Foetal membrane and placenta Flashcards
What is the purpose of the placenta?
- Protection (prevents micro-organisms from reaching foetus)
- Nutrition (provide nutrients from maternal circulation)
- Respiration (exchange of O2 and CO2 with maternal circulation)
- Excretion (removal of waste products which are excreted by maternal kidneys)
- Endocrine (takes over progesterone and oestrogen function from corpus luteum)
What nutrients are provided by the mother to the foetus?
calcium, iron, carbohydrates and proteins
What organisms can cross the placenta?
mumps, rubella and norovirus
What is the role of the maternal hormones in the direction of nutrition
direct metabolism to the foetus
Does foetal and maternal blood supply mix?
No never mix
What is the decidua reaction?
- Decidua is the maternal endometrium in pregnancy
- reaction occurs after implantation
- connective tissue of the endometrium turns into decidua
- progesterone induces increased vascular swelling stromal cells with accumulation of glycogen granules (that provide nourishment to early embryo
What happens on day 7 if there is egg fertilisation?
Implantation begins via integral connections and HB-EGF
What happens on day 8 if there is egg fertilisation?
amniotic sac starts to form in the epiblast layer of the blastocyst
What happens on day 9 if there is egg fertilisation?
- yolk sac starts to form in the hypoblast layer
- and extra embryonic mesoderm (connective tissue secreted by yolk sac) begins to develop
What happens on day 12 if there is egg fertilisation?
Extra-embryonic mesoderm surrounds the amniotic and yolk sac pushing them into centre
specialised mesoderm surrounds each sac:
- Yolk sac = extra embryonic splanchnic mesoderm
- Amnion = Extra embryonic somatic mesoderm
What do the Somatic and splanchnic end up forming?
Somatic = body splanchnic = some organs specifically GI
Describe structure during day 12?
- trophoblastic lacunae have formed in the syncitotropoblast layer which will fill with the maternal blood
- Maternal sinusoids (blood vessels which will breakopen and spurt into lacunae
- Extra embryonic coelom which continuously grow until they combine together to form chorionic cavity
How do chorionic villi develop?
Primary - Cytotophoblasts
Secondary - villi begin to Infiltrate the extra embryonic mesoderm creating an internal cavity of mesoderm
Tertiary - Mesoderm differentiates to form blood vessels and foetal blood
What are the decidua and chorion?
Decidua = The maternal contribution to the placenta Chorion = foetal contribution to the placenta
What are the components of the decidua?
Decidua Basalis - embryonic pole which becomes the placenta
Decidua Capsularis - opposite the basalis
Decidua Parietalis - all other endometrial surfaces not directly associated with embryo
What does the amniotic sac turn into later in gestation?
amniochorionic membrane
What is the function of the amniotic sac?
- Reduces friction
- holds and supports foetus
- ## hydrates skin, lungs and GI tract
What can occur if foetal and maternal blood mixes?
- Haemolytic disease in new-born of later pregnancies
- mother sets up immune defence if comes into contact with rhesus positive blood if she is rhesus negative
- She can then give the immune cells across the placenta to later babies which will destroy their own RBCs
What are the hormones necessary in pregnancy?
- HCG
- Progesterone
- Oestrogen
- Placental PTH
- Relaxin
- Corticotropin releasing hormone
- Chorionic somatomammotrophin
What umbilical abnormalities can there be?
- Single umbilical artery
- Entanglement (knots and restriction of foetal aspects)
- Compression (prevents flow)
- Prolapse (compression in birth canal)
What are example of placental abnormalities?
- abnormal shape
- placenta previa
- Pre-eclampsia
- Abnormal implantation
- Trophoblastic disease
What is placenta previa?
Placenta blocks the normal route of vaginal birth
- will require C section
- If not mother will haemorrhage
What is pre-eclampsia?
- hypertension and protein in urine
- both abnormal placentation and immunologic factors appear involved
Describe the formation of the yolk sac?
Hypoblast cells send out a ring of cells called heusers membrane (also called exocoelomic membrane) these cells together encapsulate the yolk sac
What is the function of the exocoelomic membrane?
secretes connective tissue called extra-embryonic mesoderm
At what point does embryo become a foetus?
Week 9
What is the function of cytotrophoblasts?
give rise to syncytiotrophoblasts and form villi of placenta
What changes occur between days 12-16?
- by day 12 all of embryo and developing placental cells are within the endometrium of uterus
- lacunae fill with the maternal blood from sinusoids
- these lacunae are very close to what will become placental villi (forms foetal maternal boundary)
- chorionic cavity fully forms pushing extra embryonic mesoderm to peripheries (layer surrounds central amniotic and cold sacs also)
What is the Connecting stalk?
attaches the amniotic cavity and yolk sac to the extraembryonic mesoderm
this will form the umbilical cord
What occurs in week three of pregnancy?
- foetal and maternal blood supply start to connect via the chorionic villi
- cytotrophoblasts start to proliferate out around the synctiotrophoblasts in ‘collars’
- chorionic cavity surrounds fatal tissue but remains connected via connecting stalk
What occurs in week four?
- foetal blood vessels arise in the extra embryonic mesoderm
- Tertiary villi have formed contain blood vessels
- Cytotrophoblast shell forms as cytotrophoblasts encompass the syncytiotrophoblasts which are holding maternal blood
- connecting stalk also starts to develop foetal capillaries as well as forming primitive umbilical cord
Describe the feet-maternal boundary?
- ## Maternal blood held in intervillious space of lacunae which are coated in outer layer of synctiotrophoblasts
