8.1 Flashcards
When does the blastocyst implant into the endometrium?
Day 6
Fully imbedded by day 10
What occurs in implantation?
Interaction between invasive trophoblast cells and epithelium of the uterus.
What are 3 aims of implantation?
Establish basic unit of exchange
Anchor the placenta
- Establishment of outermost cytotrophoblast shell.
Establish maternal blood flow within the placenta.
What does haemonochorial mean?
Placenta is haemonochorial
One layer of trophoblast ultimately separates maternal blood from the fetal capillary wall.
How does the placenta membrane change over time?
Placenta membrane becomes progressively thinner as needs of fetus increases.
What are the primary, secondary and tertiary villi?
• Primary villi
o Early, finger-like projections of trophoblast
• Secondary villi
o Invasion of mesenchyme into core
• Tertiary villi
o Invasion of mesenchyme core by fetal vessels
What are the two components of the trophoblast?
Syncytiotrophoblast
Cytotrophoblast
How is the endometrium prepared for implantation?
Decidualisation
Pre decimal cells
The decimal reaction provides balancing force for the invasive force of the trophoblast.
Stimualted by progesterone.
Without this, conditions characterised by excessive invasion - haemorrhage, ectopic pregnancy can occur.
Remodelling of the spiral arteries
Creation of low resistance vascular bed
Maintains the high flow required to meet fetal demand, particularly in late gestation.
Describe decidualisation
Pre decidual cells
The decimal reaction provides balancing force for the invasive force of the trophoblast.
Stimualted by progesterone.
Without this, conditions characterised by excessive invasion - haemorrhage, ectopic pregnancy can occur.
Describe remodelling of the spiral arteries.
Creation of low resistance vascular bed
Maintains the high flow required to meet fetal demand, particularly in late gestation.
Describe ectopic pregnacny.
o Implantation at site other than uterine body
o Most commonly fallopian tube
o Can be peritoneal or ovarian
o Can very quickly become a life-threatening emergency
Describe placenta praevia.
o Implantation in the lower uterine segment
o Can cause haemorrhage in pregnancy
o Requires C-Section delivery
What is pre-eclampsia?
Hypertension and high protein in urine.
What are the 2 components of the placenta and what forms them?
- A fetal portion
o Formed by the chorion frondsum
o Bordered by the chorionic plate - A maternal portion
o Formed by the decidua basalis
o The decidual plate is most intimately incorporated into the placenta
What is found between the decidua and chorionic plate?
Intervillous spaces, filled with maternal blood.
What are cotyledons?
Dedcidua form a number of decimal septa which project into intervillous spas but do not reach the chorionic plate.
These divide the placenta into cotyledon compartments.
Describe the first trimester placenta.
- Placenta established
- Placental ‘barrier’ to diffusion still relatively thick
- Complete cytotrophoblast layer beneath syncytiotrophoblast
Describe the term placenta.
- Surface area for exchange dramatically increased
- Placental ‘barrier’ is now thin
- Cytotrophoblast layer beneath syncytiotrophoblast lost
Descibe the umbilical cord vessels.
Two Umbilical Arteries
• Deoxygenated blood from fetus → Placenta
One Umbilical Vein
• Oxygenated blood from Placenta → Fetus
How do cotyledons receive blood?
Cotyledons receive their blood through 80 – 100 spiral arteries that pierce the decidual plate. Pressure in these arteries forces oxygenated blood deep into the intervillous spaces and bathes the numerous small villi of the villous tree in oxygenated blood.
As the pressure decreases, blood flows back form the chorionic plate towards the decidua, where it enters the endometrial veins.
What are the factors influencing the passive diffusion of substances across the placenta?
• Concentration Gradient
o The steeper the gradient, the more diffusion
• Barrier to diffusion
o Placental membrane gradually thins throughout pregnancy as the demand of the fetus increases
• Diffusion distance
o Haemomonochorial
What substances pass through the placenta by simple diffusion?
• Water • Electrolytes • Urea and uric acid • Gases o Flow limited, not diffusion-limited o Fetal O2 stores are small – maintenance of adequate flow is essential
What substances pass through the placenta by facilitated diffusion?
Glucose
What substances pass through the placenta by active transport?
Specific transporters are expressed by the syncytiotrophoblast:
• Amino acids
• Iron
• Vitamins
