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REPRO > ferilisation > Flashcards

ferilisation Flashcards

week 6

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….

A

2 days before and 0.5 days after ovulation

23
Q

How long does sperm and occytes last for?

A

Sperm = 28-48hrs

oocyte= 6-24hrs

24
Q

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

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
Q

Pluripotent vs totipotent

A

P= generate complete individual excluding placenta

T= generate complete individualincluding placenta

26
Q

Morula - structure and actions

A

outer and inner cell populations

gap junctions between inner cells

tight junctions between outer cells

Na pumped in = influx of water

27
Q

What are the three stages of implantation?

A

Adherence

Invasion

Completion

28
Q

When does adherence occur and what occurs in it?

A

6 days after

Protein mediated binding of the trophoblast –> endomer\trium

Digestive enzymes from the trophoblast erode the endometrial layer

29
Q

Why do syncytiotrophoblasts secrete hCG? When does it do this?

A

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
Q

What occurs in the invasion stage of implantation and when does it occur?

A

Trophoblasts differentiate = cytotrophoblasts and syncytiotrophoblasts

Syncytiotrophoblast digest and invade endometrium to secrete hCG = maintenance of CL

7 days after F

31
Q

What occurs in the completion stage of implantation and when does it occur?

A

12 days after feralization

Blastocysts enveloped by endometrium

32
Q

Outline the 4 steps in the formation of the bilaminar embryonic disc

A
  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
Q

What are the 2 fluid-filled cavities form in stage 2 of Bilaminat embryonic disc formation?

A

Amniotic cavity: between epiblasts and amnion

Yolk-sac: lined by hypoblasts

34
Q

what are the 4 extraembryonic membranes?

A

Amnion

Yolk Sac

Allantois

Chorion and Chorionic villi

35
Q

Functions of the Amnion

A

Prevents physical trauma

Maintains temperature

Fluid avoids embryonic structures fusing

Permits movement

36
Q

Functions of Yolk Sac

A

Brief nutrient supply

Become spat of gut

Source of early blood cells and blood vessels

37
Q

Function of Allantois

A

Forms base of umbilical cord

38
Q

Function of Chorion and Chorionic villi

A

Forms true placenta with maternal decidua

39
Q

During week 3 of pregnancy, the primitive streak forms. What is this and on what does it form?

A

Days 13-14 = primitive streak = midline groove forms along the caudal end of bilaminar disc = longitudinal axis of the embryo

40
Q

How is the endoderm germ layer formed?

A

from the epiblast cell that displaces hypoblasts

41
Q

How is the mesoderm germ layer formed?

A

from the Epiblast cell that fills middle layer

42
Q

In what weeks do the germ layers differentiate?

A

4-8

43
Q

What do the ectoderm, endoderm and mesoderm differentiate into respectively?

A

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
Q

What are the 3 steps to sperm penetrating an egg?

A
  1. hyperactive motility → buries itself by physically penetrating cumulus cells
    1. hyaluronidase → penetrates corona radiata (innermost cumulus cells)
    2. acrosin → digests zona pellucida
45
Q

What does the zona pellucida do during the cleavage stage?

A

holds together the cells of the cleaving embryo and protects it from attack by macrophages.

46
Q

Why must the zona pellucida be removed before the expanded blastocyst can attach itself to endometrium?

How is it removed?

A

If not removed, it would form a physical barrier preventing contact between trophoblast and endometrial epithelium

47
Q

How does the blastocyst remove the zona pelluida?

A

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
Q

What is the trophoblas?

A

The outer cell layer of a blastocyst

secretes enzymes that help digest the zona pellucida

49
Q

Why is the uterus the best spot for implantation?

A
  • endometrium (secretory phase so highly vascularised)
    • space for growth and development
    • myometrium for muscular contractions in parturition
    • structural support
50
Q

When the embryo attaches to the uterine wall, what does the trophoblast proliferate and differentiate into?

(what are the two layers of a trophoblast)

A

Two cell populaions:

Syncytiotrophoblast

Cytotrophoblast

51
Q

cytotrophoblast

A

cell population in which cell structure is retained

surround the blastocyst cavity and overlie inner mass = responsible for the proliferation and further differentiation

52
Q

Syncytiotrophoblast

A

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
Q

Why do trophoblasts invade uterine wall?

A

The trophoblast needs to invade the uterine lining to establish a connection with the maternal blood supply,

REPRO (14 decks)

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