Download Early Development of Heart LEARNING OBJECTICES: Describe

Early Development
of
Heart
LEARNING OBJECTICES:
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Describe Vasculogenesis and Angiogenesis
Discuss the formation of Endothelial tube
Discuss the Carcinogenic Area
Describe the formation of heart tube
Discuss the further development of heart
Discuss the formation of different layers of heart
Discuss the division of heart tube
Describe the Rotation of Heart tube
Development of Cardiovascular System
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The cardiovascular system is first system to function in the embryo.
The primordial of heart and blood vascular system appear in the middle of third
week of embryonic development.
The heart start to function at the beginning of fourth
week
External Features of Heart
Internal Features of Heart
Vasculogenesis and Angiogenesis
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Vasculogenesis means formation of blood vessels and Angiogenesis means
formation of blood cells. Both the vasculogenesis and angiogenesis both occur
parallel and both processes are controlled by one regulating gene factor. VEGF
is a major regulator of both cell types and plays a critical role, in coordination with
other signaling pathways and transcriptional regulators, in controlling the
differentiation and behavior of endothelial and blood cells during early embryonic
development.
The formation of embryonic vascular system involves two processes:
vasculogenesis and angiogenesis. Blood vessel formation (vasculogenesis) in
the embryo and extraembryonic membrane during the third week: the different
step of vasculogenesis are:
Mesenchymal cells differentiate into endothelial cell precursor- Angioblast
(vessel forming cells) which aggregate to form isolated angiogenic cell clusters,
the blood islands
Small cavities appear within the blood island by confluence of intercellular clefts.
Angioblasts flatten to form the endothelial cells that arrange themselves around
the cavities in the blood island to form endothelium
These endothelium lined cavities soon fused to form the endothelial channels
(vasculogenesis)
ENDOTHELIUM
BLOOD ISLAND
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From Noden and La Hunta p 211
Vessels sprout into adjacent areas by endothelia budding and fuse other vessels
The first blood cells arise in the splanchnic mesoderm on the endodermal wall of
the yolk sac.
Cells in the outer zone of these blood islands become vascular endothelium and
enclose haematopoietic stem cells.
The function of haematopoiesis is transferred during foetal development from
yolk sac to liver to bone marrow.
Formation of Endothelial Tubes
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Day 17 - Blood islands form first in the extra-embryonic mesoderm
Day 18 - Blood islands form next in the intra-embryonic mesoderm
Day 19 - Blood islands form in the cardiogenic mesoderm and coalesce to form
a pair of endothelial heart tubes
Cardiogenic area
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The carcinogenic area first forms between cranial edge of the trilaminar germ
disc and the neural plate and just lateral to the cranial end of the neural plate, on
about day 19. Splanchnopleuric mesodermal cells in, adjacent to the endodermal
layer will form angioblasts that form vascular cords which will begin to coalesce
into the paired lateral endocardial tubes. Later these lateral endocardial tubes will
fold under the embryo, fuse, and form the primitive heart tube
Formation of Heart Tube
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The endothelial heart tubes fuse to form a single primitive heart tube with a
cranial (arterial) end and a caudal (venous) end.
The heart tubes are derived from the cardiogenic mesoderm situated next to
the pericardial cavity, the cranial-most end of the intra-embryonic coelom. After
the formation of the head fold (at 20 days) the carcinogenic mesoderm is shifted
ventrally and comes to lie ventral to the primitive pharynx.
Folding of Embryo
Location of Cardiogenic Area
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At first the horseshoe-shaped cardiogenic area lies lateral and cranial to the
neural tube
At later stage of development, due in folding of embryo in carnio-cadual and
lateral directions, the cardiogenic area changes its position and lies in front of
foregut (Primitive Pharynx)
Different steps of in-folding of embryo and shifting of
developing heart and pericardium
Development of Heart
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The primordium of the heart first evident at 18 days. In the cardiogenic area,
splanchnic mesenchymal cells ventral to the pericardial coelom aggregates and
arrange themselves side by side to form two cardiac primodium, the Angioblastic
Cords. These cords canalize to form two thin walled endocardial heart tubes. As
the lateral folding occurs, the endocardial tubes approach each other and fuse to
form single heart tube. Fusion of heart tubes begins at the cranial end of
developing heart and extends caudally.
Development of Three Layers of Heart
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Primodium of myocardium develops from the Splanchnic mesoderm surrounding
the pericardial coelom. Twenty-three days following conception, the single,
simple epithelial heart tube lies within the embryo's pericardial cavity. At this time
there are three cell layers present within the heart tube.
Layers of Heart
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Inner thin layer is the thin endothelial tube, that is separated from a thick
muscular tube (primodium of myocardium) by gelatinous connective tissue called
as cardiac jelly. The cardiac jelly is a structure less mass of cells which contain
very few nuclei.
Layers of Developing Heart
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The endothelial tube becomes the internal endothelial lining of heart, the
Endocardium, and the primodium of myocardium becomes the muscular wall of
heart, the Myocardium. The visceral pericardium, or Epicardium is derived from
mesothelial cells that arise from the eternal surface of sinus venosus
Division of Heart Tube
As folding of head region of embryo occurs, the heart and pericardial cavity come
to lie ventral to the foregut and caudal to the oropharyngeal membrane. At the
same time the tubular heart elongates and develops alternate constrictions and
dilatations, the trunsus arteriosus, bulbus cordis, ventricle, atrium and sinus
venosus.
Division of Heart Tube
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The tubular Truncus Arteriosus is continuous cranially with the aortic sac from
which the aortic arches are arising. The Sinus Venosus receives the umbilical,
vitelline and common cardinal veins from the chorion, yolk sac and embryo
respectively. The arterial and venous ends of the heart are fixed by the
pharyngeal arches and septum transverum respectively.
Rotation of different Parts of Heart
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The bulbus cordis and ventricle grow faster than other regions, so that heart
bends on itself forming U-shaped Bulbo-ventricular loop. As the primordial heart
bends the atrium and sinus venosus come to lie dorsal to the truncus arteriosus ,
blubus cordis and ventricle. At this stage the sinus venosus has developed lateral
expansion, the right and left horns of sinus venosus. As the heart develops it
gradually invaginates the pericardial cavity. The heart initially suspended from
the dorsal wall by mesentery, the dorsal mesocardium.
Formation & Rotation of Heart Tube
Transverse Pericardial Sinus
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The central part of dorsal mesocardium soon degenerates, forming a
communication called as Transverse Pericardial sinus between right and left
sides of the pericardial cavity. At this stage the heart is attached only at its cranial
and caudal ends.
Circulation Through the Primordial heart
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The initial contractions of heart originate in muscle, that is they are of myogenic
origin. Blood enters the sinus venosus from a number of sites, including the:
Embryo through common cardinal veins
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Placenta through the umbilical veins
Yolk sac through the vitelline veins
Development of Veins associated with the Heart
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Three paired Veins drain into tubular heart of four week embryo;
Vitelline veins return poorly oxygenated blood from the yolk sac
Umbilical veins carry well-oxygenated blood from chorion, the primordial
placenta, only the left umbilical vein persists.
Common Cardinal Veins return poorly oxygenated blood from the body of
embryo