Implantation, Placentation & Hormone Changes in Pregnancy Flashcards
What is Implantation?
blastocyst attaches to uterine wall
What are the Requirements for implantation?
Fully Developed Blastocyst
- 5th/6th day of development
- hatched out from zona pellucida
Receptive Endometrium
- thickened endometrium during proliferative phase
- expression of embryo receptivity markers to communicate with blastocyst
Describe the Blastocyst structure.
Embryoblast (inner cell mass)
-forms foetus
Trophoblast (outer cells)
-forms placenta
Blastocoel (fluid filled cavity)
What is the embryonic pole of the blastocyst?
pole where embryoblast (inner cell mass) is located
What is the aembryonic pole of the blastocyst?
pole where trophoblasts are concentrated
When and how does the blastocyst hatch from the zona pellucida?
Day 5:
- enzymes dissolve zona pellucida at aembryonic pole
- rhythmic contraction enable blastocyst to herniate and bulge out of the zona pellucida
Why is hatching essential for implantation?
because the zona coat prevents blastocyst from communicating with endometrium
What are the Stages of Implantation?
3 stages:
APPOSITION
-close positioning of blastocyst to endometrium (decidua basalis)
ATTACHMENT
-trophoblast cells attach to endometrium
INVASION
-trophoblast cells multiply and invade into endometrium, implanting embryo in endometrium
Describe the Days 7-8 of the Implantation Timeline.
Blastocyst attaches to surface of endometrial wall
Trophoblast cells assemble to form Syncytiotrophoblast in order to facilitate invasion of endometrium
Describe days Days 9-11 of the implantation timeline.
Syncytiotrophoblast further invades endometrial wall
By day 11, blastocyst is almost completely buried in endometrium
Describe day 12 of the implantation timeline.
Decidual Reaction
- high progesterone levels enlarge and coat decidual cells in glycogen and lipid-rich fluid
- fluid taken up by syncytiotrophoblast to sustain the blastocyst before placenta is formed
Describe day 14 of the implantation timeline.
Syncytiotrophoblast cells protrude out to form tree-like structures “Primary Villi” which are then formed all around the blastocyst
Decidual cells between primary villi clear out, leaving behind empty spaces called Lacunae
Maternal arteries and veins start to grow into the decidua basali and merge with Lacunae; arteries fill them with oxygenated blood and veins return deoxygenated blood to maternal circulation
Blood filled lacunae merge into one large one pool of blood connected to multiple arteries and veins known as the Junctional Zone (circulatory foundation for placenta formation)
When is the umbilical cord formed?
5th week
-then connected to capillaries formed by the foetal mesoderm cells which then feed into the junctional zone and supplied by maternal circulation
What is the foetal contribution to the placenta?
Chorionic Frondosum
What is the maternal contribution to the placenta?
Maternal Spiral Arteries
What happens in 4th/5th months of pregnancy to placenta?
decidual septa forms, dividing the placenta into 15-20 regions known as Cotyledons
this provides efficiency maternal-foetal exchange of nutrients due to an increase in surface area
Placenta takes up…
- O2 and glucose
- immunoglobulins
- hormones
- toxins (in some cases)
- amino acids
- vitamins
- minerals
- fats
Waste products the placenta drops off from foetus are…
CO2 Waste products (urea, ammonia, etc)
Where is the placenta formed?
upper part of the uterus
What is the umbilical cord made of?
2 arteries and 1 vein
What is the Pre-eclampsia?
maternal spiral arteries are fibrous and narrow, limiting blood supply to the placenta (placental insufficiency)
What is Eclampsia?
preeclampsia + seizures
Describe the Response of placenta to pre-eclampsia.
1) Secretes pro-inflammatory proteins that make way into maternal circulation and cause endothelial cell dysfunction
2) Endothelial cell dysfunction affects other body systems causing:
- vasoconstriction> maternal hypertension
- vasoconstriction>glomerular damage from hypertension> proteinuria
What are the Risk factors for pre-eclampsia?
- first pregnancy
- multiple gestation
- increased maternal age (>35)
- hypertension
- diabetes
- obesity
- family history of pre-eclampsia
What is a Hydatidiform mole?
overgrowth of placental cells on uterus
What is Placental Abruption?
maternal spiral arteries supplying blood to placenta degenerate and rupture, causing haemorrhage and premature separation of all or part of the placenta from the endometrium
What are the Symptoms of placental abruption?
vaginal bleeding
pain in back/abdomen
What are the Maternal Complications of Placental Abruption?
- Hypovolaemic shock
- Sheehan Syndrome (perinatal pituitary necrosis)- hypopituitarism
- renal failure
- disseminated intravascular coagulation (DIC)
What are the Foetal Complications of Placental Abruption?
Intrauterine hypoxia and asphyxia
Premature birth
What is Placenta Previa?
placenta implants in lower uterus, either fully or partially covering the internal cervical os
What are the Risk factors for placenta previa?
- previous C section
- previous uterine/endometrial surgery
- uterine fibroids
- previous placenta previa
- smoking & recreational drug use
- multiple gestation
- increased maternal age
What is the Risk of placenta previa?
increased risk of pre-term birth and foetal hypoxia
Which cells secrete hCG?
trophoblast cells in corpus luteum after implantation
What is the basis of urinary tests?
β-hCG
Initial hCG production is by…
corpus luteum
Around week 7, hCG production is by…
placenta
*also decrease in hCG due to degeneration of corpus luteum
What are the Hormones the placenta synthesizes and releases into maternal circulation?
Oestrogens from foetal androgens from foetal cortex
Progesterone from maternal cholesterol
human Placental Lactogen (hPL), making mother more insulin resistant so glucose available for both mother and foetus
