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MD3002 Physiology > Placentation and implantation > Flashcards

Placentation and implantation Flashcards

1
Q

What are the 3 phases of linking between the foetus and mother?

A
  • Invasion - of conceptus to endometrium
  • Decidualisation - endometrial remodeling including secretory transformation of the uterine glands, influx of specialised uterine natural killer cells
  • Placentation - i.e placenta formation
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2
Q

What is the embryonic portion of the placenta supplied by?

A

Outermost layers of trophoblast cells (ie the chorion)

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3
Q

What is the chorion?

A

The outermost membrane surrounding the embryo

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4
Q

What is each villi surrounded by?

A

Pool/sinus of maternal blood (due to endometrium being changed by enzymes and paracrine agents)

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5
Q

What happens to the blastocyst around day 6/7?

A

Leaves the zona pelucida and bathed by uterine secretions for 2 days:

  • Progesterone prepares supportive uterine environment increasing glandular tissue
  • Oestrodiol is required to release the glandular secretions
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6
Q

How does attachment and implantation work?

A
  • Very limited time window
  • Synciotrophoblast cells ‘flow’ into the endometrium
  • Causes oedema, glycogen synthesis and increased vascularisation (decidualisation). The pregnant endometrium is now termed the decidua
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7
Q

What do syncytiotrophoblast cells do around day 13?

A

They erde through the walls of large maternal capillaries which then bleed into the spaces - primitive placental circulation

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8
Q

What is the 1st trimester embryo largely dependant on for nutrients and O2?

A

Uterine tissues

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9
Q

What seperates maternal and foetal blood?

A

Placental membrane

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10
Q

What is thought to account for a large amount of 1st trimester pregnancy losses?

A

Lack of hormonal support (luteal phase defect)

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11
Q

How thick should the endometrium ne for successful implantation?

A

8mm

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12
Q

What do maternal blood vessels near the syncytiotrophoblast expand to become?

A

MAternal sinusoids

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13
Q

What are trophoblastic lacunae?

A

Interconnected cords from the syncytiotrophoblast which invade the endometrium and erode maternal capillaries

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14
Q

For how long does LH support the steroid secretion of the corpus luteum?

A

10 - 12 days

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15
Q

What day is attachment usually in the menstraul cycle?

A

22

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16
Q

How does hCG influence progesterone?

A

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

17
Q

When do syncytiotrophoblasrs secrete hCG?

A

Soon after implantation (peaks 8-10 weeks of gestation)

18
Q

When does hCG become measurable?

A

7 - 8 days postconception

19
Q

When does the CL fail in a non-fertile cycle?

A

10 days after menstruation

20
Q

How does an implanted embryo prevent menstruation?

A
  • The syncytiotrophoblasts secrete hCG
  • hCG mimics the action of LH and supports the steroid synthesis of the corpus luteum terefore preventing menstruation and any further follicular development
21
Q

When can hCG be detected in the blood by immunoassay?

A

From day 6-7

22
Q

When can Commercial kits detect hCG in the urine?

A

After 14 days

23
Q

What does hCG stimulate in male fetuses?

A

Stimulates Leydig cells to produce testosterone - important for development of the male duct system

24
Q

When is the CL not required / when can the placenta secrete all steroid hormones required for pregnancy?

A

After 4 - 5 weeks

25
Q

What does progesterone do in pregnancy?

A

Increases throughout

  • Suppression of follicular growth and ovulation
  • Suppression of immune response
  • Maintenance of endometrium
26
Q

What is the substrate for progesterone production?

A

Cholesterol from the maternal circulation

27
Q

What are the functions of oestrogen/oestrodiol in pregnancy?

A
  • Stimulate continuous growth of uterine myometrium
  • Stimulates growth (with progesterone) of ductal tissue of breasts
  • 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
  • Foetal well being and placental function can be measured by monitoring oestrogen levels
28
Q

What does the foetus and placenta make up?

A

Feto-placental unit

29
Q

What are the functions of the placenta?

A
  • Essential complex endocrine organ - synthesises steroids and proteins that affect both maternal and foetal metabolism
  • 1st month - villus formation
  • 2nd month -increasing surface area and circulation
  • 3rd month - growing, becoming increasingly efficient
  • Adopts functions of the GI, respiratory and renal systems
  • Supplies nutrients, exchanges O2 and CO2, regulates fluid volumes and disposes of waste and metabolites
30
Q

After 20 weeks what happens to the placental membrane?

A

thins even more due to loss of cytotrophoblasts (most molecules can move through)

31
Q

What can happen to 3rd trimester syncytiotrophoblastic cells?

A

Can be lost into maternal blood

32
Q

WHat do lipids cross the placenta as?

A

Free fatty acids

33
Q

How are amino acids transported across the placenta?

A

Actively

34
Q

How does nutrient exchange vary throughout pregnancy?

A

Rapid and increases as pregnancy does, decreases slightly near term

35
Q

How does glucose pass through the placenta?

A

Via facillitated diffusion, some glycogen stored in liver for postnatal requirments (foetus has little capacity for gluconeogenesis)

36
Q

Why are babies of diabetic mothers usually heavier than average?

A

They are exposed more glucose

37
Q

What happens to gas exchange towards the end of pregnancy?

A

Exchange capacity decreases and placenta is less able to meet demands of foetus

38
Q

What has a greter affinity for oxygen foetal or adult haemoglobin?

A

Foetal (contains 2 gamma subunits insted of 2 beta) (both contain 2 alpha)

MD3002 Physiology (24 decks)

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