Implantation, Placentation and Hormonal Changes in Pregnancy Flashcards Preview

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Flashcards in Implantation, Placentation and Hormonal Changes in Pregnancy Deck (58)
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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

β†’The 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
β†’this 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
β†’Barrier - 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