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HEART TUBE
&
PERICARDIUM
Dr. Mujahid Khan
Early Development of Heart

The earliest sign of heart is the appearance of
paired endothelial strands called angioblastic
cords

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
ultrasonography
Development of Heart
 The
endocardial 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
caudally
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
 At
this stage the developing heart is
composed of a thin endothelial tube,
separated from thick muscular tube by
gelatinous connective tissue, cardiac jelly
Endocardium
 The
endothelial tube becomes the internal
endothelial lining of the heart, called
endocardium
 The
primordial myocardium becomes 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
 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 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
degenerates

Forms a communication, the transverse
pericardial sinus between the right and left sides
of the pericardial cavity
Pericardial Cavity
 During
the fourth week three well defined
body cavities are formed:
 Pericardial
2
cavity
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