Pregnancy Flashcards
Before fertilisation, where is the egg situated?
Within the Fallopian tube
What is the role of the fimbriae?
They sweep the egg from the ovary into the Fallopian tube at ovulation
When sperm enters the body, what is the passage it takes?
How does the uterus aid in movement of the sperm?
It moves up the cervix, through the cervical mucus and into the uterus
It passes through the ostia and into the Fallopian tube
The uterus contracts to aid the movement of the sperm
What are the ostia?
Small openings where the Fallopian tubes meet the uterus
What forms when the oocyte is fertilised?
The zygote
This is surrounded entirely by the zona pellucida to prevent entry of further sperm
What is early cleavage?
After fertilisation, the zygote begins to divide
When it reaches the 4-cell stage, this is early cleavage
What is formed 3-4 days post-fertilisation?
The morula
This is formed by further divisions of the fertilised oocyte
What is formed 4-5 days post-fertilisation?
Blastocyst
This consists of an inner cell mass and a blastocoele (fluid-filled space)
What is the trophoblast of the blastocyst?
It is the outer layer of cells that will go on to form the placenta
When does the blastocyst implant into the endometrium of the uterus?
Day 6 post-fertilisation
What are the 5 stages of early implantation?
- shedding of the zona pellucida
- pre-contact blastocyst orientation
- apposition cellular contracts
- adhesion
- penetration of endometrium
What happens during pre-contact blastocyst orientation?
The trophoblast cells invade the endometrium
The amniotic cavity forms within the inner cell mass
What will the amniotic cavity go on to form?
The amniotic fluid
What is the decidua?
it is part of the endometrium
What is the extravillous trophoblast?
The trophoblast cells which are burying their way into the decidua
What did Medawar suggest?
The foetal allograft survival
Why does the foetus survive in the body even though it is “foreign”?
What does Medawar suggest as the reasons why the foetus survives?
- antigenic immaturity in the foetus
- placental protection
- the foetus can block certain antibodies
- immune privilege
- altered host immunity
What is meant by placental protection?
The placenta doesn’t make certain chemicals that would usually be recognised by the body as foreign
e.g. MHC class I
How can the foetus block antibodies?
There are certain antibodies that do not make it across the placenta as they are too big
What is meant by immune privilege and altered host immunity?
In the maternal blood, there are less cell-mediated immune cells
e.g. cytotoxic T cells
What are the 2 types of trophoblasts involved in the decidua interaction?
Villous trophoblast - this is inert
Extravillous (invasive) trophoblast
What antigens are expressed on the surface of the extravillous trophoblast?
What is not expressed?
ONLY class I human leucocyte antigens
It does NOT express:
Cw, G, E, A and B
What is significant about the invasive trophoblast not expressing certain antigens?
This makes it less attractive to cytotoxic T-cells
It enables binding to NK cells
The mother’s immune system does not attack the foetus
What type of NK cells are secreted during the luteal/secretory phase of the cycle?
Why are they present?
CD56 (bright)
Their presence is due to progesterone
What is the role of the CD56 NK cells?
They have the capacity both to facilitate and impede trophoblast invasion
How may the CD56 NK cells determine the maternal response to pregnancy?
They are the main source of decidual cytokines
What is an example of systemic signalling in pregnancy?
As the trophoblast comes into the decidua, it begins to make hCG
The hCG acts on the ovary, causing it to make more progesterone
How do levels of hCG vary in early pregnancy?
hCG levels roughly double every 48 hours
It rises rapidly to peak at just over 2-3 months
When do hCG levels drop?
They drop rapidly between 2-3 months
It then plateaus and remains at a lower level until the end of pregnancy
How do progesterone and oestrogen levels change during pregnancy?
They both steadily rise throughout pregnancy
Oestrogen is at a higher concentration than progesterone
What happens to the levels of hCG, oestrogen and progesterone at parturition?
The levels rapidly drop down to 0
What type of molecule is hCG and from where is it produced?
It is a glycoprotein with a similar structure to LH and FSH ( alpha and beta chains)
It is produced by trophoblast cells
Why is hCG described as a luteotrophic hormone?
It continues to stimulate the corpus luteum to make progesterone
What is meant by the production of hCG being autonomous?
Production is independent of the hypothalamus and pituitary
What is hCG thought to be the cause of?
Morning sickness
Morning sickness usually tends to drop off when the levels of hCG begin to drop
What is the clinical use of hCG?
Pregnancy test
this uses an immunoassay that detects the beta subunit of hCG in urine
How is pregnancy dated clinically?
From last menstrual period
What will be visible in a pregnancy image in weeks 5, 6, 7, and 8?
5 - gestation sac, placenta (brighter white)
6 - foetal pole, yolk sac, vitelline veins
7 - fetal heart activity, 3 vessel cord
8 - foetal limbs, movement
yolk sac, amniotic and chorionic cavities