1. DEVELOPMENT OF THE CIRCULATORY SYSTEM

2. I. Develops relative to embryo’s needs
A. During early development diffusion of oxygen, wastes, nutrients, etc. suffices
B. As embryo grows larger, metabolic needs increase, diffusion no longer sufficient.
C. Circulatory system begins to develop
II. First evidence of circulatory structures seen in yolk sac, extraembryonic splanchnic mesoderm - area opaca vasculosa - blood islands

4. (primitive blood cells
and blood stem cells)

5. III. Blood stem cells - where do they come from?
A. Sites of production from stem cells change as the human embryo develops.
1. At 4 weeks after fertilization - stem cells are located in the extraembryonic splanchnic mesoderm of the yolk sac.
2. At 5 weeks - in body mesenchyme of embryo.
3. At 6 weeks - in developing liver.
4. At 8-16 weeks - in developing spleen, thymus and lymph nodes.
5. At 16 weeks and beyond - in bone marrow

6. B. Evidence suggests there are two different sources for blood stem cells.
1. Initially derived from extraembryonic splanchnic mesoderm of the yolk sac.
a. “Primitive stem cells”
b. Produce mature erythrocytes that have a nucleus.
2. Later in development a new population of stem cells arises. Recent research suggests that these stem cells arise from endothelial cells that line the aorta.
a. By 16 weeks of development these stem cells populate the bone marrow
b. These cells are the blood stem cells that give rise to enucleate erythrocytes (red blood cells).

7. IV. Circulatory system in mammals
A. Basic circulatory loop
arterioles
capillaries
arteries
venules
ventricle
atrium
veins

8. B. Basic adult mammalian circulation

9. C. Early embryonic circulation

10. D. How is the adult circulatory pattern established?

11. If we look at adult vertebrate species from primitive fish, to reptiles, to birds, to mammals, there are gross structural differences in the pattern of circulation. These differences are there to accommodate the specific adult needs (e.g. fish have gills, mammals don’t).
These differences are so great, that if only the adult circulatory system was used to establish taxonomic classification, in some cases we would probably say that 2 or more species of vertebrates were not related.
If we look at the embryonic circulatory systems of all vertebrates, we find that they are basically the same.
The adult systems are derived from the basic embryonic system.

12. Conversion of the early embryonic circulatory system to the adult configuration.
Involves:
A. Degeneration of parts of some embryonic vessels or their parts.
B. Hypertrophy of parts of some vessels.
C. Anastomosis (fusion) of some vessels.
D. Separation of one embryonic vessel into two.
E. Loss of connection between some vessels.
F. Formation of new vessels.

13. Views from the ventral side of the animal
Right
Left
Views from the ventral side of the animal
Right
Left
From Carlson, B.M Patten’s Foundations of Embryology. McGraw-Hill, Inc. New York. 6th edition. p. 618

14. Right
Left

15. In the embryo
Right
Left

16. Fate of the Trunkus Arteriosus4
trunkus
pulmonary trunk
4th
systemic trunk
Right
Left
Fate of the Trunkus Arteriosus
Contributes to the systemic trunk and a portion of the pulmonary trunk.
Divided into the bases of the pulmonary and systemic trunks

17. RIGHT LEFT green - dorsal aortic roots purple - 3rd aortic arches
(Seventh intersegmental)
green - dorsal aortic roots
Modified from Carlson, B.M Patten’s Foundations of Embryology. McGraw-Hill, Inc. New York. 6th edition. p. 618
purple - 3rd aortic arches
red - 4th aortic arches
black - ventral aortic roots and trunkus arteriosus
orange - 6th aortic arches
yellow - bulbus arteriosus
blue - intersegmental
arteries
These figures present a ventral view

18. Adult vessels Right Left Right Left Color indicates embryonic
derivation
green - dorsal aortic roots
purple - 3rd aortic arches
red - 4th aortic arches
black - ventral aortic roots and trunkus
orange - 6th aortic arches
yellow - bulbus arteriosus
blue - interseg-mental arteries
Vertebral artery
Subclavian artery
These figures present a ventral view
Modified from Carlson, B.M Patten’s Foundations of Embryology. McGraw-Hill, Inc. New York. 6th edition. p. 618

19. Venous Circulation Four Major Systems 1. Systemic (other than hepatic)
3. Pulmonary
4. Placental (Umbilical)

20. Conversion of the early embryonic circulatory system to the adult configuration.
Involves:
A. Degeneration of some embryonic vessels or their parts.*
B. Hypertrophy of parts of some vessels.*
C. Anastomosis (fusion) of some vessels.*
D. Loss of connection between some vessels.*
E. Formation of new vessels.*

21. Formation of the inferior vena cava
Posterior Systemic circulation
Formation of the inferior vena cava
posterior
anterior
anterior
posterior
Adapted from Hopper, A.F. and N.H. Hart, Foundations of animal development. Oxford University press. New York, p. 434

23. These figures present a ventral view
Green - anterior cardinal veins
Yellow - vitelline veins
Orange - supracardinal veins
Purple - common cardinal veins
Blue, blue - posterior cardinal veins
Olive - sinus venosus
Red, red - subcardinal veins
Hepatic segment
Mesenteric segment
Renal segment
Sub-/Supra-cardinal anastomosis
Adapted from Hopper, A.F. and N.H. Hart, Foundations of animal development. Oxford University press. New York, p. 434

24. These figures present a ventral view
Green - anterior cardinal veins
Yellow - vitelline veins
Orange - supracardinal veins
Purple - common cardinal veins
Blue, blue - posterior cardinal veins
Olive - sinus venosus
Red, red - subcardinal veins
(Mesenteric segment)
Internal iliac
Adapted from Hopper, A.F. and N.H. Hart, Foundations of animal development. Oxford University press. New York, p. 434

25. These figures present a ventral view
Green - anterior cardinal veins
Yellow - vitelline veins
Orange - supracardinal veins
Purple - common cardinal veins
Blue, blue - posterior cardinal veins
Olive - sinus venosus
Red, red - subcardinal veins
Adapted from Hopper, A.F. and N.H. Hart, Foundations of animal development. Oxford University press. New York, p. 434

26. portion between the right subclavian and the left brachiocephalic vein forms the right brachiocephalic (innominate) vein.

28. (brachiocephalic) anterior cardinal veins
Common cardinal vein
(brachiocephalic)

29. anterior cardinal
veins
Common cardinal vein
(brachiocephalic)

32. These figures present a ventral view
Right
Left
Right
Left
Right
Left
Right vitelline
vein
These figures present a ventral view
Green - anterior cardinal vein
Purple - common cardinal veins
Future Inferior vena cava
Blue - posterior cardinal veins
Brown - sinus venosus
Orange - umbilical veins
Red - right vitelline vein
Yellow - left vitelline vein
Right
Left
Red/yellow speckles - anastomoses between right and left vitelline veins
Adapted from Hopper, A.F. and N.H. Hart, Foundations of animal development. Oxford University press. New York, p. 431

33. Ductus venosus:
Present at birth, but looses functionality within minutes.
Structurally closed 3-7 days after birth
Leaves a fibrous remnant in the liver called the ligamentum venosum

34. Pulmonary venous system
The pulmonary veins are not derived from pre-existing embryonic veins.
They form de novo as the lungs develop and drain the capillary beds of the lung tissue into the left atrium.
Initially this drainage is via a single trunk; however, as the embryo develops, this trunk is incorporated into the wall of the left atrium.
By 8-9 weeks, this results in the 4 pulmonary veins that originally connected to the common trunk, emptying separately into the left atrium.

35. Umbilical Arteries
Develop as branches off the posterior dorsal aorta that extend along the allantoic stalk out to the placenta.
Umbilical Veins
As the placental circulation develops, two umbilical veins initially return blood from the placenta to the sinus venosus.
As development continues, the right umbilical vein degenerates and the placental blood ends up being returned to the heart by the left umbilical vein via the ductus venosus.
This blood flow ceases at birth when the umbilical cord is cut.
Subsequently, the lumen within the left umbilical vein is obliterated by cell growth from the walls and the remnant of this vessel becomes the round ligament of the liver.