Foetal membrane and placenta

Question 1

What is the purpose of the placenta?

Answer 1

• 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)

Question 2

What nutrients are provided by the mother to the foetus?

Answer 2

calcium, iron, carbohydrates and proteins

Question 3

What organisms can cross the placenta?

Answer 3

mumps, rubella and norovirus

Question 4

What is the role of the maternal hormones in the direction of nutrition

Answer 4

direct metabolism to the foetus

Question 5

Does foetal and maternal blood supply mix?

Answer 5

No never mix

Question 6

What is the decidua reaction?

Answer 6

• 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

Question 7

What happens on day 7 if there is egg fertilisation?

Answer 7

Implantation begins via integral connections and HB-EGF

Question 8

What happens on day 8 if there is egg fertilisation?

Answer 8

amniotic sac starts to form in the epiblast layer of the blastocyst

Question 9

What happens on day 9 if there is egg fertilisation?

Answer 9

• yolk sac starts to form in the hypoblast layer

- and extra embryonic mesoderm (connective tissue secreted by yolk sac) begins to develop

Question 10

What happens on day 12 if there is egg fertilisation?

Answer 10

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

Question 11

What do the Somatic and splanchnic end up forming?

Answer 11

Somatic = body 
splanchnic = some organs specifically GI

Question 12

Describe structure during day 12?

Answer 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

Question 13

How do chorionic villi develop?

Answer 13

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

Question 14

What are the decidua and chorion?

Answer 14

Decidua = The maternal contribution to the placenta
Chorion = foetal contribution to the placenta

Question 15

What are the components of the decidua?

Answer 15

Decidua Basalis - embryonic pole which becomes the placenta
Decidua Capsularis - opposite the basalis
Decidua Parietalis - all other endometrial surfaces not directly associated with embryo

Question 16

What does the amniotic sac turn into later in gestation?

Answer 16

amniochorionic membrane

Question 17

What is the function of the amniotic sac?

Answer 17

• Reduces friction
• holds and supports foetus
• ## hydrates skin, lungs and GI tract

Question 18

What can occur if foetal and maternal blood mixes?

Answer 18

• 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

Question 19

What are the hormones necessary in pregnancy?

Answer 19

• HCG
• Progesterone
• Oestrogen
• Placental PTH
• Relaxin
• Corticotropin releasing hormone
• Chorionic somatomammotrophin

Question 20

What umbilical abnormalities can there be?

Answer 20

• Single umbilical artery
• Entanglement (knots and restriction of foetal aspects)
• Compression (prevents flow)
• Prolapse (compression in birth canal)

Question 21

What are example of placental abnormalities?

Answer 21

• abnormal shape
• placenta previa
• Pre-eclampsia
• Abnormal implantation
• Trophoblastic disease

Question 22

What is placenta previa?

Answer 22

Placenta blocks the normal route of vaginal birth

• will require C section
• If not mother will haemorrhage

Question 23

What is pre-eclampsia?

Answer 23

• hypertension and protein in urine

- both abnormal placentation and immunologic factors appear involved

Question 24

Describe the formation of the yolk sac?

Answer 24

Hypoblast cells send out a ring of cells called heusers membrane (also called exocoelomic membrane) these cells together encapsulate the yolk sac

Question 25

What is the function of the exocoelomic membrane?

Answer 25

secretes connective tissue called extra-embryonic mesoderm

Question 26

At what point does embryo become a foetus?

Answer 26

Week 9

Question 27

What is the function of cytotrophoblasts?

Answer 27

give rise to syncytiotrophoblasts and form villi of placenta

Question 28

What changes occur between days 12-16?

Answer 28

• 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)

Question 29

What is the Connecting stalk?

Answer 29

attaches the amniotic cavity and yolk sac to the extraembryonic mesoderm
this will form the umbilical cord

Question 30

What occurs in week three of pregnancy?

Answer 30

• 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

Question 31

What occurs in week four?

Answer 31

• 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

Question 32

Describe the feet-maternal boundary?

Answer 32

• ## Maternal blood held in intervillious space of lacunae which are coated in outer layer of synctiotrophoblasts