Implantation, placentation and hormone changes in pregnancy Flashcards
what 2 things do we need for implantation to occur?
- a fully fledged blastocyst
- Fully expanded
- Hatched out from the zona pellucida - a receptive endometrium
- Thickened endometrial lining
- Expression of embryo receptivity markers
blastocyst structure?
- made up of 2 cell lineages
- trophoblasts, outer layer, forms the placenta
- embryoblast, inner cell mass, forms the foetus - blastocoel is the fluid filled cavity
what does the blastocyst bathe in and when does it hatch?
bathes in uterine fluid, begins to hatch around the end of day 5
when does the zona pellucida become thinner?
after full blastocyst expansion
how is hatching achieved?
- enzymes dissolve the ZP at the abembryonic pole
- series of rhythmic expansions and contractions cause the blastocyst to bulge out of the ZP
summary of the stages of implantation:
apposition
-blastocyst positions itself close to the uterine wall or endometrium
attachment
-trophoblast cells attach to endometrium
invasion
-trophoblast cells multiply, invade into the endometrium and bury the blastocyst
is implantation tightly regulated?
Really tight regulated window of implantation, about 24-36 hours where implantation can take place
timeline of implantation
days 7-8
- blastocyst attaches to the surface of the endometrial wall (decidua basalis)
- trophoblast cells assemble and form a syncytiotrophoblast to facilitate invasion of decidua basalis
day 9-11
- syncytiotrophoblast further invades the decidua basalis
- by Day 11 almost completely buried in the decidua
day 12
- decidual reaction occurs
- high progesterone levels cause enlargement and coating of the decidual cells in glycogen and lipid-rich fluid
- fluid taken up by the syncytiotrophoblast, helps sustain the blastocyst early on before placenta formation
what happens to the blastocyst at around day 14?
junctional zone formation
- cells of the blastocyst protrude outwards and form tree-like structures called primary villi which form all around the blastocyst
- decidual cells behind the primary villi clear out forming lacunae
- maternal arteries and veins grow into the decidua basalis, and merge with the lacunae, arteries fill the lacunae with oxygenated blood
- veins return deoxygenated blood
- blood filled lacunae merge into a large pool of blood connected to many arteries and veins - junctional zone
is the placenta created by the mother?
no, the placenta is co-created by the mother and the foetus
-contributions from the endometrium and embryonic cells
formation of the placenta
- foetal mesoderm cells form blood vessels within the villi
- villi grow in size and develop into the Chorionic Frondosum
- endothelial cell wall and Syncytiotrophoblast (villi) lining separate maternal and foetal red blood cells
what forms in the fourth and fifth months of pregnancy?
decidual septa
what is the role of the decidual septa?
divides the placenta into 15-20 regions called Cotyledons.
- all supplied by different spiral arteries
- gives a larger SA in contact with maternal blood, more efficient with nutrient exchange
is the placenta formed in the upper or lower uterus?
upper
maternal foetal exchange?
foetus takes up oxygen and glucose, immunoglobins and hormones
-drops off co2 and waste products
functions of the placenta?
- Provision of maternal O2, CHO, fats, amino acids, vitamins, minerals, antibodies.
- Metabolism e.g. synthesis of glycogen.
- Barrier e.g. bacteria, viruses, drugs etc.
- Removal of foetal waste products e.g. CO2, urea, NH4, minerals.
- Endocrine secretion e.g. hCG, oestrogens, progesterone, HPL, cortisol.
Why is the placenta good at it’s job?
Huge maternal uterine blood supply – low pressure.
Huge surface area in contact with maternal blood.
Huge reserve in function.
name 3 placental disorders?
- pre-eclampsia
- placental abruption
- placenta previa
explain pre-eclampsia
- 3-4% of pregnancies
- constriction of maternal spiral arterioles which supply blood to the foetus
- results in placental insufficiency
- placenta responds to narrowing by releasing pro-inflammatory proteins which enter maternal circulation
- vasoconstriiiton, hypertension
- glomerular damage and proteinuria
what is placental insufficiency?
inadequate maternal blood flow to the placenta during pregnancy
risk factors for pre-eclampsia
First pregnancy Multiple gestation Maternal age >35yo Hypertension Diabetes Obesity Family history of pre-eclampsia
placental abruption
- premature separation of all or part of the placenta
- caused by degeneration of maternal arteries supplying blood to the placenta
- arteries rupture
- haemorrhage and placental separation
risk factors of placental abruption
- Blunt force trauma e.g. car crash, fall
- Smoking & recreational drug use – risk of vasoconstriction and increased blood pressure
- Multiple gestation
- Maternal age >35yo
- Previous placental abruption
- Hypertension from severe pre-eclampsia
complications of placental abruption?
COMPLICATIONS – MATERNAL
Hypovolemic shock
Sheehan Syndrome (Perinatal Pituitary Necrosis)
Renal failure
Disseminated Intravascular Coagulation (from release of thromboplastin)
COMPLICATIONS – FOETAL
Intrauterine hypoxia and asphyxia
Premature birth
explain how placental abruption causes coagulation?
Degeneration of blood vessels means clotting factors released into blood circulation, causing coagulation
explain what is meant by hypovolemic shock and why it causes Sheehan Syndrome
heart doesn’t have enough blood to circulate to all the regions of the body - not enough blood supplied to the pituitary so it dies. Loss of secondary sexual features
what is placenta previa?
placenta implants in the lower uterus, partially covering the lower os
-associated with increased chances of pre-term birth and foetal hypoxia
in placenta previa, why might the placenta implant in the lower uterus?
endometrium in the upper uterus might not be well vascularised
caesarean delivery or uterus surgery can cause upper uterus to be less vascularised, and when the blastocyst is trying to find an implantation point it will move to a more vascularised area.
once the blastocyst has implanted what is secreted?
trophoblasts start to secrete hcg which binds to LH receptors on CL, causing synthesis and secretion of oestrogen and progesterone
-progesterone produced in much higher amounts than oestrogen
when does serum HCG reach peak level?
by 9-11 weeks
when does the placenta take over from the CL?
week 7
what does the placenta synthesise?
- synthesises oestrogens from foetal androgens from the foetal adrenal cortex
- placenta synthesises progesterone from maternal cholesterol
beta-HCG levels
Very rapid increase, gradual fall in HCG
