Essential anatomy and physiology in maternity care

Thus at the center of each maternal vascular unit there is 1 artery that terminates in a thin-walled sac, but there are numerous maternal veins that open through the basal plate at random. As the chorionic plate is pushed away from the basal plate, the anchoring villi pull the maternal basal plate up into septa (columns of fibrous tissue that virtually surround the major cotyledons). The remaining 24вЂ“45 tapped arterioles form minor vascular units that become crowded between the larger units. The pulsatile arterial pressure of blood that spurts from each of these major vessels pushes the chorionic plate away from the decidua to form 12вЂ“15 вЂњtents,вЂќ or maternal cotyledons. An occasional maternal artery then opens, and a sluggish circulation is established (hematotropic phase of the embryo).ДЄt approximately 40 days after conception, the trophoblast has invaded approximately 40вЂ“60 spiral arterioles, of which 12вЂ“15 may be called major arteries. These lacunae fill with maternal blood by reflux from previously tapped veins. Maternal capillaries and venules are tapped by the invading fetal tissue to cause extravasation of maternal blood and the formation of small lakes (lacunae), the forerunners of the intervillous space. Thus the syncytial layer becomes the front line of the invading fetal tissue. Next, these transitional cells fuse, lose their individual membranes, and form the multinucleated syncytiotrophoblast. As the cytotrophoblasts ( Langhans' cells) divide and proliferate, they form transitional cells that are the likely source of hCG. Within a few hours after implantation, the trophoblast invades the endometrium and begins to produce human chorionic gonadotropin ( hCG), which is thought to be important in converting the normal corpus luteum into the corpus luteum of pregnancy.

Essential anatomy and physiology in maternity care