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Reproduction (Physiology 2) > Implantation, Placentation & Hormone Changes in Pregnancy > Flashcards

Implantation, Placentation & Hormone Changes in Pregnancy Flashcards

1
Q

What is a trophoblast?

A

cells of blastocyst that invade endometrium and myometrium (D 5-6)
- secrete ßHCG (Human Chorionic Gonadotrophin)

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2
Q

What is a chorion?

A

The outermost membrane surrounding an embryo contributes to become the placenta

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3
Q

What is the amnion?

A

Membrane layer that becomes the amniotic sac

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4
Q

What is a blastocyst?

A

Blastocyst is an embryo at the 5/6th day of development. It has 2 definitive cell lines

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5
Q

What are the requirements of implantation?

A
  • Fully expanded Blastocyst
  • Blastocyst hatched out of zona pellucida
  • Thickened endometrial lining
  • Embryo receptivity marker expression
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6
Q

What are the 2 definitive cell lines of a blastocyst?

A

Embryoblasts give rise to foetus

Tropoblasts give rise to placenta

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7
Q

What is the endometrium?

A

A receptive endometrium is a receptive uterus lining.

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8
Q

Outline the features of the lining at implantation

A

The lining should have thickened during the secretory phase and should now be expressing receptivity markers to communicate with the blastocyst

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9
Q

How does the blastocyst hatch out the zona pellucida?

A

The blastocyst bathes in uterine fluid and then begins to hatch around the end of day 5.

After full blastocyst expansion the zona pellucida becomes a lot thinner and hatching is achieved via a combination of 2 mechanisms

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10
Q

What are the 2 mechanisms responsible for blastocyst hatching?

A

(1) Enzymes that dissolve the zona at the abembryonic
pole

(2) A series of rhythmic expansions and contractions that
enable the blastocyst herniate and bulge out of the
zona pellucida

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11
Q

What are the stages of implantation?

A

The process of implantation can be summarised in 3 steps:

  1. Apposition
  2. Attachment
  3. Invasion
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12
Q

Explain what occurs at days 7 - 8 of implantation

A

Blastocyst attaches itself 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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13
Q

Explain the events of implantation at Days 9 - 11

A

Syncytiotrophoblast further invades the decidua basalis and by Day 11 its almost completely buried in the decidua

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14
Q

Outline the events of implantation on Day 12

A

Decidual reaction occurs
High progesterone levels cause enlargement and coating of 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 forms

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15
Q

What happens to the syncytiotrophoblasts around Day 14?

A

Cells of the Syncytiotrophoblast start to protrude out to form tree-like structures known as Primary Villi, which are then formed all around the blastocyst

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16
Q

At Day 14 of implantation what happens to the decidual cells?

A

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

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17
Q

Explain the vasculature forming at Day 14 of implantation

A

Maternal arteries and veins start to grow into decidua basalis.
These blood vessels merge with lacunae – arteries filling the lacunae with oxygenated blood and veins returning deoxygenated blood into maternal circulation

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18
Q

What happens to the lacunae filled with blood?

A

Blood-filled lacunae merge into a single large pool of blood connected to multiple arteries and veins. This is known as the Junctional Zone

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19
Q

What is the junctional zone?

A

Junctional zone is the circulatory foundation for the formation of the placenta

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20
Q

What are the consequences of incorrect implantation?

A

Implantation disorders include ectopic pregnancy and recurrent miscarriage

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21
Q

How is the placenta formed?

A

The placenta is co-created by the mother and foetus, with contributions from endometrial as well as embryonic cells/tissue

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22
Q

When does the placenta formation begin to occur?

A

Around Day 17

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23
Q

What are the first steps of placenta formation?

A

The foetal 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 (formed around week 5)

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24
Q

What is the chorionic frondosum formed from?

A

Villi grows larger in size, develops into the Chorionic Frondosum

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25
Q

What separates maternal and foetal red blood cells?

A

At this point, endothelial cell wall and Syncytiotrophoblast (villi) lining separate
maternal and foetal red blood cells

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26
Q

How is blood exchanged between mother and foetus?

A

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

27
Q

How are cotyledons formed?

A

In the 4TH & 5TH months of pregnancy, decidual septa form as they divide the placenta into 15-20 regions known as Cotyledons

28
Q

Where is the placenta formed?

A

The placenta is typically formed in the upper uterus.

29
Q

What is the vasculature of the umbilical cord?

A

Umbilical cord normally contains two arteries and one vein

30
Q

What substances are taken up by the umbilical cord?

A
  • Oxygen and glucose
  • immunoglobulins
  • Hormones
  • toxins (in some cases)
31
Q

What substances are removed from the baby via the umbilical cord?

A
  • CO2

- waste products

32
Q

What are the functions of the placenta?

A
  • Provision of maternal O2, CHO, fats, amino acids,
    vitamins, minerals, antibodies.
  • 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
33
Q

How is the placenta good at it’s job?

A

Huge maternal uterine blood supply – low pressure.
Huge surface area in contact with maternal blood.
Huge reserve in function

34
Q

How many pregnancies are affected by preeclampsia?

A

3-4% of pregnancies

≥20 weeks gestation (up to 6 weeks after delivery)

35
Q

What is the consequence of preeclampsia?

A

Results in placental insufficiency – inadequate maternal blood flow to the placenta during pregnancy.

Causes new onset maternal hypertension and proteinuria

Symptoms range from mild to life-threatening

36
Q

What is eclampsia?

A

Preeclampsia + seizures = Eclampsia

37
Q

What are the risk factors for preeclampsia?

A 
First pregnancy
Multiple gestation
Maternal age >35yo
Hypertension
Diabetes
Obesity
Family history of preeclampsia
38
Q

What are the causes of preeclampsia?

A

Primary cause is still unclear.

39
Q

What are the symptoms of preeclampsia?

A

Characterised by the narrowing of the maternal spiral arteries supplying blood to the placenta

40
Q

What is placental insufficiency?

A

inadequate maternal blood flow to the placenta during pregnancy
This in turn compromises the transfer of necessary nutrients to support the development of the foetus

41
Q

When does preeclampsia occur during the pregnancy?

A

Pre-eclampsia usually occurs after around 20 weeks gestation. Could still develop after delivery – up to 6 weeks after delivery

42
Q

What are the risk factors of placental abruption?

A
  • Blunt force trauma e.g. car crash, fall
  • Smoking & recreational drug use
  • Risk of vasoconstriction & increased blood pressure
  • Multiple gestation
  • Maternal age >35yo
  • Previous placental abruption
  • Hypertension from severe pre-eclampsia
43
Q

What is Placental abruption?

A

Premature separation of all / part of the placenta

44
Q

What are the symptoms of placental abruption?

A

Symptoms include vaginal bleeding and pain in the back and abdomen

45
Q

What causes placental abruption?

A

Caused by the degeneration of maternal arteries supplying blood to the placenta

Degenerated vessels rupture causing haemorrhage and separation of the placenta

46
Q

What are the maternal complications associated with placental abruption?

A
  • Hypovolemic shock
  • Sheehan Syndrome (Perinatal Pituitary Necrosis)
  • Renal failure
  • Disseminated Intravascular Coagulation (from release of
    thromboplastin)
47
Q

What complications may arise in the foetus due to placental abruption?

A

Intrauterine hypoxia and asphyxia

Premature birth

48
Q

What is placenta previa?

A

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

49
Q

What does placenta previa cause?

A

Associated with increased chances of preterm birth and foetal hypoxia.
Cause still unclear.
Associated with increased chances of preterm birth and foetal hypoxia

50
Q

What causes placenta previa?

A

Cause still unclear

Endometrium in the upper uterus not well vascularised

51
Q

What are the risk factors associated with placenta previa?

A
  • Previous caesarean delivery
  • Previous uterine/endometrial surgery
  • Uterine fibroids
  • Previous placenta previa
  • Smoking & recreational drug use
  • Multiple gestation
  • Maternal age >35yo
52
Q

What is Hydatiform mole?

A

Overgrowth of placental cells on to the uterus

53
Q

What is the consequence of low oestrogen : progesterone ratio during pregnancy?

A

The continued presence of the low oestrogen : progesterone ratio suppresses maturation of other follicles in the ovary

54
Q

Describe the basis of urinary pregnancy tests

A

βhCG can be detected in the bloodstream as early as Day 9 and is the basis of urinary pregnancy tests (qualitative)

55
Q

What is the significance of βhCG?

A

Serum βhCG (quantitative) is useful for monitoring early pregnancy complications e.g. ectopic pregnancy, miscarriage. Serum hCG hits peak levels by 9-11 weeks

56
Q

When does the placenta begin synthesising oestrogens?

A

Placenta takes over around week 7

Placenta synthesises oestrogens from foetal androgens from the foetal adrenal cortex

57
Q

How does the placenta form progesterone?

A

Placenta synthesises progesterone from maternal cholesterol

Pregnenolone is converted to progesterone in placental mitochondria

58
Q

Where is HPL produced?

A

HPL synthesized by cells of the Syncytiotrophoblast. Structurally and functionally similar to growth hormone

59
Q

Describe the gene structure of HPL

A

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

60
Q

How do hCG levels vary during pregnancy?

A

hCG levels increase and peak at 12 wks where they begin to decline

61
Q

Describe the HPL levels expected throughout a pregnancy

A

Human placental lactogen levels during pregnancy gradually begin to rise at 5wks and level off towards the end of the pregnancy

62
Q

What are the progesterone and oestrogen levels like during pregnancy?

A

Gradually increase throughout the pregnancy

63
Q

What is the significance of E2 and P during pregnancy?

A

Oestrogen and progesterone work alongside other hormones to trigger the physiological changes observed during pregnancy

Reproduction (Physiology 2) (12 decks)

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