The cardiovascular system is the first major regulatory system to develop in the embryo, appearing in the third week of development. By the beginning of the fourth week, the heart has started functioning and the earliest sign of the heart is the appearance of paired endothelial cords. This early development of the cardiovascular system is necessary to meet the nutrient and oxygen demands of the rapidly growing embryo, as diffusion alone can no longer satisfy these needs. The vascular system develops from mesoderm cells that proliferate to form blood vessels and blood cells.

1. CARDIOVASCULAR
SYSTEM

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.

6. Cardiovascular system
develops from mesoderm.
• Mesenchymal cells in the mesoderm

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).

8. • Three angiogenetic cell clusters.

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.

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

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