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Repro > The placenta > Flashcards

The placenta Flashcards

1
Q

When does the placenta begin to develop?

A

2nd week

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2
Q

What is the focus of development in the early stages of pregnancy?

A

Development of the foetal membranes - eg sacs supporting the embryo/foetus, the placenta

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3
Q

Importance of placenta, what happens if it’s bad?

A

Cannot have healthy pregnancy without healthy placenta

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4
Q

What is the placenta?

A

A specialised foetal membrane allowing transport between maternal and foetal blood

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5
Q

What happens in week 2 of embryology?

A

Week of twos - bilaminar disk and two distinct layers:

Outer cell mass - synctiotrophoblast and cytotrophoblast

Inner cell mass - bilaminar disc epiblast and hypoblast

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6
Q

What do the inner and outer cell mass become?

A

Outer: The foetal membranes

Inner - embryo

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7
Q

Which part of the embryo produces hCG?

A

synctiotrophoblast - this hCG maintains the corpus luteum

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8
Q

What happens on implantation?

A

Day 6 - syncytiotrophoblast moves into endometrial layer

Day 9 - conceptus is fully embedded within wall of uterus

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9
Q

What is formed by the end of the 2nd week of development structure wise?

A

Implanted conceptus

Embryo and two cavities - yolk sac and amniotic cavity

Connecting stalk connects these to trophoblast

Chorionic cavity surrounds all these sacs/cavities

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10
Q

What is the fate of the 3 sacs/cavities?

A

Primative gut tube formed and yolk sac disappears

Amniotic sac enlarges - surrounds the embryo/foetus

Chorionic sac is occupied by amniotic sac and they eventually fuse forming amniochorionic membrane

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11
Q

What happens when amniochorionic membrane ruptures?

A

That is what results in the feeling of ‘waters breaking’

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12
Q

What does implantation allow to happen? (3)

A

Allows exchange between mother and foetus

Anchors the placenta

Establishes blood flow within the placenta

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13
Q

What structures are formed to form the exchange unit between foetus and mother? What are the 3 stages?

A

Chorionic villi:
Primary villi - early finger like projections of trophoblast

Secondary villi - invasion of mesenchyme (connective tissue) into core

Tertiary villi - invasion of mesenchyme core by foetal vessels

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14
Q

Why do we need exchange and placenta?

A

Remove foetus’ waste

Deliver nutrients to foetus from mother

Placenta takes over from corpus luteum eventually and produces oestrogen and progesterone

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15
Q

What is implantation classed as?

A

Interstitial - uterine epithelium is breached and conceptus implants within stroma

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16
Q

What happens to the placental membrane as time goes on?

A

Becomes thinner and thinner as the needs of the foetus increase

(optimal waste out and nutrients in for increased needs)

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17
Q

What makes the placental membrane seperating the maternal and foetal blood flow?

A

Single layer of trophoblast ultimately

AND THEY NEVER MIX - two circulations exchange but dont mix

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18
Q

What is the main reason for increased metabolic needs of foetus?

A

Large size of foetal brain - more energy needed

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19
Q

What is a chorionic villus?

A

Finger like projections

Made from trophoblast (both layers) with an inner connective tissue core containing fetal blood vessels

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20
Q

What is the chorionic villus also called?

A

Chorion frondosum (look like fern)

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21
Q

When is a functional villus fully established? - what are the stages

A

By day 23

Synctiotrophoblast and cytotrophoblast form projection
Connective tissue core forms
Fetal blood vessels fill core

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22
Q

Two types of implantation defects and what these lead to

A

Implantation in wrong place:
Placenta praevia
Ectopic pregnancy

Incomplete invasion:
Placental insufficiency
Pre-eclampsia

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23
Q

Placenta praevia problem

A

Implantation in lower uterine segment
Can cause haemorrhage and need C section delivery

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24
Q

How is the invasion controlled when embryo implants?

A

The endometrium becomes the ‘decidua’ when conceptus is present

Decidual reaction provides balance between the invasive force of the synctiotrophoblast and the resistance of the ‘decidua’

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25
Q

How does the synctiotrophoblast implant?

A

Produces enzymes to digest the endometrium so it can bury in

This burying is resisted by the decidua (the endometrium)

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26
Q

What happens in ectopic pregancy with the decidua?

A

There is no decidua present - no control over how deep the embryo implants so can breach into peritoneal cavity and blood vessels causing haemorrhage

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27
Q

What happens if the decidua is sub-optimal? ie not too resistant or not resistant enough?

A

If not resistant enough (premature senescence) - preterm birth, fetal death

If too resistant resulting in shallow invasion - pre-eclampsia

(depth needs to be just right)

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28
Q

Decidua (aka endometrium) function

A

Manage depth of invasion of embryo by resisting the synctiotrophoblast force

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29
Q

Describe the gross morphology of the placenta - fetal aspect (what it looks like, whats in contact with foetus)

A

Umbilical cord
Umbilical vessels forming chorionic vessels

Amnion - shiny transparent outside layer

Chorionic vessels

30
Q

Gross morphology of materal aspect of placenta (what is in contact with mother)

A

Cotyledons - functional units containing chorionic villi

Cobblestone structure

Amniochorion membrane on outside

31
Q

Describe the structure of a chorionic villus

A

Foetal arteries and veins enter villus at base

Branch up into fetal capillaries within villus

Form arteriovenous network at the tips of villus for exchange

32
Q

Change in chorionic villus structure through trimesters?

A

Initially - thicker barrier between maternal and foetal blood (ST + CT and fetal capillary endothelium)

Later eg third trimester - barrier is optimal thickness and very thin (just ST and fetal capillary endothelium)

33
Q

What layers seperate 1st trimester vs 3rd?

A

1st - cytotrophoblast, syncytiotrophoblast, fetal capillary endothelium

3rd - synctiotrophoblast and fetal capillary endothelium

34
Q

Why does chorionic villus barrier thin?

A

Increase metabolic demand of foetus means diffusion needs to be optimal

35
Q

What happens to capillary endothelium as pregnancy goes on?

A

Marginalises closer to maternal blood so diffusion distance is smaller

36
Q

What does the umbilical cord contain?

A

Two umbilical arteries
One umbilical vein

37
Q

Function of tow umbilical arteries

A

Takes deoxygenated blood from foetus to placenta

38
Q

Function of umbilical vein

A

Takes oxygenated blood from placenta to foetus

(through liver, then hepatic vein to IVC and heart, bypass lungs and through body)

39
Q

What vessels communicate with chorionic villus?

A

Endometrial arteries and veins communicate with umbilical arteries and veins

Umbilical arteries with endometrial veins (send blood away from foetus)

Umbilical veins with endometrial arteries (send blood to foetus)

40
Q

What does umbilical vein contain?

A

Oxygen rich blood

(artery has oxygen poor blood)

41
Q

What other functions do villus have other than exchange?

A

Anchoring villus - anchor placenta to endometrium

(look on slide 20 at good diagram)

42
Q

Hormones produced by the placenta types

A

Steroid and protein

43
Q

Steroid hormones produced by placenta

A

Progesterone
Oestrogen

Placenta takes over from corpus luteum by the end of the 1st trimester (11th week)

44
Q

Protein hormones placenta produces

A

Human chorionic gonadotrophin (hCG)
Human chorionic somatomammotrophin
Human chorionic thyrotrophin
Human chorionic corticotrophin

45
Q

When is hCG produced?

A

For the first 2 months of pregnancy

46
Q

Function of hCG?

A

Secretory function of corpus luteum - maintains it and allows oestrogen and progesterone to be made

47
Q

What is hCG used for?

A

Pregnancy testing - pregnancy specific as produced by synctiotrophblast

48
Q

When can hCG be abnormally elevated?

A

Trophoblast disease:
Molar pregnancy (hyatidiform - mass of tissue in uterus that will not become a baby)
Choriocarcinoma - rare cancer in pregnancy

49
Q

What does progesterone do in pregnancy?

A

Increases appetite

50
Q

Function of human chorionic somatomammotrophin

A

Increases glucose availability to foetus - foetus gets glucose before mother can store it

(get insulin resistance)

51
Q

4 types of transport from mother to baby via placenta

A

Simple diffusion
Facilitated diffusion
Active transport
Receptor mediated endocytosis

52
Q

What molecules simply diffuse through placenta?

A

Water
Electrolytes
Urea and uric acid
Gases

53
Q

What molecule uses facilitated diffusion?

A

Glucose

54
Q

What is needed for good simple diffusion?

A

Need good blood flow to foetus - MAIN THING for good diffusion

55
Q

What is gas exchange limited by?

A

FLOW LIMITED - not diffusion - good maternal blood flow is KEY

56
Q

What can happen to maternal blood flow during birth and contractions?

A

Increase pressure can limit uteroplacental blood flow
Decreased O2 to foetus
Stress on baby

57
Q

What are fetal O2 stores like?

A

SMALL - need adequate blood flow from mother at all times

58
Q

What molecules travel via active transport across placenta?

A

Amino acids
Iron
Vitamins

using special transporters

59
Q

What antibodies can cross the barrier and be transferred to foetus?

A

IgG ONLY

60
Q

IgG concentration mother compared with foetus

A

Fetal plasma concentrations exceed mothers - very good transport

61
Q

Why does baby need immunity from mother?

A

Immune system immature
Needs passive immunity initially until can develop

62
Q

Is the placenta a true barrier?

A

NO - teratogens can access the fetus via the placenta

Unintentional outcomes from physiological processes - haemolytic disease of foetus secondary to Rhesus incompatability (IgG antibodies against foetus and attack RBC)

63
Q

What are teratogens?

A

Molecules that can disturb foetal development process

64
Q

Examples of teratogens and harmful substances crossing the placenta

A

Thalidomide - limb defects (reduce endothelial vascular genesis, was initially prescribed for morning sickness)

Alcohol - foetal alcohol syndrome, alcohol related neurodevelopmental disorder

Therapeutic drugs - anti-epileptic, warfarin, ACEi

Drugs of abuse - foetus can then develop dependency and withdrawals when born

Smoking - influences size and structure of placenta affecting growth

65
Q

What is key with teratogenesis (harm to growth)?

A

Timing - sensitive at different points and specific organ sensitivity

66
Q

Stages and teterogenesis

A

Pre-embryonic - LETHAL

Embryonic - most sensitive, narrow windows for some system damage

Fetal - less sensitive

After embryonic - risk of structureal defects low except for CNS defects

67
Q

What is it called if a fertilised ovum invades into the myometrium (too deep)?

A

Placenta accreta

68
Q

Can tubal pregnancies always be diagnosed via ultrasound?

A

NO not always

69
Q

How soon after fetilisation can hCG be detected reliably?

A

14 days - day of 1st period (14 days after ovulation)

70
Q

Most common complication of pre-eclampsia

A

Oligohydramnios (low amniotic fluid)

Repro (22 decks)

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