Implantation 6

Question 1

What are the major components of the placenta?

Answer 1

• Membranes
• Umbilical cord
• Placental disc

Question 2

What are the major membranes of the placenta?

Answer 2

• Amnion
  
  • lines amniotic sac
  • single layer of cuboidal epithelium, basement membrane, and collagen layer
• Chorion
  
  • fibrous chorion and a layer of extravillous trophoblast
  • lies deep to the amnion and has sparsely cellular collagen layer
• Decidual layer
  
  • maternal in origin
  • contains decidualized maternal cells, vessels, fibrin
  • some degree of hemorrhage here

Question 3

Describe the histology of the umbilical cord.

Answer 3

• Single layer of cuboidal amniotic epithelium on the outer surface
• Three vessels, 2 arteries and a veinembedded in a myxoid paucicellular matrix called Wharton’s gelly
  
  • proteoglycans with some fibroblasts and macrophages
  • vein carries nutrient rich blood to fetus
  • arteries carry deoxygenated blood and waste products back to placenta
• Can show remnant blood vessels (vitelline) and epithelial remnants (omphalomesenteric and allantoic in origin

Question 4

What are the major components of the placental disk?

Answer 4

• Chorionic plate
• Basal plate

Question 5

Describe the histological features of the chorionic plate.

Answer 5

• Single layer of cuboidal amniotic epithelium overlying a paucicellular collagenous matrix (fibrous chorion)
• Below are fetal villi separated by blood containing spaces where maternal blood circulates around fetal villi (intervillous space)
  
  • stem villi - fetal vessels with smooth muscle layers
  • terminal villi - only have capillaries
  • outer layer of syncitiotrophoblast cells
    
    • true syncytium, no membranes separating nuclei
  • inner layer is cytotrophoblast cells that act as stem cells, become less numerous as development progresses
• Macrophages (Hofbauer cells) and fibroblasts in cellular matrix of villi

Question 6

Describe the histological features of the basal plate of the placental disk.

Answer 6

• Extravillous trophoblast cells
• Decidualized maternal cells
  
  • maternal endometrial stromal cells
  • form interface between fetal tissues and maternal myometrium
• Two well defined fibrinoid layers
  
  • Rohr’s fibrinoid and Nitabuch’s fibrinoid (deeper layer)
• Maternal vessels