structure of the placenta

Question 1

structure of mature placenta

Answer 1

• side of placenta that faces fetus: chorionic plate, where umbilical cord is attached (unit: villus tree)
• basal plate: apposed to decidua basalis, through which maternal blood enters the stroma

Question 2

describe the fetal villus tree

Answer 2

• arises from chorionic plate: consists of syncytio and cytotrophoblast surrounding fetal capillaries
• each is bathed directly in maternal blood that circulates in the intervillus space

Question 3

describe the initial dev of the placenta

Answer 3

• appear as trophoectoderm
• at implantation, mediated invasion
• have inner layer called cytotrophoblast (mononuclear), and outer layer called syncytiotrophoblast (multinuclear)
• syncytiotrophoblast are non-proliferative, generated by fusion of cytotrophoblast
• syncytiotrophoblast cells break into maternal decidua, endometrial glands & capillaries

Question 4

what happens around the time of syncytiotrophoblast invasion into maternal decidua

Answer 4

• lacunae form
• which will eventually fill with glandular secretions and maternal blood

Question 5

how does the placental network develop

Answer 5

• syncytiotrophoblast form trabeculae between lacunae, into which cytotrophoblast and extraembryonic mesoderm penetrate > earliest placental villi
• branching occurs
• lacunae = intervillus space
• fetal vascular network develops within extraembryonic mesoderm to link to the fetus via the connecting stalk

Question 6

are the placental villi formed fort the entire chorionic sac?

Answer 6

• initially yes
• but at 20w, regress to one pole > discoid placenta
• placental membrane remain where villi have regressed; provide an exit route at birth

Question 7

what is histiotrophic nutrition? when does it happen?

Answer 7

• conceptus relying on nutrients (carbs and lipids from endometrial glands stimulated by progesterone and trophoblast cells) and gases from trophoblast cells or yolk sac
• happens in low O2 because sensitive to ROS and teratogenesis; also favours stem cell dev
• 10-12w of pregnancy

Question 8

when switch to haemotrophic nutrition

Answer 8

• when placental villi are established
• and maternal blood circulates in intervillus space

Question 9

when do the major organ systems differentiate

Answer 9

embryonic period, aka 0-8w post fertilisation (so highest risk of congenital malformations & risk of external factors)

Question 10

when is the fetal period of dev

Answer 10

9-38w post fertilisation

Question 11

clinical dates of pregnancy start with? significance?

Answer 11

• 1st day of last menstrual period
• so 2w longer than post-fertilisation dates

Question 12

uterine blood supply flows through

Answer 12

uterine > arcuate > spiral

Question 13

how are maternal-fetal exchange units created

Answer 13

• villi arranged in lobules
• maternal spiral artery opens in centre of each lobule