Page 27, Early Development, Devel. Physiol., Dr. D. Penney

Maternal Blood Pressure and Vascular Resistance:

In the maternal circulation arterial blood pressure is at adult values of near 100 mmHg through the aorta, the uterine arteries, and into the spiral arteries (Figure 2.16).

It is in the latter vessels that a large pressure drop is encountered as blood spurts from them very energetically into the maternal blood pool. As in an electrical circuit with a large voltage drop, this indicates a site of very high resistance. The spurting blood serves the very important function of stirring the blood bathing the fetal villi, enhancing gaseous diffusion.

Blood pressure in the intervillous space is about 10 mmHg.

Remarkably the embryonic heart develops along with other organs of the body, but unlike many, almost from the first it serves the vital function of circulating the blood.

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