?

A

It goes through the ductus arteriosus into the aorta, since pulmonary blood pressure is higher than systemic in infants. (there is more resistance)

52
Q

Why does any blood return from the lungs of the fetus?

A

Some oxygenated blood needs to go through to lead to development

53
Q

Where does most of the blood go to the descending aorta?

A

Back to the placenta via umbilical arteries. Only a small amount goes to the lower limbs

54
Q

What maintains the patency of the ductus arteriosus + ductus venosus?

A

Prostaglandins + bradykinin

55
Q

What causes the pressure in the left atrium + ventricle to increase so greatly after birth?

A

When the baby takes his first breath, blood is allowed to finally enter the pulmonary vascular bed. This reduces pressure of ductus arteriosus (carrying blood from pulmonary trunk directly to aorta), and finally lets blood flow through the lungs and into the left atrium of the heart

56
Q

What causes blood pressure to drop in the right atrium?

A

Cutting the umbilical cord leads to immediate cessation of blood entering the body via the umbilical vein, reducing the amount of blood entering the right atrium

57
Q

How does foramen ovale close?

A

When left atrial pressure exceeds right, the septum primum (valve) is pushed against septum secundum, and fibrin deposits along the line of contact will secure it shut. It will be replaced by fibrous connective tissue over several months.

58
Q

What is the most vulnerable period of cardiovascular development? What is the most frequent group of serious malformations?

A

3rd through 7th week. Congenital heart defects is most frequent: 8 per 1,000 live births that can have many causes

59
Q

What are the three types of atrial septal defects (ASDs)?

A
  1. Patent forament ovale - incomplete adhesion, not clinically significant
  2. Secundum ASD - opening in fossa ovalis either from too much resorption of septum primum or not enough formation of septum secundum
  3. Endocardial cushion defect with primum ASD - endocardial cushions don’t fuse properly, which leaves foramen primum open
60
Q

What is the common heart defect of Down’s syndrome?

A

Interventricular septal defect + abnormal mitral valve. Often occurs with endocardial cushion defect with primum ASD

61
Q

What are the two types of ventricular septal defects?

A

Most common cardiac defect (25%)

  1. Membranous: Defect in formation of membranous IV septum
  2. Muscular: Excessive cavitation of myocardial tissue in formation of muscular IV septum
62
Q

What is persistent truncus arteriosus?

A

When the spiral swellings fail to grow, and the blood from both ventricles empty into a single artery, allowing both blood supplies to mix. There will be two arteries distally separated by an incomplete septum.

63
Q

What is transposition of great vessels?

A

When truncoconal swellings fail to grow in normal spiral direction, so the aorta and pulmonary arteries arise from opposite ventricles. Accompanied by VSD. This causes patent ductus arteriosus (since blood supply to pulmonary artery BP will be higher), which is actually good, allows oxygenated blood to reach the aorta, making life possible.

64
Q

What is Tetralogy of Fallot?

A

Most common cause of blue baby, resulting from a single error: anterior displacement of conus septum, leading to large aorta and pulmonary trunk stenosis

65
Q

What are the four main characteristics of Tetralogy of Fallot:

A
  1. Pulmonary stenosis
  2. VSD of membranous portion, since septum is displaced too far anteriorly to contribute to septum
  3. Overriding aorta: Aorta lies over the VSD
  4. Right ventricular hypertrophy - pressure of right ventricle is increased due to pulmonary stenosis
66
Q

What causes aortic or pulmonary stenosis normally? What does it lead to?

A

Aortic or pulmonary valve is thickened, increasing pressure in their respective ventricles. Ventricle becomes hypertrophied since the stenotic valve restricts flow.

Leads to heart murmur (from blood passing through smaller opening) and heart strain

67
Q

What is persistent ductus arteriosus and what is a common cause?

A

Duct fails to close: normally happens functionally within a few days, and anatomically within a few weeks after birth.

Associated with premature birth and rubella, where blood flows from aorta to pulmonary artery

68
Q

What is coarctation of the aorta? How might the patient present?

A

Narrowing of the aorta due to underdevelopment, usually proximal to ductus arteriosus, in the isthmus
Presentation:
Delayed femoral pulse, increased size of intercostals. There is collateral circulation through the anastomoses which connects with the intercostal arteries, and internal thoracic to femoral via epigastrics

69
Q

What is dextrocardia? When will this happen?

A

When the heart tube folds to the left in a mirror image of a normal bulboventricular loop. Usually occurs with situs inversus and it’s chill

Histology / Embryology Unit 3 (9 decks)

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