Function of the Placenta and stages of labour

what is placental growth caused by?

progesterone

(assisted by relaxin + oestrogen)

what are the two layers of the trophoblast and what do they form?

• synchytiotrophoblast

• cytotrophoblast

they form the chorionic villi

what is the function of maternal large granular lymphocytes?

they aid in implantation + maturation of the placenta by forming dilated capacitance vessels within the uteroplacental vasculature to accommodate the increased blood flow needed during pregnancy

what are the characteristics of preeclampsia?

• hypertension and endothelial dysfunction

• caused by faulty implantation of the trophoblast in the uterine wall resulting in inflammatory reaction in the mother’s body

what are the 3 function of placenta?

1. respiratory function

2. barrier + immunological function

3. nutrition + excretion

what four types of transport does the placenta aid in? and what is transported in each?

• Simple diffusion: O2, CO2 and fat-soluble vitamins.

• Facilitated diffusion (carrier mediated) : glucose

• Active transfer (against conc gradient): water soluble vitamins

• Endocytosis : Immunoglobulin IgG

what are the fat soluble vitamins?

KADE

enumerate the excretory function of the placenta?

metabolites produced in the foetus via simple diffusion → excreted by mother’s liver/kidneys

what contains prorenin?

the cytotrophoblast of the human chorion

what regulates placental blood flow?

prostaglandins

what does syncytiotrophoblast produce and what does it stimulate?

• synthesises Corticotropin-releasing hormone which stimulates prostaglandins + raises DHEA

• produces oestrogen

• produces progesterone

what does cytotrophoblasts produce?

relaxin

what is the PO2 of foetal venous vs oxygenated blood?

• PO2 in fetal venous blood is 15 mmHg

• PO2 in fetal blood after oxygenation is 30 mmHg

what is the PO2 of the maternal foetal blood?

50 mmHg

this allows adequate CO2 diffusion

what is the protective function of the placenta? what is it impermeable to?

• impermeable to toxins

• barrier against bacteria but not some viruses

• drugs cross

which antibody can cross the placental barrier?

IgG crosses barrier but IgM cannot

Why doesn’t the mother’s immune system attack the foetus? name 3 reasons

1. Altered HLA Expression

2. Fas Ligand.

3. Placental Indoleamine-2,3 Dioxygenase (IDO).

what does altered HLA expression mean?

trophoblast expresses atypical HLA-G cell surface proteins that interact with the mother’s natural killer cells/cytotoxic T cells which makes maternal immune cells more tolerant of foreign cells of foetus

what is a “fas ligand”?

it is a transmembrane protein produced by trophoblasts that causes apoptosis of mother’s T lymphocytes → less likely to attack the foetus

what does (IDO) do?

it is an enzyme that breaks down tryptophan into kynurenine → tryptophan is needed for t cells → no tryptophan → lowered immunity

what are the four stages of parturition?

1. early labour/dilation

2. expulsion

3. placental

4. recovery

how long does early labour last?

first time → 10-12 hours

multiple → 6-8 hours

how frequent are contractions?

• lasts 10-20 seconds

• occur every 15-30 minutes

what does the expulsion stage involve?

• full dilation/effacement until infant is delivered

• lasts 30 minutes up to two hours

• baby here moves down birth canal

what is the mechanism behind the placental stage?

oxytocin stimulates uterus to detach the placenta from the uterine wall for up to 30 minutes

what are the 2 main complications in recovery stage?

• postpartum haemorrhage

• eclampsia

how long is puerperium?

period of delivery → 6 weeks

what is lochia?

fluid discharge expelled from the vagina after delivery for several weeks