Development of Heart S-II CVS MOD 67
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Objectives
Describe Vasculogenesis and Angiogenesis
Discuss the formation of Endothelial tube
Discuss the Cardiogenic 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
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 starts to function at the beginning of fourth week
Vasculogenesis and Angiogenesis
Vasculogenesis means formation of blood vessels
Angiogenesis means formation of blood cells.
Both occur parallel
Controlled by one regulating gene factor VEGF.
Vasculogenesis
Vasculogenesis occurs in the embryo and extraembryonic membrane during
the third week:
Mesenchymal cells differentiate into endothelial cell precursor- Angioblast
Angioblast (vessel forming cells) 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)
Vessels sprout into adjacent areas by endothelial budding and fuse with
other vessels
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Formation of Endothelial Tubes
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
The cardiogenic 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 cell, later forms angioblasts that form
vascular cords which coalesce into the paired lateral endocardial tubes which
forms the primitive heart tube
Formation of Heart Tube
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 cardiogenic mesoderm is
shifted ventrally and comes to lie ventral to the primitive pharynx.
Folding of Embryo
Location of Cardiogenic Area
Development of Heart
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
23 days following conception, the single, simple epithelial heart tube lies
within the embryo's pericardial cavity.
Development of Three Layers of Heart
Primodium of myocardium develops from the Splanchnic mesoderm
surrounding the pericardial coelom.
At 23days there are three cell layers present within the heart tube.
Layers of Heart
Inner thin layer is the endothelial tube
It is separated from thick muscular tube (primodium of myocardium) by
gelatinous connective tissue called as cardiac jelly.
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The cardiac jelly is a structure less mass of cells which contain very few
nuclei.
Layers of Developing Heart
The endothelial tube becomes the internal endothelial lining of heart, the
Endocardium
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 external surface of sinus venosus
Division of Heart Tube
With folding of the head region, 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
The Truncus Arteriosus is continuous cranially with the aortic sac from
which the aortic arches arise.
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
The bulbus cordis and ventricle grow faster causing the heart to bend 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.
Initially suspended from the dorsal wall by mesentery, the dorsal
mesocardium.
Formation & Rotation of Heart Tube
Transverse Pericardial Sinus
The central part of dorsal mesocardium soon degenerates, forming a
communication called 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
The initial contractions of heart originate in muscle which are of myogenic
origin.
Blood enters the sinus venosus from a number of sites, including the:
Development of Veins associated with the Heart
Three paired Veins drain into tubular heart of four week embryo;
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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
SELF ASSESSMENT
In which week does the heart tube first appear?
From which layer(s) of the embryo do the three layers of heart are derived?
Name the important vessels of fetal circulation
REFERENCES
• Langman’s embryology
• KLM introduction to embryology