Table 2.

Milestones in coronary vessel formation and development. S, Carnegie Stage.

S15 Blood islands, capillaries and epicardium are present

S17–18 Subepicardial expansion at AV groove contains capillaries, mesenchymal cells and erythroblasts, which invade the aortic wall to form coronary ostia; primitive coronary plexus connects with sinus venosus sprouts

S19 Both coronary ostia and stems are present; smooth muscle recruitment occurs in the proximal portions of coronary artery stems

S22–23 Tunica media formation in coronary artery branches; nerves with associated chromaffin (ganglionic) cells invade region around the aortic base: onset of lymphatic development

9–12 weeks Formation of tunica media in large veins and small arteries

16 weeks Transmural arteries and arterioles are well-developed; epicardial vessel density is increased

26–30 weeks Elastic fibers added to main coronary arteries; the thickness of the adventitia is greatly increased