Vascular Embryology: Development of all the human veins and arteries
Formation of the Vasculature
- vascular system begins early
- it would be good for it to function early since the embryo is getting too large to depend only on diffusion for nutrients
- should see a primitive heart beat between 18-21 days–(this is before folding)
- The whole circulatory system is one way
- cardiac tubes work in peristaltic action
- in anterior end -> out posterior end
- venous blood in
- common cardinals carry blood from developing body
- umbilical veins carry blood from placenta
- vitelline veins carry blood from the gut
Blood vessel formation dates to day 17 in splanchnopleuric mesoderm of the yolk sac
Veins
- At about 3 weeks of age, you see blood islands in the yolk sac
- vasculature-angiogenesis is the formation of the vessels
- hematopoiesis is formation of the blood
- Out in the yolk sac, you see the islands of Wolff and Pander
- these islands have core hemoblasts(presumptive blood cells) and an epithelial covering that becomes vascular
- formation of vessels and blood is related-but in the embryonic disc, vessel formation is separate from blood formation
- Angioblasts form cysts, then cords-cords lengthen and spread through the embryo in plexuses
- In blood island there’s epithelial covering, there’s also cysts that develop
- within the cyst, there are cells that become blood cells
- cysts grow and connect with each other and become the vessels
- externally, the blood vessel and blood cells develop separate from each other
- Blood producing organs probably receive their original stem cells from the yolk sac
- there ain’t an interrelation between the embryo and the fetus
- formation of blood is not going on in the organs
- it has to start in the yolk sac-hematopoeitic cells of yolk sac are derived from EPIBLAST
- there is a hematopoietic center that starts in the liver, then goes to the spleen, then goes to bone marrow
Hematopoietic center- liver first, then spleen, then bone marrow
- hematopoiesis-shifts from liver, to spleen, lymph nodes, to bone marrow-main point, the liver may not be a hematopoietic organ at term
- blood islands are important b/c they begin the formation of blood and vessels
- heart has to take blood coming from posterior and pump it out of anterior end-so anything coming in posterior is the vein, and anything going out anterior is artery
- umbilical circulation has to be fused into system, then eliminated
- blood coming from the gut is the vitelline circulation-vitelline veins
- systemic veins-the anterior and posterior cardinal veins-these unite to form the common cardinal
- common cardinal come on either side of the heart-they receive the umbilical and vitelline veins on each side
- this forms a two pumping station heart
1) Ventral Aorta-goes to a series of aortic arches which go to a dorsal aorta
2) Dorsal Aorta-two come together to form one, from which arise systemic arteries
Pumping Heart System
- sending blood out anterior to a series of aortic arches
- You can separate the formation of one venous system from another
- Vitelline veins become connected both anterior and posterior to the gut by connections-picture in Larson
- Liver invades channels formed by these vitelline veins
- pathway goes from anterior to posterior so that ventrally, the hepatic portal vein goes from anterior to the gut to posterior to the gut
- IT TAKES BOTH VITELLINE VEINS TO FORM THE HEPATIC PORTAL VEIN
- The vitelline veins are interconnected on either side of the gut-this allows the formation of the hepatic portal vein and the portal circulation
- Hepatic portal vein develops in three segments: a portion proximal to the liver, an intermediate portion and a distal portion adjacent to the gut
- Proximal and distal portions are derived from the right vitelline vein
- Intermediate portions derive from interconnections b/t the right and left vitelline veins and a portion of the left vitelline vein
Umbilical veins
- at term, there is only one dominant umbilical vein-the LEFT Umbilical Vein is dominant
- the liver is developing on the right side-this starts to obliterate the connection of the right umbilical vein with the common cardinal venous system-thus the left predominates-but there is a bypass that persists through the liver-the ductus venosus
- ductus venosus shunts blood through liver to the inferior vena cava
- the umbilical vein is connected through the substance of the liver to the hepatic vein, via the ductus venosus
- benefit-if you want to get oxygen rich blood you want it not to go through the liver-this a blood flow phenomenon(speeds up flow to heart)-this channel remains open until after birth and closes as the left umbilical vein regresses
- left umbilical vein predominates and the ductus venosus gets blood back to heart without having it percolate through the liver
Heart Pulling in blood from its venous end
- blood coming in anteriorly and posteriorly
- common cardinal vein has anterior and posterior cardinal veins coming into it
- there is not enough blood drainage by the cardinals to offer drainage to all of the developing body, so a subcardinal venous system develops-”sub” because it is ventral, or below, the cardinal venous system-they are actually anterior to the posterior cardinals
- also, there’s a supra-cardinal venous system that connect across the midline to the cardinal system-the posterior cardinal veins lose continuity such that circulation is taken up by subcardinal veins
- this is the beginning of formation of the inferior vena cava-takes vitelline, subcardinal, supra-cardinal, and posterior cardinal veins
INFERIOR VENA CAVA-includes vitelline, supra-cardinal, subcardinal, and posterior cardinal, and the anastomosis between all of these-the connection between sub- and supra-cardinals
Superior Vena Cava-shunt develops from left anterior cardinal vein and right anterior cardinal vein; drainage is to the right side rather than to the left. This asymmetry continues in the longer more horizontally positioned left brachiocephalic vein. The superior vena cava is formed from right anterior cardinal vein and a portion of the right common cardinal vein
Superior Vena Cava = right anterior cardinal and portion of right common cardinal
- anterior cardinals were originally separated-but a connection grows from the left to the right anterior cardinal so that you form the brachiocephalic-this is why the left brachiocephalic vein is longer than the right(in adult)
- the brachiocephalic enters into the anterior cardinal system-there’s a bypass from the left to right that brings a connection at the base of the neck-note, the connection becomes the brachiocephalic-it’s the innominate trunk
Azygos Venous system-DERIVED FROM SUPRACARDINAL VENOUS SYSTEM
- formed by remaining portions of the supra-cardinal veins within the vein
Azygos-supra-cardinals
- since the supracardinals were at one time connected to both the anterior and posterior cardinals, there is a lot of room for variation
- there can be the absence of a vena cava
- supracardinal venous system loses connection to the left cardinal venous system and maintains communication to the right side where it enters into the mature superior vena cava
From Larson-showing the formation of right and left brachiocephalic veins
- the remnants of the left cardinal vein include the coronary sinus and the oblique vein of the left atrium (Marshall)
Posterior to the Heart
- the enlarged common cardinals receive from the vitelline and the umbilical veins to form large extensions, horns of sinus venosus, that enter the primitive right atrium-there is a right and left horn of the sinus venosus
- with the development of the inferior vena cava there is a right side bias
- the right side develops in the right side of heart
Variations
- if the connection between the anterior cardinal veins does not proceed as it supposed to, it leaves dominant anterior cardinal veins that will encircle around the left atrium-end up with left and right anterior cardinal vein and thus a double superior vena cava
Lymphatic system
- begins as an outgrowth from the venous system
- early in development of venous system, 6 sacs develop in close association with the venous system
- 2 jugular sacs
- 2 iliac sacs
- 1 retroperitoneal sac
- 1 cisterna chyli
- it has bilateral symmetry-throughout term, this bilateral symmetry is lost
- at the junction of the jugular and the subclavian veins there are jugular lymph sacs
- there’s retroperitoneal sac
- there are two iliac sacs-or posterior lymph sacs
- if you draw a line down middle of head and neck through the diaphragm
- see two main lymph trunks
1) smaller one-drains the upper right quadrant
2) larger-drains left upper quadrant and all the rest of the body
- there is a shift from the right side to the left side somewhere above the cisterna chyl
- it is bilateral below the chyl
- thoracic duct goes up from the cisterna chyl to the upper right and left lymph sacs
- the thoracic duct passes from the right to left side of the esophagus(in adult)
Arteries
- intimately connected with the heart formation
- ventral aorta forms out of the heart to flow out to aortic arches
- the aortic arches converge with the ventral arch to form back into the dorsal aorta
- ventral aorta are ventral to the gut and the pharynx
- the dorsal aorta is posterior
- the aortic arches are to the sides of the foregut and pharynx
- ventral aorta has a cranial dilation, the aortic sac-from the sac and ventral aorta a series of paired right and left aortic arches connect to paired dorsal aortae which are fused into a single dorsal aorta caudal to the last pair of arches
- brachiocephalic-forms from truncus and aortic sac
- left subclavian-from 7th intersegmental artery, a branch of the left dorsal aorta distal to the last arch
- right subclavian-from the right 4th arch, dorsal aorta, and right 7th intersegmental artery
- common carotids-right and left 3rd arches
- internal carotids-right and left 3rd arches and dorsal aortae
- Pulmonary trunk-truncus arteriosus, left 6th aortic arch-the ductus arteriosus is from the left 6th aortic arch
- Pulmonary arteries-proximal right and left 6th arches and outgrowths from them
- Aorta-aortic sac, left 4th arch and left dorsal aorta
Tags: azygous supracardinals, azygous vein, blood islands, cardinal vein, ductus venosus, hematopoietic center, hepatic portal vein, inferior vena cava, splanchnopleuric mesoderm, superior vena cava, vitelline veins, yolk sac
