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Repro > Implantation, placentation and hormone changes in pregnancy > Flashcards

Implantation, placentation and hormone changes in pregnancy Flashcards

1
Q

What do we need for implantation to occur?

A
  • A fully developed blastocyst

- A receptive endometrium

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2
Q

What are the two cell lineages that make up the blastocyst?

A
  • Trophoblast

- Embryoblast

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3
Q

What does the trophoblast form?

A

The placenta

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4
Q

What does the embryoblast form?

A

The inner cell mass that forms the foetus

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5
Q

What is the fluid-filled cavity in the blastocyst called?

A

The blastocoel

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6
Q

Where is the embryoblast concentrated?

A

It is concentrated at the ‘embryonic pole’

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7
Q

Where are the trophoblast cells concentrated?

A

At the opposite pole called the ‘abembryonic pole’

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8
Q

Where does the blastocyst hatch out from?

A

The zona pellucida

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9
Q

What is the state of a receptive endometrium?

A
  • Thickened endometrial lining

- Expression of embryo receptivity markers

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10
Q

Describe the process of the blasocyst hatching

A
  1. The blastocyst bathes in uterine fluid and then begins to hatch around the endo of day 5.
  2. After full blastocyst expansion, the zona pellucida becomes a lot thinner and hatching is achieved via a combination of mechanisms.
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11
Q

What mechanisms allow the blastocyst to hatch?

A
  • Enzymes that dissolve the zona at the abembryonic pole
  • A series of rhythmic expansions and contractions that enable the blastocyst to herniate and bulge out of the zona pellucida
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12
Q

What day does the blastocyst hatch from the zona pellucida?

A

Day 5

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13
Q

What are the 3 stages of implantation?

A
  1. Apposition
  2. Attachment
  3. Invasion
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14
Q

What happens around day 7-8 of implantation?

A
  • Blastocyst attaches to the surface of the endometrial wall (decidua basalis)
  • Trophoblast cells start to assemble to form a syncytiotrophoblast in order to facilitate invasion of the decidua basalis.
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15
Q

What happens around day 9-11 of implantation?

A

Syncytiotrophoblast further invades the decidua basalis and by day 11, it almost completely buried in the decidua

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16
Q

What happens around day 12 of implantation?

A
  • Decidual reaction occurs - high levels of progesterone result in the enlargement and coating of the decidual cells in glycogen and lipid-rich fluid.
  • This fluid is taken up by the syncytiotrophoblast and helps sustain the blastocyst early on before the placenta is formed.
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17
Q

What happens around day 14 of implantation?

A
  • Cells of the syncytiotrophoblast protrude to form tree-like structures known as primary villi around the blastocyst.
  • Decidual cells between the primary villi start to clear out, leaving empty spaces called lacunae.
  • The junctional zone forms which is when the maternal arteries and veins grow into the decidua basalis merging with the lacunae filling it with oxygenated blood and the veins returning deoxygenated blood to maternal circulation.
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18
Q

What is the junctional zone?

A

The circulatory foundation for the formation of the placenta

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19
Q

What creates the placenta?

A

It is co-created by the mother and foetus, with contributions from endometrial as well as embryonic cells/tissues.

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20
Q

What does the foetus contribute to the placenta?

A

The chorionic frondosum

The chorionic plate

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21
Q

What does the mother contribute to the placenta?

A

Maternal arteries - spiral arteries

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22
Q

What happens around day 17?

A

The foetal mesoderm cells start to form blood vessels within the villi. Capillaries connect with the blood vessels in the umbilical cord.

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23
Q

When is the umbilical cord formed?

A

Around week 5

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24
Q

What forms the chorionic frondosum?

A

The villi growing larger in size

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25
Q

What separates the maternal and foetal red blood cells?

A

The endothelial cell wall and syncytiotrophoblast (villi).

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26
Q

What are the cotyledons and when do they form?

A

The cotyledons are divisions of the placenta by the decidual septa forming 15-20 regions. This occurs in the 4th and 5th months of pregnancy

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27
Q

What supplies the cotyledons?

A

Numerous maternal spiral arteries supply blood to each cotyledons, facilitating the maternal-foetal exchange

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28
Q

Describe the exchange of the placenta maternal and foetal

A

Takes up:

  • O2 and glucose
  • Immunoglobulins
  • Hormones
  • Toxins (in some cases)

Drops off

  • CO2
  • Waste products
29
Q

Where does the placenta form?

A

In the upper uterus

30
Q

What does the umbilical cord contain?

A

It contains two arteries and one vein

31
Q

What are the functions of the placenta?

A
  • Provision of material e.g. O2, CHO, fats, amino acids, vitamins, minerals, antibodies etc
  • Metabolism e.g. synthesis of glycogen
  • Barrier e.g. bacteria, viruses, drugs etc
  • Removal of foetal waste products e.g. CO2, urea, NH4, minerals
  • Endocrine secretion e.g. hCG, oestrogens, progesterone, hPL, cortisol
32
Q

What specialisms does the placenta have to do its function?

A
  • Huge maternal-uterine blood supply and low pressure (High volume, low pressure)
  • Huge surface area in contact with maternal blood
  • Huge reserve in function
  • Barrier formed by the cells of the villi
33
Q

What percentage of pregnancies does pre-eclampsia affect?

A

3-4% of pregnancies

34
Q

What does pre-eclampsia cause?

A
  • Placental insufficiency
  • Maternal hypertension
  • Proteinuria
35
Q

What is placental insufficiency?

A

Inadequate maternal blood flow to the placenta during pregnancy

36
Q

What are the risk factors of pre-eclampsia?

A
  • First pregnancy
  • Multiple gestation
  • Maternal age > 35 years old
  • Hypertension
  • Diabetes
  • Obesity
  • Family history of pre-eclampsia
37
Q

Pre-eclampsia + seizures =

A

eclampsia

38
Q

What is the primary cause of pre-eclampsia?

A

Still unclear

39
Q

What is pre-eclampsia characterised by?

A

The narrowing of the maternal spiral arteries supplying blood to the placenta.

40
Q

Why is placental insufficiency dangerous?

A

It can compromises the transfer of necessary nutrients to support the development of the foetus.

41
Q

When does pre-eclampsia occur?

A

It occurs usually around 20 weeks gestation or could still develop after delivery - up to 6 weeks after delivery.

42
Q

How does pre-eclampsia cause proteinuria and maternal hypertension?

A

Pro-inflammatory proteins enter the mother’s circulation causing endothelial cell dysfunction. This causes vasoconstriction, hypertension and glomerular damage. If there is glomerular damage, this can cause proteinuria.

43
Q

How severe are the symptoms of pre-eclampsia?

A

mild to life-threatening

44
Q

What is placenta abruption?

A

Premature separation of all or part of the placenta

45
Q

What are the symptoms of placenta abruption?

A

Vaginal bleeding and pain in the back and abdomen

46
Q

What are the risk factors of placenta abruption?

A
  • Blunt force trauma e.g. car crash, fall
  • Smoking and recreational drug use
  • Multiple gestation
  • Maternal age > 35 yo
  • Previous placental abruption
  • Hypertension from severe pre-eclampsia
47
Q

What causes placenta abruption?

A

The degeneration of maternal arteries supplying blood to the placenta. Degenerated vessels rupture causing haemorrhage and separation of the placenta.

48
Q

What are the maternal complications of placenta abruption?

A
  • Hypovolemic shock
  • Sheehan syndrome (perinatal pituitary necrosis)
  • Renal failure
  • Disseminated intravascular coagulation (from release of thromboplastin)
49
Q

What are the foetal complications of placenta abruption?

A
  • Intrauterine hypoxia and asphyxia

- Premature birth

50
Q

What is placenta previa?

A

This is when the placenta implants in lower uterus, fully or partially covering the internal cervical os.

51
Q

What is placenta previa associated with?

A

It is associated with increased chances of pre-term birth and foetal hypoxia.

52
Q

What causes placenta previa?

A

Still unclear but could be due to endometrium in the upper uterus not well vascularised.

53
Q

What are the risk factors for placenta previa?

A
  • Previous caesarean delivery
  • Previous uterine/endometrial surgery
  • Uterine fibroids
  • Previous placenta previa
  • Smoking and re-creational drug use
  • Multiple gestation
  • Maternal age > 35yo
54
Q

What is hydatiform mole?

A

Overgrowth of placental cells on to the uterus

55
Q

What suppresses the maturation of other follicles in the ovary?

A

The continued presence of the low oestrogen: progesterone ratio

56
Q

When is beta hCG detected and by what?

A

It can be detected in the blood stream as early as Day 9 and is the basis of urinary qualitative pregnancy tests

57
Q

What is serum beta hCG (quantitative) useful for?

A

It is useful for monitoring early pregnancy complications e.g. ecotopic pregnancy, miscarriage

58
Q

When does serum hCG hit peak levels?

A

By 9-11 weeks

59
Q

When does the placenta take over producing hormones?

A
  • Around week 7
60
Q

What does the placenta synthesis oestrogens from?

A

From foetal androgens from the foetal adrenal cortex.

61
Q

What does the placenta synthesis progesterone from?

A

From maternal cholesterol

62
Q

What is pregnenolone converted into and where?

A

Converted to progesterone in placental mitochondria

63
Q

What synthesises HPL?

A

It is synthesised by cells of the syncytiotrophoblast.

It is structurally and functionally similar to growth hormone.

64
Q

What encodes polypeptide hormone and what mediates it?

A

It is encoded by a cluster of genes on chromosome 17. Effects are believed to be mediated via a variant of the growth hormone receptor.

65
Q

What do oestrogen and progesterone do?

A

They work alongside other hormones to trigger the physiological changes observed during pregnancy such as:

  • Shallow breathing
  • Increase in blood volume
  • Increase in urinary output
  • Breast changes
  • Loosened ligaments
  • Nausea and taste changes
  • Mood changes
66
Q

What happens to the levels of hCG during pregnancy?

A

At week 10, hCG is at the highest levels by the end of the weeks of gestation, the hCG are at the lowest.

67
Q

What happens to the levels of human placental lactogen

(hPL) levels during pregnancy?

A

Increases gradually from week 5 to week 40 (end of gestation)

68
Q

What happens to progesterone and oestrogen ?

A

Increase gradually over the 40 weeks of gestation

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