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									HEART TUBE

Dr. Mujahid Khan
     Early Development of Heart
   The earliest sign of heart is the appearance of
    paired endothelial strands called angioblastic

   They develop in the cardiogenic mesoderm
    during the third week

   These cords canalize to form heart tubes

   These cords fuse together to form the tubular
    heart late in the third week
  Early Development of Heart

 Primordium  of heart is first evident at 18
 days in the cardiogenic area

 The   heart begins to beat at 22-23 days

 Blood flow begins during the fourth week
 and can be visualized by Doppler
        Development of Heart

 Theendocardial heart tubes approach
 each other and fuse to form a single heart
 tube after lateral folding

 Fusion of tubes begins at the cranial end
 of the developing heart and extends
       Primordial Myocardium
 As the heart tubes fuse, an external layer
 of the embryonic heart, the primordial
 myocardium is formed from splanchnic
 mesoderm around pericardial coelom

   this stage the developing heart is
 At
 composed of a thin endothelial tube,
 separated from thick muscular tube by
 gelatinous connective tissue, cardiac jelly
 Theendothelial tube becomes the internal
 endothelial lining of the heart, called

    primordial myocardium becomes the
 The
 muscular wall of the heart or myocardium

 The visceral pericardium or epicardium is
 derived from mesothelial cells and spread
 over the myocardium
               After Folding

 As   folding of head region occurs

 The heart and pericardial cavity come to
 lie ventral to the foregut and caudal to the
 oropharyngeal membrane
        Fate of Heart Tubes

 The tubular heart elongates and develops
 alternate dilations and constrictions:

 Truncus  Arteriosus
 Bulbus Cordis
 Ventricle
 Atrium
 Sinus venosus
           Fate of Heart Tubes
   As the developing heart elongates and bends, it
    gradually invaginates into the pericardial cavity

   Initially suspended from the dorsal wall by a
    mesentery, the dorsal mesocardium

   Central part of this mesentery soon degenerates

   Heart is now attached only at its cranial and
    caudal ends
            Truncus Arteriosus
   Is continuous cranially with the aortic sac, from
    which the aortic arches arise

   The sinus venosus receives umbilical, vitelline,
    and common cardinal veins from the chorion,
    yolk sac, and embryo respectively

   Bulbus cordis and ventricle grow faster than
    other regions, the heart bends upon itself,
    forming bulboventricular loop
        Truncus Arteriosus

 Asthe primordial heart bends, the atrium
 and sinus venosus come to lie dorsal to
 the truncus arteriosus, bulbus cordis, and

 Bythis stage the sinus venosus has
 developed lateral expansions, the right
 and left horns of the sinus venosus
             Pericardial Cavity
   As the heart elongates and bends, it gradually
    invaginates into the pericardial cavity

   The heart is initially suspended from the dorsal
    wall by a mesentery, the dorsal mesocardium

   The central part of the mesentery soon

   Forms a communication, the transverse
    pericardial sinus between the right and left sides
    of the pericardial cavity
           Pericardial Cavity

       the fourth week three well defined
 During
 body cavities are formed:

 Pericardial   cavity

2   pericardioperitoneal canals

 Peritoneal    cavity
    Pleuropericardial Membranes
   As the pleuropericardial folds enlarge, they form
    partitions that separate the pericardial cavity
    from the pleural cavities

   As the primordial pleural cavities expand
    ventrally around the heart, they extend into the
    body wall, splitting the mesenchyme into:

   An outer layer that becomes the thoracic wall

   An inner layer becomes the fibrous pericardium,
    the outer layer of the pericardial sac enclosing
    the heart

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