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Repro > Implantation, the placenta and hormonal changes in pregnancy > Flashcards

Implantation, the placenta and hormonal changes in pregnancy Flashcards

1
Q

What do we need for implantation to occur?

A

A fully developed blastocyst - Fully expanded
Hatched out from the zona pellucida

-Blastocyst is made up of 2 cell lineages – Trophoblast (Purple - forms the placenta) and Embryoblast or inner cell mass (Green - forms the foetus).
Also present inside the blastocyst is a fluid-filled cavity known as the Blastocoel.
The embryoblast is concentrated at the ‘embryonic pole’ while the opposite pole (where trophoblast cells are concentrated) is known as the ‘abembryonic pole’

A receptive endometrium - thickened endometrial lining and expression of embryo receptivity markers

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2
Q

What are the stages of implantation?

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

How are the days broken up in the implantation timeline?

A

Days 7-8
Days 9-11
Days 12
Days 14

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4
Q

What happens on 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 decidua basalis

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5
Q

What happens on day 9-11 of implantation?

A

Syncytiotrophoblast further invades the decidua basalis

By day 11, it’s almost completely buried in the decidua

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6
Q

What happens on day 12 of implantation?

A

Decidual reaction occurs
High levels of progesterone –> enlargement and coating of the decidual cells in glycogen and lipid-rich fluid

The fluid is taken up by syncytiotrophoblast and helps to sustain the blastocyst early on before placenta formation

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7
Q

What happens on day 14 of implantation?

A

Cells of syncytiotrophoblast start to protrude out to form primary villi (tree like structures) which are then formed all around the blastocyst

Decidual cells between primary villi start to clear out leaving behind Lacunes (empty spaces)

Maternal arteries + veins start to grow into the decidua basalis, they merge w/ lacunae

  • arteries filling the lacunae w/ oxygenated blood
  • veins returning deoxygenated blood into the maternal circulation

Blood filled lacunae merge into a single large pool of blood connected to the multiple arteries and veins – JUNCTIONAL ZONE

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8
Q

What happens around day 17?

A

Placenta formation begins

foetal mesoderm cells start to form blood vessels within the villi - a basic network of arteries, veins and capillaries
- capillaries connect w blood vessels in the umbilical cord (formed ~ week 5)

villi grows larger in size –> Chorionic Frondosum

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

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9
Q

What happens in the 4th and 5th months of pregnancy?

A

decidual septa form as they divide the placenta into 15-20 regions –> Cotyledons

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

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10
Q

What is exchanged between the mother and foetus?

A

Through the umbilical cord, the foetus:

Takes up:

  • oxygen and glucose
  • immunoglobulins
  • hormones
  • toxins in some cases

drops off:

  • CO2
  • waste products
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11
Q

What are the functions of the placenta?

A

provision of maternal O2, CO2, fats, aa’s, vits, minerals, antibodies

metabolism e.g. synthesis of glycogen

barrier e.g. bacteria, viruses, drugs

Removal of foetal waste products, CO2, urea, NH4, minerals

Endocrine secretion e.g. hCG, oestrogens, progesterone, hPL, cortisol

The placenta is typically formed in the upper uterus.
Umbilical cord normally contains two arteries and one vein.

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12
Q

Why is the placenta good at its job?

A

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

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13
Q

What is pre eclampsia?

A

Disorder of the placenta

3-4% of pregnancies.
≥20 weeks gestation (up to 6 weeks after delivery).
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.

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14
Q

Disorders of implantation

A

Implantation disorders include ectopic pregnancy and recurrent miscarriage.

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15
Q

What are the risk factors for pre-eclampsia?

A 
First pregnancy
Multiple gestation
Maternal age >35yo
Hypertension
Diabetes
Obesity
Family history of pre-eclampsia
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16
Q

What does pre-eclampsia +seizures equal?

A

eclampsia

17
Q

What is the cause of pre-eclampsia and what is it characterised by?

A

Primary cause is still unclear.

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

18
Q

How does the placenta respond to the narrowing of the maternal spiral arteries in pre-eclampsia?

A

secretes pro-inflammatory proteins –> maternal circulation –> cause endothelial cell dysfunction (affects other systems leading to seizures in more serious case) –> vasoconstriction –> hypertension –> glomerular damage –> proteinuria

19
Q

Explain placental abruption as a placental disorder.

A

Premature separation of all or part of the placenta.

Symptoms include vaginal bleeding and pain in the back and abdomen

20
Q

What are the risk factors for placental abruption?

A 
Blunt force trauma e.g. car crash, fall
Smoking & recreational drug use – risk of vasoconstriction and increased blood pressure. 
Multiple gestation
Maternal age >35yo
Previous placental abruption
Hypertension from severe pre-eclampsia
21
Q

What is placental abruption caused by?

A

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

Degenerated vessels rupture causing haemorrhage and separation of the placenta.

22
Q

What maternal complications can you have?

A

Hypovolemic shock
Sheehan Syndrome - degeneration of pituitary gland (Perinatal Pituitary Necrosis) –> loss of secondary sexual features and impaired repro function
Renal failure
Disseminated Intravascular Coagulation (from release of thromboplastin)

23
Q

What foetal complications can you have?

A

Intrauterine hypoxia and asphyxia

Premature birth

24
Q

Explain placenta previa as a disorder of the placenta

A

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

Associated with increased chances of pre-term birth and foetal hypoxia.

25
Q

What are the risk factors of placenta previa?

A 
Previous caesarean delivery
Previous uterine/endometrial surgery
Uterine fibroids
Previous placenta previa 
Smoking & recreational drug use
Multiple gestation
Maternal age >35yo
26
Q

What is the cause of placenta previa?

A

Cause still unclear.

? Endometrium in the upper uterus not well vascularised?

27
Q

What is hydatiform mole?

A

Overgrowth of placental cells on to the uterus.

28
Q

Discuss hormonal changes in pregnancy

A

The continued presence of the low oestrogen : progesterone ratio supresses maturation of other follicles in the ovary.
βhCG can be detected in the bloodstream as early as Day 9 and is the basis of urinary pregnancy tests (qualitative).
Serum βhCG (quantitative) is useful for monitoring early pregnancy complications e.g. ectopic pregnancy, miscarriage. Serum hCG hits peak levels by 9-11 weeks.

29
Q

What happens around week 7?

A

Placenta takes over around week 7
Placenta synthesises oestrogens from foetal androgens from the foetal adrenal cortex.
Placenta synthesises progesterone from maternal cholesterol.

30
Q

How is the progesterone formed in the placenta?

A

Cholesterol and LDL are received from the mother into the placenta

Cholesterol and LDL –> pregnenolone –> Progesterone which goes back to the mother

31
Q

What is hPL synthesised by?

A

cells of the Syncytiotrophoblast

this then goes to the maternal blood

32
Q

What physiological changes does the low E2:P lead to?

A 
increase blood volume 
increase urinary output
shallow breathing 
loosened ligaments 
breast changes and darkened skin 
nausea and taste changes 
mood changes

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