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==Introduction==

==Introduction==

Blood vessel formation is a combination of the following three processes:

Blood vessel formation is a combination of the following three processes:

The volume and pressure of blood flowing in the network dictates the degree of development of individual vessels. The channels which carry blood at high pressure develop additional tissue layers from the surrounding mesoderm thereby becoming thick-walled. The diameter of these vessels also increases and they become known as arteries. Differentiation of mesenchymal cells to smooth muscle is driven by growth factors released from endothelial cells.

The volume and pressure of blood flowing in the network dictates the degree of development of individual vessels. The channels which carry blood at high pressure develop additional tissue layers from the surrounding mesoderm thereby becoming thick-walled. The diameter of these vessels also increases and they become known as arteries. Differentiation of mesenchymal cells to smooth muscle is driven by growth factors released from endothelial cells.

==Fate of the Aortic Arches==

==Fate of the [[Aortic Arches - Anatomy & Physiology|Aortic Arches]]==

The primitive heart is a simple tube with one inlet and one outlet and empties into embryonic structures called aortic arches. These are organised along the same lines as the blood vessels supplying the gills of fish. Most vertebrate embryos have six aortic arches but in the majority of mammals the fifth arch does not develop. Ultimately, some of the arches are remodelled whereas others atrophy. Not all of the arches are present simultaneously; the first and second develop before the fourth and sixth and by the time the sixth pair of arteries have formed, very little of the first two pairs remains. Major changes to the aortic arches occur between the third and fourth week of gestation in dogs and between the third and seventh week in horses.

The primitive heart is a simple tube with one inlet and one outlet and empties into embryonic structures called aortic arches. These are organised along the same lines as the blood vessels supplying the gills of fish. Most vertebrate embryos have six aortic arches but in the majority of mammals the fifth arch does not develop. Ultimately, some of the arches are remodelled whereas others atrophy. Not all of the arches are present simultaneously; the first and second develop before the fourth and sixth and by the time the sixth pair of arteries have formed, very little of the first two pairs remains. Major changes to the aortic arches occur between the third and fourth week of gestation in dogs and between the third and seventh week in horses.

The first pair of aortic arch arteries atrophy and only remnants of the second pair persist as the stapedial arteries supplying the middle ear. The common, external and internal carotid arteries are all derived from the third aortic arch. The left fourth aortic arch contributes to the arch of the aorta and the right fourth aortic arch forms the proximal region of the right subclavian artery. The development of the sixth aortic arch arteries is complex with the proximal section of the left arch forming the proximal part of the left pulmonary artery and the distal region fashioning the ductus arteriosus. The proximal section of the right sixth aortic artery persists as the proximal region of the right pulmonary artery and the distal part atrophies.

The first pair of aortic arch arteries atrophy and only remnants of the second pair persist as the stapedial arteries supplying the middle ear. The common, external and internal carotid arteries are all derived from the third aortic arch. The left fourth aortic arch contributes to the arch of the aorta and the right fourth aortic arch forms the proximal region of the right subclavian artery. The development of the sixth aortic arch arteries is complex with the proximal section of the left arch forming the proximal part of the left pulmonary artery and the distal region fashioning the ductus arteriosus. The proximal section of the right sixth aortic artery persists as the proximal region of the right pulmonary artery and the distal part atrophies.

 

[[Category:Cardiovascular System]]

[[Category:Vascular System - Anatomy & Physiology]]

[[Category:Cardiology Section]]