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Early Embryonic development 1 Flashcards

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0
Q

When is the embryonic period?

A

-3-8 weeks

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1
Q

When is the pre-embryonic period?

A

-1-2 weeks

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2
Q

When is the foetal period?

A

9-38 weeks

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3
Q

Which hormones stimulate oocyte release?

A
  • Leutinising hormone

- Prostaglandin

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4
Q

By what physical mechanism is an oocyte released?

A

-Local muscular contractions in the ovarian wall extrudes the oocyte

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5
Q

What helps the oocyte enter the uterine tube?

A

-Fimbrae which sweep over the surface of the ovary

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6
Q

What happens after an oocyte has been released into the uterine tube?

A

-Oocyte travels along the uterine tube by peristaltic muscular contraction od the tube and by cilia in the mucosae

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7
Q

Where does fertilisation occur?

A

-In the ampillary region of the uterine tube (widest part, close to the ovary)

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8
Q

What is the name for a fertilised egg?

A

-Zygote

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9
Q

Where is the ideal site for implantation of a zygote?

A

-High up on the posterior uterine wall

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10
Q

What are the two main results of fertilisation?

A
  • Restoration of diploid number by fusing of two haploid gametes
  • determination of sex
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11
Q

How is the sex determined during fertilisation?

A

-The fertilising sperm is either carrying an x-chromosome or a y-chromosome

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12
Q

What is cleavage and what is its purpose?

A
  • A series of mitotic divisions

- To increase cell number

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13
Q

What happens to the cells size as cleavage occurs?

A

-They become smaller

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14
Q

When does cleavage begin?

A

-approx. 30 hrs after fertilisation when the zygote has reached the two-cell stage

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15
Q

What potency are the cells after cleavage?

A

-Totipotent

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16
Q

What is the end product of cleavage?

A

-Morula

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17
Q

What is compaction?

A

-The process by which the morula form a compact ball of cells held together by tight junction with no spaces in between, maximising contact with one another

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18
Q

Why is compaction said to be the start of the first cavity?

A

-Compaction causes segregation of inner cells which communicate extensively by gap junctions from outer cells

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19
Q

To what does the inner cell mass give rise to?

A

-Embryoblast

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20
Q

To what does the outer cell mass give rise to?

A

-Trophoblast which later contributes to the placenta

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21
Q

What is the Zona Pellicuda and what is its function?

A
  • A transient glycoprotein shell which surrounds a zygote created by a chemical change which occurs at fertilisation
  • Keeps other spermatozoa on the outside preventing polyspermy
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22
Q

Define zygote

A

-Diploid cell resulting from the fusion of two haploid gametes

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23
Q

Define morula

A

-Solid ball of identical cells resulting from the division of a fertilised ovum

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24
Define ovary
-Female reproductive organ in which ova/eggs are produced
25
Define fallopian tube
-Uterine tube which are female tubes which eggs travel from the ovary to the uterus
26
Define Uterus
- The womb | - Hollow muscular organ located in the pelvic cavity of female mammals in which a fertilised ovum implants
27
Define Cleavage
-Series of repeated mitotic cell divisions that occur in the ovum immediately after fertilisation up until the formation of the morula
28
When does blastocyst formation occur?
-At the same time as the morula is entering the uterine cavity (uterus/womb)
29
Describe blastocyst formation
- Fluid begins to penetrate zona pellicuda into the intracellular spaces of the inner cell mass - The intracellular spaces become confluent, pushing the inner cell mass to one pole and a blastocyst cavity forms
30
Why is blastocyst formation known as the first differentiation stage?
- The inner cell mass develops into embryo and is known as the embryoblast - The outer cell mass is strictly placenta and is known as the trophoblast - The cells are now pluripotent
31
What is hatching?
-Blastocyst hatching from the zona pellicuda as the risk of polyspermi decreases
32
What is the purpose of hatching?
-The blastocyst becomes free to enlarge and can interact with the uterine surface to implant
33
What has happened to the endometrium during the menstrual cycle?
-It has become more suitable for the implantation of the conceptus
34
When does implantation occur?
-Day 6/7 after fertilisation
35
How many cells are in the conceptus at time of implantation and how are these made up?
- 107 - 8 make embryo - 99 begin to develop the foetal membranes
36
What is the first stage of implantation?
-Attachment to epithelial cells which is mediated by selected integrins and ECM molecules
37
What does the trophoblast do at the beginning of implantation?
-Trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa
38
When does the development of the bilaminar disc occur?
-When the blastocyst is partially embedded in the endometrial stroma
39
Describe initial trophoblast differentiation
- Trophoblast develops into two layers - Cytotrophoblast - Syncytiotrohpblast
40
What is the cytotrophoblast?
-Protective inner layer of the trophoblast
41
What is the syncytiotrophoblast?
-Outer multinucleate layer of trophoblast that serves to invade the endometrium of the uterus
42
How does the syncytiotrophoblast develop?
-Mitotic divisions occur in the cytotrophoblast which migrate to the syncytiotrophoblast, fuse together and loose individual cell membranes
43
Describe the differentiation of the embryoblast to the bilaminar disc
- Embryoblast differentiates into two layers - Hypoblast -> layer of small cuboidal cells adjacent to the blastocyst cavity - Epiblast-> Layer of high columnar cells adjacent to the amniotic cavity
44
Where does the amniotic cavity develop from?
- A small cavity which appears in the epiblast
45
In the pre-embryonic period, what has priority?
-The placenta
46
Define embryoblast
-Cluster of cells segregated to one pole of the blastocyst from which the embryo develops
47
Define trophoblast
-Outer layer of cells surrounding the blastocyst from which placental tissues are derived
48
Define blastocyst
-Stage of embryogenesis at the time of implantation where outer trophoblast cells form a fluid filled sphere with a small group of embryoblast cells at one pole
49
Define implantation
-Attachment of the blastocyst to the epithelial lining of the uterus, penetration through the endomertrium occuring 6/7 days after fertilisation of the oocyte
50
When does bilaminar disc formation occur?
-Day 8
51
What is the purpose of implantation?
- Access to glands and vasculature to access O2 and nutrients - To allow maternal blood flow in placenta
52
Once the conceptus is embedded in the stroma, what happens to the penetration defect?
- Closed by fibrin coagulum forming fibrin plug | - Surface epithelium almost covers the entire defect by day 11/12
53
Why can bleeding occur during this stage of preganancy?
-Implantation is very invasive
54
How does the syncytiotrophoblast develop throughout week 2 to provide uroplacental circulation?
- Considerable development, particularly at embryonic pole - Vacuoles appear and fuse to form lacunae - Large lacunae form an intercommunicating network - Further cellular development leads to deeper erosion into stroma - Erosion of endothelial lining of maternal sinusoids - Development of uroplacental circulation
55
How does the support of the embryo change throughout week 2?
-Changes from histiotrophic (diffusion) to haemotrophic
56
How does the primitive yolk sac develop and when does this occur?
- Day 9/10 - At the embryonic pole, flattened cells originiating from the hypoblast line the inner surface of the cytiotrophoblast. This is the extracoelemic membrane - The extracoelemic membrane together with the hypoblast form the primitive yolk sac
57
What is extraembryonic mesoderm? When and how does it develop?
Day 11/12 - Connective tissue which lies betweeen the extracoelemic membrane and the cytiotrophpblast - New population of cells derived from the primitive yolk sace develop inbetween the extracoelemic membrane and the cytiotrophoblast - Eventually this extraembryonic mesoderm fills the space between the trophoblast and the amniotic/yolk sac/extracoelemic membrane
58
How does the extraembryonic cavity form?
- Once extraembryonic mesoderm fills the space between the trophoblast and the amniotic sac/extracoelemic membrane, large cavities/vacuoles begin to appear - These cavities become confluent and form the extraembryonic cavity; the trophoblast is surrounded by a thin layer of extraembryonic mesoderm - Cavity surrounds the amniotic cavity and the primitive yolk sac except for the connecting stalk
59
What are primary villi and describe their development
- Units of foetal/maternal exchange - Caused by the development of the cytotrophoblast - Cells proliferate locally and penetrate into syncytium - cellular columns surrounded by syncytium are villi
60
Describe the development of the definitive yolk sac and when does it occur?
- Day 13 - Hypoblast begins to produce additional cells - Cells migrate and proliferate to form new cavities - Cavities pinch off and merge at the opposite pole to form the definitive yolk sac
61
What is the chorionic cavity?
-The extraembryonic cavity once all other cavities in wekk 2 have formed
62
What is the connecting stalk?
-Extraembryonic mesoderm which connects the embryo and its specific cavities (Amniotic and secondary yolk) to the supporting trophoblast
63
What is Interuterine growth restriction?
-Growth of conceptus not supported as there is sub-optimal establishment of an implantation environment
64
What is Placenta Previa
- Implantation of the conceptus low down in the uterus such that development blocks the opening of the cervix - Can cause haemorrhage and requires C section
65
What is an ectopic pregnancy?
- Implantation takes place outside the uterus; abdominal cavity, ovary, uterine tube - Can become life threatening due to intra-abdominal haemorrhaging

Tissues of the body (17 decks)

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