Placentation and implantation Flashcards
What are the 3 phases of linking between the foetus and mother?
- Invasion - of conceptus to endometrium
- Decidualisation - endometrial remodeling including secretory transformation of the uterine glands, influx of specialised uterine natural killer cells
- Placentation - i.e placenta formation
What is the embryonic portion of the placenta supplied by?
Outermost layers of trophoblast cells (ie the chorion)
What is the chorion?
The outermost membrane surrounding the embryo
What is each villi surrounded by?
Pool/sinus of maternal blood (due to endometrium being changed by enzymes and paracrine agents)
What happens to the blastocyst around day 6/7?
Leaves the zona pelucida and bathed by uterine secretions for 2 days:
- Progesterone prepares supportive uterine environment increasing glandular tissue
- Oestrodiol is required to release the glandular secretions
How does attachment and implantation work?
- Very limited time window
- Synciotrophoblast cells ‘flow’ into the endometrium
- Causes oedema, glycogen synthesis and increased vascularisation (decidualisation). The pregnant endometrium is now termed the decidua
What do syncytiotrophoblast cells do around day 13?
They erde through the walls of large maternal capillaries which then bleed into the spaces - primitive placental circulation
What is the 1st trimester embryo largely dependant on for nutrients and O2?
Uterine tissues
What seperates maternal and foetal blood?
Placental membrane
What is thought to account for a large amount of 1st trimester pregnancy losses?
Lack of hormonal support (luteal phase defect)
How thick should the endometrium ne for successful implantation?
8mm
What do maternal blood vessels near the syncytiotrophoblast expand to become?
MAternal sinusoids
What are trophoblastic lacunae?
Interconnected cords from the syncytiotrophoblast which invade the endometrium and erode maternal capillaries
For how long does LH support the steroid secretion of the corpus luteum?
10 - 12 days
What day is attachment usually in the menstraul cycle?
22
How does hCG influence progesterone?
hCG maintains progesterone secretion from the corpus luteum until the placenta can synthesise its own progesterone
When do syncytiotrophoblasrs secrete hCG?
Soon after implantation (peaks 8-10 weeks of gestation)
When does hCG become measurable?
7 - 8 days postconception
When does the CL fail in a non-fertile cycle?
10 days after menstruation
How does an implanted embryo prevent menstruation?
- The syncytiotrophoblasts secrete hCG
- hCG mimics the action of LH and supports the steroid synthesis of the corpus luteum terefore preventing menstruation and any further follicular development
When can hCG be detected in the blood by immunoassay?
From day 6-7
When can Commercial kits detect hCG in the urine?
After 14 days
What does hCG stimulate in male fetuses?
Stimulates Leydig cells to produce testosterone - important for development of the male duct system
When is the CL not required / when can the placenta secrete all steroid hormones required for pregnancy?
After 4 - 5 weeks
What does progesterone do in pregnancy?
Increases throughout
- Suppression of follicular growth and ovulation
- Suppression of immune response
- Maintenance of endometrium
What is the substrate for progesterone production?
Cholesterol from the maternal circulation
What are the functions of oestrogen/oestrodiol in pregnancy?
- Stimulate continuous growth of uterine myometrium
- Stimulates growth (with progesterone) of ductal tissue of breasts
- Along with relaxin, relaxes and softens maternal pelvic ligaments and symphysis pubis of pelvic bones - allows expansion of uterus
- Stimulate LDL cholesterol uptake and activity of P450 enzymes - contribute to progesterone synthesis
- Foetal well being and placental function can be measured by monitoring oestrogen levels
What does the foetus and placenta make up?
Feto-placental unit
What are the functions of the placenta?
- Essential complex endocrine organ - synthesises steroids and proteins that affect both maternal and foetal metabolism
- 1st month - villus formation
- 2nd month -increasing surface area and circulation
- 3rd month - growing, becoming increasingly efficient
- Adopts functions of the GI, respiratory and renal systems
- Supplies nutrients, exchanges O2 and CO2, regulates fluid volumes and disposes of waste and metabolites
After 20 weeks what happens to the placental membrane?
thins even more due to loss of cytotrophoblasts (most molecules can move through)
What can happen to 3rd trimester syncytiotrophoblastic cells?
Can be lost into maternal blood
WHat do lipids cross the placenta as?
Free fatty acids
How are amino acids transported across the placenta?
Actively
How does nutrient exchange vary throughout pregnancy?
Rapid and increases as pregnancy does, decreases slightly near term
How does glucose pass through the placenta?
Via facillitated diffusion, some glycogen stored in liver for postnatal requirments (foetus has little capacity for gluconeogenesis)
Why are babies of diabetic mothers usually heavier than average?
They are exposed more glucose
What happens to gas exchange towards the end of pregnancy?
Exchange capacity decreases and placenta is less able to meet demands of foetus
What has a greter affinity for oxygen foetal or adult haemoglobin?
Foetal (contains 2 gamma subunits insted of 2 beta) (both contain 2 alpha)
