BGDA Practical Placenta - Maternal Decidua

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Uterus

Menstrual Changes

• 

  Proliferative phase

• 

  Uterine gland proliferative phase

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  Secretory phase

• 

  Uterine gland secretory phase

• Endometrium - 3 layers in secretory phase of menstrual cycle: compact, spongy, basal
• Myometrium - muscular layer outside endometrium, contracts in parturition
• Perimetrium - tunica serosa of the uterus continuous with the peritoneal wall

Endometrial Layers

• Compact - implantation occurs in this layer, dense stromal cells, uterine gland necks, capillaries of spiral arteries.
• Spongy - swollen stromal cells, uterine gland bodies, spiral arteries.
• Basal - not lost during menstruation or childbirth, own blood supply.

Uterine glands

• still well-developed and highly active at 6 weeks (GA).
• gradually regress in length and epithelium height as the first trimester advances.

Decidual Reaction

• occurs initially at site of implantation and includes both cellular and matrix changes
• reaction spreads throughout entire uterus, not at cervix
• deposition of fibrinoid and glycogen and epithelial plaque formation (at anchoring villi)
• presence of decidual cells are indicative of pregnancy

Cervix - at mouth of uterus, secretes mucus (CMP), forms a plug/barrier, mechanical and antibacterial Vascular - increased number of blood vessels

Decidua

The endometrium becomes the decidua and forms 3 distinct anatomical regions (at approx 3 weeks)

• Decidua Basalis at implantation site
• Decidua Capsularis enclosing the conceptus
• Decidua Parietalis the remainder of uterus
  • Decidua Capsularis and Parietalis fuse eventually fuse and uterine cavity is lost by 12 weeks

Placental Classification

Classification of placenta is on the basis of histological (microscopic) structural organization and layers between fetal and maternal circulation.

Three main groups:

1. Haemochorial - placenta where the chorion comes in direct contact with maternal blood (human).
2. Endotheliochorial - maternal endometrial blood vessels are bare to their endothelium and these comes in contact with the chorion (dogs, cats).
3. Epitheliochorial - maternal epithelium of the uterus comes in contact with the chorion, considered as primitive (pigs, cows).

The presence of these three differing types of placenta have also been used to describe the pattern mammalian evolution.

Maternal Blood Vessels

Uterine and Placental Vasculature in Non-pregnant, Pregnant and immediate Post-partum State Diagrammatic representation of uterine and placental vasculature (red shading = arterial; blue shading = venous) in the non-pregnant, pregnant and immediate post-partum state. Normal pregnancy is characterized by the formation of large arterio-venous shunts that persist in the immediate post-partum period. Extravillous cytotrophoblast invasion in normal pregnancy (diamonds) extends beyond the decidua into the inner myometrium resulting in the formation of funnels at the discharging tips of the spiral arteries. Pregnancies complicated by severe preeclampsia are characterized by minimal arterio-venous shunts, and thus narrower uterine arteries. Contrast with severe preeclampsia.