Placenta function and dysfunction

Question 1

What is implantation?

Answer 1

loss of zona pellucida - the trophoblast cells interact with endometrial lining in the uterus - now called the blastocyst - and interacts with increased vasculature and secretory glands for nutrients

Question 2

Where does implantation occur?

Answer 2

in the superior body of the uterus

Question 3

What is an ectopic pregnancy?

Answer 3

where implantations occurs outside of the endometrium

Question 4

What is placenta praevia?

Answer 4

where implantation occurs at a site within the lower uterine segment close to or covering the internal os

Question 5

What is placenta accreta?

Answer 5

invasion and implantation that is too deep

Question 6

When does the placenta begin to develop?

Answer 6

2nd week of pregnancy

Question 7

Why is the placenta so important?

Answer 7

Develops first before any embryological development and the placenta ensures the foetus has all its metabolic needs catered for

Question 8

What happens in week2?

Answer 8

2 distinct cellular layers emerge from
outer cell mass
- syncytiotrophoblast
-cytotrophoblast

inner cells mass becomes the bilaminar disk

• epiblast
• hypoblast

Question 9

What does the syncytiotrophoblast do?

Answer 9

secretes HCG to maintain the corpus luteum

Question 10

What happens to the amniotic and chorionic cavities?

Answer 10

initially following implantation, they are separate. But as the amniotic sac grows, the chorionic cavity disappears and just becomes 1 amniotic cavity

Question 11

What are chorionic villi and where do they come from?

Answer 11

They come from the trophoblast cells - branch from the syncytiotrophoblast to the functional endometrium
They increase the SA in contact with the maternal blood
-Core of the chorionic villi is connective tissue that foetal blood vessels develop from

Question 12

How does exchange occur?

Answer 12

The maternal blood vessels surround the chorionic villi to allow exchange to occur

Question 13

What are they 3 stages of its development?

Answer 13

primary - finger-like projections of the cytrotrophoblast extend into the syncytiotrophoblast and branch

secondary - mesenchyme from the embryo invades cytotrophoblast of the primary villi and extends upwards

tertiary - foetal blood vessels form from the mesenchyme that link with foetal circulation formed by the 3rd week

the placenta now has a blood supply from the mother and the fetus and effect exchange of nutrients gases and waste products can occur

Question 14

What does implantation achieve?

Answer 14

1. establishes exchange
2. anchors the placenta
3. establishes maternal blood flow within the placenta

Question 15

What is the barrier between maternal and fetal blood flow?

Answer 15

single layer of trophoblast (syncytiotrophoblast)

• starts of relatively thick as full layer of cytotrophoblast and synctiotrophoblast
• as pregnancy progresses, becomes thinner as loss of cytotrophoblast cells leaving just 1 layer of trophoblast

Question 16

What is the decidua and the decidual reaction?

Answer 16

Decidua is the term given to the endometrial cells that have becomed specialised following the decidual reaction. They are a thick layer of modified mucous membrane which lines the uterus during pregnancy. The modification allows modulation of the degree of invasion of the conceptus once implanted

Question 17

What happens if implantation occurs in an area with no decidua?

Answer 17

There is no decidual reaction so no control on degree of invasion - nothing to stop it invading too deep
This occurs in tubal ectopic pregnancy

Question 18

What are the maternal blood vessels called and what do they do?

Answer 18

the endometrial arteries and veins - bathe the outside of the villi in maternal blood for exchange to occur

Question 19

What are the foetal vessels called and what do they do?

Answer 19

through the umbilical arteries (pleural), waste is brough to the villi and oxygen and nutrients is taken to the fetus via the umbilical vein (singular)

Question 20

What are the broad functions of the placenta?

Answer 20

• endocrine
• metbaolic changes
• transport

Question 21

What hormones are produced by the placenta?

Answer 21

Protein;
-hCG
Steroid;
-progeseteron
-oestrogen

Question 22

What is the role of hCG and where is produced?

Answer 22

produced by the syncytiotrophoblast (pregnancy specific)
supports the secretory function of the CL
only produced in the first 2 months of pregnancy

Question 23

Why is hCG a marker of pregnancy?

Answer 23

it is secreted in maternal urine

Question 24

Why does the placenta also produce progesterone and oestrogen?

Answer 24

When the placenta becomes large enough it can take over secretion from the CL (after the first trimester) - keeps the HPG axis in the pregnant state

Question 25

What metabolic changes occur in the mother and how do they occur?

Answer 25

increase appetite due to increased progesterone - allows increased fat deposition to help support the fetus and breastfeeding hPL - creates diabetogenic state to cause insulin resistance in the mother increasing the glucose availability to the fetus

Question 26

What are the transport functions of the placenta?

Answer 26

- gas exchange | - immunity transfer

Question 27

What molecules cross the membrane by simple diffusion?

Answer 27

water, electrolytes, urea, uric acid, gases

Question 28

What molecules cross the membrane by facilitated diffusion?

Answer 28

glucose

Question 29

What is the rate of gaseous exchange limited by?

Answer 29

flow limited NOT diffusion limited so adequate uteroplacental circulation is required

Question 30

What happens if the uteroplacental circulation is compromised in labour?

Answer 30

contractions can lead to compression of the blood vessels causing fatal distress

Question 31

What substances are transported across the placenta by AT?

Answer 31

AA, ions, vitamins - via transporters expressed by the syncytiotrophoblast

Question 32

What immunoglobulins can cross the placenta?

Answer 32

only IgG via receptor-mediated endocytosis

Question 33

Why do they need to cross the placenta?

Answer 33

so when the baby is born they have SOME defence against infection

Question 34

What are tetrogens?

Answer 34

a drug/factor that causes malformation of an embryo

Question 35

When do teratogens have their greatest effect/

Answer 35

in the first few weeks of pregnancy (especially 3-8 as this is the key time for development) - in the foetal period, there is less risk of damaging the fetus as they are just growing (except for CNS)

Question 36

What are the harmful substances that can cross the placenta?

Answer 36

- thalomide (limb defects) - alcohol (CNS) - theraputic drugs - drugs of abuse (dependancy) - maternal smoking

Question 37

Why is maternal smoking bad for the fetus?

Answer 37

Baby can't get enough oxygen as the CO binds to Hb and moves into the fetus which means the fetus get lets O2 causing distress