14 - Placenta Flashcards
What day does implanation occur and where does it occur?
- Day 6 after it has hatched from zona pellucida
- Usually implants on superior body of uterus but can implant lower down or on previous C-section scars that are not viable or not in the uterus
What are some problems with invasion of the conceptus into the endometrial wall?
- Too deep: placenta accreata
- Incomplete invasion: miscarriage or placental insufficiency that can lead to preeclampsia
When does the placenta develop and how?
- Week 2 before anything else
- From fetal membranes
- Chorionic sac and amniotic sac separate but then as the amniotic sac enlarges it displaces the chorion and fuses with the chorionic membrane
- Projections around all surfaces of this membrane concentrated into a small disc like space that becomes the placenta
What does implanation achieve?
- Basic unit of exchange
- Anchor the placenta
- Establish maternal blood flow
What are chorionic villi?
- Villi that sprout from the chorion membrane
- Inner connective tissue core, where fetal vessels can form, and outer layer of syncytiotrophoblasts
- Maternal blood vessels surround villi so exchange can occur but mixing of circulations never
How do the chorionic villi change over pregnancy?
1st trimester: barrier between maternal and fetal blood vessels thick. Full layers of cytotrophoblasts and syncytiotrophoblasts
3rd trimester: barrier less, becomes one layer of trophoblast by reducing cytotrophoblasts
Margination of fetal capillaries and loss of trophoblasts
How is the degree of invasion of the conceptus controlled?
Decidua = endometrial becomes specialised through decidualisation
If implantation in correct place but decidual reaction is suboptimal can lead to complications like miscarriage, infertility or placental insufficiency leading to pre-eclampsia
Implanation in incorrect place then no decidual reaction so ectopic
Label the gross morphology of the placenta.
- Amnion on outside with chorion vessels underneath
- Need to check placenta for cotyledons to check none of them have fallen out and can cause post partum haemorraghe
What are the main blood vessels exchanging the placenta and how are they arranged?
- Endometrial arteries bathe the villi
- Paired umbilical arteries carry waste products to villi
- Single umbilical vein takes oxygen and nutrients to fetus
What is the endocrine function of the placenta?
- hCG from syncytiotrophoblasts maintain corpus luteum in first trimester. urine and blood tests
- Steroid hormones made to take over corpus luteum and produce enough oestrogen and progesterone to keep body in pregnant state
Why may someone have high levels of hCG in their blood?
- Pregnancy specific, from syncytiotrophoblasts
- Molar pregnancy
- Testicular cancer
- Choriocarcinoma
How do placenta hormones change the metabolic state of the mother?
- Progesterone: increases appetite to allow increased fat deposition to support fetus and breast feeding
- Human Placental Lactogen (hCS): creates diabetogenetic state by causing insulin resistance to mother so more glucose availability for fetus
How does transport across the placenta occur?
- Simple diffusion: water, gases, electrolytes
- Facilitated diffusion: glucose
- Active transport: aa’s, Fe, vitamins
- Receptor mediated endocytosis: IgG’s
How does gas exchange occurs across the placenta?
- Simple diffusion
- Flow limited and fetal O2 stores are low so adequate flow essential
- Can have fetal distress (hypoxia) in labour contractions as they compress uteroplacental circulation
How does the baby confer immunity?
- IgG antibodies from mother can pass across placenta via receptor mediated endocytosis
- Protects baby
What is rhesus disease of the newborn?
- Haemolytic disorder that can occur due to being able to transfer across placenta. Not common as screened for now
- Causes baby jaundice and anaemia
When do teratogens cause the greatest effect in pregnancy?
- Preembryonic: fatal
- Embryonic (3-6 weeks): sensitive as body systems developing
- Fetal (9-36 weeks): +/- sensitive apart from CNS
What are some harmful substances to the fetus?
- Thalidomide
- Alcohol (FAS and ARND)
- Therapeutic drugs (antiepileptic, warfarin, ACEi)
- Smoking (low birth weight)
- Drugs (dependency)
What are some dangerous infections to have in pregnancy and why?
Mother is in immunocompromised state so infections more serious, need to check mother’s immunisation status. Poor pregnancy outcomes
