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Embryology > Gametogenesis, Fertilisation and the Blastocyst > Flashcards

Gametogenesis, Fertilisation and the Blastocyst Flashcards

1
Q

What is teratology ?

A

Study of birth defects

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2
Q

Label the 4 parts of the Fallopian tube

A
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3
Q

The Fallopian tubes end in …

A

Fimbrae

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4
Q

Oogenesis

explain what happens in stages 4 and 5

A

most growing follicles degenerate to form corpus acreticum

fluid filled antrum made by the follicular cells

thecal layer forms around the growing follicle

follicle call secondary follicle now

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5
Q

How does the ovum get into the Fallopian tube?

what consequences does this have ?

A

Ovum is shed into abdominal cavity and then caught by the fimbrae

makes infection more likely

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6
Q

Female gametogenesis (oogenesis)

explain what happens in the first three stages

A
  1. Primary oocyte is surrounded by a single layer of follicular cells = primary follicle
  2. At beginning of each monthly cycle, 5-12 primary follicle develop to become growing follicles (only one reaches full maturity however)
  3. growing follicles are multiple layered; separated from ovum via the septum pellucidium
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7
Q

Where do the follicular cells come from?

A

Ovarian epithelium

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8
Q

What is the septum pellucidum made from ?

A

Acellular mucopolysaccharide(aka GAGs) layer

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9
Q

What two parts does the thecal layer divide into ?

A
  1. Vascular theca interna - produces oestrogen
  2. Avascular inactive theca external
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10
Q

What happens to the cells of the theca interna and stratum granulosum after the ovum is released?

A

They enlarge , turn yellowish and form the corpus luteum to secrete lots of progesterone and some oestrogen

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11
Q

Oogenesis

explain what happens in stages 6&7

A

Follicle now called a mature/Graafian follicle

the majority of the follicular cells form the stratum granulosum and secrete progesterone

the others form the outer layer called the cumulus oophorus ; now called secondary oocyte

mature follicle ruptures to release the ovum

ovum covered by corona radiata now

septum pellucidum expanded to become the zona pellucida

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12
Q

What happens to the corpus luteum if fertilisation does not occur after 12 days

A

Corpus luteum degenerates into the corpus alibicans which terminates hormonal output leading to menstruation

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13
Q

What happens to the corpus luteum if pregnancy occurs ?

A

Corpus luteum is sustained by HCG produced by conceptual and forms a large corpus luteum of pregnancy

eventually forms a large corpus albicans

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14
Q

Male gametogenesis

(Spermatogenesis)

A

Occurs in testes

stem cells divide by mitosis to for spermatogonium with 46 XY chromosomes

spermatogonium divide to form primary spermatocytes (still with 46 XY)

1st meiotic division to form secondary spermatocytes with 23X or 23Y chromosomes (double chromatids present at this point)

2nd meiotic division = spermatids with 23X/Y (single chromatid)

spermatids mature to form spermatozoa

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15
Q

Label the diagram with he terms :

Acrosomal cap

nucleus

mitochondria

axial bundle

A

Nucleus covered by sparse cytoplasmic layer

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16
Q

Purpose of acrosomal cap in spermatozoa and where is it derived from?

A

Derived from the Golgi apparatus

contains enzymes that aid in penetration of ovum

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17
Q

Describe the structure of the middle piece of the sperm

how does this relate to its function ?

A

Helically wound mito surrounds central axial bundle of fibril

fibrils have a 9+ 2 arrangement

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18
Q

How are ova moved along Fallopian tubes?

A

Via the action of cilia

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19
Q

Main difference between male and female gametogenesis

A

Spermatogenesis occurs continuously throughout a males life

Females are already born with their lifetime supply of oogonia ; they mature throughout their , once every month and the supply runs out between 45 and 55

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20
Q

Compare oogenesis and Spermatogenesis :

which process of division are involved ?

is it continuous/discontinuous ?

how long does it take ?

how many produced in each cycle ? / how many in one ejaculate ?

motile or non/motile?

cytoplasmic:nuclear ratio

does it require additional substances ?

A
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21
Q

Label the prostate gland

A
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22
Q

Label this Sagittal section of the female reproductive system

A
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23
Q

The abdominal cavity in a male is ….

A

Closed

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24
Q

Describe the events occurring before fertilisation

A

When the sperm reach the isthmus they become less motile and wait for chemoattractants released from the cumulus cells on ovulation tomake sperm motile again

sperm reach ampulla where fertilisation occurs

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25
Q

What is capacitation

A

Changes to spermatazoa that must occur for successful fertilisation; takes place upon ejaculation - conditioning in female reproductive tract during which acrosomal cap loses glycoprotein coat and increased motility occurs

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26
Q

Describe first 3 the events which occur upon fertilisation

A

Penetration by spermatazoon prompts completion of 2nd meiotic division

fusion of plasma membrane of both gametes ; male nucleus is injected

Zona reaction occurs ; ovum shrinks to form the perivitelline space

27
Q

What is the role of the acrosomal enzymes in fertilisation

A

Help disperse corona radiata and aid penetration of zona pellucida

28
Q

What is the zona reaction ?

Why is it important

A

When fertilisation occurs, the permeability of zona pellucida is altered to prevent further penetration

enzymes released by cortical granules digest sperm receptor proteins so that they can no longer bind

this prevents polyspermy (implantation of more than one sperm)

29
Q

Stage 4/5 of fertilisation

A

Cleavage

~30h post fertilisation 2 daughter blastomeres formed by mitosis

cells continue to cleave to form progressively smaller blastomeres (DNA synthesis occurs but no new proteins)

30
Q

Formation of morula

A

Stage 6 of fertilisation

morula refers to solid ball of cells

cytoplasmic:nuclear ratio near normal

cytoplasm differential packaged

Free within uterine cavity

zona pellucida still remains to prevent implantation

31
Q

Blastocyst formation

A

Occurs during 2nd week

morula cells undergo compaction

tight junctions between surface cells

zona pellucida begins to breakdown (called hatching)

Formation of inner cell mass and trophoblast

blastocyst now has a cavity

32
Q

Function of inner cell mass and trophoblast

A

Inner cell mass goes on to form the embryo

trophoblast form extra embryonic membranes and placenta

33
Q

Label the inner cell mass and trophoblasts in this image

A
34
Q

one spermatogonium divides to make _____ spermatozoa

one oogonium divides to make ______ ovum due to ______ division of the cytoplasm

A

4 spermatozoa

1 ovum (asymmetrical division of cytoplasm)

35
Q

what are polar bodies?

A

small residual cells produced during the first and second meiotic divisions of oogenesis that have very little cytoplasm and no use

1 polar body produced during meiosis I

3 polar bodies formed during meisois II

36
Q

give a brief summary of oogenesis

A

at foetal stage, female jas 400,000 primary follicles already produced

primary oocyte arrested at prophase I of meiosis I until puberty

primary oocytes completes meiosis I at beginning of menstrual cycle to form the secondary oocyte

secondary oocyte arrested at prophase II of meiosis II until fertilisation occurs

meiosis II completed upon fertilisation

37
Q

Where and when does implantation occur

A

6 days after fertilisation

in the posterior wall of uterus nearer the fungus than the cervix

38
Q

What are the 3 words that can be used to describe the trophoblast

A

Invasive , ingestive and digestive ; can get past the uterine epithelium

39
Q

What is the decidual reaction ?

A

Upon implantation of the blastocyst in the uterine lining ,

Thickening of the endometrium occurs

increased secretion occurs from the endometrium (uterus lining)

Glandular epithelial cells will now contain more glycogen and lipids

40
Q

What are the 3 populations of cells present upon implantation of the blastocyst?

A

Primitive ectoderm (epiblast)

primitive endoderm (hypoblast)

trophoblast

41
Q

Events occurring in early implantation

A

Epiblast surrounds the amniotic cavity

hypoblast surrrounds the yolk sac cavity

wall of blastocyst is two layered now

42
Q

What happens on day 10 after implantation

A

Blastocyst completely embedded ; epithelial continuity restored

trophoblast produces extra embryonic mesoderm which separates edges of trophoblast and epiblast/hypoblast , thus providing space for expansion of the embryo

cavities form in the extra embryonic mesoderm

Trophoblast splits into two types - syncytial trophoblast and cytotrophoblast

43
Q

What does conceptus mean ?

A

Fertilised egg

44
Q

What occurs after the extraembryonic mesoderm is produced ?

A

The cavities merge to form the chorionic cavity/extraembryonic coelom

derivative of trophoblast begin to form the placenta

extraembryonic mesoderm connects the conceptus to the trophoblast via the connecting stalk

45
Q

Give a brief summary of what happens in the first 2 weeks after implantation

A

2 cell layers (Epiblast and hypoblast )

2 cavities ( amniotic and yolk sac)

2 trophoblast derivatives (cyto and syncytium trophoblast)

46
Q

Describe the structure of the conceptus at the end of the 2 weeks post fertilisation

A

Bilaminar disc forms where the epiblast and hypoblast meet

the majority of the foetus will be produced from this

47
Q

What are dichorionic - diamniotic twins

A

splitting of zygote at day 3 or separate fertilisation of 2 ova by 2 sperm - comprises almost all cases of dizygotic twins and 1/4 of monozygotic twins

lowest mortality risk but still higher than that of singleton

48
Q

Monochorionic twins

A

2 types :

  1. share the same placenta
    1. Occurs in most cases of monozygotic twins
    2. risk of twin-twin blood transfusion
  2. share the same amnion
    1. Occurs when split is after 9th day but before 12th day
    2. 50% survival risk ; risk of umbilical chord wrapping around babies
    3. rarely occurs
49
Q

How do conjoined twins occur

A

When division of zygote occurs later tha 12 days

highest mortality

50
Q

What happens in the third week post fertilisation

A

process is called gastriculation

3 germ layers - Formation of intraembryonic mesoderm and definitive ecto/endoderm to form trilaminar disc

3 important structures formed :

notochord , primitive streak and neural tube

51
Q

Label this cross section of the embryo

A
52
Q

gastrulation

A

process of cellular rearrangement within the epiblast that leads to the formation of the 3 germ layers and a trilaminar disc

epiblast cells migrate towards primitive pit and penetrate through the epiblast layer

53
Q

What happens at the prochordial plate during the 3rd week post fertilisation

A

Endoderm thickens and becones firmly adherent to the overlying ectoderm in the region of the prochordal plate

this is the future mouth region

54
Q

Formation of the notochord (notogenesis)

what is the function of the notochord

A

Epiblast cells migrate from the primitive node and extend cranially to form a midline structure called the notochordal process.

Notochord then forms from the mesoderm - it is a flexible cylindrical tube

fucntions:

guide the formation of the nervous system and vertebral column

induce overlying ectoderm to form the neuroectoderm of the neural plate ; the notochord eventually underlies the neural tube

55
Q

Formation of the neural tube

A

Neural plater form neural fold which become the neurectoderm

the neural fold fuse to form a neural tube which eventually becomes the brain and spinal chord

the neural tube loses contact with the overlying ectoderm

56
Q

name the structures derived from the endoderm

A

Epithelial lining of digestive and respiratory tracts,

Lining of urethra, bladder and reproductive System

Liver and pancreas

57
Q

name the structures derived from the mesoderm

A

Notochord

Musculoskeletal system

Muscular layer of stomach, intestine etc

Circulatory system

58
Q

name the structures derived from the ectoderm

A

Epidermis of skin

Cornea and lens of eye

Nervous system

59
Q

what is the purpose of the syncytiotrophoblast

A

syncytiotrophoblast becomes continuous with the uterus

maternal blood vessels invade spaces between the syncytiotrophoblast

this allows uterplacental circulation to begin

60
Q

what is the primitive streak ?

describe its structure

A

a groove in the midline of the epiblast which appears in the third week post fertilisation

primitive node found at cranial end

primitive pit within primitive node

epiblast cells migrate through the primitive pit to form the notochord between the hypoblast and epiblast

61
Q

how is the endoderm formed ?

A

formed by epiblast cells that migrate through the primitive pit and displace the hypoblast cells.

62
Q

how is the mesoderm formed ?

A

formed by epiblast cells that migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm.

63
Q

how is the ectoderm formed?

A

formed by the epiblast cells that remain in position

64
Q

purpose of notochord

A

essential for the development of the nervous system and primitive skeletal structures

Embryology (8 decks)

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