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Embryo first semester 23-24 > Block III: Heart development (conf 2) > Flashcards

Block III: Heart development (conf 2) Flashcards

1
Q

When is the primordium of the heart first evident?

A

day 18 in the cardiogenic area, which is the cranial-most area at this point.

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2
Q

Which type of folding causes heart to be below head?

A

cranio-caudal folding

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3
Q

What forms the angioblastic cords?

A

Splanchnic mesenchymal cells ventral to the pericardial coelom aggregate and arrange to form angioblastic cords

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4
Q

What do the angioblastic cords give rise to?

A

cords canalize to form thin-walled endocardial heart tubes » which then fuse to form a single heart tube (fusion begins at the cranial end of the developing heart and extends caudally).

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5
Q

What is the primordial myocardium?

A

(external layer of the embryonic heart) forms from splanchnic mesoderm surrounding the pericardial coelom.

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6
Q

What holds the wall of the heart tube along with the fusing heart tubes (queda colgando)?

A

dorsal mesocardium

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7
Q

Where do heart tubes fuse?

A

cranial

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8
Q

aortic arches go from where to where?

A

from aortic sac to dorsal aorta

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9
Q

What does the cranio-caudal fold cause?

A

As folding of the head region occurs, the heart and pericardial cavity come to lie ventral to the foregut and caudal to the oropharyngeal membrane.

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10
Q

What envelopes the heart tube?

A

pericardial cavity

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11
Q

What are the regions of the fused heart tube?

A
  • Truncus arteriosus
  • Bulbus cordis
  • Primitive ventricle
  • Primitive atrium
  • Sinus venosus
    (aortic sac is not part of heart)
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12
Q

blood returns to heart through?

A

sinus venosus

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13
Q

Where is truncus arteriosus located?

A

(upper part of the tube) is continuous cranially with the aortic sac, from which the aortic arches arise

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14
Q

from where does sinus venosus receives blood?

A

umbilical, vitelline, and common cardinal veins from the chorion, yolk sac, and embryo, respectively (“fusing tubes”)

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15
Q

What is the bulboventricular loop?

A

Because the bulbus cordis and ventricle grow faster than other regions, the heart bends upon itself, forming a U- shaped bulboventricular loop.

As the primordial heart bends, the atrium and sinus venosus come to lie dorsal to
the truncus arteriosus, bulbus cordis, and ventricle.

By this stage, the right and left horns of the sinus venosus have developed.

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16
Q

When does bulboventricular loop happen?

A

23

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17
Q

Where do heart contractions begin?

A

Sinus Venosus by peristalsis-like waves (muscle layers of atrium and ventricle are continuous).

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18
Q

Whta happens by week 4 with heart contractions?

A

By end of 4th week, contractions of the heart result in unidirectional flow.

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19
Q

Where does blood that enters the sinus venosus come from?

A
  • embryo through the common cardinal veins.
  • developing placenta through the umbilical veins.
  • yolk sac through the vitelline veins
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20
Q

explain the circulation of primordial heart

A
  1. Blood from the sinus venosus enters the primordial atrium (flow is controlled by
    sinuatrial valves – they develop from the inner walls of the developing vessels)
  2. blood then passes through the atrioventricular canal into the primordial ventricle
  3. as ventricle contracts, blood is pumped through the bulbus cordis and truncus arteriosus into the aortic sac
  4. then distributed to the aortic arches (arterial channels) in the pharyngeal arches
  5. blood then passes into the dorsal aortae for distribution to the embryo, yolk sac, and placenta.
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21
Q

What are the partitions of the primordial heart?

A

3 partitions occur: wwek 4-5

  1. Atrioventricular canal
  2. Primordial atrium
  3. Primordial ventricle
  • Although described separately, these processes
    occur concurrently
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22
Q

What structure appears and partitions the atrioventricular canals?

A

Endocardial cushions (masses of tissue) form on the dorsal and ventral walls of the atrioventricular (AV) canal.

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23
Q

Where are endocardial cushions derived from?

A

Derived from specialized extracellular matrix (ECM) or cardiac jelly (gelatinous
connective tissue).

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24
Q

Explain how does the partitioning of atrioventricular canals occur?

A

During the 5th week, induced by invading mesenchymal cells, the AV endocardial cushions fuse dividing the AV canal into right and left AV canals (partial separation of primordial atrium and ventricle; the endocardial cushions function as AV valves).

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25
Q

What membrane starts to grow as the partition of primordial atrium?

A

septum primum

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26
Q

What is the space between septum primum and endocardial cushions that comunicates both atriums?

A

foramen primum

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27
Q

Explain the partitioning of the primordial atrium

A
  1. Septum primum grows toward the fusing endocardial cushions from the roof of the primordial atrium, dividing the common atrium into right and left halves.
  2. As it grows, the foramen primum (large opening) forms between its free growing edge and the endocardial cushions.
  3. Perforations appear in the central part of the septum primum (apoptosis).
  4. Foramen primum becomes smaller and later disappears as the septum primum fuses with the fused endocardial cushions to form a primordial AV septum.
  5. As the septum primum fuses with the endocardial cushions, the perforations
    coalesce and form the foramen secundum
  6. Septum secundum – muscular membrane that grows from the ventrocranial wall of the atrium (immediately to the right of the septum primum). As it grows (5th and 6th week), it gradually overlaps the foramen secundum in the septum primum and forms an incomplete partition between the atria = oval foramen.
  7. Cranial part of septum primum (initially attached to roof of left atrium) gradually disappears; remaining part of the septum primum, attached to the fused endocardial cushions forms the flaplike valve of the oval foramen (blood pressure equilibrium dictates the fate of these structures)
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28
Q

What is the function of the foramen primum?

A

It allows O2-rich blood to pass from the right to the left atrium.

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29
Q

how are the perforations in the septum primum called?

A

foramen secundum

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30
Q

What is the function of foramen secundum?

A

(ensuring continuous flow of O2-rich blood from the right to the left atria).

31
Q

What is the septum secundum and where does it grow?

A

muscular membrane that grows from the ventrocranial wall of the atrium (immediately to the right of the septum primum).

32
Q

Where does the valve of oval foramen come from?

A

remaining part of septum primum attached to fused endocardial cushions

33
Q

What is the function of the oval foramen before birth?

A

Before birth the oval foramen allows most of the O2- rich blood entering the right atrium from the IVC to pass into the left atrium, and prevents flow to opposite direction because the septum primum closes against the rigid septum secundum.

34
Q

What is the function of the oval foramen after birth?

A

After birth the oval foramen closes and the valve of the oval foramen fuses with the septum secundum = interatrial septum becomes a complete partition between the atria.

35
Q

what is the interatrial septum?

A

becomes a complete partition between the atria.

36
Q

what is the oval fossa and is remnant of?

A

depression in the lower part of the interatrial septum of the right atrium (remnant of the oval foramen).

37
Q

sinus venosus becomes part of what structure?

A

right atrium

38
Q

What happens to the sinus venosus by the end of 4th week?

A

right horn is larger than the left; the sinuatrial orifice has moved to the right and opens in the part of the primordial atrium that will become the adult right atrium.

39
Q

What are the results of the two left-to-right shunts in the sinus venosus?

A
  • Left horn of sinus venosus decreases in size and importance.
  • Right horn enlarges and receives all the blood from head and neck through the SVC, and from the placenta and caudal regions of the body through the IVC.
40
Q

Where does coronary sinus come from?

A

left horn

41
Q

Explain the changes in sinus venosus

A
  1. Initially the sinus venosus is a separate chamber of the heart and opens into the dorsal wall of the right atrium.
  2. As heart development proceeds, the left horn becomes the coronary sinus, and the right horn becomes incorporated into the wall of the right atrium (light pink in figure).
  3. The sinus venarum is the smooth part of the right atrium (derived from the sinus
    venosum); remaining of the internal surface of the wall of the right atrium and the auricle (conical muscular pouch), have a rough appearance (both derived from primordial atrium).
42
Q

What is the sinus venarum and its embryonic origin?

A

this is the smooth part of the right atrium (derived from the sinus venosum)

43
Q

How is the texture of the atrium and auricle and its origin when sinus venosus changes?

A

remaining of the internal surface of the wall of the right atrium and the auricle (conical muscular pouch), have a rough appearance (both derived from primordial atrium)

44
Q

What demarks the separation of the sinus venarum and primordial atrium?

A

demarcated internally in the right atrium by the crista terminalis and externally by the sulcus terminalis (shallow inconspicuous groove).

45
Q

Where does the formation of primordial pulmonary vein occur?

A

left atrium

46
Q

Why is most of the wall of the left atrium smooth?

A

because its formed by incorporation of the primordial pulmonary vein

47
Q

how does the primordial pulmonary vein develop?

A

it develops as an outgrowth of the dorsal atrial wall, just to the left of the septum primum.

48
Q

how are the 4 pulmonary veins achieved?

A

As the atrium expands, the primordial pulmonary vein and its main branches
are incorporated into the wall of the left atrium (four pulmonary veins are formed).

49
Q

By what is the partitioning of the primordial ventricle first indicated?

A

Its division is first indicated by the primordial interventricular (IV) septum in the floor of the ventricle

50
Q

What is the primordial interventricular septum, what does it do and where does it originate?

A

starts in the floor of the ventricle when the median walls of the enlarging ventricles approach and fuse to form the primordium of the muscular part of the IV septum.

51
Q

What aperture surges from the growth of the IV septum?

A

Interventricular foramen is a communication between the right and left ventricles; located between the free edge of the IV septum and the fused endocardial cushions.

52
Q

When does the IV foramen close?

A

closes by the end of the 7th week as the bulbar ridges (right and left) fuse with the endocardial cushion.

53
Q

What does the closure of the IV foramen and formation of membranous part of the IV septum involves?

A

fusion of the right and left bulbar ridges and the endocardial cushion.

54
Q

What is the membranous part of the IV septum?

A

extension of tissue from the right side of the endocardial cushion to the muscular part of the IV septum

55
Q

What happens after closure of IV foramen and formation of the membranous part of the IV septum?

A

the pulmonary trunk communicates with the right ventricle and the aorta communicates with the left ventricle

56
Q

what is the partitioning of the bulbus cordis and truncus arteriosus?

A

complete separation of aorta and pulmonary trunk

57
Q

where does bulbar ridges come from?

A

form in the walls of the bulbus cordis (proliferation of mesenchymal cells) during the 5th week

58
Q

where does truncal ridges come from?

A

Similar ridged of bulbar ridges, form in the truncus arteriosus that are continuous with the bulbar ridges (truncal ridges).

59
Q

where are bulbar and truncal ridges derived from? and what do they form?

A

both derived from neural crest cells migrating through the primordial pharynx and pharyngeal arches to reach the ridges;

as this occurs, both ridges undergo a 180-degree spiraling (possibly caused by the streaming of blood from the ventricles leading to the formation of a spiral aorticopulmonary septum when the ridges fuse).

60
Q

What does the aorticopulmonary septum divides?

A

divides the bulbus cordis and truncus arteriosus into the aorta
(connected to left ventricle) and the pulmonary trunk (connected to right ventricle).

61
Q

why does the pulmonary trunk twist around the ascending aorta?

A

Because of the spiraling of the aorticopulmonary septum

62
Q

How is the bulbus cordis incorporated in the right ventricle?

A

the bulbus cordis is represented by the conus arteriosus (infundibulum)

63
Q

What does the infundibulum or conus arteriosus give rise to?

A

gives origin to the pulmonary trunk

64
Q

How is the bulbus cordis incorporated in the left ventricle?

A

the bulbus cordis forms the walls of the aortic vestibule, the part of the ventricular cavity just inferior to the aortic valve

65
Q

When does the semilunar valves develop and how?

A

When partitioning of the truncus arteriosus is nearly completed;

begin to develop from 3 swellings of subendocardial tissue around the orifices of the aorta and pulmonary trunk.

66
Q

How does the atrioventricular valves (tricuspid and mitral valves) develop?

A

develop similarly to the semilunar valves, from localized proliferations of tissue around the AV canals.

67
Q

Mention the valves of the pulmonary trunk?

A

in adult: anterior, right, left

68
Q

Mention the valves of the aorta?

A

in adult: posterior, right, left

69
Q

What structure acts as the interim pacemaker of the heart?

A

primordial atrium but sinus venosus takes over the function soon

70
Q

what is the function of the sinuatrial node, when does it develop amd where is to found?

A

gives the first electrical signal and marks the first pace for the heart for atriums to contract; signal arrives into the atriventricular node which excites walls of ventricles to contract and pump blood for circulation.

The sinuatrial (SA) node (develops during the 5th week) is originally found in the right wall of the sinus venosus, but it is incorporated into the wall of the right atrium with the sinus venosus. The SA node is located high in the right atrium, near the entrance of the Superior Vena Cava

71
Q

What composed the atrioventricular node and bundle?

A

SA node cells + cells from the AV region are located just superior to the endocardial cushions.

72
Q

what supplies the Sinuatrial node, atrioventricular node and atrioventricular bundle and what controls them?

A

supplied by nerves (modified cardiac muscle) under the control of the autonomic nervous system (ANS)

73
Q

What is ectopia cordis?

A

Rare condition where the heart is in an abnormal location.

In the thoracic form of ectopia cordis, the heart is partly or completely exposed on the surface of the thorax. Death occurs in most cases during the early neonatal period, usually from infection, cardiac failure, or hypoxemia.

Common thoracic form of ectopia cordis = results from faulty development of the sternum and pericardium secondary to incomplete fusion of the lateral folds in the formation of the thoracic wall during the fourth week. If no severe cardiac defects
are present, surgical therapy usually consists of covering the heart with skin

74
Q

What is the tetralogy of fallot?

A
  • Pulmonary stenosis (obstructed right ventricular outflow)
  • Ventricular septal defect
  • Dextroposition of the aorta (straddling or overriding both ventricles)
  • Right ventricular hypertrophy

Embryo first semester 23-24 (9 decks)

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