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EMBRYOLOGY (foundation B) > Intro 27: from fertilised egg to bi-laminar disc > Flashcards

Intro 27: from fertilised egg to bi-laminar disc Flashcards

1
Q

Definition of Embryology

A

the science of the development of an embryo from the fertilisation of OOCYTE to the FOETUS stage.

but most often means from fertilised oocyte into newborn human being. (includes investigations of the molecular, cellular and structural factors that contribute to the formation of an organism)

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2
Q

How long does Embryogenesis take (fertilised oocyte to foetus)
aka first trimester

A

8 weeks

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3
Q

How long from foetus to newborn (fatal period)

A

34 weeks

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4
Q

When is the initiation of spermatogenesis and how

A

at Puberty
triggered by Testosterone

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5
Q

at puberty Spermatogonia undergo mitotic division to form…

A

Primary Spermatocyte
- undergoes meiosis I one into..
Secondary Spermatocyte
- meiosis II -
Spermatids

..spermatozoa

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6
Q

Oogenesis, what happens before birth

A

most of oogonia die
surviving OOGONIA undergo MITOSIS to form PRIMARY OOCYTE

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7
Q

Primary Oocyte remains arrest in prophase I until…

A

Puberty - start of Menstrual Cycle

undergoes MEIOSIS I to form SECONDARY OOCYTE and first polar body

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8
Q

Secondary Oocyte remains arrest in Metaphase II until…

A

Fertilisation

undergoes MEIOSIS II to form OVUM and secondary polar body

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9
Q

Size of Sperm

A

approx 0.55 micrometres

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10
Q

size of Ovum

A

approx 0.1 mm (large)

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11
Q

out of the 200-300 million spermatozoa normally deposited in the female genital tract, how many reach the site of fertilisation (ampullary region of the uterine tube)

A

only 300-500

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12
Q

What must sperm undergo in order to fertilise the egg

A

CAPACITATION
conditioning process (7 hours)

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13
Q

What does CAPACITATION of sperm allow for and how

A

Liberation of acrosomal region from seminal plasma membrane so acrosome can perform its function in fertilisation

involves epithelial interactions between the sperm and the mucosal surface of the uterine tube

A glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa.

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14
Q

What is the 1ST PHASE of FERTILISATION

A

PENETRATION OF THE CORONA RADIATA

Enzyme HYALURONIDASE (released from the acrosome) assisted by TUBAL MUCOSAL ENZYMES disperse follicular cells of corona radiata so sperm can penetrate

This process is also aided by
movements of the tail of the
sperm.

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15
Q

Enzymes used in PENETRATION OF THE CORONA RADIATA

A

HYALURONIDASE
TUBAL MUCOSAL ENZYMES

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16
Q

What is the 2ND PHASE of FERTILISATION

A

PENETRATION OF THE ZONA PELLUCIDA

ZONA PELLUCIDA induces ACROSOME REACTION, releasing proteolytic enzyme ACROSIN and ESTERASES and NEURAMINIDASE that cause the LYSIS OF THE ZONA PELLUCIDA so sperm can come into contact with plasma membrane of the ovum

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17
Q

Zone Pellucida is composed of…
and also facilitates and maintains..

A

composed of GLYCOPROTEINS.
facilitates and maintains SPERM BINDING

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18
Q

enzymes used in PENETRATION OF THE ZONA PELLUCIDA

A

proteolytic enzyme ACROSIN
ESTERASES
NEURAMINIDASE

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19
Q

3RD PHASE of FERTILISATION

A

FUSION OF PLASMA CELL MEMBRANES OF THE OVUM AND SPERM

The HEAD and TAIL of the
sperm ENTER the cytoplasm of the
ovum

PLASMA MEMBRANE and
MITOCHONDRIA of the sperm
REMAIN behind.
(All mitochondria inherited from mother)

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20
Q

In fertilisation, which parts of the sperm enter ovum and which parts remain behind

A

Head and Tail ENTER

Pl. membrane and Mitochondria REMAIN

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21
Q

What does the fusion of ovum and sperm result in

A

CORTICAL or
ZONA REACTION

CHANGE IN ZONA PELLUCIDA
that prevents other sperm from
entering

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22
Q

What is the 4TH PHASE of FERTILISATION

A

completion of 2ND MEIOTIC DIVISION OF THE OVUM

ovum completes the
second meiotic division
immediately after entry of the
sperm and forms 2 DAUGHTER CELLS: one that receives hardly
any cytoplasm - SECOND POLAR BODY and MATURE OVUM

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23
Q

The chromatin material of the
mature ovum is
arranged into the…

A

female pronucleus

24
Q

5TH PHASE of FERTILISATION

A

FORMATION of the MALE PRONUCLEUS

Within the cytoplasm of the ovum
the chromatin material of the
sperm (22, x or 22, Y) is
organised into male pronucleus.

The combination of 23
chromosomes in each
pronucleus results in a zygote
with 46 chromosomes.

During growth of male and female
pronuclei (both haploid) each
pronucleus replicates its DNA.

25
Q

What happens to the sperm tail during 5th phase (formation of male pronucleus)

A

detaches and degenerates

26
Q

6TH PHASE of FERTILISATION

A

METABOLIC ACTIVATION of the OVUM

Immediately after DNA
synthesis,
- BREAKDOWN OF PRONUCLEAR MEMBRANES
- followed by CONDENSATION
- MIXING OF MATERNAL AND PATERNAL CHROMOSOMES.

Chromosomes organise on the spindle in
preparation for a NORMAL MITOTIC DIVISION and the FIRST CLEAVAGE DIVISION of the zygote

(approx. 30 hrs after
fertilization)

27
Q

What are the 5 Results of FERTILISATION

A
  • Stimulation of the secondary oocyte to complete the 2ND MEIOTIC DIVISION, producing the 2ND POLAR BODY
  • RESTORATION OF DIPLOID NUMBER in zygote (46)

-VARIATION

  • determination of chromosomal SEX of embryo
  • METABOLIC ACTIVATION of oocyte that initiates CLEAVAGE OF ZYGOTE
28
Q

How do we get Variation from fertilisation

A

mingling of maternal and paternal chromosomes

Fertilization is RANDOM
- approximately 70 trillion diploid combinations are possible when solely taking account of independent assortment and random fertilization

Crossing over and other mutations also add to this number.

29
Q

What is an example of a fertilisation ABNORMALITY

A

DIZYGOTIC and MONOZYGOTIC TWINNING

30
Q

how do we get DIZYGOTIC TWINNING (fraternal, non-identical)

A

2 SEPARATE fertilization events involving 2 OOCYTE (released at ovulation) fertilised by 2 SPERMATOZOA

31
Q

how do we get MONOZYGOTIC TWINNING (identical)

A

a SINGLE fertilization
event
- 1 fertilized oocyte
- 1 spermatozoa
a division occurs
- share same genome

32
Q

Cleavage consists of…

A

repeated mitotic divisions of the zygote

33
Q

Cleavage of zygote results in the increase in the number of cells that are called…

A

BLASTOMERES

34
Q

After the 3rd Cleavage, what takes place

A

Compaction

35
Q

Approx 3 days after fertilisation what is formed…

A

16 Cell MORULA
(looks like a raspberry)

36
Q

Approx 4 days after fertilisation, what happens…

A

MORULA enters the UTERINE CAVITY

37
Q

What happens when MORULA moves into UTERINE CAVITY

A

BLASTOCYST CAVITY / BLASTOCOELE is formed.

Blastomeres are organised into the TROPHOBLAST and the EMBRYOBLAST / ICM (inner cell mass)

38
Q

On 4th/5th day what is the embryo then called

A

BLASTOCYST

39
Q

What happens approx 5 days after fertilisation

A

HATCHING
embryo frees itself from the Zona Pellucida
(ready for implantation)

40
Q

Hatching is a result of..

A

a series of EXPANSION-CONTRACTION CYCLES
that are also supported by ENZYMES that DISSOLVE ZONA PELLUCIDA

41
Q

approx 6 days after fertilisation, what happens to the hatched blastocyte

A

Hatched BLASTOCYTE attaches to the ENDOMETRIAL EPITHELIUM (decidua)

42
Q

what happens as a result of TROPHOBLAST and ENDOMETRIAL interaction

A

TROPHOBLAST CELLS rapidly PROLIFERATE
DIFFERENTIATE into 2 layers:
CYTOTROPHOBLAST
SYNCYTIOTROPHOBLAST

43
Q

what is the role of the SYNCYTIOTROPHOBLAST

A

produces PROTEOLYTIC ENZYMES
- erode maternal tissue
- enable embryo to burrow into endometrium

44
Q

by the end of the first week the embryo is…

A

superficially implanted into the endometrium
- deriving its nourishment from the eroded maternal tissues

45
Q

Beginning of 2ND WEEK:
DAY 7-8 TROPHOBLAST cells continue to…

A

DIFFERENTIATE into CYTOTROPHOBLAST and SYNCYTIOTROPHOBLAST

46
Q

SYNCYTIOTROPHOBLAST release

A

hCG, lytic enzymes, factors

47
Q

also at DAY 7-8,
DECIDUAL REACTION:

A

increase in secretory function of the endometrium

48
Q

what is the DECIDUA

A

MUCOSAL LINING of
the uterus or endometrium,
modified by the pregnancy

49
Q

What also happens on DAY 7-8

A

EMBRYOBLAST / ICM cells DIFFERENTIATE into 2 layers:
- EPIBLAST (columnar epithelial cells)
- HYPOBLAST (cuboidal epithelial cells)
to form a flattened, almost circular BI-LAMINAR EMBRYONIC DISC

50
Q

When is IMPLANTATION COMPLETE

A

DAY 9-10

51
Q

What also happens on DAY 9-10

A
  • EXTRACELLULAR VACUOLES appear in SYNCYTIOTROPHOBLAST and join to form LACUNAE
  • AMNIOBLASTS separate from epiblast and organise into AMNION (thin memb. that encloses
    the amniotic cavity)
  • cells of HYPOBLAST extend to surround the YOLK SAC forming PRIMARY YOLK SAC / PRIMARY UNBILICAL VESICLE
52
Q

What happens at DAY 11-13
(5)

A
  • Formation of the EXTRAEMBRYONIC MESODERM: supports the epithelium of the amnion and primary yolk sac
  • Formation of CHORIONIC / EXTRAEMBRYONIC CAVITY
  • Transformation of the primary into the SECONDARY YOLK SAC (5) (secondary umbilical vesicle)
  • LACUNAE are filled with maternal blood (beginning of utero-placental circulation)
  • Formation of PRIMARY CHORIONIC VILLI
53
Q

The formation of the BI-LAMINAR DISC sets the…

A

DORSAL-VENTRAL AXIS

  • EPIBLAST is DORSAL to the HYPOBLASTE
54
Q

The formation of the BI-LAMINAR DISC sets the…

A

DORSAL-VENTRAL AXIS

  • EPIBLAST is DORSAL to the HYPOBLAST
55
Q

Examples of WEEK 2 ABNORMALITIES

A
  • Abnormal implantation: Ectopic pregnancy
    Implantation occurs in the uterine tube or outside the uterus (external surface of uterus,ovary, bowel, GI tract, peritoneal wall)
  • Molar pregnancy: Hydatidiform Mole
    only the trophoblast layers of the
    embryo proliferate and not the epiblast (embryoblast/ICM)
    so no embryo develops

EMBRYOLOGY (foundation B) (4 decks)

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