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Development%20of%20the%20Heart

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Title: Development%20of%20the%20Heart


1
Development of the Heart
2
Development of primitive heart tube
  • It develops early in the middle of 3rd week ,
    from aggregation of splanchnic mesodermal cells,
    in cardiogenic area ,ventral to pericardial
    coelom, and dorsal to yolk sac.
  • They form 2 angioblastic cords that canalize to
    form 2 endocardial heart
    tubes.

B,transverse C,longitudinal
3
  • After lateral folding of embryo, 2 endocard.tubes
    fuse to form. Single heart tube (C,D) T.S of
    21,22 days.
  • This heart tube lies inside the pericardial
    cavity , its dorsal wall is connected to foregut
    by dorsal mesocardium (D,22 days).
  • The central part of dorsal mesocardium
    degenerates ,forming transverse passage dorsal to
    heart ,called transverse sinus of pericardium,
    (E,F) schematic T.S of 28
    days.

4
The layers of primitive heart wall
  • T.S in D, at 22 days and in F at 28-days ,
    showing
  • Thin endothelial tube becomes internal
    endothelial lining of the heart or endocardium.
  • Splanchnic mesoderm surrounding the pericardial
    coelom becomes.. primordial myocardium
    (muscular wall of heart).
  • Thin endothelial tube is separated from thick
    muscular tube (myocardium) by gelatinous C.T.
    (cardiac jelly). Forming AV septum valves.
  • Visceral pericardium is derived from mesothelial
    cells and forms the epicardium.

5
After head folding of embryonic disc
  • A,B,long. sections as the head fold develops
    (during 4th week) , heart tube pericardial
    cavity lie ventral to foregut and caudal to
    oropharyngeal membrane.
  • The position of heart tube is reversed ,it lies
    dorsal to pericardium.
  • C,Long. Section, during 4th week showing
    complete head folding and reversion of heart tube
    , pericardium septum transverse (future
    central tendon of diaphragm).
  • Note also the heart tube lies inside the
    pericardial cavity.

6
  • The primitive heart tube elongates and develops
    alternate dilatations and constrictions
    1-truncus arteriosus.
    2-bulbus cordis. 3-primitive
    ventricle. 4-primitive atrium.
    5-sinus venosus.
  • Truncus arteriosus is continous cranially with
    aortic sac ,from which aortic arches develop.
  • Sinus venosus has right left hornes .
  • Each horn receives umbilical, vitelline , common
    cardinal veins from the chorion, yolk sac
    embryo, respectively.

Ventral veiw ,By the end of 4th week
  • Heart tube bends upon itself,giving rise an
    s-shaped heart,then u-shaped.

7
  • Bulbus cordis ventricle grow faster than other
    regions, so the heart bends upon itself,forming
    U-shaped bulboventricular loop (by the end of
    4th week). The atrium sinus venosus also come
    to lie dorsal to truncus arteriosus, bulbus
    cordis ventricle.

8
  • Blood Flow through the Primitive Heart
  • By the end of 4th week, unidirectional blood
    flow begins at sinus venosus by peristalsis- like
    waves. A
  • Blood passes through sinuatrial valves into
    atrium Atrioventricular canal ventricle..
    Bulbus cordis Truncus arteriosus aortic sac
    aortic arches (arterial channels)
    2 dorsal aortae into body of embryo, yolk sac
    , and placenta. A

A,sagittal section of primordial heart(24
days),showing blood flow. B,dorsal view of heart
(26 days) ,illustrating hornes of sinus venosus
Note also dorsal location of primordial atrium
sinus venosus.
9
  • C,ventral view of heart (35 days),Note the
    aortic arches arising from aortic sac and
    terminate in the dorsal aortae.

10
Partitioning of the primitive Heart
A, sagittal section of primordial heart
(24days),showing blood flow.
  • Dividing of A-V canal , primitive atrium
    primitive ventricle.. Begins at the middle or
    end of 4th week.
  • It is completed by the end of 5th week.
  • These processes occur concurrently.

11
Partitioning of Atrioventricular Canal
  • At the end of 4th week, 2 endocardial cushions on
    dorsal ventral walls of atrioventricular canal
    , develop from mesenchymal cells of cardiac
    jelly. (B)
  • During 5th week, the AV- endocardial cushions
    meet and unite in the middle line to form a
    septum and divide the common A-V canal into
    right left A-V canals. (C,D)
  • Endocardial cushions also form the AV- valves
    membranous septa of interventricular septum.
  • Note in D,cronal section ,begining of development
    of interatrial intervent. septa.

12
  • Partitioning of primordial Atrium
  • It begins at the end of 4th week by development
    of 2 septa.
  • 1-Septum primum a thin crescent-shaped membrane
    grows from the roof of common atrium into the
    fusing endocardial cushions dividing common
    primitive atrium into right left halves.
  • -Foramen primum is formed to pass oxyg.blood from
    righ to left atrium. It disapears as septum
    primum fuses with the endocard.cushions,(A1-C1).
  • Before closure of foramen primum , perforations
    appear in central part of septum primium
    coalesce to form Foramen Secundum (C1-D1).
  • A1 to D1 coronal sections
  • A to D views of interatrial septum from right
    side.

13
  • 2-Septum secundum a
    crescentic muscular memb.grows and descends from
    roof of atrium during 5th week. It overlaps
    foramen secondum in septum primum .
  • The gap between the lower free border of
    S.secundum and the upper edge of S.primum form
    foramen ovale.
  • Cranial part of S.primum disappears and remaining
    part of S.primum which attached to endocardial
    cushions forms flaplike valve of the foramen
    ovale.

14
  • In the fetus (before birth) the pressure is
    higher in right atrium than in the left and
    highly oxygenayed blood flows directly from right
    atrium to left atrium through open foramen ovale.
  • After birth when the circulation of the lungs
    begins the blood pressure in left atrium rises
    ,the upper edge of septum primum is pressed
    against the upper limb of septum secundum. This
    will close the foramen ovale ,forming a complete
    partition between the 2 atria.
  • An oval depression in the lower part of
    interatrial septum of right atrium. The fossa
    ovalis is a remnant of the foramen ovale.

15
Left side embryonic cardiovascular system (26
days) 4 week embryo
16
  • Changes in Sinus venosus (A) It consists of
    body and 2 hornes,right left.each horn receives
    3 veins
    1- Vitelline vein from yolk sac.
    2- Umbilical vein from
    placenta, 3-Common
    cardinal vein from body of embryo.
  • (B) Later , due to shuting of blood from left
    side to right side in the connection by
    anastomosis between the 2 anterior cardinal
    veins. this shunt becomes left brachiocephalic
    vein (C)

17
  • Changes on left side (B,C)
    1- left horn
    body of sinus venosus form the coronary sinus.

2-left common cardinal vein becomes small to form
oblique vein of left atrium.

3- left vitelline left umbilical veins,
degenerat.
18
  • Changes on right side

1- The right horn becomes absorbed into right
atrium to form its smooth part ,sinus venarum.
2- Right common cardinal vein enlarges to form
SVC.
3- Right vitelline vein becomes IVC. 4- Right
umbilical vein disapears.
19
What happen to Sinus Venosus to share in
formation of Right Atrium?
1- left horn becoms the coronary sinus.
2- right horn becomes
incorporated into wall of right atrium to form
the smooth part (sinus venarum) B, 8-weeks
3- The remainder of the wall
of right atrium conical muscular pouch
(auricle).. have rough
trabeculated area and derived from primordial
atrium.
20
4- The smooth part , (sinus venarum ) rough
part (primordial atrium) are demarcated
internally by a ridge, crista terminalis.
-crista terminalis valves of IVC valves of
coronary sinus are derived from right sinuatrial
valve. / But left sinuatrial valve fuses with
S.secundum and incorporated with it into
interatrial septum.
21
Primordial pulmonary vein Development of left
atrium
  • At first, a single common pulmonary vein is seen
    opening in left atrium ,just to left of S.primum.
  • Most smooth part of left atrium is derived
    from incorporation of the single common
    primordial pulm. vein at 5th week, (A B).
  • then absorption of the 2-pulm.veins at 6th week
    , (C).
  • lastly , aborption of the 4- pulm.veins into
    left atrium , with separate orifices at 8th week.
    (D).
  • Left auricle is derived from primordial left
    atrium.

22
Embryological origin of the definitive atrium
Right Atrium
Left Atrium
1-Its rough part auricle from Right ½ of
primitive atrium. 2-right ½ of A-V
canal. 3- Its smooth part from Absorbed right
horn of sinus venosus.
1- Its rough part auricle from left ½ of
primitive atrium. 2- left ½ of A-V canal. 3- Its
smooth part from Absorbed part of pulmonary veins.
23
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24
Development of muscular part of interventricular
septum
  • Primordial muscular interventricular( IV )septum
    arises in the floor of ventricle , as thick
    crescentic fold with concave free edge.
  • This septum subdivides the original ventricular
    cavity incompletely into right left ventricles
    that communicate together through IV foramen.
  • This foramen closes by the end of 7th week as the
    2 bulbar ridges fuse with the endocadial cushion.
  • A-sagittal section 5th week.
  • Coronal section.6th week.

25
Incorporation of the proximal part of bulus
cordis into the ventricles
  • A sagittal s.at 5th w., showing the bulbus cordis
    in the primitive heart.
  • B coronal s.at 6th w. after incorporation of the
    proximal part of bulbus cordis into the
    ventricles to forms
  • In right ventricle Conus arteriosus
    (infundibulum), which gives origin of pulmonary
    trunk.
  • In left ventricle. Aortic vestibule part of
    ventricular cavity just inferior to aortic valve.

26
  • Closure of IV foramen formation of membranous
    part of IV septum result from fusion of the
    following 1-right bulbar
    ridge. 2-left bulbuar
    rige. 3-fused
    endocardial cushions.
  • A,sagittal s.at 5th w.
  • B, coronal s.at 6th w.after incorporation of the
    proximal part of bulbus cordis into the
    ventricles.
  • C,5th w.,showing the bulbar ridges fused
    endocardial cushions.
  • D,6th w., proliferation of endocardial cushions
    to diminish I V foramen.
  • E,7th w.,fusion of bulbar ridges extensions of
    endocardial cushions upward with
    aortico-pulmonary septum and down with muscular I
    V septum to close I V foramen , so memb.
    IV septum is formed

27
Cavitation of Ventricular Walls
  • Leads to formation of spongy muscular bundles
    (trabeculae carneae).
  • These bundles become the papillary muscles
    tendinous cords (attached to the
    cusps of tricuspid mitral valves).
  • A-5 weeks.
  • B-6weeks.
  • C-7weeks.
  • D-20 weeks.

28
Partitioning of distal part of the Bulbus Cordis
Truncus Arteriosus
  • A, 5th w. ventral v.of heart.
  • B,5th w. transverse sections of truncus
    arteriosus bulbus cordis,illustrating truncal
    bulbar ridges.
  • C,5th w. truncal bulbar ridges , after removal
    of ventral wall of heart truncus arteriosus.
  • D,heart after partitioning of truncus arteriosus
    into aorta pulmonary trunk.
  • E, transverse sections through newly formed aorta
    pulm.trunk showing aortico-pulmonary septum.
  • F,6th w.removal of ventral wall to show
    aotico-pulmonary septum.

29
Partitioning of distal part of the Bulbus Cordis
Truncus Arteriosus
  • G,diagram illustrating the spiral form of
    aortico-pulmonary septum.
  • H,drawing showing aorta pulmonary trunk
    twisting around each other as they leave the
    heart.

30
Partitioning of distal part of the Bulbus Cordis
Truncus Arteriosus
  • During 5th w. firstly , a right left bulbar
    ridges are developed in the lower part.
  • Another ant. post. Bulbar ridges in the middle
    part.
  • Right left truncal ridges are developed in the
    upper part.
  • Bulbar truncal ridges are developed from
    proliferation of mesenchymal cells of their wall.
  • They are also derived from neural crest
    mesenchyme by passing through the primitive
    pharynx

31
Partitioning of distal part of the Bulbus Cordis
Truncus Arteriosus
  • as development proceeds, the ridges fuse
    together following a spiral course, forming
    aortico-pulmonary septum which has a spiral shape
    at the 6th week , (as in G).
  • This septum divides bulbus cordid truncus
    arteriosus into aorta pulmonary trunk.
  • Because of spiraling of aortico-pulmonary septum,
    pulm.trunk twists around the aorta. Firstly
    pulm.trunk lies ant. to right of the aorta near
    the ventricles, then upward,it lies post. to
    left of aorta.

32

Development of Atrioventricular Valves
  • A,5thw.,showing right left AV canals and
    begining of valve swellings due to proliferations
    of tissue (subendocardial tissue) around AV
    canals.
  • B,6th w.
  • C,7th w. complete development of tricuspid
    mitral valves.. Note also development of
    compelete interventricular septum(muscularmemb.pa
    rt)

33
Development of aortic pulmonary valves
  • Results after development of bulbar truncal
    ridges and formation of aorticopulmonary septum.
  • 3 Semilunar valves begin to develop from 3
    swellings of subendocardial tissue around aortic
    pulmonary orifices.
  • These swellings are hollowed out to form the thin
    walled semilunar cusps.

34
Development of aortic pulmonary valves
  • A, long. Section showing bulbar truncal ridges.
  • B, transverse section of bulbus cordis.
  • C,fusion of bulbar ridges.
  • D,formation of walls valves of aorta
    pulmonary trunk.
  • E, rotation of the vessels the valves.
  • F, long.sections showing hollowing thinning of
    valve swelling to form the cusps.

35

Development of conducting system
  • Sinuatrial (SA) node begins to develop during 5th
    w.as it is present in right wall of sinus
    venosus.
  • SA-node is incorporated into wall of right atrium
    with sinus venosus. SA-node is located high in
    the right atrium ,near entrance of SVC.
  • Right sinuatrial valve (cranial part). Forms
    crista terminalis,but the caudal part forms the
    valves of IVC coronary sinus.

36

Development of conducting system
  • Left sinuatrial valve is incorporated into the
    interatrial septum forming AV-node bundle
    ,which are located superior to endocardial
    cushions.
  • Right left bundle branches arising from
    AV-bundle , pass from atrium into the ventricular
    myocardium.
  • A band of C.T. grows in from the epicardium and
    separates the muscle of atria from that of
    ventricles to form the cardiac skeleton (fibrous
    skeleton of heart).

37
Atrial Septal defects (ASD)
  • There are 4 types of clinically significant types
    of ASD 1-ostium secundum
    defect. (with patent oval
    foramen).
    2-endocardial cushion defect. (with
    ostium primum defect).
    3-sinus venosus defect.
    4-common atrium. Rare cardiac defect ,in which
    the interatrial septum is absent due to failure
    of septum primum septum secundum to develop.

38
Atrial septal defect (ASD)(ostium secundum
defect) A probe patent oval foramen
  • A, normal postnatal, right veiw of interatrial
    septum after adhesion of septum primum to septum
    secondum.
  • A1, interatrial septum, illustrating development
    of oval fossa in right atrium.
  • B and B1, note incomplete adhesion of septum
    primum TO septum secundum and development of a
    probe patent oval foramen.

39
Various Types of Atrial Septal Defect (ASD) in
the right aspect of interatrial septum
The most common form of ASD is patent oval
foramen
  • A, patent oval foramen due to abnormal resorption
    or perforations of septum primum, (in abnormal
    locations), during formation of foramen
    secondum.
  • B, patent oval foramen due to excessive
    resorption of septum primum short flap
    defect.

40
Various Types of Atrial Septal Defect (ASD) in
the right aspect of interatrial septum
Patent oval foramen
  • C, patent oval foramen ,resulting from an
    abnormally large oval foramen because of
    defective development of septum secundum ,so a
    normal septum primum will not close the abnormal
    oval foramen at birth.
  • D, patent oval foramen resulting from a
    combination of an abnormally large oval foramen
    excessive resorption of septum primum.

41
Various Types of Atrial Septal Defect (ASD) in
the right aspect of interatrial septum
  • E, a deficiency of fusion of endocardial
    cushions with septum primum and AV septal defect
    results and leads to a patent foramen primum
    -Ostium primum defect. Less common.
  • F, sinus venosus ASDs (high ASDs) in the
    superior part of interatrial septum close to
    entry of SVC. Rare type, results from
    incomplete absorption of sinus venosus into right
    atrium and/or abnormal development of septum
    secundum.

42
Tetralogy of Fallot
  • It contains 4 cardiac defects
  • 1- Pulmonary stenosis (obstruction of right
    ventricular outflow).
  • 2- Ventricular Septal Defect (VSD).
  • 3- Dextroposition of aorta (overriding aorta).
  • 4- Right ventricular hypertrophy.
  • cyanosis is one of the obvious signs of
    tetralogy .

43
Ventricular Septal Defects (VSDs)Membranous
VSD . Is the most common type.
  • Results from incomplete closure of IV foramen due
    to failure of development of memb. part of IV
    septum.
  • Large VSDs with excessive pulmonary blood flow
    pulm.hypertension result in dyspnea (difficult
    breathing) heart failure.

44
Muscular VSD
  • Due to excessive cavitation of the muscular part
    of the interventricular septum.. Producing
    multiple small defects (Swiss Cheese VSD).
  • Or absence of the IV septum--Single ventricle
    Transposition of aorta pulmonary trunk.
  • Complication heart failure and death.
  • This diagram showing transposition of great
    arteries (TGA) which leads to cyanosis. VSDASD
    allow mixing arterial venous blood.
  • Transposition results from that the
    aortico-pulmonary septum descends straight
    (instead of spiral).

45
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46
The Aortic Arches Derivatives
  • During the 4th week, as the pharyngeal arches
    develop, they are supplied by the aortic
    arches.
  • Aortic arches arise from the aortic sac and
    terminate in the dorsal aorta.
  • There are 6 pairs of aortic arches, but they are
    never present at the same time.
  • During 8th w.,the primitive aortic arch pattern
    is transformed into final fetal arteries.

47
Aortic Arch Arteries
48
Left side embryonic cardiovascular system (26
days) 4 week embryo
  • The paired dorsal aortae fuse to form a single
    dorsal aorta, just caudal to the pharyngeal
    arches.
  • Branches of the dorsal aorta
    1- Cervical dorsal intersegmental arteies join
    to form vertebral artery on each side
    (7th cervical
    intersegmental artery forms the subclavian
    artery).
    2- Thoracic dorsal intersegmental arteries
    persist as intercostal arteries.
    3- in the lumbar region, they persist
    forming lumbar arteries, but 5th lumbar enlarge
    and forms common iliac artery.
    4- in the sacral region, they form
    lateral sacral arteries , but the caudal end of
    dorsal aorta becomes the median sacral artery.

49
The aortic Arches
  • A, left sided-embryo (26- days) showing the
    pharyngeal arches.
  • B, schematic drawing showing left aortic arches
    arising from the aortic sac.
  • C, an embryo (37days), showing the single dorsal
    aorta and degeneration of most of the first two
    pairs of aortic arches.

50
Development of the final fetal arterial pattern
  • A, aortic arches at 6 weeks, note largely
    disappearance of the first two pairs of aortic
    arches.
  • B,aortic arches at 7 weeks, showing normal
    degeneration of aortic arches and dorsal aortae.
  • C, final arterial arrangement at 8 weeks, note
    open ductus arteriosus.
  • D, 6-month-old infant, note the final
    arrangement of the vessels - and that the
    ascending aorta pulmonary arteries are smaller
    in C than in D. Note also, obliterated
    fibrosed ductus arteriosus forming ligamentum
    arteriosum within few days after birth.

51
Derivatives of 1st 2nd pairs of aortic arches
  • The 1st aortic arches largely disappear. small
    parts persist to form the maxillary artereis.
  • The 2nd aortic arches disappear leaving small
    parts forming the stapedial artereis (run
    through the ring of the stapes, a small bone in
    middle ear).

52
Aortic Arches Arteries

53
Derivatives of 3rd 4th pairs of aortic arches
  • The 3rd arch artery persists forming the common
    carotid artery and proximal part of internal
    carotid artery (on both sides), it joins with
    the dorsal aorta to form the distal part of
    int.c.artery. The ext.c.artery develops as
    a new branch from 3rd arch.
  • The 4th arch forms the main part of the arch of
    aorta on left side, and forms the
    proximal part of right subclavian artery on
    the right side.
  • The distal part of Rt.subclavian artery
    develops from the right dorsal aorta right 7th
    intersegmental artery.
  • The left subclavian artery . is not derived
    from aortic arch but from the left 7th
    intersegmental artery.
  • Proximal part of the arch of aorta develops from
    the aortic sac , and the distal part
    from left dorsal aorta.

54
Aortic arches arteries

55
Derivatives of 5th 6th pairs of aortic arches
  • The portion of dorsal aorta connecting the 3rd
    4th arches disappears on both sides.
  • The 5th arch artery disappears in 50 and in the
    other 50 of the embryos, these arteries do not
    develop.
  • The 6th arch artery a-
    proximal part on both sides forms the
    pulmonary artery. b- distal part of
    left artery forms ductus arteriosus which
    connects left pulmonary artery with arch of
    aorta. C- distal part of right artery
    disappears.
  • The dorsal aorta on the right side caudal to 4th
    arch disappears down to the single dorsal aorta,
    while persists on left side to form descending
    aorta.

56
Aortic Arches Arteries

57
Development of the arch of aorta
  • 1- its
    proximal part develops from left part of
    distal part of aortic sac (right part of aortic
    sac forms brachio -cephalic artery).
  • Proximal part of aortic sac forms the pulmonary
    trunk. 2- its
    main middle part develops from left 4th aortic
    arch. 3- its distal
    part develops from the left dorsal aorta
    between 4th 6th aortic arches.

58
Final development of the arteries from the
aortic arches arteries
59
The relation of recurrent laryngeal nerves to the
aortic arches
  • A, 6-weeks, showing R.L.Ns. hooked around the
    distal part of 6th pair of aortic arches.
  • B, 8-weeks, showing the Rt.R.L.N. hooked around
    the Rt. Subclavian artery, and the left R.L.N.
    hooked around the ductus arteriosus arch of
    aorta.
  • Child, showing the left R.L.N. hooked around
    ligamentum arteriosum arch of aorta.

60
Development of Recurrent Laryngeal Nerves
  • Firstly, these nerves supply the 6th pharyngeal
    arch so, they hook around the 6th pair of aortic
    arches.
  • On the right , the distal part of right 6th
    aortic arch degenerates ,so right R.L.N. hooks
    around the right subclavian artery.
  • On the left , the left R.L.N. hooks around the
    ductus arteriosus formed by the distal part of
    6th aortic arch.
  • when DA is transformed after birth into
    ligamentum arteriosum ,left R.L.N. hooks around
    lig.arteriosum arch of aorta.

61
Coarctation of the aorta
  • A, postductal coarctation of aorta.
  • B, development of collateral circulation.
  • C and D, preductal coarctation.
  • E, 7-week embryo, showing normal area of
    involution in the distal segment of right dorsal
    aorta as the right subclavian artery develops.
  • F, abnormal area of involution in the distal
    segment of the left dorsal aorta.
  • G, later stage, showing the abnormally involuted
    segment appearing as a coarctation of aorta which
    moves with the left subclavian artery to the
    region of ductus arteriosus.. E to G illustrate
    one hypothesis about the embryological basis of
    coarctation of aorta.

62
Coarctation of Aorta
  • In postductal coarctation , the constriction is
    distal (below) to ductus arteriosus. This
    permits development of a collateral circulation
    during the fetal period to assist passage of
    blood to lower part of the body.
  • In preductal coarctation , the constriction is
    proximal or above the ductus arteriosus which
    remains open and maintain the circulation (below
    the narrowing) to the lower part of the body.

63
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