HOME > 11.5 - Specialized Circulatory Structures

11.5 - Specialized Circulatory Structures

The fetal circulation and brain circulation are both specialized to move blood in different ways than most of the adult circulatory system.

Brain circulation

The body cannot survive without the brain receiving enough oxygen and nutrients from the arterial blood. The circle of Willis is a circular structure that allows the arterial blood from multiple blood vessels to flow together. This allows the blood to continue to reach all parts of the brain even if one of the blood vessels becomes blocked.

The circle of Willis connects connects arterial blood flow from the following arteries together:

• anterior cerebral artery
• internal carotid artery
• cerebral arteries
• communicating arteries

Jimhutchins at the English language Wikipedia [GFDL (www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Fetal circulation

The fetal circulation is very different from the adult circulation because the fetus has very different physiological requirements while it is in the womb:

• The fetus does not have fully developed organs with the ability to take in its own oxygen and nutrients.
• The blood of the mother must be kept separate from that of the developing fetus so that any pathogens and immune system components in the mother's blood do not attack the fetus
• The lungs of the fetus are not working to supply oxygen, but instead only consume oxygen and nutrients to grow

Several specialized fetal circulation structures fulfill these requirements and disappear shortly after birth:

Umbilical vein

• Carries highly oxygenated blood from the placenta to the liver

Ductus venosus

• Shunts about half of the highly oxygenated blood from the umbilical vein to the inferior vena cava

Foramen ovale

• A hole between the right and left atria that allows some of the oxygenated blood to flow directly from the right atrium to the left atrium so that more oxygenated blood reaches the systemic circuit

Ductus arteriosus

• Shunts some of the oxygenated blood from the pulmonary trunk to the aorta so that more oxygenated blood reaches the systemic circuit

Umbilical artery

• Carries blood with a low oxygen content from the abdominal aorta to the placenta

There are also some notable differences in structures that are present in adults:

Pulmonary arteries and veins

• The pulmonary arteries carry oxygenated blood coming from the placenta and the pulmonary veins carry deoxygenated blood that has been stripped of its oxygen and nutrients by the develping lung tissue

Aorta

• Carries only moderately oxygenated blood, since the highly oxygenated blood from the placenta mixes with the deoxygenated blood from the systemic and pulmonary circuits before leaving the heart

Inferior vena cava

• Carries moderately oxygenated blood since the deoxygenated blood from the inferior parts of the body mixes with the highly oxygenated blood from the ductus venosus before the inferior vena cava reaches the heart

 

Modified from "Circulation of a fetus" of Grey's Anatomy, obtained from the Wikimedia Commons

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