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