Placenta and Amniotic Fluid

Question 1

Formation of Placenta

Answer 1

formed as endometrium of uterus in invaded by developing embryo + as trophoblast forms chorionic villus

Question 2

Maternal component of placenta

Answer 2

• Decidua basalis
  
  • derived from endometrium
• decidua basalis and parietals shed as part of after birth
• descidua capsularis
  
  • portion of endometrium that covers blastocyst and separates it from uterine cavity
  • becomes attenuated and degenerates at week 22
• hemochorial type

Question 3

Fetal component of Placenta

Answer 3

• tertiary chorionic villi ⇒ villous chorion
• villous chorion develops at site of decidua basalis
• smooth chorion ⇒ no villous

Question 4

Placenta in Afterbirth

Answer 4

MATERNAL SURFACE:
- cotyledons ⇒ separated by decidual septa
- dark red in color
FETAL SURFACE:
- chorionic plate + chorionic blood vessels
- smooth and shiny appearance due to amnion

Question 5

Functions of Placenta

Answer 5

A. Metabolism
- synthesizes + metabolizes glycogen, cholesterol + FA
B. Transport
- via diffusion, facilitated diffusion + pinocytosis
- excretion of waste
C. Hormone production
- human chorionic gonadotropin hCG
- human placental lactogen hPL
- progesterone, estrogen etc

Question 6

Placental mebrane

Answer 6

A. Layers

• early pregnancy: syncytiotrophoblast, cytotrophoblast, CT, endothelium
• late pregnancy: syncytiotrophoblast + endothelium

Question 7

Umbilical cord

Answer 7

• primitive umbilical ring
• 3 structures through umbilical ring:
  
  • yolk sac
  • connecting stalk
  • allantois
• they form primitive umbilical cord
• week 6 ⇒ physiological umbilical herniation
• gut tube back to abdominal cavity, allantois + yolk sac degenerate
• definitive umbilical cord: umbilical arteries, umbilical vein + Wharton’s jelly

Question 8

Amniotic fluid components

Answer 8

water
carbohydrates
lipids
proteins
desquamated fetal cells
fetal urine

Question 9

Aminotic fluid production

Answer 9

1. Dialysis of maternal blood through blood vessels in placenta
2. Dialysis of fetal blood through vessels in placenta + umbilical cord
3. Excretion of fetal urine into amniotic sac

Question 10

Amniotic fluid resorption

Answer 10

1. Fetus swallows fluid
2. FLuid absorbed into fetal blood stream through GI
3. Excess fluid removed via placenta into maternal blood stream

Question 11

Amniotic fluid amount

Answer 11

• from 50mL at week 12⇒ 1000mL
• rate of water exchange: 400-500mL/h
• fetus swallows 400mL amniotic fluid per day