Placentation and Implantation Flashcards
What are the phases in the earlier stages of pregnancy that forms the anatomical link between the mother and foetus?
Invasion
Decidulisation
Placentation
What happens at days 6/7?
The blastocyst leaves the zona pellucida and is bathed by uterine secretions for 2 days
What is the decidua?
The pregnant endometrium
What happens at the end of week 1 to allow attachment?
Trophoblast interacts with maternal epithelial tissue resulting in syncytiotrophoblast cells to flow into the endometrium causing oedema, glycogen synthesis and vascularisation
What happens when implantation occurs?
Syncytiotrophoblas cells erode through the walls of largee maternal capillaries which then bleed into spaces providing the primitive maternal circulation
“Break through bleeding” may occur
Nutrition is still from uterine secretions and tissues
When does implantation occur?
6/7 days after LH surge
What is a chorionic villi?
Villi formed by syncytiotrophoblast that projects into blood filled spaces
In the core of the villus is the foetal capillary loop (dilated at tip)
Bathed in maternal blood
Where does the embryo get most its nutrients and oxygen from during the first trimester and why?
Uterine tissues and secretions
Maternal side of placental circulation is restricted and is not functional util 10-12 weeks
Describe the structure of a chorionic villi
Inner core of extra embryonic mesoderm
Middle cytotrophoblast layer
Outer syncytiotrophoblast layer
Foetal capillaries within the villus core
Intervillous space full of maternal blood from spiral arteries
What may be the reason for early pregnancy losses?
Lack of hormonal support due to luteal phase defect
What is the blood supply of the placenta?
Maternal - uterine artery and vein
Foetal - umbilical artery and vein
What is the function of hCG in early pregnancy?
Maintains progesterone secretion from CL after luteal phase until the placenta can synthesise its own progesterone (mimics LH)
This prevents menstruation and follicle development and maintains the endometrium
Where is hCG secreted from and when?
Secreted from syncytiotrophoblasts soon after implantation
Measured by 7-8 days post conception in maternal blood
What is the function of hCG in males?
Stimulates Leydig cells to produce testosterone which is important for formation of the male duct system
What is the function of progesterone in pregnancy?
Suppression of follicular growth and ovulation
Suppression of immune response
Maintenance of endometrium
When is the placenta producing enough steroid hormones for the CL to not be needed?
5 weeks
What is the substrate for cholesterol production in the placenta?
Cholesterol from the maternal circulation
What are the functions of estradiol in pregnancy?
Stimulates growth of myometrium
Stimulates growth (with progesterone) of ductal tissue of the breast
Along with relaxin, softens the maternal pelvic ligaments and pubic symphysis to allow expansion of the uterus
Stimulates LDL uptake and P450 enzymes (progesterone synthesis)
How do you measure placental function and foetal wellbeing?
Oestrogen levels
How doe amino acids cross the placenta?
Active transport
How does glucose cross the placenta?
Facilitated diffusion
How does foetal Hb differ from adult Hb?
Greater affinity for oxygen
What happens to nutrient exchange towards the end of pregnancy?
Capacity decreases and the placenta is less able to meet demands of foetus
What may predispose ectopic pregnancy?
Adhesions from PID or endometriosis
Where do most ectopic pregnancies attach?
Ampulla/isthmus of uterine tube
What happens to the placental membrane after 20 weeks?
Thins due to loss of cytotrophoblast
What may be detected in the maternal blood in the 3rd trimester?
Syncytiotrophoblast cells
