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Tissues of the body > Early Embryonic development 1 > Flashcards

Early Embryonic development 1 Flashcards

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
Q

Define ovary

A

-Female reproductive organ in which ova/eggs are produced

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25
Q

Define fallopian tube

A

-Uterine tube which are female tubes which eggs travel from the ovary to the uterus

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26
Q

Define Uterus

A
  • The womb

- Hollow muscular organ located in the pelvic cavity of female mammals in which a fertilised ovum implants

27
Q

Define Cleavage

A

-Series of repeated mitotic cell divisions that occur in the ovum immediately after fertilisation up until the formation of the morula

28
Q

When does blastocyst formation occur?

A

-At the same time as the morula is entering the uterine cavity (uterus/womb)

29
Q

Describe blastocyst formation

A
  • 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
Q

Why is blastocyst formation known as the first differentiation stage?

A
  • 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
Q

What is hatching?

A

-Blastocyst hatching from the zona pellicuda as the risk of polyspermi decreases

32
Q

What is the purpose of hatching?

A

-The blastocyst becomes free to enlarge and can interact with the uterine surface to implant

33
Q

What has happened to the endometrium during the menstrual cycle?

A

-It has become more suitable for the implantation of the conceptus

34
Q

When does implantation occur?

A

-Day 6/7 after fertilisation

35
Q

How many cells are in the conceptus at time of implantation and how are these made up?

A
  • 107
  • 8 make embryo
  • 99 begin to develop the foetal membranes
36
Q

What is the first stage of implantation?

A

-Attachment to epithelial cells which is mediated by selected integrins and ECM molecules

37
Q

What does the trophoblast do at the beginning of implantation?

A

-Trophoblastic cells over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa

38
Q

When does the development of the bilaminar disc occur?

A

-When the blastocyst is partially embedded in the endometrial stroma

39
Q

Describe initial trophoblast differentiation

A
  • Trophoblast develops into two layers
  • Cytotrophoblast
  • Syncytiotrohpblast
40
Q

What is the cytotrophoblast?

A

-Protective inner layer of the trophoblast

41
Q

What is the syncytiotrophoblast?

A

-Outer multinucleate layer of trophoblast that serves to invade the endometrium of the uterus

42
Q

How does the syncytiotrophoblast develop?

A

-Mitotic divisions occur in the cytotrophoblast which migrate to the syncytiotrophoblast, fuse together and loose individual cell membranes

43
Q

Describe the differentiation of the embryoblast to the bilaminar disc

A
  • 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
Q

Where does the amniotic cavity develop from?

A
  • A small cavity which appears in the epiblast
45
Q

In the pre-embryonic period, what has priority?

A

-The placenta

46
Q

Define embryoblast

A

-Cluster of cells segregated to one pole of the blastocyst from which the embryo develops

47
Q

Define trophoblast

A

-Outer layer of cells surrounding the blastocyst from which placental tissues are derived

48
Q

Define blastocyst

A

-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
Q

Define implantation

A

-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
Q

When does bilaminar disc formation occur?

A

-Day 8

51
Q

What is the purpose of implantation?

A
  • Access to glands and vasculature to access O2 and nutrients
  • To allow maternal blood flow in placenta
52
Q

Once the conceptus is embedded in the stroma, what happens to the penetration defect?

A
  • Closed by fibrin coagulum forming fibrin plug

- Surface epithelium almost covers the entire defect by day 11/12

53
Q

Why can bleeding occur during this stage of preganancy?

A

-Implantation is very invasive

54
Q

How does the syncytiotrophoblast develop throughout week 2 to provide uroplacental circulation?

A
  • 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
Q

How does the support of the embryo change throughout week 2?

A

-Changes from histiotrophic (diffusion) to haemotrophic

56
Q

How does the primitive yolk sac develop and when does this occur?

A
  • 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
Q

What is extraembryonic mesoderm? When and how does it develop?

A

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
Q

How does the extraembryonic cavity form?

A
  • 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
Q

What are primary villi and describe their development

A
  • 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
Q

Describe the development of the definitive yolk sac and when does it occur?

A
  • 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
Q

What is the chorionic cavity?

A

-The extraembryonic cavity once all other cavities in wekk 2 have formed

62
Q

What is the connecting stalk?

A

-Extraembryonic mesoderm which connects the embryo and its specific cavities (Amniotic and secondary yolk) to the supporting trophoblast

63
Q

What is Interuterine growth restriction?

A

-Growth of conceptus not supported as there is sub-optimal establishment of an implantation environment

64
Q

What is Placenta Previa

A
  • 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
Q

What is an ectopic pregnancy?

A
  • 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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