Implantation, Placentation and Hormonal Changes in Pregnancy Flashcards
What is a blastocyst?
→ An embryo at the 5th or 6th day of development
What does the embryoblast give rise to?
→ The fetus
What are the three layers of the blastocyst?
→ Trophoblast
→ Blastocoel
→ Embryoblast
What does the trophoblast give rise to?
→ The placenta
What is the blastocoel?
→ The fluid filled cavity
What are the two things needed for implantation to occur?
→ The blastocyst has to be fully mature
→ A receptive endometrium is needed which expresses receptivity markers to communicate with the blastocyst
Describe hatching
→The blastocyst hatches out of the zona pellucida due to expansions and contractions
→ this herniates the blastocyst out of the zona
→ digestive enzymes break down the opposite pole of where the blastocyst is
Where do the enzymes dissolve the zona?
→ Abembryonic pole
What are the three stages of implantation?
1) Apposition
2) Attachment
3) Invasion
What is Apposition?
→ Close positioning of the blastocyst to the endometrium
What is Attachment?
→ Cells of the trophoblast attaching to endometrium
What is Invasion?
→ Trophoblast cells multiply and invade the endometrium
Describe how the embryo implants (days 7-11)
→ The blastocyst attaches itself to the surface of the endometrial wall (decidua basalis)
→ Trophoblast cells start to assemble to form a syncytiotrophoblast to facilitate invasion
→ Syncytiotrophoblast further invades the decidua basalis and by day 11 it is almost completely buried
Describe the decidual reaction
→ High levels of progesterone results in the enlargement and coating of the decidual cells in glycogen and lipid-rich fluid
→ the fluid is taken up by the syncytiotrophoblast and helps sustain the blastocyst early on before the placenta is formed
What is a syncytiotrophoblast?
→ A group of trophoblast cells which are multinucleated
How are primary villi formed?
→ Cells of the syncytiotrophoblast start to protrude out to form tree-like structures known as primary villi which are formed around the blastocyst
How are lacunae formed?
→ Decidual cells between the primary villi begin to clear out leaving behind empty spaces known as lacunae
How does the junctional zone form?
→ Maternal arteries and veins grow into the decidua basalis
→ Blood vessels merge with the lacunae
→ Arteries fill the lacunae with oxygenated blood
→ Veins return the deoxygenated blood to the maternal circulation
→ Blood filled lacunae merge to a single large pool of blood connected to multiple arteries and veins
→this is known as the junctional zone
When is the umbilical cord formed?
→ Around week 5
Describe how chorionic frondosum form?
→ Day 17 the fetal mesoderm cells start to form blood vessels within the villi
→ a basic network of arteries, veins and capillaries
→ capillaries connect with blood vessels in the umbilical cord
→ villi grow larger in size and develop into chorionic frondosum
What separates maternal and fetal blood cells?
→ The outer lining of the primary villi is in contact with the junctional zone
→ The lining of the endothelial cells of the decidual from the mothers side
When do the decidual septa form?
→ 4th and 5th month
What is the function of decidual septa?
→ They divide the placenta into 15-20 regions
→ This gives it a much larger surface area in contact with the maternal blood
What is the umbilical cord made up of?
→ Two arteries and one vein
What does the placenta take up?
→ O2 and glucose
→ immunoglobulins
→ hormones
→ toxins
What does the placenta drop off?
→ Co2
→ Waste products
What are the 4 functions of the placenta?
→ Provision of maternal O2, CHO, Fats, amino acids, vitamins, minerals, antibodies
→ metabolism - synthesis of glycogen
→Barrier - bacteria, viruses, drugs
→ Removal of fetal waste products : CO2, urea, NH4, minerals
→ Endocrine secretion e.g : hCG, estrogens, progesterone, HPL, cortisol
How is the placenta adapted to its function?
→ Huge maternal uterine supply - low pressure
→ huge surface area in contact with maternal blood
→ huge reserve in function
What is the placental barrier formed by?
→ Cells of the villi
How many pregnancies does pre-eclampsia affect?
→ 3-4%
When does pre-eclampsia start and how long can it last?
→ >20 weeks of gestation
→ can show up upto 6 weeks after delivery
What does pre-eclampsia result in?
→ Placental insufficiency - inadequate maternal blood flow to the placenta during pregnancy
What does pre-eclampsia cause?
→ new onset maternal hypertension and proteinuria
What are the 7 risk factors for pre-eclampsia?
→ First pregnancy → Multiple gestation → Maternal age > 35 → Hypertension → DIabetes → Obesity → Family history of pre-eclampsia
What is eclampsia?
→ Pre-eclampsia + seizures
What is pre-eclampsia caused by?
→ narrowing of maternal spiral arteries supplying blood to the placenta
Describe how pre-eclampsia works?
→ Placenta responds by secreting pro inflammatory proteins
→ these enter the maternal circulation and cause dysfunction of the maternal endothelial cells
→ this causes vasoconstriction and affects other body systems
What are the first signs of pre-eclampsia?
→ Proteinuria (impaired filtration)
→ high blood pressure
Why does proteinuria occur during pre-eclampsia?
→ Glomerular damage
What are the 6 risk factors for placental abruption?
→ Blunt force trauma → Smoking and drug use → multiple gestation → Maternal age > 35 → previous placental abruption → hypertension from previous pre-eclampsia
What are the symptoms of placental abruption?
→ Vaginal bleeding
→ Pain in back and abdomen
What are the causes of placental abruption?
→ Degeneration of maternal arteries supplying blood to the placenta
→ Degenerated vessels rupture causing haemorrhage and separation of the placenta
What are 4 complications that occur as a result of placental abruption?
→ Hypovolemic shock
→ Sheehan syndrome
→ Renal failure
→ Disseminated intravascular coagulation
What is Sheehan syndrome?
→ Not enough blood to the pituitary
→ perinatal pituitary necrosis
What are fatal complications of placental abruption?
→ Intrauterine hypoxia and premature birth
What is placenta previa?
→ Placenta implants in the lower uterus
→ fully or partially covering the internal cervical os
What is placenta previa associated with?
→ Increased chances of preterm birth and fetal hypoxia
What are 7 risk factors associated with placenta previa?
→ Previous C section → previous uterine/endometrial surgery → uterine fibroids → previous placenta previa → smoking and drug use → multiple gestation → maternal age > 35
What is the cause of placenta previa?
→ Endometrium in upper uterus not well vascularised
What do trophoblasts secrete?
→ hCG
What is the function of hCG?
→ It binds to LH receptors on the CL
→ results in synthesis and secretion of progesterone and estrogen
What is the ratio of progesterone to estrogen?
→ Progesterone is much higher
When is there a decline in hCG and why?
→ At week 7
→ Placenta takes over and produces progesterone
When does hPL increase?
→ Around week 5
What is the function of hPL?
→ Makes the mother a bit more resistant to insulin so there is more glucose in the bloodstream available for mother and fetus
How does the placenta make progesterone?
→ Cholesterol is received from the placenta
→ converted into pregnenolone and progesterone
→ it makes its way to the mothers circulation
How does the placenta make estrogen?
→ Adrenal androgens from the fetus DHEA and DHEAS
→ placenta converts these into estrogens
What is the cause of gestational diabetes?
→ hPL not functioning properly
