test 3 Flashcards
Vascular Development occurs in what two mechanisms
Vasculogenesis
- making of new blood vessels
Angiogenesis
- vessels sprout from existing vessels
3 weeks of development
1st blood islands appear in mesoderm
Surrounding wall of yolk sac
Arise from mesoderm cells
Induced for form hemangioblasts
Precursor to vessels and blood formation
Hematopoietic stem cells
Come from mesoderm surrounding aorta near kidney
Colonize liver (source of first blood cells
Becomes hematopoietic organ of the embryo and fetus
2-7 months gestation
Stem cells from liver colonize bone marrow (@ 7th month bones start to form)
Liver loses RBC making function.
Major vessels (Dorsal aorta, cardinal vein) for via
Form via Vasculogensis
- making of new blood vessels
Remainder of vascular system other than the major vessels form via
Angiogensis
Sprout off existing blood vessels
The major arterial conduits in the early embryo
dorsal aortas
Simply a continuation of the endocardial tubes.
Arise from the Aortic Sac (Distal most part of the truncus arteriosus)
Cranial portions of the Dorsal aortas become
first pair of aortic
arches.
How many aortic arch systems are there
There are six pairs of aortic arches present at some point during development, but the 5th aortic arch is only transient.
5th Aortic Arch never forms or forms incompletely and regresses
Arches are numbered I, II, III, IV, and VI
As they develop, some become modified and other regress
3 mm Embryo
- The first pair of arches is large
- Second pair is just forming
- All the other arches develop from the region of the aortic sac.
- Distally (not shown here), the dorsal aortas fuse to form a single vessel.
4 mm Embryo – Day 27
- Aortic arch I has largely disappeared
* Part of it remains - becomes the Maxillary Artery. (goes to the front of your face) - Aortic arch II is regressing.
* Remnants of arch II – becomes the Stapedial Artery. (to your ear) - Aortic arch III is already large and well developed.
- Aortic arches IV and VI are being formed as ventral and dorsal sprouts.
* aortic arch VI already has a sprouting branch of the primitive pulmonary artery
10mm Embryo – Day 29
- The first two aortic arches have disappeared
- Aortic arches III, IV, and VI are quite large.
- The truncoaortic sac has been divided
* Arch VI is now continuous with the pulmonary trunk. - Starting to lose symmetry
- The intersegmental arteries will be important in the formation of the subclavian arteries.
14mm Embryo
- The symmetrical pattern is largely gone.
- There is further division of the aorta and pulmonary artery.
- Arch III forms the common carotid artery and first part of the internal carotid artery
- Arch IV stays on each side but becomes different structures.
- Left Arch IV – part of Aortic arch between LCC and L. Subclavian
- Right Arch IV – Proximal R. Subclavian
- Intersegmental arteries have migrated upward to become the subclavian arteries.
- **Remember the Arch V never forms
- Arch VI (aka. Pulmonary Arch)
* Gives off branches that grows toward the developing lung buds
* The dorsal portion of the right arch VI has disappeared and the left arch VI will become the ductus arteriosus.
17mm Embryo
- A portion of the vessel that was formerly the right dorsal aorta disappears.
- Proximal portion persists and becomes the right subclavian artery.
At Birth
- At birth, the distal part of the left sixth aortic arch (the ductus arteriosus) normally obliterates
* ligamentum arteriosum. - The adult aortic arch system is now established.
Sinus Venosus
- The sinus venosus is the major point of entry into the common atria.
* Remains paired until the embryo is 4mm
* Even after the endocardial tubes fuse.
In a 4 mm embryo, there is a
distinguishable (venous)
- Central (unpaired) portion,
- Transverse portion
- Right and left sinus horns.
Mid 4th week (venous)
Sinus venosus receives blood from the right and left sinus horns.
Each horn receives blood from 3 veins
Vitelline vein
Umbilical vein
Common Cardinal vein
Communication between sinus and atrium is wide open
Communication will eventually shift to the right
Caused by shift in blood in venous system
Occurs at about 4-5 weeks.
5th week (venous)
Obliteration of the right umbilical vein and left vitelline vein
Left sinus horn loses importance
week 10 (venous)
Left common cardinal vein become obliterated
All that remains of the left sinus horn is the oblique vein of the left atrium and the coronary sinus.
Right Sinus horn
Shunt of blood left to right enlarges right sinus horn
Right horn and vein are the only communication between the original sinus venosus and the atrium
Forms the smooth walled part of the right atrium.
Sinuatrial valves
Sinuatrial orifice (entrance to the common atrium) is flanked on each side by valvular folds.
Right and left venous valves
Left venous valve fuses with the atrial septum
Superior part of the right venous valve disappears
Inferior part of the right venous valve becomes the valve of the inferior vena cava and the valve of the coronary sinus.
- held direct the flow
The sinus venosus receives three pairs of veins
• Vitelline veins
• Carry blood from the yolk sac to the sinus venosus
- provides nutrients for the embryo
• Umbilical veins
• Goes to the placenta and gets blood to embryo
• Common cardinal veins
• Drain the body of the embryo
Vitelline venous system
- Enters the sinus venosus
* Gives rise to the hepatic veins
Umbilical venous system
- Enter the sinus venosus lateral to the vitelline veins.
* Persists as the umbilical vein in the term fetus.
Cardinal venous system
- Enters the sinus venosus lateral/superior to the umbilical veins
- Forms a large complex network of veins throughout the body.
Embryonic Venous Systems – 10mm Embryo
- Left vitelline vein has disappeared
- Right Vitelline vein is transforming into a structure that will eventually be the hepatic veins and all of the veins of the hepatic portal system.
- The left umbilical vein has joined the hepatic system.
* The left umbilical vein will persist in the fetus as the umbilical vein. - Inferior portion of the cardinal venous system is gaining complexity.
* The left side and right side are migrating inward and joining. - Right umbilical vein turns into the subcardinohepatic anastomosis
Embryonic Venous Systems – 14mm Embryo
- The left sinus horn has separated from the right
* Will eventually become the coronary sinus. - The right side of the subcardinal venous system is developing into the principle venous channels to the heart from the lower body.
Embryonic Venous Systems – 17mm Embryo
- The upper limbs are now drained by veins which empty into the anterior cardinal veins.
- The major portions of the posterior cardinal veins have disappeared
* There is even greater demand on the right subcardinal vein.
Embryonic Venous Systems – 24mm Embryo
- The anterior cardinal veins now have a channel between them (the left brachiocephalic vein).
* These cardinal veins will drain the entire head and upper extremities. - The subcardinal veins have completely fused
* Make up a large portion of what will become the inferior vena cava. - There are now clear venous channels to the kidneys and adrenal glands.
Embryonic Venous Systems – Term Embryo
- Further development leads to the complete venous system.
- Notice that the umbilical vein still persists and enters the portal vein.
- Notice the ductus venosus.
