DEVELOPMENT OF THE CIRCULATORY SYSTEM and the structures

DEVELOPMENT OF THE CIRCULATORY SYSTEM and the structures that carry it

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

(primitive blood cells and blood stem cells)

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

B. Evidence suggests there are two different sources for blood stem cells. 1. Initially from the extraembryonic splanchnic mesoderm of the yolk sac, and then migrate into the embryo. 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).

IV. Circulatory system in mammals A. Basic circulatory loop arterioles arteries capillaries ventricle venules atrium veins There are 3 major arcs (or loops) associated with the developing embryo. 1. Embryonic, 2. Vitelline (yolk sac), 3. Allantoic

B. Basic adult mammalian circulation

C. Early embryonic circulation

D. How is the adult circulatory pattern established?

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, for example, fish and mammals are 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 such that they meet the needs of the adult.

Conversion of the early embryonic circulatory system to the adult configuration. Involves: A. Degeneration of some embryonic vessels or of parts of embryonic vessels. B. Hypertrophy of parts of some vessels. C. Anastomosis (fusion) of some vessels. D. Separations of single embryonic vessels into two. E. Loss of connection between some vessels and in some cases reconnection somewhere else. F. Formation of new vessels.

Views from the ventral side of the animal Right Left From Carlson, B. M. 1996. Patten’s Foundations of Embryology. Mc. Graw-Hill, Inc. New York. 6 th edition. p. 618

Right Left

human in the embryo Right Left

trunkus truncus 4 4 th us brachiocephalic artery and pulmonary trunkus truncus systemic trunk and ascending aorta The conotruncus Fate of the Truncus Arteriosus Contributes to the systemic trunk and a portion of the pulmonary trunk. Conus Divided into the bases of the pulmonary and systemic trunks

green - dorsal aortic roots purple - 3 rd aortic arches red - 4 th aortic arches Modified from Carlson, B. M. 1996. Patten’s Foundations of Embryology. Mc. Graw-Hill, Inc. New York. 6 th edition. p. 618 black - ventral aortic roots and trunkus arteriosus orange - 6 th aortic arches yellow - conotruncus blue - intersegmental arteries These figures present a ventral view

Adult vessels Right Left Color indicates embryonic derivation green - dorsal aortic roots purple - 3 rd aortic arches red - 4 th aortic arches Brachiocephalic artery black - ventral aortic roots and trunkus orange - 6 th aortic arches yellow - conotruncus blue - intersegmental arteries Vertebral artery Subclavian artery These figures present a ventral view Modified from Carlson, B. M. 1996. Patten’s Foundations of Embryology. Mc. Graw-Hill, Inc. New York. 6 th edition. p. 618

Venous Circulation Four Major Systems 1. Systemic (other than hepatic) 2. Hepatic 3. Pulmonary 4. Placental (Umbilical)

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 and in some cases reconnection to another vessel. E. Formation of new vessels.

Posterior Systemic circulation Formation of the inferior vena cava anterior posterior Adapted from Hopper, A. F. and N. H. Hart, 1985. Foundations of animal development. Oxford University press. New York, p. 434

Components of the inferior vena cava

These figures present a ventral view Green - anterior cardinal veins Yellow - vitelline veins Purple - common cardinal veins Blue, blue - posterior cardinal veins Olive - sinus venosus Red, red - subcardinal veins Orange - supracardinal veins Hepatic segment Mesenteric segment Renal segment Sub-/Supra-cardinal anastomosis Adapted from Hopper, A. F. and N. H. Hart, 1985. Foundations of animal development. Oxford University press. New York, p. 434

These figures present a ventral view Green - anterior cardinal veins Yellow - vitelline veins Purple - common cardinal veins Blue, blue - posterior cardinal veins Olive - sinus venosus Red, red - subcardinal veins Orange - supracardinal veins (Mesenteric segment) Internal iliac Adapted from Hopper, A. F. and N. H. Hart, 1985. Foundations of animal development. Oxford University press. New York, p. 434

These figures present a ventral view Green - anterior cardinal veins Yellow - vitelline veins Purple - common cardinal veins Blue, blue - posterior cardinal veins Olive - sinus venosus Red, red - subcardinal veins Orange - supracardinal veins Adapted from Hopper, A. F. and N. H. Hart, 1985. Foundations of animal development. Oxford University press. New York, p. 434

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

Right Left http: //education. yahoo. com/reference/gray/subjects/subject? id=135

(brachiocephalic) anterior cardinal veins Common cardinal vein Right Left Right http: //education. yahoo. com/reference/gray/subjects/subject? id=135 Left

(brachiocephalic) anterior cardinal veins Common cardinal vein Right Left

Right brachiocephalic Left

Right Left Right vitelline vein These figures present a ventral view Green - anterior cardinal vein Purple - common cardinal veins Blue - posterior cardinal veins Future Inferior vena cava Brown - sinus venosus Orange - umbilical veins Red - right vitelline vein Yellow - left vitelline vein Red/yellow speckles - anastomoses between right and left vitelline veins Right Left Adapted from Hopper, A. F. and N. H. Hart, 1985. Foundations of animal development. Oxford University press. New York, p. 431

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

Pulmonary venous system The 4 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 the 4 pulmonary veins connect to a single trunk that connects to the left atrium; 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.

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 within the embryo 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 ligamentum teres hepatis = round ligament of the liver.