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.
