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ferilisation Flashcards

week 6 (53 cards)

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1
Q

What are the two phases pf embryology?

A

prenatal and postnatal

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2
Q

What are the two periods within prenatal development?

A

Embryonic period

Fertilisation –> end of 8th week

Fetal period

9th week –> birth

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3
Q

How long is pregnancy?

A

38 weeks
(three trimesters)

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4
Q

How is the due date calculated?

A

40wks + 7 days FROM the First day of last normal menstrual period (LNMP)

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5
Q

What occurs in the embryonic period?

A

Placenta develops

All major adult organs formed (gastrulation and organogenesis)

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6
Q

What occurs in the fetal period?

A

growth and development

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7
Q

What occurs in week 1 of embryonic period?

A

Day 0 = fertilization

Pre-implantation events: cleavage and blastocyst formation

Day 6= implantation: adherence

Day 7 = implantation: invasion

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8
Q

What occurs in week 2 of embryonic period?

A

Development of placenta begins

Day 12: implantation complete

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9
Q

What occurs in week 3 of embryonic period?

A

Days 13-14 = primitive streak

Days 14-16 = Gastrulation

Day 17 = start of organogenesis

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10
Q

What happens in week 12 of pregnancy?

A

placenta maturation

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11
Q

What happens during fetal development?

A

differentiation and refinement of body structure

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12
Q

Sperm capacitation ( what and how)

A

Sperm Capacitation
-Sperm can’t immediately fertilize as must spend a few hours in female repro tract to attain capacity to fertilize.

Process
-Osterogen and Vaginal mucus destabilize sperm plasma and trigger motility

-Removal of protein coating

-Reorganization of plasma to expose binding sites

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13
Q

What is the acrosome reaction, what is it stimulated by and what are its actions?

A

What:
Ca-dependent event in which the acrosome swells and outer acromsal membrabe fuses with overlaying membrane

stimulated by
progesterone and ZP3 (protein)

Actions:
releases digestive enzymes (hyaluronidase and acrosin) from acrosome

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14
Q

What does Hyalurnidase do?

A

penetration of corona radiata

(digestive enzyme released in acrosome reaction).

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15
Q

What does acrosin do?

A

zona pellucida digestion

(digestive enzyme released in acrosome reaction).

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16
Q

Summarise the four events of fertilisation

A

Capacitation: estrogen/mucus destabilize sperm PM and hyperactive motility

Acrosome reaction: progesterone and binding of ZP3 cause increase Ca and release of digestive enzymes from sperm.

Fertilization: sperm digests zona, binds to sperm-binding receptor and fuses with oocyte PM.

Polyspermy block: fusion causes increase Ca and electrical block of oocyte OM, cortical granule release hardens zona and removes sperm binding receptors.

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17
Q

what are the three stages of implantation development?

A

Cleavage stage

Morula stage

Blastocysts stage

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18
Q

What occurs in the cleavage stage?

A

2-8 cells

Increase number of cells (but no increase in cell size)

Totipotent blastomeres (generate complete individual)

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19
Q

What happens in the morula stage? How does it appear?

A

16-32 cells

Inner and outer cell populations formed

= solid ball of blastomeres

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20
Q

What happens in the early blastocysts phase?

A

morula hollows out, fills with fluid and hatches from the ona pellucide

4 days

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21
Q

What occurs (overall) in the blastocysts stage?

A

64+ cells

First cell differentation event

Pluripotent inner cell mass = generate complete individual excluding individual

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22
Q

For successful fertilisation, Coitus (sexual intercourse) should occur….

Study These Flashcards
A

2 days before and 0.5 days after ovulation

23
Q

How long does sperm and occytes last for?

Study These Flashcards
A

Sperm = 28-48hrs

oocyte= 6-24hrs

24
Q

For IVF, how can it be microscopically shown that fertilisation has occurred?

Study These Flashcards
A

presence of 2 polar bodies
(trapped by zona pellucida)

can’t use cell division as an indicator as high Ca exposure will cause them to divide even if bot fertilised

25
Pluripotent vs totipotent
P= generate complete individual excluding placenta T= generate complete individualincluding placenta
26
Morula - structure and actions
outer and inner cell populations gap junctions between inner cells tight junctions between outer cells Na pumped in = influx of water
27
What are the three stages of implantation?
Adherence Invasion Completion
28
When does adherence occur and what occurs in it?
6 days after Protein mediated binding of the trophoblast --> endomer\trium Digestive enzymes from the trophoblast erode the endometrial layer
29
Why do syncytiotrophoblasts secrete hCG? When does it do this?
hCG maintains CL and enables it to produce progesterone to support endometrium and pause menstrual cycle 6-8 after fertilsation, for 8-12 wks
30
What occurs in the invasion stage of implantation and when does it occur?
Trophoblasts differentiate = cytotrophoblasts and syncytiotrophoblasts Syncytiotrophoblast digest and invade endometrium to secrete hCG = maintenance of CL 7 days after F
31
What occurs in the completion stage of implantation and when does it occur?
12 days after feralization Blastocysts enveloped by endometrium
32
Outline the 4 steps in the formation of the bilaminar embryonic disc
1. Inner cell mass differentiates = epiblasts and hypoblasts 2. Fluid filled cavities form 3. Hypoblast invaginates = allantois with extraembryonic mesoderm. 4. extraembryonic mesoderm, cytotrophoblasts and syncytiotrophoblasts = chorion and chorionic villi
33
What are the 2 fluid-filled cavities form in stage 2 of Bilaminat embryonic disc formation?
Amniotic cavity: between epiblasts and amnion Yolk-sac: lined by hypoblasts
34
what are the 4 extraembryonic membranes?
Amnion Yolk Sac Allantois Chorion and Chorionic villi
35
Functions of the Amnion
Prevents physical trauma Maintains temperature Fluid avoids embryonic structures fusing Permits movement
36
Functions of Yolk Sac
Brief nutrient supply Become spat of gut Source of early blood cells and blood vessels
37
Function of Allantois
Forms base of umbilical cord
38
Function of Chorion and Chorionic villi
Forms true placenta with maternal decidua
39
During week 3 of pregnancy, the primitive streak forms. What is this and on what does it form?
Days 13-14 = primitive streak = midline groove forms along the caudal end of bilaminar disc = longitudinal axis of the embryo
40
How is the endoderm germ layer formed?
from the epiblast cell that displaces hypoblasts
41
How is the mesoderm germ layer formed?
from the Epiblast cell that fills middle layer
42
In what weeks do the germ layers differentiate?
4-8
43
What do the ectoderm, endoderm and mesoderm differentiate into respectively?
Ectoderm Nervous system and epidermis Mesoderm Most blood vessels, connective tissues, bone and muscles Endoderm Epithelial linings and associated glands of digetsive, respiratory and urogenital systems.
44
What are the 3 steps to sperm penetrating an egg?
1. hyperactive motility → buries itself by physically penetrating cumulus cells 2. hyaluronidase → penetrates corona radiata (innermost cumulus cells) 3. acrosin → digests zona pellucida
45
What does the zona pellucida do during the cleavage stage?
holds together the cells of the cleaving embryo and protects it from attack by macrophages.
46
Why must the zona pellucida be removed before the expanded blastocyst can attach itself to endometrium? How is it removed?
If not removed, it would form a physical barrier preventing contact between trophoblast and endometrial epithelium
47
How does the blastocyst remove the zona pelluida?
Blastocyst Expansion: fluid accumulation increases the internal pressure within the blastocyst. Enzyme Production: The blastocyst produces and secretes enzymes, (proteases such as trophoblast proteases) degrade the zona pellucida. Mechanical Pressure: The accumulation of fluid + enzymatic breakdown= mechanical pressure = zona pellucida to thin and eventually rupture or crack. Zona Pellucida Rupture:
48
What is the trophoblas?
The outer cell layer of a blastocyst secretes enzymes that help digest the zona pellucida
49
Why is the uterus the best spot for implantation?
- endometrium (secretory phase so highly vascularised) - space for growth and development - myometrium for muscular contractions in parturition - structural support
50
When the embryo attaches to the uterine wall, what does the trophoblast proliferate and differentiate into? (what are the two layers of a trophoblast)
Two cell populaions: Syncytiotrophoblast Cytotrophoblast
51
cytotrophoblast
cell population in which cell structure is retained surround the blastocyst cavity and overlie inner mass = responsible for the proliferation and further differentiation
52
Syncytiotrophoblast
a cell population in which individual cells have lost cell membrane forms the 'leading edge' of cytotrophoblasts = produce enzymes that allow embryo to invade uterine wall.
53
Why do trophoblasts invade uterine wall?
The trophoblast needs to invade the uterine lining to establish a connection with the maternal blood supply,

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