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Life Cycle > Implantation and Pregnancy > Flashcards

Implantation and Pregnancy Flashcards

1
Q

What is the trophoblast?

A
  • cells of the blastocyst
  • invade the endometrium and myometrium (days 5-6)
  • secrete beta hCG, which maintains the CL
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2
Q

What is the chorion?

A

membranous structure

becomes the foetal aspect of the placenta

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3
Q

What is the amnion?

A

layer that becomes the amniotic sac

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4
Q

Which stage of fertilisation occurs in which part of the uterine tubes?

A

PRONUCLEAR STAGE
day 0
fimbriated infundibulum/ampulla

2-CELL ZYGOTE
24h
ampulla (thicker portion of tube)

4-CELL ZYGOTE
48h
moving more medially from ampulla to isthmus

MORULA
day 4 (96h)
moving medially towards the corpus of uterus

BLASTOCYST
Day 5 (120h)
enters uterus
secretes proteolytic enzymes to degrade the ZP
implants in posterior wall of endometrium

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5
Q

What is the time window for fertilisation to occur?

A

once released, oocyte can only be fertilised for <24h

enters uterus as blastocyst ~5d later

timing is crucial for CL maintenance and endometrial change

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6
Q

What changes must occur for implantation?

A
  • differentiation of the trophoblast
  • trophoblastic invasion of the decidua and myometrium
  • remodelling of maternal vasculature in utero-placental circulation
  • development of vasculature within trophoblast
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7
Q

What is the decidua?

A

pregnant endometrium

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8
Q

What occurs during implantation?

A

DAY 5-6
implantation window
24-36h

DAY 10 
trophoblast produces hCG 
(maternal recognition of pregnancy)
CL is maintained, P produced 
P causes decidualisation of the endometrium
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9
Q

What is the purpose of decidualisation?

A

mediated by P (produced by CL)

which promotes steroidogenesis in CL during first trimester

vital until placental steroidogenesis is established (<7wks)

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10
Q

What is beta hCG?

A

basis of urinary pregnancy tests (qualitative)

beta hCG levels maximal by 9-11 wks

serum hCG: quantitative
- useful for monitoring early pregnancy complications e.g. ectopic, miscarriage

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11
Q

What is the structure of hCG?

A 
2 subunits (alpha and beta) 
joined by 2x disulphide bonds

serum/urinary hCG testing: detects beta subunit

hence called BETA hCG testing

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12
Q

Does the urinary beta hCG test pick up LH?

A

no.
contains Ab targeting the beta subunit of hCG
this is different in LH and therefore will not pick up LH

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13
Q

How do hCG levels change during pregnancy?

A

4-8 WKS
exponential rise in levels

MISCARRIAGE
falling hCG in this time (early pregnancy)

ECTOPIC PREGNANCY
rise in hCG and then fall during early pregnancy
(if fall is sufficient, surgery to remove ectopic may not be required)

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14
Q

What are the functions of the placenta?

A
  • steroidogenesis: oestrogen, progesterone, hPL, cortisol
  • nutrients: provision of maternal O2, CHO, fats, AAs, vitamins, minerals, Ab (IgG)
  • waste products: removal of CO2, urea, NH4, minerals
  • barrier to pathogens, drugs etc
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15
Q

How many types of oestrogen are there?

A 
LEAST POTENT
E1: (one OH group)
E2: menstrual cycle 
E3: pregnancy 
MOST POTENT
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16
Q

What adaptations does the placenta have to aid function?

A

huge maternal uterine blood supply: low pressure

huge reserve in function

huge SA, in contact with maternal blood

highly adapted + efficient transfer system

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17
Q

What are the different types of trophoblast cells?

A

SYNCYTIOTROPHOBLASTs
contains no PMs, just one large multinucleate entity
spread out and mediate multiple contact points for embedding in uterine wall

CYTOTROPHOBLASTs
found within the syncytiotrophoblast
contain PMs

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18
Q

What is the function of the extra-embryonic mesoderm?

A

surrounds the embryo

will go onto form the foetal blood supply

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19
Q

How does the placental and foetal blood network develop?

A

initially have lakes of maternal blood that form (LACUNAE)

invasion of trophoblasts into the lacunae and mesoderm

trophoblasts get thinner as this happens

this allows the formation of maternal and foetal blood vessels

whilst the vessels run very close to each other, there is no direct contact between
the maternal and foetal blood, so no mixing occurs

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20
Q

What changes to the foetal blood supply occur between the 1st and 2nd trimester?

A

branching of vessels

allowing closer contact between maternal and foetal blood

(~1 membrane endothelium) distance between them)

21
Q

What is the vessel composition of the umbilical cord?

A

normally 3 vessels:

  • 2 arteries
  • 1 vein

variations to this exist - “2 vessel baby”

22
Q

What is the function of the amniotic cavity?

A

HOMEOSTASIS
temperature
fluid
ions/electrolytes

DEVELOPMENT
limbs
lungs etc

PROTECTION
physical barrier
e.g. ascending infection

23
Q

What is the composition of amniotic fluid?

A

essentially foetal urine
minus the waste products
(which are excreted by maternal kidneys)

24
Q

What info does premature membrane rupture provide about foetal development?

A

Premature (16-17wks)
abnormal limb and lung development often seen in premies

=> fluid is v. important for correct development

25
Q

What are the main barriers that protect the foetus from infection?

A
  • cervical mucous plug
  • amniotic membrane

prevents entry of microbes from vaginal canal

PATHOLOGY: if abnormalities in membrane, can increase risk of gestational infection

26
Q

What does the septum transversum go on to form?

A

formation during neural folding process

will go on to form the thoracic cavity and abdominal mesentery

27
Q

What does the rotation and fusion of the neural folds go on to develop?

A

will become the CNS/brain matter

28
Q

How does the amnion develop into the amniotic sac?

A

initially it is laid on top of the ectoderm and neural fold

folding of this entire structure, occurs downwards towards the yolk sac and umbilical stalk

this causes wrap-around structure of the amniotic sac

29
Q

What are the main disorders of the placenta?

A
  • miscarriage (15-40% of pregnancies)
  • pre-eclampsia (10% of pregnancies)
  • hydatiform mole (rare)
  • placental insufficiency
  • transfer of other substances e.g. drugs, toxins, infections
30
Q

What is a hydatidiform mole?

A

= molar pregnancy

rare, occurs in early pregnancy

genetically abnormal or excessive growth of trophoblast

contains male DNA only, oocyte has been expelled or is anuclear

31
Q

What is a common cause of miscarriage?

A

abnormal placental morphology and function

32
Q

What is placental insufficiency?

A

often associated with pre-eclampsia

recognised when weeks of gestation do not correlate with growth parameters for mum

33
Q

What infections may cause placental disorders?

A

(usually maternal transfer)

  • HIV
  • Chlamydia
34
Q

What are disorders of the amnion?

A
  • polyhydramnios
  • oligohydramnios
  • premature rupture of membranes
35
Q

What is a common cause of polyhydramnios?

A

gestational DM

baby has foetal polyuria, which leads to polyhydramnios

36
Q

What is oligohydramnios?

A

not enough amniotic fluid

indicates that foetus may be hypoperfused

can be identified by USS

37
Q

Why does premature rupture of membranes occur?

A

usually an inflammatory response

if this occurs at 28wks, baby will be delivered premature

38
Q

What types of hormones are active during pregnancy?

A
  • placental steroids
  • maternal steroids
  • foetal steroids
  • placental peptide hormones
39
Q

At what gestational age, does placental steroidogenesis occur?

A

7-8 weeks

40
Q

What effects does P have during pregnancy?

A
  • decidualisation of the CL
  • smooth muscle relaxation (uterine quiescence)
  • mineralocorticoid effect (CVS changes)
  • breast development
41
Q

Why does P cause an increased maternal HR during pregnancy?

A

Progesterone has a similar biochemical structure to aldosterone

increased Na (and H2O) retention

increased HR

42
Q

Where does oestrogen synthesis occur during pregnancy?

A

androgens produced in foetus
then maternal adrenals convert to oestrogen

placenta cannot make oestrogen on its own

43
Q

What is the order of oestrogen potency?

A

most potent

E3 > E2 > E1

44
Q

What is function of oestrogen during pregnancy?

A
  • development of uterine hypertrophy
  • metabolic changes (INS resistance caused by antagonism of insulin by E3)
  • CVS changes
  • breast changes
45
Q

Which oestrogen molecules increase during pregnancy?

A

all of them

highest E2
then E3
then E1
[serum levels]

46
Q

Which androgens are made by the adrenal glands during pregnancy?

A

made by both maternal and foetal adrenal glands

  • dihydroandrosterone
  • androstenedione
  • testosterone
47
Q

When do the main hormonal changes occur during pregnancy?

A

PLACENTAL CRH
increase from trimester 2 onwards
may be involved in labour initiation (beyond threshold)

CORTISOL
increase from trim 2 onwards
metabolic changed (INS resistance)
foetal lung maturity

hPL
similar to GH structure (differs by 1aa)
mediates INS resistance
some function in lactation

PROLACTIN
levels increase throughout pregnancy
activity suppressed by high oestrogen in utero
but after delivery, oestrogen falls and PRL can act
breast development for lactation e.g. colostrum

48
Q

How do steroid binding protein levels change during pregnancy?

A

[albumin] in pregnancy drop due to maternal haemodilution

therefore, there are less available steroid binding hormones compared to circulating steroids (more are in the active free state)

Life Cycle (29 decks)

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