L26, L27 – Development of the Heart Flashcards Preview

MBBS I CPRS > L26, L27 – Development of the Heart > Flashcards

Flashcards in L26, L27 – Development of the Heart Deck (98):
1

What does gastrulation involve? (think primitive streak and action of germ layers)

Formation of 3 germ layers

Epiblast migrate through primitive streak

Mesoderm spread between ectoderm and endoderm

2

What happens to hypoblast cells during gastrulation?

Displaced by invaginating definitive mesoderm

3

What are the three segments of mesoderm?

Starting from medial, next to notochord to lateral edge:

Paraxial mesoderm > Intermediate mesoderm> Lateral plate mesoderm

4

What does lateral plate mesoderm further divide into?

Somatic mesoderm and Splanchnic mesoderm

5

What structure does paraxial mesoderm give rise to?

Somites

6

What do somites give rise to? (give 4 examples)

 Axial skeleton
 Axial muscles
 Limb muscles
 Dermis

7

What system does intermediate mesoderm give rise to?

Gives rise to urogenital system

8

What does somatic mesoderm contribute to? What tissue and where specifically?

Contributes to
connective tissue of
body wall

9

What does splanchnic mesoderm give rise to? (give the 2 blast cells name and the walls of 2 organs)

Blasts:
Cardiomyoblasts > Heart
Hemangioblasts > Blood, lining of blood vessels

Walls:
Wall of Gut
Wall of Respiratory tract

10

Which germ layer does the heart arise from?

Splanchnic mesoderm

11

What is the movement and direction of heart progenitor cells in Day 18 which establishes the primary heart field?

Heart progenitor cells in EPIBLAST move through primitive streak > migrate in CRANIAL-LATERAL direction within SPLANCHNIC MESODERM > form HORSESHOE SHAPE clusters of cells lateral to neural folds

12

How does the progenitor heart cells, after moving through primitive streak and splachnic mesoderm, form the primitive heart?

Horseshoe shape clusters = primary heart field/ cardiogenic area in cranial-lateral area

Clusters UNITE TO FORM HEART TUBE

13

What cells surrounds the heart tube after establishment of primary heart field?

Cardiomyoblasts (from splanchnic mesoderm)

14

What 5 structures of the primitive heart is predetermined in the primary heart field?

Truncus arteriosus
Conus cordis
Right Ventricle
Left ventricle
Atria

15

How many layers does the heart tube have?

3 layers

16

What are the layers of the heart tube?

Endocardium
Myocardium
Epicardium

17

What is the heart tube endocardium's fate and origin?

Origin: epiblast-derived mesenchymal cells in splanchnic mesoderm

Fate: Forms internal endothelial lining of heart

18

What is the heart tube myocardium's fate and origin?

Origin: Splachnic mesoderm

Fate: form cardiac myocytes

19

What is the heart tube epicardium's fate and origin?

Origin: Proepicardial organ near sinus venous, adjacent to atrium in mesoderm

Fate: Covering of heart tube

20

What exists between the endocardium and myocardium in heart tube?

Cardiac jelly, Endocardial cushion

21

When is the primary heart field + heart tube formed?

Day 18

22

When is the secondary heart field formed?

Days 20-21

23

Where are the cells forming secondary heart field from?

Splachnic mesoderm ventral of pharynx (pharyngeal mesoderm)

24

What is the secondary heart field's fate?

contribute to development of:
 Right ventricle
 Outflow tract (connected to right ventricle)
 Part of the atria

25

Both heart fields are from which germ layer? Do the 2 heart fields form the same chambers?

mesoderm

No, each contribute to different chambers, some overlap e.g. formation of atria involves both fields

26

Summarize the structures from the the two heart fields.

Primary heart field :
Left Ventricle, Part of Atria,

Secondary heart field:
Right Ventricle, Outflow tract, Part of Atria

27

After formation of the 2 heart fields, What are the 4 key events in human heart development? (PClCsO)

1) Position of heart tube
2) Cardiac looping
3) Chamber septation
4) Outflow tract division and Valves formation

28

What 2 foldings are involved in positioning of heart tube?

Cephalic folding + Lateral folding

29

How does cephalic folding bring heart tube to different position? (3 points)

Centre of cardiogenic area originally anterior to oropharyngeal membrane

Subsequent growth of CNS/ Nerual plate extends over Cardiogenic area and Pericardial cavity > curvature towards foregut

Cephalic folding brings heart tube to cervical > thorax region

30

What fuses in primitive heart during lateral folding of embryo?

Fusion of paired endocardial tubes (heart tubes)

31

What is the role of dorsal mesocardium?

Attach primitive heart tube (after fusion) to dorsal side of pericardial cavity

32

What do endocardial tubes fuse into?

Primitive heart tube

33

What are the 4 segments of primitive heart tube after 2 endocardial tubes fuse?

(Aortic roots)>
Truncus arteriosus >
Bulbus cordis >
Primitive ventricle >
Primitive atrium >
(Sinus venosus)

34

When does cephalic and lateral folding of the embryo take place?

Week 3

35

When does the cardiac looping occur?

Day 23-28

36

Cardiac looping involves translocation of 2 portions of primitive heart tube. How does the anterior portion translocate?

Anterior portion (ventricles) bends:

Ventrally ,Caudally
To the right

37

How does the caudal portion of primitive heart tube shift in cardiac looping?

Caudal portion (atrial) shifts:

Dorso-cranially
To the left

38

What structure is incorporated in cardiac looping into the pericardial cavity?

Atrial/ caudal portion of primitive heart tube

39

When does the endocardial/ heart tubes start draining and pumping blood?

Week 3

Drain at caudal sinus venosus

Pump at cranial dorsal aorta

40

How is the bulboventricular sulcus formed in cardiac looping?

After ventricle (anterior) portion shift Ventrally, Caudally and to the right

Bulbis cordis lies anterior to ventricles. Sulcus inbetween bulbis cordis and ventricle

41

What is dextrocardia an abnormality of?

Adnormal cardiac looping

42

When is dextrocardiac induced?

During gastrulation when laterality is established

or

During cardiac looping

43

How come dextrocardia results in heart lying in right? (think about which portion loops wrong)

Mistake in cardiac looping: Ventricle (anterior) portion shifts to the LEFT instead of the right

44

What is the specific location of endocardial/ heart tubes after cephalic folding?

Ventral to foregut
Neck of embryo

45

What process follows cardiac looping?

Chamber septation

46

When are the major septa of heart formed?

27th to 37th day

47

What is the layer between endocaridum and myocardium in primitive heart tube that causes septation?

Cardiac jelly/ endocardial cushion

48

In what structures is septation simultaneous during chamber septation?

Common atrium

Ventricle

Atrioventricular canal

Truncus arteriosus and conus cordis

49

What 2 steps are there for endocardial cushions to form a septum?

1. endocardial cushion in opposite ridges grow

2. Cardiac chambers expand passively > walls elongate and merge to form septum

50

Does the endocardial tissue completely seal off structures in chamber septation?

No

Always leave a small gap to be filled by other tissue

51

What is the initial direction of blood flow in atria after chamber septation?

From right to left

52

What structure grows first in spetation of common atrium?

Septum Primum

53

How does Septum primum start dividing the atria?

Septum primum extends downwards toward the endocardial cushion in AV canal

54

What is the Opening between BOTTOM edge of septum primum and endocardial cushions? What does it allow?

ostium primum
Allow blood flow from RA to LA

55

How many endocardial cushions frow in the AV canal?

4
Left, right, anterior, posterior

56

What happens before the closure of ostium primum?

Cell death in UPPER portion of septum primum > form perforations that coalesce > form ostium secundum

57

What is the difference between ostium primum and ostium secundum?

Formation: Primum is a gap left between encardial cushion and septum primum
Secundum is cell death > perforation coalesce to form hole

Location: Primum is at bottom edge of septum primum, secundum is at upper edge

Timing: Primum first, then Secundum

58

What is the function of the ostium primum and secundum?

Allow passage of blood from RA to LA

59

Where does the Septum secundum form?

From UPPER WALL of RA, grow downwards towards AV canal

60

How does the Septum secundum form?

Growth of RA results in invagination of muscular atrial roof

61

How does septum secundum relate to ostium secundum?

Septum secundum's free edge overlaps with ostium secundum

62

What is the small passageway between the septum secundum and the ostium secundum?

Foramen ovale

63

What is the role of foramen ovale?

shunts oxygenated blood from placenta via inferior vena cava from right atrium to left atrium

64

How is foramen ovale VALVE formed?

Upper part of septum primum gradually disappears / degenerates > remaining part becomes valve of oval foramen

65

How does foramen ovale shut tight at birth and cause complete separation of atria? (think lung circulation starting...)

lung circulation begins > Increased blood pressure in left atrium + Decreased pressure in right atrium

left atrial pressure > right

valve of oval foramen functionally closes against
septum secundum

separates right and left atria

66

How is atrial septal defect (ASD) caused in relation to primitive septum formation? (3)

 Excessive cell death and
resorption (e.g. absence) of septum primum; and/or
 Inadequate development/ abscence of septum secundum
 Abscence of both septum

67

What does the AV canal initially only give access to?

Initially gives access only
to the primitive LEFT
ventricle

68

What blocks blood from moving from LV to RV initially before septum formation?

Bulboventricular flange, AV canal lies to the left and doesnt supply RV

Separates RV (Bulbus cordis) from AV canal (which only access LV)

69

What 3 parts is the bulbus cordis (later forms RV) divided into?

Trabeculated part of RV > Conus Cordis > Truncus Arteriosus

70

What two structures change to allow Blood passing through both ventricles originally separated by Bulboventricular flange?

Bulboventricular flange regresses half way along base of superior endocardial cushion

AV canal enlargement to the right

71

What structure does RV arise from?

Proximal Bulbus Cordis

72

Which 2 endocardial cushions fuse to allow sealing of primitive interventricular foramen? When?

Posterior and Anterior endocardial cushion grows and fuse in middle of AV canal > form L/R AV canal


Day 35

73

How does L/R AV canal shift?

Canal shifts toward middle:
 Left AV canal lines up with left ventricle
 Right AV canal lines up with right ventricle

Both ventricles now have blood flow towards outflow tract

74

What transient structure surrounds the atrioventricular cushion tissue and ventricular walls in each AV canal ?

mesenchymal myocardium tissue

75

What happens to the proliferated mesenchymal myocardium and the muscular chord durrounding the lumen of ventricle?

mesenchymal tissue CAVITATED (hollowed
and thinned) by bloodstream > form atrioventricular (AV) valve leaflets

Muscular chords degenerate and replaced by Chordae Tendinae (dense connective tissue)

76

How do AV valves leaflets attach to ventricles?

Leaflets > chordae tendinae > papillary muscles

77

What is a common ventricular septal defect?

Tricuspid atresia

78

How does tricuspid atresia arise?

Obliteration of Right AV Canal >
Absence or fusion of tricuspid valve, no connection between RA and RV

79

What are the physiological consequences of Tricuspid atresia?

 Underdevelopment of right ventricles
 Hypertrophy of left ventricle
 No blood flow to lung tissue, pulmonary stenosis

80

What is the consequence of blood mixing in tricuspid atresia?

Blood passes through foramen ovale > mixing of deoxygenated and oxygenated blood > Low oxygen levels in blood

81

What are some symptoms of Tricuspid atresia?

bluish color to skin, shortness of breath, fatigue

82

What are the two components to the outflow tract?

Truncus arteriosus
Conus cordis

83

What starts the partitioning of the outflow tract?

In truncus arteriosus > Pairs of OPPOSING SWELLINGS (right, left) appear

84

What do the opposing swellings of truncus arteriosus form?

Pairs of opposing swellings (right, left) appear > grow
toward aortic sac and twist around each other >
completely fuse (spiral closure) to form aorticopulmonary septum

85

What is the role of aorticopulmonary septum?

divides truncus into:
1. Aortic channel (aortic arch)
2. Pulmonary channel
(pulmonary trunk)

86

How come pulmonary trunk ends up anterior to aorta?

Spiral closure of opposing swellings in truncus arteriosus in RIGHT-HANDED twist

87

What divides the conus cordis into separate outflow tracts of LV and RV? (think 2 truncoconal swellings grow and fuse)

Conus cordis swell along L/R ventral walls > Fuse and unite with truncus septum at Truncoconal transition > divide conus cordis into L/R outflow tracts

88

What do the L/R outflow tracts connect to?

Left: Aorta
Right: Pulmonary artery

89

What forms the primitive septum between ventricles?

Medial walls of expanding ventricles > apposed and merge > Muscular Interventricular Septum

90

The space between the top edge of muscular septum and endocardial cushions allow what? How is it sealed?

Allow flow between 2 ventricles

Aortico-pulmonary septum fuses with POSTERIOR Atrioventricular cushion to close gap in septum > form membranous septum

91

How are semilunar valves formed? (think tubercules, truncus arteriosus)

Main truncus arteriosus swelling > semilunar valves primordia become visible as 3 small tubercles > Tubercules hollowed out/ cavitated by blood in UPPER SURFACE > semilunar valves

92

Which is the most common congenital heart defect?

VSD

93

Which part of IV spetum deforms in majority of VSD?

Muscular part

94

What is the consequence and symptoms of VSD?

Mixing deoxy and oxy blood
Symptoms = fatigue, fat breathing, no appetite

95

What 4 defects does Tetralogy of Fallot Disease demonstrate? (start with VSD and Aorta displacement...)

1. Ventricular septal defects (VSDs)
2. Overriding / displacement of aorta over VSDs (not
to left ventricle)
3. Narrowing of pulmonary valve (pulmonic stenosis)
> restricts blood flow to lung, leading to…
4. …Thickening / hypertrophy of right ventricular wall

96

What symptoms for Tetralogy of Fallot?

Symptoms:
 Bluish tint to skin, fingertips, lips (cyanosis)
 Difficulty breathing
 Tiredness

97

What is persistent/ common truncus arteriosus?

Failure in formation of conotruncal ridges = no septation of outflow tracts + interventricular septal defect

98

What causes transposition/ swap of great vessels?

No spiral conotruncal septum (defect = straight septum)

Switch aorta and pulmonary artery

Require immediate surgery

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