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82 Placentation and implantation Flashcards

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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?

Study These Flashcards
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?

Study These Flashcards
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?

Study These Flashcards
A
  • A core of cytotrophoblast

* Covered by multinucleated syncytiotrophoblast

25
What forms the secondary villus?
* An inner core of extraembryonic mesoderm (enters the primary villi) * A middle cytotrophoblast layer * An outer syncytiotrophoblast layer
26
After ovulation, what supports the steroid secretion of the CL for 10-12 days until attachment occurs?
LH
27
Role of hCG?
Maintains progesterone secretion from the corpus luteum until the placenta can synthesise its own progesterone
28
What secretes hCG soon after implantation?
Syncytiotrophoblasts | peaks ~8-10 weeks of gestation
29
When is hCG measurable by?
By day 7-8 postconception
30
Role of hCG?
• 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
What happens to CL in a non-fertile cycle?
CL will fail after 10 days and menstruation will occur
32
Detecting of hCG?
* 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
Evolution of placenta functions from 1st to 3rd month?
* 1st month - villus formation * 2nd month - increasing surface area and circulation * 3rd month - growing, becoming increasingly efficient
34
Loss of cytotrophoblast from placenta?
After 20 weeks placental membrane thins even more with loss of cytotrophoblast
35
___ trimester syncytiotrophoblastic cells may be lost into the maternal blood
3rd trimester syncytiotrophoblastic cells may be lost into the maternal blood
36
Placental functions
1. Combination of interlocking foetal and maternal tissue 2. Serves as the organ of exchange between mother and foetus for remainder of pregnancy
37
``` How does the placenta act as the foetal: Gut? Lung? Kidney? Endocrine gland? ```
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
Why is progesterone key for maintaining pregnancy?
* Suppression of follicular growth and ovulation * Suppression of the immune response * Maintenance of endometrium
39
At which point is the CL not required anymore to maintain pregnancy? Why?
After 4-5 weeks placenta is secreting all steroid hormones required for pregnancy (CL not required after 5 weeks)
40
What is the substrate from the maternal circulation for progesterone production?
Cholesterol
41
What is the main oestrogen in pregnancy?
Oestriol
42
What is responsible for oestrogen (mainly oestriol) secretion in pregnancy?
Foetus and placenta (feto-placental unit) co-operate
43
Functions of oestrogen in pregnancy?
* 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
How can foetal well being and placental function be measured?
By monitoring oestrogen levels
45
What nutrients are exchanged across the placenta?
• 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
Fetal ______ has a greater affinity for O2 than adult ______
Fetal haemoglobin has a greater affinity for O2 than adult | haemoglobin
47
Gas exchange ability towards end of pregnancy?
Towards end of pregnancy exchange capacity decreases and placenta is less able to meet the demands of the foetus
48
Concentration gradients are influenced by ______. | Quantity of O2 reaching the foetus is ______
Concentration gradients are influenced by blood flow rates. | Quantity of O2 reaching the foetus is flow limited
49
Cause of ectopic pregnancy?
1. Adhesions caused by pelvic inflammatory disease (PID) | 2. Endometriosis
50
Where do ectopic pregnancies occur?
95 - 97% are in the ampulla/isthmus of the tube with the vast majority in the ampulla
51
Where does attachment usually occur?
Posterior wall of the fundus of the uterus
52
What is the consequence of ectopic pregnancy?
Rupture of the tube causes blood loss that may be life threatening to mother and fatal for the embryo
53
What can the symptoms of ectopic pregnancy be confused with?
Appendicitis

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