The placenta Flashcards
1
Q
What are the functions of the placenta?
A
- Provides nutrients and removes wastes
- Partial immunological barrier
- Synthesises and secretes hormones required for maintenance of pregnancy and foetal growth:
- Progesterone and oestrogen
- Prostaglandins
- hCG, hPL
- CRH, GH, ACTH, GnRH, TSH
- Relaxin
2
Q
Where does blood exchange occur in the foetus?
A
- Foetal circulation passes through the umbilical cord and enters chorionic villi - this is where exchange happens
3
Q
How is the placenta formed? (9 steps)
A
- After implantation, syncytiotrophoblast cells for multinucleated wall
- Decidualisation response has damaged uterine blood vessels
- Blood from the uterine arteries pools in lacunae of syncytiotrophoblasts
- Lacunae merge
- Cytotrophoblast sends cells to anchor placenta to the endometrium - forms primary chorionic villi
- Week 3 - foetal mesoderm layer expands under cytotrophoblast - forms secondary chorionic villi
- Blood vessels enter villi - becomes tertiary chorionic villi
- Cytotrophoblasts form cytotrophoblastic shell:
- Villi attached to this: anchoring villi
- Villi branchin of this: branching villi
- Foetal blood flow established by week 4
4
Q
What is the conversion process?
A
- The differentiation of cytotrophoblast cells
- Mature maternal blood flow by week 10-12, results in formation of extravillous trophoblast cells:
- Cytotrophoblast cells detach from villi and migrate into maternal endometrium and myometrium
- Some migrate along spiral arteries - these become endovascular extravillous trophoblasts (these condvert vessels into low pressure, high capacity circulation)
5
Q
What are the complications of conversion failure?
A
- Villi will break and will cause poor diffusion
- It can lead to an increase in pressure that is too high:
- Pre-eclampsia
- Intrauterine growth restriction
6
Q
What is histotrophic nutrition?
A
- Occurs before implantation -> early implantation
- Endometrial fluids (from endometrial glands) provide nutrition
- Substances pass through thin trophoblast and distributed via diffusion
- Blood vessels develop as mesoderm develops
7
Q
What is haemotrophic nutrition?
A
- Blood-borne via placenta - complete by week 14
- NOTE: maternal and foetal circulation are separate
- Uterine a./v. between mother and placenta
- Umbilical a./v. between foetus and placenta
8
Q
How are different molecules transported across the placenta?
A
- Simple diffusion: low-molecular weight, non-polar molecules
- Facilitated diffusion: glucose, lactate
- Active transport: amino acids, Fe, Ca, P, vitamins
9
Q
Outline the different sections of the foetal membrane and spaces.
A
- Chorion
- Amnion
- Yolk sac
- Atlantois
10
Q
What is the chorionic membrane?
A
- Mesodermal inner cells mass + trophoblast (both parts)
11
Q
What is the amnion?
A
- Transparent sac filled with amniotic fluid - protects embryo and provides optimal conditions
- Amniotic membrane: ectodermal and mesodermal inner cell mass
12
Q
What is the yolk sac?
A
- Endodermal and mesodermal layers under the trophoblast
13
Q
What is the allantois?
A
- Allantoic endoderm at caudal end of embryo - grows out, surrounded by mesoderm, to form allantois
14
Q
What is the fusion of allantoic and chorionic mesoderm?
A
- This marks the site of chorio-allantoic placenta and the umbilical cord
15
Q
Development of chorion, yolk sac and amnion throughout pregnancy
A
- Chorion and yolk sac decrease in size
- Amnion increases
