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BIOL2045 > Extraembryonic membranes > Flashcards

Extraembryonic membranes Flashcards

1
Q

What are the 4 extraembryonic membranes in placental mammals?

A
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2
Q

What are the roles of EEMs?

A
  • Transfer of nutrients in and breakdown products out
  • Physically protect the embryo
  • Protect the embryo from toxins and hormonal changes
  • Protect the embryo from temperature changes
  • Protect from maternal immune system
  • Allow growth (not pressing on the embryo)
  • Cellular differentiation – Gonadal stem cells, haematopoietic stem cells
  • Drive hormonal changes:
  • Signal to mother pregnancy is occurring (hCG)
  • Maintain uterine relaxations and secretions (progesterone)
  • End pregnancy and Induce parturition (oestrogen- CRH)
  • hGC- maintains CL and later runs proesterone from placenta
  • (chorio-allantois and yolk sac)
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3
Q

Role of progesterone + 17beta oestradiol in uterine growth and implantation

A
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4
Q

What was the first EEM to appear?

A

Chorion the first membrane to appear – foetal side formed from the trophectoderm

Forms the chorionic membrane from the highly motile trophoblast cells which migrate into the uterine wall (endometrium)

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5
Q

Tell me the two placeta that form and due to what?

A

The foetal placenta will form from these cells -

  • The allantois fuses with this and mesoderm migrates in from the embryo itself (forms blood vessels) —chorio- allantoic placenta

The maternal placenta forms usually at the upper surface of the uterus (more later)

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6
Q

When trophoblasts enter the maternal tissue they differentiate into 2 layers, what are these layers?

A

Trophoblast when they enter the maternal tissue differentiate to 2 layers

  1. Inner Cytotrophoblasts
  2. Outer Syncytiotrophobasts

In time some of the Cytotrophoblasts lining the cavity form Giant cells which help remodel blood vessels

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7
Q

Chorion

A
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8
Q

Chorion

A
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9
Q

What is the cytotrophoblast?

A

The cytotrophoblast is the trophoblastic stem cell

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10
Q

What are the four lineages of the cytotrophoblast?

A

Forms four lineages

  1. The fusion lineage -Syncytiotrophoblast
  2. The invasive lineage interstitial Cytotrophoblast

Then later…

  1. Through endoreduplication- TrophoblastGiant Cells
  2. Structural Spongiotrophoblasts
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11
Q

What does the Syncytiotrophoblast control?

A

Syncytiotrophoblasts control both maternal adaptive and innate immunity, Physical separation

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12
Q

What does the Syncytiotrophoblast express, block and produce?

A
  • Express cell surface non-classical MHCI molecules (C-E-G) inhibit NK cells, suppress CTL activity and upregulate the local CD4’ Treg cell differentiation.
  • Block innate immunity via the modification of neutrophil function and NET formation.
  • Produce hCG- signal to mother pregnancy has started
  • Not HLA-A and HLA-B, but atypical MHC class I isotypes HLA-E and HLA-G, as well as HLA-C
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13
Q

What can the LH not support after ovulation?

A

LH (from pituitary reduces) cannot support Corpus Luteum (CL) after ovulation.

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14
Q

Tell me about the co-dependence of the corpus luteum and the embryo

A
  • Corpus luteum needs embryo to survive
  • Embryo needs corpus luteum to survive
  • In absence of embryo- no hCG produced, CL will die (10-14 days after ovulation )
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15
Q

What is the hormone of pregnancy?

A

Progesterone

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16
Q

Tell me the roles of progesterone

A
  • Blocks further follicle development and ovulation (blocks FSH and LH)- so single embryo (or one timed wave of ovulation).
  • Barrier at cervix for sperm entry- mucus plug stops entry of microorganisms. Cervical plug.
  • Induces uterine endometrium to make a nutrient-rich food source for embryo (secretory phase- needs estrogen too).
  • Keeps uterine myometrium ‘quiescent’
  • Induces breast tissue growth ready for lactation
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17
Q

What is progesterone made by?

A

Progesterone made by placenta later in pregnancy between 4-7 weeks

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18
Q

Tell me the formation of the placenta at human E14?

A
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19
Q

Tell me the formation of the placenta at human E16

A
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20
Q

Tell me the formation of the placenta at human E20

A
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21
Q

Tell me the formation of the human placenta E14- E20

A
  1. At human E14 Cytotrophoblasts grow out into the endometrium increasing the contact surface the primary chorionic villus
  2. At human E16 Extra-embryonic mesoderm grows out into the primary villi increasing the contact surface further - the secondary chorionic villus
  3. At human E20 vessels form in the secondary villi mesoderm– this forms the tertiary chorionic villus
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22
Q

What are trophoblast giant cells and what their role?

A
  • Trophoblast giant cells.
  • highly polyploid (switched from a mitotic to endoreduplicative cell)
  • Like metastatic tumour cells, they breach basement membranes and invade deeply into the maternal decidualized uterine stroma.
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23
Q

Tell me the properties of trophoblast giant cells

A

Highly angiogenic and vasodilatory properties, remodel arterial walls, enable them to redirect maternal blood flow towards the implantation site.

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24
Q

What are the trophoblast giant cell subtypes?

A
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25
Q

What are the trophoblast giant cell characteristics?

A
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26
Q

Maternal vessel entry and placental development doesn’t occur over the whole chorion Villus formation is biased to the upper region – decidua basalis/ placentalis

A
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27
Q

Tell me about the discoid placenta in humans/rodents average sizings and role?

A
  • The placenta averages 22-24 cm diameter long and 2cm thick
  • Typically weighs 500 grams
  • It connects to the foetus by an umbilical cord of approximately 55–60 cm long
  • Contains two umbilical arteries and one umbilical vein.
28
Q

Does the placenta shape alter between different mammalian species?

A
  • Yes
  • In some species the placenta regions are grouped into lobules placentomes
  • the maternal side – caruncles
  • and on the foetal side - cotyledons
29
Q

Main substances transferred from the mother to the foetus through the placenta? And from the foetus to the mother?

A
  • From the mother to the foetus: water, oxygen, nutrients and IgG antibodies.
  • From the foetus to the mother: metabolic wastes, including urea, uric acid, and creatinine (via developing foetal kidney and the allantois), and carbon dioxide.
30
Q

Do the mother and the foetus exchange cells through the placenta?

A
  • Under normal conditions, maternal cells do not cross the placenta during gestation.
  • This placental barrier. Although permeable to some substances (selective permeability), the placental barrier largely prevents the passage of cells.
  • However foetal cells are highly invasive – and often enter the mother’s tissues
31
Q

Tell me the role of Human chorionic gonadotropin hormone?

A

Prevent shedding of uterine wall (menses) when the corpus luteum atrophies- similarities to LH and induces progesterone formation (HCGH signals that pregnancy has started and to stop the cycle)

32
Q

Tell me the role of Progesterone?

A

Progesterone increases uterine secretions (foetal nutrition). Progesterone, it prevents contractions of the uterus

33
Q

Tell me the role of Oestrogen?

A

Oestrogen drives growth of the uterus and increases uterine blood supply

34
Q

Tell me the role of Human placental lactogen?

A

Human placental lactogen increases foetal metabolism and general growth and development. Acts with growth hormone to stimulate IGF-1 production and regulating intermediary metabolism of embryo which increases growth

35
Q

What are the cloacks from the maternal immune system and whats their role?

A
  • Secretes neurokinin-B physically masks cells of foetal placenta
  • Lymphocytic suppressor cells in the foetal placenta block IL2 and limit maternal cytotoxic T cells
  • The Spongio trophoblasts add strength and form the wall (along with giant cells) the villi
  • Maternal cells in normal development shouldn’t cross. If they do it suggests the placenta is failing and that the pregnancy is unlikely to continue
36
Q

When does the EEM Amnion start to apper?

What from?

A

In humans, this appears just after implantation

  • The epiblast forms an epithelial plate with a lumen in it
  • The lower surface is the epiblast and the upper are amnioblasts
37
Q

The Amnion

A
38
Q

What happens when the embryo and amnion starts to grow…?

A

Then the embryo folds – head and tail, and to the sides (forming a cavity in the embryo) pulling the amnion around it so the amnion surrounds almost all the embryo– except for its junction with the yolk sac/ allantois and body stalk

39
Q

When the amnion is first formed, what is it in contact with?

What does it secrete?

What does it allow?

What testing can be done at this stage?

A
  • When first formed, the amnion is in contact with the body of the embryo
  • Its begins to secrete amniotic fluid ~ 5 weeks in man and the amnion expands to ultimately adhere to the inner surface of the chorion
  • The amniotic fluid allows the free movements of the foetus during the later stages of pregnancy, and also protects it from trauma
  • Amniocentesis - genetic and chromosomal testing
40
Q

When does the yolk sac develop?

From this development how does the EE coelom and primary yolk sac form?

A
  • This develops just after implantation (slightly different in different species)
  • The primitive endoderm (hypoblast) begins to migrate out from the embryonic disc
  • This layer (now called parietal endoderm) in time covers the inner cytotrophoblasts.
  • the spaces are the extra embryonic coelom and primary yolk sac
  • (in man this form about days 9-After this forms the chorionic growth becomes predominant
41
Q

Tell me about the formation of the secondary yolk sac between days 9 and 13?

A
42
Q

Yolk sac

A
43
Q

Mice form a little different as they grow down and then rotate

A
44
Q

Tell me the similarities between the mouse and human during yolk sac formation?

A
  • In the end the yolk sac in both has a stalk attaching to the abdomen of the foetus as it curves in at its head and side
  • In mice the rotation means the yolk sac sits around the amnion and the embryo
  • In man the yolk sac remains a bag and the embryo folds about its attachment point
45
Q

What are the three roles of the yolk sac?

A
  1. Early nutrient transfer
  2. Vascular components
  3. The primordial germ cells (originator of spermatozoa and oocytes) ancestors of the germline.
46
Q

Tell me about the early nutrient transfer role of the yolk sac

A

Early nutrient transfer important in man from E15-to ~ 3mths the only point of nutrient transfer in reptiles and birds- main storage of nutrients during embryogenesis here

47
Q

Tell me the vascular components of the yolk sac

A

Vascular components – preliminary circulatory cells

  • first site of haematopoiesis during mammalian development.
  • Yolk sac hematopoietic stem cells (YS-HSC), these forms and amplify here and then migrate into the embryo proper
  • The yolk sac is also the first site of blood vessel endothelial development. (blood islands) in the yolk sac
48
Q

Tell me about the PGCs of the yolk sac

A
49
Q

What is the Allantois?

A

This is an outgrowth (diverticulum) initially from the yolk sac and pushes into the stalk joining to the chorion (the umbilicus)

50
Q

Tell me where the allantois extends from in the embryo?

A

The hind gut

51
Q

What does the allantois fuse with and form?

A

In the chorion it fuses with it and so in time forms the chorioallantoic membrane

52
Q

What is the allantois in contact with?

A

In contact with the bladder and lets excreted fluids (kidney)- be taken to placenta where its transferred to maternal circulation

53
Q

Tell me about the size of the allantois in birds/reptiles and mammals

A
  • In birds / reptile – no placenta so this is a large structure
  • In mammals it is small as chorio-allantois allows transfer
54
Q

In what type of animals does the allantois get large?

A

In egg forming animals the allantois gets large

In mammals it remains small

55
Q

Allantois

A
56
Q

What is the primitive umbilical cord formed from?

A

Expansion of amniotic cavity, leads to elongation of umbilical cord

57
Q

What are the contents of the primitive umbilical cord?

A
  • Yolk sac and vitelline duct
  • Connecting stalk with remnant of allantois
  • Umbilical and vitelline vessels
  • Intestinal loop in its proximal part
58
Q

Tell me about the differences of the primitive umbilical cord between vertebrate species?

A
  • In fish and amphibians, only the yolk sac is present.
  • The amnion is a specialisation for terrestrial survival preventing the embryo from drying out AMIOTES
  • In reptiles and birds, in addition to the yolk sac, the amnion, the chorion and the allantois are also present
  • the yolk sac and allantois are far larger in these
  • the allantois doesn’t fuse with the chorion

(In placental mammals, the chorion and the allantois specialise to form the embryonic placenta, the endometrium forms the maternal placenta)

59
Q

Tell me about the role of the amnion in birds

A

The amnion protects the embryo in a sac filled with amniotic fluid. (shock absorber)

60
Q

Tell me about the yolk sac in birds?

A

The yolk sac contains yolk — the sole source of food until hatching. Yolk is a mixture of proteins and lipoproteins. - it is very large initially reducing during development

61
Q

Tell me about the Chorion in birds

A

The chorion lines the inner surface of the shell (which is permeable to gases) and participates in the exchange of O2 and CO2 between the embryo and the outside air.

62
Q

Tell me about the allantois in birds

A

The allantois stores metabolic wastes (chiefly uric acid) of the embryo and, as it grows larger through development, also participates in gas exchange.

63
Q

Birds EEMs

A
64
Q

Tell me about twinning

A
  • Two foetuses share a single placenta, (monochorionic twins). ~70% of identical twins – the placenta may occur anywhere in relation to the stalk position (the umbilical chord)– there is no set or predictable pattern
  • Depending on where they implant, one foetus may get a lower share of the placental exchange than its co-twin.
  • Hence although identical twins share the same genetic material, they may actually grow quite differently.
  • Only 1% of identical twins share both a single placenta and a single amniotic sac, and this poses a further risk-. unequal placental sharing and umbilical knotting
65
Q

What occurs in the second week of development?

A
66
Q

Tell me about Tetragametic chimerism and microchimerism

A

BIOL2045 (14 decks)

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