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implantation and placental function Flashcards

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1
Q

where does fertilisation take place?

A

oviduct

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2
Q

where does implantation take place?

A

lumen of the uterus

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3
Q

when it reaches the uterus, how does the embryo communicate with the mother?

A

placentation

maternal recognition of pregnancy

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4
Q

what is placentation and why is it required?

A

establishes physical and nutritional contact – required for a supply of nutrients leading to growth

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5
Q

what is maternal recognition of pregnancy and why is it required?

A

signals its presence to mother – required to prevent luteal regression. In humans, this molecule is done by hCG.

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6
Q

what are the stages in implantation and placental development?

A

first differentation step
apposition
adhesion
invasion

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7
Q

what happens in the first differentiation step?

A

6 days after fertilisation, cells of blastocyst differentiate into trophectoderm (outer cell layer) and inner cell mass

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8
Q

what does the trophoectoderm differentiate into?

A

placenta

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9
Q

what does the inner cell mass of the trophoblast differentiate into?

A

fetus

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10
Q

when does apposition happen?

A

6-7 days after fertilisation

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11
Q

what happens during apposition?

A

Positioning of the blastocyst within the uterine cavity - must face the right way

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12
Q

what happens during adhesion?

A

• Cells of the trophoblast fix to maternal tissues and to each other

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13
Q

how does adhesion occur?

A

Done via a group of cell adhesion molecules (including laminin and fibronectin) together with cell surface receptors for these molecules

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14
Q

when the trophoectoderm attaches to the uterine wall, how does it differentiate?

A

differentiates into 2 types of cells - cytotrophoblast and syncytiotrophoblast

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15
Q

describe cytotrophoblasts?

A

have single nucleus and divide rapidly in vivo

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16
Q

describe syncytiotrophoblasts?

A

o Syncytiotrophoblasts are derived from fused cytotrophoblasts

Multinucleated cell which doesn’t divide in vivo

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17
Q

what happens during invasion?

A

Trophoblast penetrates into maternal decidua (pregnancy endometrium) and endometrial spiral arteries via proteolytic processes

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18
Q

how do trophoblasts reach the maternal spiral arteries?

A
  • Trophoblasts form villous structures
  • Cytotrophoblasts break through trophoblast shell
  • Invade through decidual tissue
  • Trophoblasts reach maternal spiral arteries
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19
Q

what happens when trophoblasts reach the maternal spiral arteries and why?

A

• Spiral arteries are converted from narrow to wide vessels  allows a much greater flow of maternal blood around the villi

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20
Q

what is the barrier between maternal and fetal circulation?

A

villous trophoblasts

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21
Q

why is it important that the embryo is in a hypoxic environment?

A

oxygen tension gradient is present

O2 tension increases towards the maternal side.

Invasion is partly regulated by this gradient

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22
Q

what molecules are involved in successful implantation and what do they do?

A
  • Cyclooxygenase-2 (COX-2) - converts AA to PGE2 promotes invasion and decidualisation
  • Heparin-binding epidermal growth factor (HB-EGF) - involved in attachment and invasion
  • Vascular endothelial growth factor (VEGF) - involved in angiogenesis
  • Human leukocyte antigen-G (HLA-G) - inhibits antigen-specific lymphocyte response & decreases NK cell function
  • Indoleamine 2,3-dioxygenase (IDO) - regulated by IFNs to promote anti-proliferative effects
  • Transforming growth factor β (TGFβ) - regulates invasion and proliferation
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23
Q

if fertilisation and implantation occur, why dont progesterone levels fall?

A
  • Corpus luteum does not degenerate because of hCG.
  • Progesterone levels don’t fall bc progesterone secretion is maintained by corpus luteum (oestrogen levels do not fall either)
  • Progesterone maintains the endometrium and becomes the decidua
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24
Q

when does the luteal:placental shift occur?

A

at 12 weeks

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25
what is the luteal:placental shift?
Progesterone goes from being made by the corpus luteum to being made by the placenta
26
what happens if the placenta and corpus luteum levels of progesterone dont match up?
miscarriage can occur
27
what is an ectopic pregnancy?
pregnancies which implant in the oviduct of the fallopian tube
28
what is the risk if an ectopic pregnancy occurs in the uterine lumen?
placenta previa
29
what is placenta previa?
placenta lies low in the uterus and partially/completely covers the cervix
30
what complications can occur in placenta previa?
haemorrhage can occur during labour --> puts mother and baby’s life in risk
31
how should the baby be delivered in placenta previa?
caesarean
32
describe the structure of the mature placenta
- discoid shape - diameter of 15-20cm - weighs approx 500g and 2.5cm thickness - found in the upper uterine segment - anterior or posterior - fetal and maternal surface
33
describe the fetal surface of the placenta
o Smooth, glistening covered in amnion | o Umbilical cord inserted in the centre with vessels radiating from it
34
describe the maternal surface of the placenta
o Dull, greyish and divided into 15-20 cotyledons (lobes) | o Each cotyledon is formed of branches of one main villus stem covered by the decidua basalis
35
what is the decidua?
uterus endometrium that forms in preparation for pregnancy
36
what are the three layers of the decidua and where are they found?
``` decidua basalis (layer below the implantation site) decidua capsularis (encapsulates the growing fetus) decidua parietalis (all the remaining uterine mucosa) ```
37
describe the fetal circulation of the placenta
* 2 x umbilical arteries from baby to the placenta to carry away waste and CO2 * 1x Vein takes oxygen and nutrients to the baby * Smaller branches to chorionic villi
38
what is the main site of exchange in the placentaa?
capillary networks in terminal branches of chorionic villi
39
describe the maternal circulation of the placenta
* 80 - 100 spiral arteries open directly into the intervillous spaces * Low pressure blood (10mmHg in the relaxed uterus) * Villi bathed in maternal blood (exchanged 3-4 x/min) * Return via venous pathways in decidual plate of placenta
40
why is the placenta necessary?
* Fetus requires nutrition | * Luteal regression needs to be prevented
41
what are the functions of the placenta?
* Site for exchange of gases (02 and C02) and other molecules between maternal and fetal blood * Nutrient exchange * Waste exchange – urea, bilirubin etc. * Synthesis of proteins, hormones and enzymes
42
how do O2 and CO2 cross the placenta?
simple diffusion
43
how does fetal haemoglobin compare to adult haemoglobin?
has greater affinity and carrying capacity
44
what does the rate of diffusion across the placenta depend on?
o maternal/fetal gases gradient o maternal and fetal blood flow o placental permeability o placental surface area
45
what substances cross the placenta and how?
* H20 and electrolytes - simple diffusion * Glucose - facilitated diffusion via glucose transporter proteins (GLUTs) * Amino acids - active transport via transporter proteins (accumulative or exchangers) * Fatty acids – simple diffusion * Large proteins and cells – pinocytosis * Waste products, eg urea – simple diffusion
46
what non-nutrients with the placenta allow to pass through?
* IgG antibodies * hormones * antibiotics * sedatives * some viruses, eg rubella * some organisms, eg treponema pallida (syphilis)
47
what molecules wont the placenta allow through?
large molecules e.g. heparin and insulin
48
what fetal cells can cross the placenta?
``` o Trophoblast cells o Granulocytes o Gametocytes o Lymphocytes o Nucleated red blood cells o Primitive counterparts ```
49
what is rhesus factor?
protein found on the surface of your RBCs
50
what do Rh+ and Rh- mean?
o Rh positive – your blood cells have the protein | o Rh negative – you lack the protein
51
what happens if there is Rh incompatability between the mother and baby? (mother is - and baby is +)
* Small amount of baby’s blood can come into contact with maternal blood and cause mother to produce Rh antibodies * In the second pregnancy if the baby is Rh positive, antibodies from the mother will cross the placenta and destroy the fetal RBCs
52
what treatment is given in Rh incompatability?
Anti-D immunoglobulin can be given to remove any fetus Rh+
53
what type of hormones does the placenta make?
protein and steroid hormones
54
when does synthesis of hCG begin?
before implantation
55
what does hCG do?
maintains corpus luteum --> progesterone and oestrogen secretion during early pregnancy
56
what does human placental lactogen (hPL) do?
``` o increases free fatty acids by its lipolytic action o inhibits gluconeogenesis o it promotes fetal growth o it promotes mammary duct proliferation o exhibits lactogenic effects o resembles GH ```
57
how does the placenta produce oestrogen and progesterone?
Placenta produces progesterone and oestrogen from cholesterol precursors and in concert with the fetal adrenal gland
58
what is the human placental growth hormone needed for?
o Similar to growth hormone | o Regulation of maternal blood glucose levels to ensure adequate fetal glucose supply
59
what do insulin like growth factors do?
o Similar structure to insulin | oStimulates proliferation and differentiation of the cytotrophoblast
60
what produces relaxin and what does it do?
o Produced by decidual cells | o Softens the cervix and pelvic ligaments in preparation for childbirth
61
why is the fetus not rejected by the maternal immune system?
1) HLA expression - Trophoblast cells express HLA G which isn’t recognised by ‘host’ immune system so Cells not rejected 2) Infiltrating leucocytes secrete IL-2 which regulates the immune system 3) Decidual reaction - decidual cells become swollen and compact around developing fetus so there's a barrier between the mother and the implanting embryo
62
what pathologies are associated with abnormal placental development?
* Pre-eclampsia * Intrauterine growth restriction * Early miscarriage
63
what placental complication can occur with placental completeness?
retained placental tissue associated with haemorrhage and infection after birth.
64
what complications can arise from the size of the placenta?
- less than 2.5 cm: intrauterine growth retardation of the fetus. - More than 4cm: association with maternal diabetes mellitus
65
what colour should the maternal surface of the placenta be in a term infant?
dark maroon
66
what colour should the maternal surface of the placenta be in a premature infant?
light maroon
67
what does paleness of the maternal surface of the placenta indicate?
presence of fetal anaemia  sign of haemorrhage
68
what do clots on the maternal surface of the placenta indicate?
shows placental abruption
69
what does a thick ring of membrane on the placenta show?
prematurity and prenatal bleeding
70
how does a true cord knot occur?
occurs when fetus passes through a loop of the umbilical cord (usually in early pregnancy)
71
when and how does a cord knot cause compromise?
sufficient tension on the cord before or during delivery/labour then blood flow may be cut off and signs of fetal asphyxia may occur
72
what happens if the umbilical cord only has 1 artery and 1 vein?
fetal anomaly rate is nearly 50%
73
what cord complications can occur?
cord knots cord vessels thromboses

human development (20 decks)

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