Implantation, Placentation and Hormonal Changes in Pregnancy

Question 1

What is a blastocyst?

Answer 1

→ An embryo at the 5th or 6th day of development

Question 2

What does the embryoblast give rise to?

Answer 2

→ The fetus

Question 3

What are the three layers of the blastocyst?

Answer 3

→ Trophoblast
→ Blastocoel
→ Embryoblast

Question 4

What does the trophoblast give rise to?

Answer 4

→ The placenta

Question 5

What is the blastocoel?

Answer 5

→ The fluid filled cavity

Question 6

What are the two things needed for implantation to occur?

Answer 6

→ The blastocyst has to be fully mature

→ A receptive endometrium is needed which expresses receptivity markers to communicate with the blastocyst

Question 7

Describe hatching

Answer 7

→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

Question 8

Where do the enzymes dissolve the zona?

Answer 8

→ Abembryonic pole

Question 9

What are the three stages of implantation?

Answer 9

1) Apposition
2) Attachment
3) Invasion

Question 10

What is Apposition?

Answer 10

→ Close positioning of the blastocyst to the endometrium

Question 11

What is Attachment?

Answer 11

→ Cells of the trophoblast attaching to endometrium

Question 12

What is Invasion?

Answer 12

→ Trophoblast cells multiply and invade the endometrium

Question 13

Describe how the embryo implants (days 7-11)

Answer 13

→ 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

Question 14

Describe the decidual reaction

Answer 14

→ 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

Question 15

What is a syncytiotrophoblast?

Answer 15

→ A group of trophoblast cells which are multinucleated

Question 16

How are primary villi formed?

Answer 16

→ Cells of the syncytiotrophoblast start to protrude out to form tree-like structures known as primary villi which are formed around the blastocyst

Question 17

How are lacunae formed?

Answer 17

→ Decidual cells between the primary villi begin to clear out leaving behind empty spaces known as lacunae

Question 18

How does the junctional zone form?

Answer 18

→ 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

Question 19

When is the umbilical cord formed?

Answer 19

→ Around week 5

Question 20

Describe how chorionic frondosum form?

Answer 20

→ 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

Question 21

What separates maternal and fetal blood cells?

Answer 21

→ 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

Question 22

When do the decidual septa form?

Answer 22

→ 4th and 5th month

Question 23

What is the function of decidual septa?

Answer 23

→ They divide the placenta into 15-20 regions

→ This gives it a much larger surface area in contact with the maternal blood

Question 24

What is the umbilical cord made up of?

Answer 24

→ Two arteries and one vein

Question 25

What does the placenta take up?

Answer 25

→ O2 and glucose → immunoglobulins → hormones → toxins

Question 26

What does the placenta drop off?

Answer 26

→ Co2 | → Waste products

Question 27

What are the 4 functions of the placenta?

Answer 27

→ 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

Question 28

How is the placenta adapted to its function?

Answer 28

→ Huge maternal uterine supply - low pressure → huge surface area in contact with maternal blood → huge reserve in function

Question 29

What is the placental barrier formed by?

Answer 29

→ Cells of the villi

Question 30

How many pregnancies does pre-eclampsia affect?

Answer 30

→ 3-4%

Question 31

When does pre-eclampsia start and how long can it last?

Answer 31

→ >20 weeks of gestation | → can show up upto 6 weeks after delivery

Question 32

What does pre-eclampsia result in?

Answer 32

→ Placental insufficiency - inadequate maternal blood flow to the placenta during pregnancy

Question 33

What does pre-eclampsia cause?

Answer 33

→ new onset maternal hypertension and proteinuria

Question 34

What are the 7 risk factors for pre-eclampsia?

Answer 34

``` → First pregnancy → Multiple gestation → Maternal age > 35 → Hypertension → DIabetes → Obesity → Family history of pre-eclampsia ```

Question 35

What is eclampsia?

Answer 35

→ Pre-eclampsia + seizures

Question 36

What is pre-eclampsia caused by?

Answer 36

→ narrowing of maternal spiral arteries supplying blood to the placenta

Question 37

Describe how pre-eclampsia works?

Answer 37

→ 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

Question 38

What are the first signs of pre-eclampsia?

Answer 38

→ Proteinuria (impaired filtration) | → high blood pressure

Question 39

Why does proteinuria occur during pre-eclampsia?

Answer 39

→ Glomerular damage

Question 40

What are the 6 risk factors for placental abruption?

Answer 40

``` → Blunt force trauma → Smoking and drug use → multiple gestation → Maternal age > 35 → previous placental abruption → hypertension from previous pre-eclampsia ```

Question 41

What are the symptoms of placental abruption?

Answer 41

→ Vaginal bleeding | → Pain in back and abdomen

Question 42

What are the causes of placental abruption?

Answer 42

→ Degeneration of maternal arteries supplying blood to the placenta → Degenerated vessels rupture causing haemorrhage and separation of the placenta

Question 43

What are 4 complications that occur as a result of placental abruption?

Answer 43

→ Hypovolemic shock → Sheehan syndrome → Renal failure → Disseminated intravascular coagulation

Question 44

What is Sheehan syndrome?

Answer 44

→ Not enough blood to the pituitary | → perinatal pituitary necrosis

Question 45

What are fatal complications of placental abruption?

Answer 45

→ Intrauterine hypoxia and premature birth

Question 46

What is placenta previa?

Answer 46

→ Placenta implants in the lower uterus | → fully or partially covering the internal cervical os

Question 47

What is placenta previa associated with?

Answer 47

→ Increased chances of preterm birth and fetal hypoxia

Question 48

What are 7 risk factors associated with placenta previa?

Answer 48

``` → Previous C section → previous uterine/endometrial surgery → uterine fibroids → previous placenta previa → smoking and drug use → multiple gestation → maternal age > 35 ```

Question 49

What is the cause of placenta previa?

Answer 49

→ Endometrium in upper uterus not well vascularised

Question 50

What do trophoblasts secrete?

Answer 50

→ hCG

Question 51

What is the function of hCG?

Answer 51

→ It binds to LH receptors on the CL | → results in synthesis and secretion of progesterone and estrogen

Question 52

What is the ratio of progesterone to estrogen?

Answer 52

→ Progesterone is much higher

Question 53

When is there a decline in hCG and why?

Answer 53

→ At week 7 | → Placenta takes over and produces progesterone

Question 54

When does hPL increase?

Answer 54

→ Around week 5

Question 55

What is the function of hPL?

Answer 55

→ Makes the mother a bit more resistant to insulin so there is more glucose in the bloodstream available for mother and fetus

Question 56

How does the placenta make progesterone?

Answer 56

→ Cholesterol is received from the placenta → converted into pregnenolone and progesterone → it makes its way to the mothers circulation

Question 57

How does the placenta make estrogen?

Answer 57

→ Adrenal androgens from the fetus DHEA and DHEAS | → placenta converts these into estrogens

Question 58

What is the cause of gestational diabetes?

Answer 58

→ hPL not functioning properly