Implantation & placental function Flashcards
where does fertilisation usually take place?
uterine tubues / fallopian tubes
vagina
uterus
cervix
endometrium
where does fertilisation usually take place?
uterine tubues / fallopian tubes
vagina
uterus
cervix
endometrium
how long after fertilisation occurs in the fallopian tubes doe the blastocyst enter the uterus?
3 days
4 days
5 days
6 days
7 days
how long after fertilisation occurs in the fallopian tubes doe the blastocyst enter the uterus?
3 days
4 days
5 days
6 days
7 days
how long after fertilisation occurs in the fallopian tubes doe the blastocyst hatch?
3 days
4 days
5 days
6 days
7 days
how long after fertilisation occurs in the fallopian tubes doe the blastocyst hatch?
3 days
4 days
5 days
6 days
7 days
how long after fertilisation occurs does the blastocyst implant into the uterine endometrium? [1]
day 8-9
how does the embryo communicate with the mother when reaching the uterus? [2]
- *1. It establishes physical and nutritional contact**
- Required for a supply of nutrients leading to growth – placentation
- *2. It signals its presence to the mother**
- Required to prevent luteal regression ((i.e. the corpus luteum generating and therefore collapse of the endometrium) – maternal recognition of pregnancy occurs due to hormone hCG
which hormone causes maternal recognition of the pregnancy?
LH
FSH
oestrogen
testosterone
hCG
which hormone causes maternal recognition of the pregnancy?
LH
FSH
oestrogen
testosterone
hCG
• Approx 6 days after fertilisation the blastocyst has differentiated into:
The outer cell layer called WHAT? [1]
The inner cell mass called WHAT? [1]
what do each of the above turn into? [2]
• Approx 6 days after fertilisation the blastocyst has differentiated into:
The outer cell layer called trophectoderm –> placenta
The inner cell mass called embryoblast –> embryo / fetus
describe what the stage apposition is of implantation and placental development
Apposition
positioning of the blastocyst within the uterine cavity, with the inner cell mass towards the endometrium. There are mechanisms that ensure this is correct, as seen on the image, but we don’t need to know this
which part of the female genital tract does apposition occur in?
uterine tubues / fallopian tubes
vagina
uterine cavity
cervix
endometrium
which part of the female genital tract does apposition occur in?
uterine tubues / fallopian tubes
vagina
uterine cavity
cervix
endometrium
explain stage of adhesion of implantation of embryo
The cells of the trophoblast fix to maternal tissues and to each other. This is achieved via a group of cell adhesion molecules, including laminin and fibronectin, together with cell surface receptors for these molecules.
after the blastocyst attches to the uterine wall, what does the trophectoderm differentiate into? [2]
Trophectoderm differentiates into cytotrophoblast and syncytiotrophoblast
Cytotrophoblasts: have a single nucleus and divide rapidly in vivo
Syncytiotrophoblasts are derived from fused cytotrophoblasts, are a multinucleated cell and do not divide in vivo
explain how invasion occurs in the process of implantation of embryo
(what is the overall aim?)
invasion
trophoblast, through proteolytic processes, penetrates into the maternal decidua and endometrial spinal arteries.
aim: It is looking to get closer to the maternal blood supply.
The cytotrophoblasts will break through the syncytiotrophoblasts in search for the spiral arteries, and when they reach there they will remodel the spiral arteries to make them much bigger
during placental formation and develeopment of the chorionic vill:
what do trophoblasts turn into? [1]
what do cytotrophoblasts do? [1]
what happens when trophoblasts reach the maternal spiral arteries? [1]
what do trophoblasts turn into: villous structures
what do cytotrophoblasts do: break through trophoblasts shell, invade the decidual tissue
what happens when trophoblasts reach the maternal spiral arteries? [1]
spiral arteries are converted from narrow to wide vessels (greater flow of maternal blood around villi)
which cellular layer froms the barrier betwen maternal and fetal circulation? [1]
villous trophoblast
during chorionic villus formation what is the blood supply like to the embryo?
At this stage there is very little maternal blood supply to embryo. The embryo exists in a relatively hypoxic environment
- An oxygen tension gradient is present
- O2 tension increases towards the maternal side
- Invasion is partly regulated by this gradient
which cell types causes the increase in size of spiral arteries during placental development? [1]
explain how this occurs [2]
cytotrophoblasts (after invading through syncytiotrophoblasts)
replaces the endothelium and smooth muscle of the arteries with themselves (i.e. trophoblasts).
as soon as implantation has occured, WHICH cells secreted WHICH hormone? [2]
Syncytiotrophoblasts secrete hCG as soon as implantation has occurred
the molecules that are thought are important to be a success in successful implantation are:
what are their roles?
Cyclooxygenase-2 (COX-2) -
Heparin-binding epidermal growth factor (HB-EGF) -
Vascular endothelial growth factor (VEGF) -
Human leukocyte antigen-G (HLA-G)
Indoleamine 2,3-dioxygenase (IDO) -
Transforming growth factor β (TGFβ)
Cyclooxygenase-2 (COX-2) - converts AA to PGE2 promotes invasion and decidualisation
Heparin-binding epidermal growth factor (HB-EGF) - involved in attachment and invasion
Vascular endothelial growth factor (VEGF) - involved in angiogenesis
Human leukocyte antigen-G (HLA-G) - inhibits antigen-specific lymphocyte response & decreases NK cell function
Indoleamine 2,3-dioxygenase (IDO) - regulated by IFNs to promote anti-proliferative effects
Transforming growth factor β (TGFβ) - regulates invasion and proliferation
as soon as implantation has occured, WHICH cells secreted WHICH hormone? [2]
Syncytiotrophoblasts secrete hCG as soon as implantation has occurred
If fertilisation and implantation occurs:
- what happens to the corpus luteum (due to which hormone) [2]
- ## what happens to progestorone levels (and why) [2]
If fertilisation and implantation occurs:
- what happens to the corpus luteum (due to which hormone) [2]
- *corpus luteum does not degenerate; due to hCG**
- what happens to progestorone levels (and why) [2]
- *maintained bc of maintence of corpus luteum -> turns into deicuda**
label A-C
A: oestrogen
B: progesterone
C: hCG
describe the levels of hCH during pregnancy [1]
what is the luteal:placental shift? [1] what does it signify? [1]
describe the levels of hCH during pregnancy [1]
peaks at 8 weeks then drops
what is the luteal:placental shift? [1] what does it signify? [1]
when hCG levels drop and cross over with progesterone - hCG is replaced by progestorone
what is an Ectopic pregnancy?
Ectopic pregnancy:
when the implantation of the fertilised oocyte goes wrong. It can be in the oviduct usually, and it will eventually rupture the tube which is extremely painful. However, this Is not the only place implantation can occur. The egg can even embedded outside the uterus (despite being rare)
which area does ectopic pregnancy usually occur?
cervix
uterus
oviduct
fallopian tube
infudibulum
which area does ectopic pregnancy usually occur?
cervix
uterus
oviduct
fallopian tube
infudibulum
what is placenta praevia? [1]
what does it require? [1]
There needs to be no placenta covering the exit, i.e. the cervical os, yet when it does it is known as placenta praevia.
If this occurs, you have to have an **elective caesarean section well before the due date.
(have lots of scans to detect this)**
what is the decidua?
what are the three different regions? [3]
**decidua is the specialized layer of endometrium that forms the base of the placental bed.
Decidua basalis**
– is beneath the implantation site
Decidua capsularis – is the layer that covers the developing embryo
Decidua parietalis – is the remaining endometrium
dsescribe fetal circulation in placenta
Fetal circulation
- 2 x umbilical arteries to the placenta
- Smaller branches to chorionic villi
- Main site of exchange are capillary networks in terminal branches of chorionic villi
Vessels consolidate –> larger venous branches –> umbilical vein leaves the placenta
The umbilical vein, coming back from the placenta, will be oxygenated and therefore red which is unlike veins. There are 2 umbilical arteries which is the waste and CO2,etc from the baby being delivered to the placenta. These 2 umblilical arteries are blue
describe the conditions of maternal placental circulation [4]
Maternal circulation
- 80 - 100 spiral arteries open directly into the intervillous spaces
- Low pressure blood (10mmHg in the relaxed uterus)
- Villi bathed in maternal blood (exchanged 3-4 x/min)
- Return via venous pathways in decidual plate of placenta
what are the functions of the placenta? [4]
Functions of a placenta
- Fetus requires nutrition
- Luteal regression needs to be prevented
- Site for exchange of gases (02 and C02) and other molecules between maternal and fetal blood
- Nutrient and waste exchange: glucose, vitamins, amino acids, electrolytes, hormones, fatty acids, etc.
- Synthesis of proteins and enzymes
- O2 and CO2 pass by simple diffusion
- Fetal haemoglobin has more affinity and carrying capacity than adult haemoglobin
what does the rate of diffusion of placenta depend on?
Rate of diffusion depends on:
- Maternal/fetal gases gradient
- Maternal and fetal blood flow
- Placental permeability
- Placental surface area
The placenta is a barrier but it will allow the following through?
- IgG antibodies
- Hormones
- Antibiotics
- Sedatives
- Some viruses, eg rubella
- Some organisms, eg treponema pallida (syphilis)
what happens if the mother is rhesus negative and the fetus is rhesus positve?
i) in the first pregnancy [1]
ii) second pregnancy [1]
If the mother is rhesus negative and the fetus is rhesus positive:
the RBC that pass through into the fetus will sensitise the fetus system,
i) first pregnancy nothing happens
ii) the second pregnancy the antibodies will cross the placenta and destroy the fetal red blood cells.
Why is the fetus not rejected by the maternal immune system? [3]
- Normally ‘foreign‘ cells express particular human leukocyte antigens recognised by ‘host’ immune system so cells rejected. Trophoblast cells express HLA G. This is not recognised by ‘host’ immune system so cells not rejected
- Infiltrating leucocytes secrete IL-2 which regulates the immune system
- Decidual reaction when the decidual cells (stromal) become swollen and tightly compacted together around the developing fetus thus forming a barrier between mother and implanting embryo
