Figure 1029

Transformation of the spiral arteries. A, The process by which the maternal spiral arteries are transformed into dilated vessels in pregnancy is believed to involve invasion of the spiral arterial walls by endovascular trophoblastic cells. These cells migrate in retrograde fashion, involving first the decidual and then the myometrial segments of the arteries and then causing considerable disruption at all layers of the vessel wall. The mechanisms involved in this complex process are only beginning to be elucidated. These mechanisms involve alterations in the adhesion molecules of the invading trophoblast cells, such that they acquire an invasive phenotype and mimic vascular endothelial cells [26].

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FIGURE 10-29 (Continued)

Myometrium

Myometrium

FIGURE 10-29 (Continued)

B, In women destined to develop preeclampsia, trophoblastic invasion of the spiral arteries is incomplete; it may occur in the decid-ual but not the myometrial segments of the artery, and in some vessels the process does not occur at all. The arteries, therefore, remain thick-walled and muscular, the diameters in the myometrial segments being half those measured during normal pregnancy. Recently, it has been reported that in preeclampsia the invading cytotrophoblasts fail to properly express adhesion receptors necessary for normal remodeling of the maternal spiral arteries [27]. This failure of cytotrophoblast invasion of the spiral arteries is considered to be the morphologic basis for decreased placental perfusion in preeclampsia. (a)—fully modified regions. (b)—partially modified vessel segments. (c)—unmodified vessel segments in the myometrium. AV-anchoring villus; CTBs—cytotrophoblast cells; FV—floating villi. (From Zhou and coworkers [27]; with permission.)

Lipid peroxides Cytokines

Placental ischemia

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