Editing Circulatory system (section)

==Development==
{{Main|Heart development|Vasculogenesis|Vascular remodelling in the embryo|Fetal circulation}}
The development of the circulatory system starts with [[vasculogenesis]] in the [[embryo]]. The human arterial and venous systems develop from different areas in the embryo. The arterial system develops mainly from the [[aortic arches]], six pairs of arches that develop on the upper part of the embryo. The venous system arises from three bilateral veins during weeks 4&nbsp;– 8 of [[Human embryogenesis|embryogenesis]]. [[Fetal circulation]] begins within the 8th week of development. Fetal circulation does not include the lungs, which are bypassed via the [[truncus arteriosus]]. Before birth the [[fetus]] obtains [[oxygen]] (and [[nutrient]]s) from the mother through the [[placenta]] and the [[umbilical cord]].<ref name="Whitaker">{{cite book |last=Whitaker |first=Kent |chapter=Fetal Circulation |chapter-url=https://books.google.com/books?id=R3WK8XyAHYgC&pg=PA18 |title=Comprehensive Perinatal and Pediatric Respiratory Care |publisher=Delmar Thomson Learning |year=2001 |isbn=978-0-7668-1373-1 |pages=18–20 }}{{Dead link|date=August 2021 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

===Arteries===
{{Main|Aortic arches}}
[[File:Erytrocyte deoxy to oxy v0.7.gif|thumb|Animation of a typical human red blood cell cycle in the circulatory system. This animation occurs at a faster rate (~20 seconds of the average [[Red blood cell#Human|60-second cycle]]) and shows the red blood cell deforming as it enters capillaries, as well as the bars changing color as the cell alternates in states of oxygenation along the circulatory system.]]

The human arterial system originates from the [[aortic arches]] and from the [[dorsal aortae]] starting from week 4 of embryonic life. The first and second aortic arches regress and form only the [[Maxillary artery|maxillary arteries]] and [[Stapedial artery|stapedial arteries]] respectively. The arterial system itself arises from aortic arches 3, 4 and 6 (aortic arch 5 completely regresses).

The dorsal aortae, present on the [[:wikt:dorsal|dorsal]] side of the embryo, are initially present on both sides of the embryo. They later fuse to form the basis for the aorta itself. Approximately thirty smaller arteries branch from this at the back and sides. These branches form the [[intercostal arteries]], arteries of the arms and legs, lumbar arteries and the lateral sacral arteries. Branches to the sides of the aorta will form the definitive [[Renal artery|renal]], [[Inferior suprarenal artery|suprarenal]] and [[Gonadal artery|gonadal arteries]]. Finally, branches at the front of the aorta consist of the [[vitelline arteries]] and [[umbilical arteries]]. The vitelline arteries form the [[Celiac artery|celiac]], [[Superior mesenteric artery|superior]] and [[Inferior mesenteric artery|inferior mesenteric arteries]] of the gastrointestinal tract. After birth, the umbilical arteries will form the [[Internal iliac artery|internal iliac arteries]].

===Veins===
{{Further|Vasculogenesis}}
The human venous system develops mainly from the [[vitelline vein]]s, the [[umbilical vein]]s and the [[Posterior cardinal vein|cardinal veins]], all of which empty into the [[sinus venosus]].