2. • Cardiovascular system is the first major
regulatory system to function in the
embryo.
• The primordial heart and vascular system
appear in the middle of the third week of
embryonic life.
• The heart starts functioning by the
beginning of the fourth week.
3. • The first regulatory system to function in
embryo is
• Nervous system
• Cardiovascular system A
• Endocrine system
• Lymphatic system
• Macrophage system
4. • This precocious cardiac development is
necessary because the rapidly growing
embryo can no longer satisfy its nutritional
and oxygen requirements by diffusion
alone.
5. • Consequently, there is a need for an
efficient method of acquiring oxygen and
nutrients from the maternal blood and
disposing of carbon dioxide and waste
products.
7. • Mesenchymal cells proliferate and form
angioblast cells.
• These are arranged in the form of isolated
cell clusters called angiogenetic cell
clusters.
• These clusters develop during third week
throughout the mesoderm (intra-
embryonic as well as extra-embryonic).
9. • Depending on location we can say there
are two types of cells in each cluster.
1. The cells present in the central
region of a cluster are central cells
2. The cells present in peripheral area
of a cluster are peripheral cells
10. • Each cluster forms a primitive capillary.
• The central cells in each cluster form
primitive blood cells and the peripheral
cells form endothelial cells.
• The adjacent primitive capillaries join to
form network of capillary vessels.
11.
12. • Adjacent primitive capillaries join each
other and form a network of capillaries in
extra-embryonic and intra-embryonic
mesoderm.
• It is interesting to note that vascular
system starts developing first in
splanchnic mesoderm around yolk sac
and spread everywhere in mesoderm.
13. • The vascular system starts developing first
in
• splanchnic mesoderm around yolk sac A
• Somatic mesoderm around amniotic cavity
• Connecting stalk
• Intraembryonic mesoderm
• The mesoderm lining the trophoblast
14.
15. • The larger vessels develop by
the union of adjacent networks
of capillaries.
16. • Primordial blood vessels
cannot be distinguished
structurally as arteries or
veins, but they are named
according to their future fates
and relationship to the heart.
17. • The earliest sign of the heart is the
appearance of paired endothelial cords
during the third week.
• These cords canalize to form endocardial
heart tubes, which fuse to form the tubular
heart in the third week.
• The heart begins to beat at 22 to 23 days.
• Blood flow begins during the fourth week.
18. • The earliest sign of the heart is
• The appearance of paired endothelial cords during fourth
week
• The appearance of paired endocardial heart tubes during
third week
• The appearance of paired endothelial cords during third
week A
• The appearance of paired endocardial heart tubes during
fourth week
• The appearance of paired endothelial capillaries
