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3002 > 82 Placentation and implantation > Flashcards

82 Placentation and implantation Flashcards

1
Q

In the earliest stages of pregnancy the anatomical link between mother and foetus develops through a series of phases. The sequence of events is…

A
  1. INVASION of conceptus to endometrium
  2. DECIDUALISATION i.e. endometrial remodelling
  3. PLACENTATION
    i. e. placenta formation
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2
Q

What are the different changes that occur during endometrial remodelling in decidualisation?

A
  • Secretory transformation of the uterine glands
  • Influx of specialised uterine natural killer cells
  • Vascular remodelling
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3
Q

Where is the embryonic portion of the placenta supplied from?

A

Outermost layers of trophoblast cells (i.e. the chorion)

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4
Q

Where is the maternal portion of the placenta supplied from?

A

Endometrium underlying the chorion

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5
Q

Chorionic villi extend from…

A

Chorion to endometrium

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6
Q

How is each chorionic villi surrounded by a pool of maternal blood?

A

As the endometrium that surrounds the villi is changed by enzymes and paracrine agents

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7
Q

What is the blood supply to the placenta?

A

• Maternal blood:

  • Enters placental sinuses/pools via uterine artery
  • Flows through sinuses
  • Exits via uterine veins

• Foetus blood:

  • Flows into capillaries of chorionic villi via umbilical arteries
  • and back to foetus via umbilical vein

• The umbilical cord connects foetus to placenta

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8
Q

Implantation and placentation timeline post ovulation?

A
  • Fertilisation occurs: 24hrs post ovulation
  • Transport to uterus: 3-4 days
  • Formation of blastocyst: 4.5 days
  • Attachement: 7-9 days
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9
Q

What does trophoblast and inner cell mass give rise to?

A
  • Trophoblast –> placenta

* Inner cell mass –> Embryo

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10
Q

Day 6 the blastocyst attaches to the endometrium adjacent to the inner cell mass (embryonic pole). Trophoblast differentiates into:

A
  1. Inner cytotrophoblast
  2. outer syncytiotrophoblast (loses cell
    boundaries)

• Fingers of syncytiotrophoblast invade the endometrium

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11
Q

Day 6/7 the blastocyst leaves the zona pellucida and is bathed by uterine secretions for 2 days, what is the purpose of this?

A
  1. Progesterone prepares supportive uterine environment increasing glandular tissue
  2. Oestrodiol is required to release the glandular secretion
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12
Q

During attachment and implantation, what interactions occur between the trophoblast and maternal epithelial tissue?

A
  1. Syncytiotrophoblast cells flow into the endometrium
  2. Oedema, glycogen synthesis and increased valcularisation (decidualisation). The pregnant endometrium is now termed the decidua
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13
Q

What is the decidua?

A

The pregnant endometrium

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14
Q

Day 13 of implantation is also the…

A

time the woman expects her next period

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15
Q

What are the events at Day 13 of implantation?

A
  • Syncytiotrophoblast cells erode through the walls of large maternal capillaries which then bleed into spaces - primitive placental circulation
  • Nutrition still depends on uterine secretion and tissues
  • Breakthrough bleeding may occur
  • Growth in the embryonic disk is slow and it remains very small (0.1-0.2mm)
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16
Q

Syncytiotrophoblast forms villi that projects into….

A

Into the blood filler spaces (chorionic villi)

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17
Q

In the core of the villus is a ……

A

Fetal capillary loop - dilated at the tip (slow flow rate)

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18
Q

Embryonic placental structure develops over several weeks, The villi eventually becomes localised where? And presents?

A

• Villi eventually becoming localised at the embryonic pole
• Presenting a huge surface area for exchange of O2, nutrients and
waste products

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19
Q

Maternal side of the placental circulation is restricted and is not functional until ….

A

10 – 12 weeks

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20
Q

First trimester embryo largely dependant on ________ for nutrients and O2

A

Uterine tissues

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21
Q

What is the maternal and fetal circulations separated by?

A
  • Separated by placental membrane

* There is no mixing of maternal and fetal blood

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22
Q

Why is there limited embryonic growth in the first trimester?

A

Nutrition of the embryo is largely based on uterine secretion and tissues

23
Q

In the first trimester, name 2 placental causes for pregnancy loss?

A
  • Lack of appropriate hormonal support (i.e. luteal phase defect)
  • Endometrium should be at least 8mm thick for successful implantation
24
Q

What forms the primary villus?

A
  • A core of cytotrophoblast

* Covered by multinucleated syncytiotrophoblast

25
Q

What forms the secondary villus?

A
  • An inner core of extraembryonic mesoderm (enters the primary villi)
  • A middle cytotrophoblast layer
  • An outer syncytiotrophoblast layer
26
Q

After ovulation, what supports the steroid secretion of the CL for 10-12 days until attachment occurs?

A

LH

27
Q

Role of hCG?

A

Maintains progesterone secretion from the corpus luteum until the placenta can synthesise its own progesterone

28
Q

What secretes hCG soon after implantation?

A

Syncytiotrophoblasts

peaks ~8-10 weeks of gestation

29
Q

When is hCG measurable by?

A

By day 7-8 postconception

30
Q

Role of hCG?

A

• An implanting embryo must prevent menstruation
=> syncytiotrophoblast secretes Human Chorionic Gonadotropin (hCG)
• hCG mimics the action of LH and supports the steroid synthesis of CL => prevents both menstruation and any further follicular development
• hCG stimulates the Leydig cells of male fetuses to produce testosterone - important for development of the male duct system

31
Q

What happens to CL in a non-fertile cycle?

A

CL will fail after 10 days and menstruation will occur

32
Q

Detecting of hCG?

A
  • From day 6-7 after fertilisation hCG can be detected in maternal blood by immunoassay
  • Commercial kits are sensitive enough to detect hCG in urine after ~14 days
33
Q

Evolution of placenta functions from 1st to 3rd month?

A
  • 1st month - villus formation
  • 2nd month - increasing surface area and circulation
  • 3rd month - growing, becoming increasingly efficient
34
Q

Loss of cytotrophoblast from placenta?

A

After 20 weeks placental membrane thins even more with loss of cytotrophoblast

35
Q

___ trimester syncytiotrophoblastic cells may be lost into the maternal blood

A

3rd trimester syncytiotrophoblastic cells may be lost into the maternal blood

36
Q

Placental functions

A
  1. Combination of interlocking foetal and maternal tissue
  2. Serves as the organ of exchange between mother and
    foetus for remainder of pregnancy
37
Q 
How does the placenta act as the foetal:
Gut?
Lung?
Kidney?
Endocrine gland?
A
  1. Foetal “gut”: supplying nutrients
  2. Foetal “lung”: exchanging O2 and CO2
  3. Foetal “kidney”: regulates fluid volumes and disposing of waste metabolites
  4. Endocrine gland: synthesises steroids and proteins that affect both maternal and foetal metabolism
38
Q

Why is progesterone key for maintaining pregnancy?

A
  • Suppression of follicular growth and ovulation
  • Suppression of the immune response
  • Maintenance of endometrium
39
Q

At which point is the CL not required anymore to maintain pregnancy? Why?

A

After 4-5 weeks placenta is secreting all steroid hormones required for pregnancy (CL not required after 5 weeks)

40
Q

What is the substrate from the maternal circulation for progesterone production?

A

Cholesterol

41
Q

What is the main oestrogen in pregnancy?

A

Oestriol

42
Q

What is responsible for oestrogen (mainly oestriol) secretion in pregnancy?

A

Foetus and placenta (feto-placental unit) co-operate

43
Q

Functions of oestrogen in pregnancy?

A
  • Stimulate continuous growth of uterine myometrium
  • Stimulates growth (with progesterone) of ductal tissue of breast
  • Along with relaxin, relaxes and softens maternal pelvic ligaments and symphysis pubis of pelvic bones – allows expansion of uterus
  • Stimulate LDL cholesterol uptake and activity of P450 enzymes - Contribute to progesterone synthesis
44
Q

How can foetal well being and placental function be measured?

A

By monitoring oestrogen levels

45
Q

What nutrients are exchanged across the placenta?

A

• Water and electrolytes diffuse freely
• Glucose passes via facilitated diffusion
- Foetus has little
capacity for gluconeogenesis
- Babies of diabetic mothers are heavier than normal range
- Storage of glycogen in liver for postnatal requirements
• Amino acids are actively transported for fetal growth
• Lipids cross as free fatty acids
• Vitamins

46
Q

Fetal ______ has a greater affinity for O2 than adult ______

A

Fetal haemoglobin has a greater affinity for O2 than adult

haemoglobin

47
Q

Gas exchange ability towards end of pregnancy?

A

Towards end of pregnancy exchange capacity decreases and placenta is less able to meet the demands of the foetus

48
Q

Concentration gradients are influenced by ______.

Quantity of O2 reaching the foetus is ______

A

Concentration gradients are influenced by blood flow rates.

Quantity of O2 reaching the foetus is flow limited

49
Q

Cause of ectopic pregnancy?

A
  1. Adhesions caused by pelvic inflammatory disease (PID)

2. Endometriosis

50
Q

Where do ectopic pregnancies occur?

A

95 - 97% are in the ampulla/isthmus of the tube with the vast majority in the ampulla

51
Q

Where does attachment usually occur?

A

Posterior wall of the fundus of the uterus

52
Q

What is the consequence of ectopic pregnancy?

A

Rupture of the tube causes blood loss that may be life threatening to mother and fatal for the embryo

53
Q

What can the symptoms of ectopic pregnancy be confused with?

A

Appendicitis

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