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Structure & Function 5 > Embryo development/placentation > Flashcards

Embryo development/placentation Flashcards

1
Q

What four steps must be achieved before the embryo can attach to the uterus?

A

Development within the confines of the zona pellucida
Hatching of the blastocyst from the zona pellucida
Maternal recognition of pregnancy
Formation of extraembryonic membranes

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2
Q

What happens during fertilisation to form diploid zygote?

A

Union of a haploid oocyte + a haploid spermatozoon producing diploid zygote
Fertilisation begins w/ gamete fusion (zygote formation)
Fertilisation ends with the initiation of zygote cell division (the start of cleavage)

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3
Q

Cleavage begins with and progresses to?

A

with a zygote and progresses through compaction of morula stage and terminates at the start of the blastocyst (blastula) stage

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4
Q

What are the first 8 blastomeres?

A

these are undifferentiated and have identical potential in mammals thereafter, blastomeres differentiate into inner & outer cells w/ different missions

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5
Q

what is a blastomere?

A

each daughter cell of the cleavage process is termed this

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6
Q

cleavage?

A

initial series of mitotic divisions by which the large zygotes is cleaved into numerous ‘normal size’ cells

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7
Q

How many cells make up blastomeres?

A

2-16 cells = totipotent

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8
Q

Pre-attachment embryo development allows?

A

allows blastomere cloning, transfer of a blastomere to a surrogate zona pellucida which can be transferred to a surrogate mother
no increase in total cell mass

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9
Q

what is a morula?

A

it is a solid ball of blastomeres within a zona pellucida (typically consisting of 16-64 blastomeres)

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10
Q

what happens to the blastomeres that form the morula?

A

the blastomeres become compacted; cells on the inside differentiate from those along the surface of the morula

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11
Q

what happens to the outer blastomeres of the morula?

A

they become flattened and form tight junctions (reducing fluid permeability)

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12
Q

epitopic pregnancy?

A

blastocyst hatches in wrong place

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13
Q

embryo development of primates?

A

embryo implants rapidly - extra-embryonic membranes form later

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14
Q

embryo development of domestic mammals?

A

prolonged pre-attachment period when extra-embryonic membranes form

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15
Q

Post blastocyst hatching development - bovine?

A

Day 13: Blastocyst 3mm diameter
Day 17: Elongated conceptus= 25 cm Day 18: Occupies both uterine horn

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16
Q

Post blastocyst hatching development - porcine?

A

Day 3: Blastocyst 2 mm diameter
Day 4.5: 20 cm in length (4-8mm/hour!)
Day 16: 80-100 cm in length
Dramatic growth = development of extra-embryonic membranes

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17
Q

Post blastocyst hatching development - cow, sow, ewe?

A

filamentous conceptus

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18
Q

Post blastocyst hatching development - mare?

A

blastocysts remain spherical and secrete an embryonic capsule

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19
Q

Placentation?

A

formation of the extra-embryonic membranes
essential for endometrial attachment

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20
Q

Where are placentae regions of apposition?

A

between uterine lining and fetal membranes where metabolites exchanged for sustaining pregnancy

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21
Q

Placenta is a complex organ - it is responsible for?

A

fetal nourishment
protection from external and internal insults
production and/or metabolisation of various hormones

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22
Q

primitive endoderm forms the?

A

yolk sac

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23
Q

Placental development?

A

formation of the extra-embryonic membranes
Essential for endometrial attachment
4 extra-embryonic membranes form

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24
Q

yolk sac?

A

analogous to the avian ‘yolk’ but no primary nutritional role
Regresses as the foetus develops (transient) but important!
(contributed primordial germ cells to the gonads)

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25
inner surface of placenta?
endoderm
26
3 germ layers?
endoderm - forms the 'tubes' inside the body (respiratory and digestive tracts) mesoderm - forms the middle bits (everything else) ectoderm - forms skin and brain
27
Chorion?
fusion of the trophoblast and mesodermal layers
28
allantois?
forms as an out-pushing of the primitive gut --> liquid waste
29
chorion made from?
trophoblast and mesoderm
30
allantois made from?
mesoderm
31
amnion made from?
trophoblast
32
what does the chorion form?
forms the surface fetal membrane; the outermost later
33
apposition areas (placental types) may be:
diffuse (pig) zonary (carnivore) discoid (primates & rodents) Cotelydonary (pockets of microvilli - placentomes based, cotyldonary placentome - mare and ruminants) Mare - microcotyldonary and diffuse
34
A placentome is?
a discrete area of interdigitation between a maternal caruncle and a fetal cotyledon. Equine placentas are microcotyledonary (microplacentomes are distributed diffusely). Ruminant placentas consist of rows of relatively large placentomes
35
progesterone from the corpora lutea is essential for what?
to establish pregnancy in all mammals
36
Corpus lutea produces progesterone - what does this prevent?
prevents further ovulation
37
if no pregnancy, the CL does what?
it regresses to allow further ovulation
38
Ovine interferon τ (oIFN-τ) and Bovine interferon τ (bTP-τ) does what?
acts on the endometrial cells of the uterus blocks oxytocin receptor synthesis Promotes attachment of blastocyst onto wall of uterus and protein synthesis
39
the migration of the conceptus distributes pregnancy factors where?
over a wide surface of the endometrium
40
conceptus of mare?
they stop - 'stopping spot' in which the conceptus will spend between 5 and 20 minutes
41
what happens to the endometrium of the mare?
cells invade maternal endometrium - forms endometrial cups these form from invasion of the fetal trophoblast into maternal endometrium at day 35 of pregnancy secrete equine chorionic gonadotrophin (eCG) Day 60-100 induce ovulation and formation of secondary CL's (corporal lutea) leads to more progesterone and support pregnancy
42
maternal recognition of pregnancy for dog and cat?
none - produce progesterone anyway and it stays high for the needed time - dogs can have phantom pregnancy - because progesterone is high so one thing to do is cause corpus luteal to break down
43
haemochorial centre placenta?
3 layers - chorion (epithelial), basement membrane, chorionic capillary (blood supply) PRIMATES and RODENTS
44
endotheliochorial placenta?
5 layers - endometrial capillary, endometrial epithelium, chorion, chorionic basement membrane, chorionic capillary DOGS and CATS
45
epitheliochorial placenta?
6 layers - endometrial capillary, endometrial basement membrane, endometrial epithelium, chorion, chorionic basement membrane, chorionic capillary = harder for large molecules to get through placenta to baby so need colostrum due to difficulty of transport of larger molecules RUMINANTS
46
convex structure of caruncle?
cow, giraffe
47
concave structure of caruncle?
sheep, goat
48
cotyledon?
foetal origin
49
caruncle?
maternal origin
50
porcine placenta?
diffuse (spread out) epithelialiochorial placenta
51
mare placenta?
diffuse microcotyledonary epitheliochorial placenta
52
how are placentas classified?
according to the tissue layers separating fetal and maternal blood
53
what happens in order to give rise to four placental types?
uterine epithelium, uterine connective tissue and uterine endothelium may be eroded
54
fixation of placenta?
association between the conceptus and endometrium
55
attachment of placenta?
the establishment of the foeto-maternal placenta
56
equine conceptus?
fixed - day 16 attached - day 36
57
what type of organ is the chorion?
it is an endocrine organ
58
what is the maternal component of the placenta?
endometrium
59
what is the foetal component of the placenta?
chorion
60
what is the functional unit of the chorion?
chorionic villi
61
What is the primary basis of placental classification?
distribution of villi
62
What types of placenta are there?
Diffuse Zonary Discoid Cotyledonary
63
What is the secondary basis of placental classification?
placental anatomy
64
What animals have a diffuse placenta?
mare + sow
65
What animals have a zonary placenta?
dog + cat
66
What animals have a discoid placenta?
rodents + primates
67
What animals have a cotyledonary placenta?
mare + ruminants
68
meaning of oviparity?
egg laying - external incubation
69
meaning of viviparity?
live birth - internal gestation
70
What are the requirements in order to allow placentation to happen?
Development of the uterus for foetal retention and support
71
What are the two major differences for maternal recognition of pregnancy of a SOW?
Conceptus secretes oestradiol as the MRP signal (Day 11-12) AND Oestradiol causes PGF2α secretion to be directed to the uterine lumen: away from the submucosal vessels
72
MRP?
maternal recognition of pregnancy
73
Describe the distribution of conceptuses along the uterine horns of the sow?
equal
74
How many conceptuses minimum per uterine horn?
two
75
What does oestradiol promote?
uterine contractions
76
CL?
corporal lutea
77
The CL produces progesterone - what does this do?
it prevents further ovulation
78
When does the CL produce progesterone?
when there is pregnancy
79
If there is no pregnancy, what does the CL do?
the CL regresses to allow further ovulation
80
What does MRP (maternal recognition of pregnancy) include?
progesterone release
81
Why do we need MRP and how does it work?
Most species do not want to risk multiple pregnancies at different stages of development - thus the embryo needs to signal to mother that it is there + prolong the progesterone release
82
meaning of subvert?
undermine the power and authority of something
83
what is luteolysis?
it refers to the cyclical regression of the corpus luteum
84
What is it that the embryo undermines/subverts when it signals to the mother that it is there and prolongs progesterone release?
it is undermining luteolysis
85
When signalling to the mother that it is there, what must the embryo be careful about?
needs to be careful as the embryo is foreign DNA so it could be attacked by the mother's immune system
86
What does the CL (corpora lutea) produce?
progesterone
87
What is essential in order to establish pregnancy in all mammals?
progesterone from the corpora lutea
88
What does amnion act like?
like a protective cushion
89
What do allantois and chorion fuse to form?
allantochorion
90
What is the allantochorion?
it is the foetal contribution to the placenta
91
in the mouse and human, what happens to the trophoblast cells that overlay the inner cells mass of the placenta?
they separate and instead of degenerating, they become amnionic wall
92
what happens to trophoblasts in domestic mammals?
they degenerate
93
What are trophoblast cells?
these cells overlay the inner cell mass of the placental cells
94
meaning of delaminate?
divide into layers
95
What happens to cells from the inner cell mass of the Blastocoel?
the cells proliferate, break loose (delaminate) and migrate to form a new cell layer inside the trophoblast layer
96
Once the cells from the inner cell mass of the blastocoel have migrated to form a new cell layer inside the trophoblast layer, what is it called and what happens after that?
the new layer is called the hypoblast - it will form a yolk sac (endoderm).
97
Aside from the hypoblast, what is the remaining inner cell mass called?
the epiblast
98
What becomes evident at the blastocyst surface as cells proliferate in the inner cell mass cells?
a thickened embryonic disc becomes evident
99
What are the three germ layers?
the ectoderm, mesoderm and endoderm
100
What is the ectoderm?
it forms the epidermis of the skin, epithelium of the oral and nasal cavities, and the nervous system and sense organs
101
What is the mesoderm?
this forms the muscle and connective tissue, including bone and components of the circulatory, urinary and genital systems
102
What is the endoderm?
this forms the mucosal epithelium and glands of respiratory and digestive systems
103
During placental development - how many extra-embryonic membranes form?
4 - these are essential for endometrial attachment
104
Describe the 3 stages of the pre-attachment embryo development?
Pressure on zona pellucida increases (early blastocyst) (due to mitosis + blastocoele expansion) - Trophoblast proteases (slide11) Zona ruptures (hatching blastocyst) Then dependant on uterine environment for further development (hatched blastocyst)
105
In the morula, what happens to the blastomeres?
they become compacted; cells on the inside differentiate from those along the surface of the morula
106
What happens to the outer blastomeres of the morula?
they become flattened and form tight junctions (reducing fluid permeability) they develop the capacity to secrete fluid internally, they are destined to become trophoblasts which form the chorion and amnion (fetal membranes) of the conceptus
107
what happens to the inner blastomeres of the morula?
they form gap junctions to maximise intercellular communication; they are destined to become inner cell mass which forms the embryo itself (plus 2 fetal membranes - allantois + yolk sac)
108
describe the inner cells of the morula?
stay as a discrete cluster
109
describe the outer cells of the morula?
differentiate to early trophoblasts & form tight junctions - alter cell permeability and fluid accumulates
110
Describe structure of morula?
outer cells compacted
111
Describe structure of blastocyst:
cavitation
112
Describe the outer cells of blastocyst:
trophoblast layer - blastocoele forms
113
describe the inner cells of the blastocyst:
inner cell mass (ICM)

Structure & Function 5 (24 decks)

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