Implantation, the placenta and hormonal changes in pregnancy Flashcards
(32 cards)
What do we need for implantation to occur?
A fully developed blastocyst - Fully expanded
Hatched out from the zona pellucida
-Blastocyst is made up of 2 cell lineages – Trophoblast (Purple - forms the placenta) and Embryoblast or inner cell mass (Green - forms the foetus).
Also present inside the blastocyst is a fluid-filled cavity known as the Blastocoel.
The embryoblast is concentrated at the ‘embryonic pole’ while the opposite pole (where trophoblast cells are concentrated) is known as the ‘abembryonic pole’
A receptive endometrium - thickened endometrial lining and expression of embryo receptivity markers
What are the stages of implantation?
- Apposition
- Attachment
- Invasion
How are the days broken up in the implantation timeline?
Days 7-8
Days 9-11
Days 12
Days 14
What happens on days 7-8 of implantation?
Blastocyst attaches itself to the surface of the endometrial wall (decidua basalis)
trophoblast cells start to assemble to form a Syncytiotrophoblast in order to facilitate invasion of decidua basalis
What happens on day 9-11 of implantation?
Syncytiotrophoblast further invades the decidua basalis
By day 11, it’s almost completely buried in the decidua
What happens on day 12 of implantation?
Decidual reaction occurs
High levels of progesterone –> enlargement and coating of the decidual cells in glycogen and lipid-rich fluid
The fluid is taken up by syncytiotrophoblast and helps to sustain the blastocyst early on before placenta formation
What happens on day 14 of implantation?
Cells of syncytiotrophoblast start to protrude out to form primary villi (tree like structures) which are then formed all around the blastocyst
Decidual cells between primary villi start to clear out leaving behind Lacunes (empty spaces)
Maternal arteries + veins start to grow into the decidua basalis, they merge w/ lacunae
- arteries filling the lacunae w/ oxygenated blood
- veins returning deoxygenated blood into the maternal circulation
Blood filled lacunae merge into a single large pool of blood connected to the multiple arteries and veins – JUNCTIONAL ZONE
What happens around day 17?
Placenta formation begins
foetal mesoderm cells start to form blood vessels within the villi - a basic network of arteries, veins and capillaries
- capillaries connect w blood vessels in the umbilical cord (formed ~ week 5)
villi grows larger in size –> Chorionic Frondosum
At this point, endothelial cell wall and Syncytiotrophoblast )(villi) lining separate maternal and foetal RBCs
What happens in the 4th and 5th months of pregnancy?
decidual septa form as they divide the placenta into 15-20 regions –> Cotyledons
Numerous maternal spiral arteries supply blood to each cotyledon, facilitating the maternal-foetal exchange
What is exchanged between the mother and foetus?
Through the umbilical cord, the foetus:
Takes up:
- oxygen and glucose
- immunoglobulins
- hormones
- toxins in some cases
drops off:
- CO2
- waste products
What are the functions of the placenta?
provision of maternal O2, CO2, fats, aa’s, vits, minerals, antibodies
metabolism e.g. synthesis of glycogen
barrier e.g. bacteria, viruses, drugs
Removal of foetal waste products, CO2, urea, NH4, minerals
Endocrine secretion e.g. hCG, oestrogens, progesterone, hPL, cortisol
The placenta is typically formed in the upper uterus.
Umbilical cord normally contains two arteries and one vein.
Why is the placenta good at its job?
Huge maternal uterine blood supply – low pressure.
Huge surface area in contact with maternal blood.
Huge reserve in function
What is pre eclampsia?
Disorder of the placenta
3-4% of pregnancies.
≥20 weeks gestation (up to 6 weeks after delivery).
Results in placental insufficiency – inadequate maternal blood flow to the placenta during pregnancy.
Causes new onset maternal hypertension and proteinuria.
Symptoms range from mild to life-threatening.
Disorders of implantation
Implantation disorders include ectopic pregnancy and recurrent miscarriage.
What are the risk factors for pre-eclampsia?
First pregnancy Multiple gestation Maternal age >35yo Hypertension Diabetes Obesity Family history of pre-eclampsia
What does pre-eclampsia +seizures equal?
eclampsia
What is the cause of pre-eclampsia and what is it characterised by?
Primary cause is still unclear.
Characterised by the narrowing of the maternal spiral arteries supplying blood to the placenta.
How does the placenta respond to the narrowing of the maternal spiral arteries in pre-eclampsia?
secretes pro-inflammatory proteins –> maternal circulation –> cause endothelial cell dysfunction (affects other systems leading to seizures in more serious case) –> vasoconstriction –> hypertension –> glomerular damage –> proteinuria
Explain placental abruption as a placental disorder.
Premature separation of all or part of the placenta.
Symptoms include vaginal bleeding and pain in the back and abdomen
What are the risk factors for 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
What is placental abruption caused by?
Caused by the degeneration of maternal arteries supplying blood to the placenta.
Degenerated vessels rupture causing haemorrhage and separation of the placenta.
What maternal complications can you have?
Hypovolemic shock
Sheehan Syndrome - degeneration of pituitary gland (Perinatal Pituitary Necrosis) –> loss of secondary sexual features and impaired repro function
Renal failure
Disseminated Intravascular Coagulation (from release of thromboplastin)
What foetal complications can you have?
Intrauterine hypoxia and asphyxia
Premature birth
Explain placenta previa as a disorder of the placenta
Placenta implants in lower uterus, fully or partially covering the internal cervical os.
Associated with increased chances of pre-term birth and foetal hypoxia.
