Talk:Basic - Vascular Heart Connections

From Embryology

--Mark Hill 13:16, 28 October 2009 (EST) OK you need to say something about the fetal oxygen levels in blood as it is different from maternal and the arterial/venous difference is much less. In addition, the requirement of a different haemoglobin.

Surely we could provide an animation to show the passage of blood throughout the embryo either here or in the more detailed modules.

--Phoebe Norville 10:56, 29 September 2009 (EST) Content added

Some understanding of the vascular system of an embryo is useful in fully understanding cardiac development. In the primitive heart tube section it was stated that the blood islands dispersed throughout the embryo form the early blood vessels. The islands coalesce to form vessels and these expand and continue to develop, forming vascular networks. The vascular system can be thought of in terms of arteries and veins and the major embryonic vessels can be seen in the diagram on the right.

Development of Veins

We already learnt that blood travels through the embryonic heart from the sinus venosus. There are three paired veins which form to drain into the sinus venosus:

  • Vitelline veins: return poorly oxygenated blood from the yolk sac
  • Umbilical veins: carry well-oxygenated blood from the primordial placenta
  • Common cardinal veins: return poorly oxygenated blood from the body of the embryo

The sinus venosus soon shifts to the right to be incorporated into the right atrium as there is a shift in the venous system from the left to the right side of the embryo. The inferior vena cava and superior vena cava form and drain into the sinus venosus. In the left atrium, the four pulmonary veins form, which will return oxygenated blood from the lungs.

Development of Arteries

We saw in the fusion animation that the dorsal aortae develop at the same time as the early heart tubes. These connect to the heart tubes prior to fusion via the first aortic arch arteries. Other arches develop which go on to form the arteries of the head and neck. We also saw previously the way in which the aorta and pulmonary trunk form. The dorsal aorta gives of branches which supply blood to the rest of the embryo:

  • Gut (ventral/front) branches
  • Lateral (side) branches
  • Intersegmental arteries

Foetal Circulation

As the embryo progresses to a foetus, the vasculature is still remarkably different to that of the adult. This is mainly due to the presence of three shunts:

  • The foramen ovale: (seen previously) blood travels from the right atrium to the left atrium
  • The ductus venosus: blood from the umbilical vein bypasses the liver to enter the inferior vena cava
  • The ductus arteriosus: blood passes from the pulmonary trunk into the aorta

These shunts allow blood to bypass the lungs, liver and kidneys, whose functions are performed by the placenta while in utero.

The following diagram shows the movement of blood throughout the foetal circulation. The main flow of blood is as follows:

Placenta → umbilical vein → ductus venosus → inferior vena cava → right atrium → foramen ovale → left atrium → left ventricle → aorta → hypogastric arteries → umbilical arteries → placenta.

Blood that passes from the right atrium to the right ventricle travels:

Right ventricle → pulmonary trunk → ductus arteriosus → aorta