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Reproductive System > Fertilisation > Flashcards

Fertilisation Flashcards

1
Q

what is cervix in relation to uterus

A

narrowest region

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2
Q

what is from cervix leading to outside

A

vagina

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3
Q

what is structurally in the outer edge of ovary called

A

cortex

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4
Q

what is structurally on inside of ovary & their overall function

A

blood vessels, nerves, CT - to take hormones away from ovary (oestrogen, progesterone) to enter systemic circulation

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5
Q

functions of ovary

A
  • development of follicles
  • production of oestrogen and progesterone
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6
Q

what does ovary cortex contain

A

developing follicles

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7
Q

what is a follicle composed of

A

oocyte w/ supporting follicular cells surrounding

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8
Q

list types of follicles from most immature to most mature

A
  • primordial follicle
  • primary follicle
  • secondary follicle
  • tertiary follicle
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9
Q

what are general structural changes that occur as follicle develops

A
  • increasing oocyte size
  • increase number of follicular cells around oocyte
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10
Q

what is a change in secondary and tertiary follicles seen in particular

A
  • in secondary and tertiary follicles, there some space between follicular cells = antrum
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11
Q

what is the antrum

A
  • filled with fluid
  • supports developing oocyte
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12
Q

describe ovulation in regard to folllciles

A
  • when tertiary follicle ruptures
  • oocyte w/ some supporting follicular cells is released from ovary
  • makes way into fallopian tubes / oviduct (where can meet sperm & fertilisation occur)
  • remnants of tertiary follicle that stays behind in ovary - cells collapse in on one another => corpus luteum
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13
Q

function of corpus luteum

A

makes hormones

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14
Q

lifespan of corpus luteum if no pregnancy

A

~14 days if fertilisation and implantation not occur
- after 14 days degenerates into bit of scar tissue => corpus albicans

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15
Q

lifespan of corpus luteum if pregnancy

A
  • if fertilisation and implantation does occur, corpus luteum kept alive >14 days
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16
Q

what cells in the ovary are responsible for oestrogen and progesterone production and when briefly

A

follicular cells but at different points in follicle development

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17
Q

follicular cells within ovary make oestrogen during which follicles

A

follicular cells in:
primordial follicle
primary follicle
secondary follicle
tertiary follicle

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18
Q

follicular cells that make oestrogen ONLY make oestrogen - true or false

A

true

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19
Q

ONLY oestrogen is made before ovulation [by follicular cells in ovary] - true or false

A

true

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20
Q

what follicular cells are progesterone not made by

A

follicular cells in:
primordial follicles
primary follicles
secondary follicles
tertiary follicles

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21
Q

what follicular cells make progesterone

A
  • remaining follicular cells in corpus luteum after ovulation make oestrogen and now progesterone
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22
Q

oestrogen and progesterone are made after ovulation [by follicular cells in ovary] - true or false

A

true

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23
Q

progesterone is only made after ovulation [by follicular cells in ovary] - true or false

A

true

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24
Q

what hormone is made before ovulation?
what hormones are made after ovulation?

A
  • before: oestrogen
  • after: oestrogen, progesterone
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25
Q

[regulation of the female reproductive cycle] what does hypothalamus make? which acts on?

A

gonadotrophin releasing hormone (GnRH)
acts on anterior pituitary

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26
Q

[regulation of the female reproductive cycle] what does anterior pituitary dominantly make during follicular phase? triggered by what? acts on what?

A
  • due to GnRH release from hypothalamus
  • anterior pituitary releases follicle stimulating hormone (FSH)
  • FSH stimulates development of follicles in ovary
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27
Q

result of FSH stimulation in ovary on oestrogen

A
  • follicles get bigger
  • produce more and more oestrogen
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28
Q

what does increased oestrogen produced by the developing follicles (due to FSH stimulation) do?

A
  • oestrogen goes to uterus
  • stimulate proliferation of stratum functionalis layer of uterus
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29
Q

[regulation of the female reproductive cycle] what does anterior pituitary dominantly make during [ovulation and] luteal phase? triggered by what? acts on what?

A
  • due to GnRH release from hypothalamus
  • anterior pituitary releases luteinising hormone (LH) just before day 14 of cycle
  • LH surge causes ovulation - tertiary / Grafiaan follicle ruptures & oocyte released
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30
Q

what does progesterone (made by follicular cells in corpus luteum) do

A
  • switches on the glands in stratum functionalis layer of uterus
  • tells them to start making glucose-rich mucous
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31
Q

what is the function of the glucose-rich mucous produced by uterine glands (turned on due to progesterone)

A
  • glucose as energy source for an egg & potentially fertilised egg and early embryo
  • until placenta develops
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32
Q

does corpus albicans make any hormones (assuming no pregnancy) & what does this indicate

A
  • no
    => no more oestrogen and progesterone made at this part of reproductive cycle
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33
Q

if there is formation of corpus albicans, and no oestrogen or progesterone is made any longer what does this mean for menstruation and why

A
  • menstruation occurs
  • since no oestrogen or progesterone to keep wall of endometrium (uterine lining) alive
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34
Q

what can ovarian cycle be split into - brief and non brief

A

brief: follicular phase (incl menstrual phase and ovulation) & luteal phase
non-brief:
- menstrual phase (bleeding occurs - shedding of endometrium lining from past cycle)
- follicular phase
- ovulation (marks release of oocyte; transition from follicular phase to luteal phase)
- luteal phase

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35
Q

what needs to occur that otherwise doesn’t, if fertilisation occurs

A

keep uterus alive

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36
Q

sperm needs to be _________________ for fertilisation to occur

A

deposited into female reproductive tract

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37
Q

what occurs for sperm to be deposited into female reproductive tract

A

ejaculation

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38
Q

how long following semen deposition will you find sperm entering cervix (bottom part of uterus)

A

~1 minute

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39
Q

how does sperm enter cervix following deposition

A
  • uterus contracts
  • moving part of cervix down into vagina
  • contraction helps pick some sperm up from vagina to bring into [bottom part of] uterus
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40
Q

how is sperm stored in uterus

A

stored in cervical crypts for some time

41
Q

how can sperm stay stored in cervix (cervical crypts)

A
  • nourished by cervical mucous
  • to keep sperm alive
42
Q

describe the cervical mucous and its function before ovulation

A
  • white, very thick - acts as barrier for sperm penetrating and entering uterus
  • since before ovulation, oocytes still developing
    (=> no point having sperm penetrate and enter uterus as no oocytes are ready for fertilisation)
43
Q

describe the cervical mucous and its function at time of ovulation

A
  • clear, slippery, thin - sperm can pass thru easily
  • since ovulation occurring, now oocyte in ovarian duct
  • want sperm to enter uterus so can try meet with and fertilise with egg
44
Q

how long can sperm survive for / viable in female reproductive tract

A

~48 hrs

45
Q

lifespan of oocyte viability

A

~14hrs

46
Q

why is there so many sperm within an ejaculate / semen when only takes one sperm to fertilise an egg

A

majority of sperm lost

47
Q

list ways sperm is lost on way to oocyte

A
  • destroyed by vaginal acid (vaginal env acidic)
  • fail to penetrate cervical mucous
  • destroyed by defence cells (sperm = foreign cells in female body)
  • enter ‘wrong’ oviduct
48
Q

why will sperm enter ‘wrong’ oviduct

A
  • ovulation occurs from one oviduct (where oocyte is)
49
Q

how does sperm move thru female reproductive tract

A
  • sperm are motile by tail lashing
  • research that sperm movement aided by female physiology - uterine contractions; chemical attractants
50
Q

describe how uterine contractions can aid in sperm movement

A

contractions of muscles in uterus can help push sperm up towards oviduct

51
Q

describe how chemical attractants can aid in sperm movement

A
  • oocyte and surrounding follicular cells may release some chemical attractants which help draw sperm towards oocyte
52
Q

what are the regions the oviduct are divided into (from closest to uterus to out)

A
  • isthmus - site of capacitation
  • ampulla - site of fertilisation; longest part of oviduct
  • infundibulum (contains fimbriae - pick up oocyte at ovulation)
53
Q

what is capacitation

A

sperm maturation

54
Q

what happens when sperm reach isthmus

A
  • sperm stored ~10hrs until ovulation occurs
  • undergo additional maturation step - ‘capacitation’- before can enter ampulla & fertilise egg
55
Q

if capacitation doesn’t occur can sperm fertilise an egg

A

no
ie/ essential for fertilisation

56
Q

what 2 events occur in capacitation

A
  • sperm become hyperactive; tails beat more vigorously
  • sperm prepare for acrosome reaction
57
Q

describe why sperm becoming hyperactive is important in capacitation

A
  • have more force when swimming now
    => more power to break thru protective coats around oocyte (can penetrate thru follicular cells surrounding oocyte in oviduct to reach oocyte)
58
Q

describe acrosome reaction of sperm

A
  • release of enzymes from acrosome by rupturing
  • required for sperm to reach oocyte
59
Q

what is acrosome

A
  • organelle in sperm head, above its nucleus
  • bag of digestive enzymes
60
Q

what is zona pellucida

A
  • oocyte protein coat
  • gelatinous protein coat
  • protective layer
  • surrounds and protects oocyte
  • surrounded by (protective) layers of follicular cells
61
Q

what must sperm overcome to reach oocyte (consider capacitation)

A
  • get thru follicular cells, get thru zona pellucida
  • before can bind to and fertilise oocyte
62
Q

why is it important to have protective coats around egg regarding sperm

A
  • don’t want abnormal sperm reaching oocyte
  • only good healthy sperm will get through all protective layers to reach oocyte
63
Q

what are the layers the sperm has to penetrate in acrosome reaction

A
  • between follicular cells
  • zona pellucida
64
Q

what are the events in acrosome reaction (5)

A

1 - sperm approaches follicular cells (acrosome becomes leaky, some digestive enzymes from acrosome escape -> break connecting junctions between follicular cells -> follicular cells separate as no longer tightly connected -> sperm w/ hyperactive tissue can burrow through betwen follicular cells)
2 - acrosome ruptures -> all remaining digestive enzymes escape from acrosome & bind to zona pellucida -> digestive enzymes digest a hole through zona pellucida -> sperm can push its way thru zona pellucida via tunnel to reach oocyte
3 - fertilisation occurs - sperm head w plasma membrane touching / binds oocyte plasma membrane
4 - sperm enters oocyte (nuclear material - egg pronuclei & sperm pronuclei -> form a single nucleus)
5 - polyspermy blocked (don’t want more than one sperm fertilising an egg) - via 1. depolarisation (sodium influx) at fertilisation) & 2. cortical granule reaction (calcium influx) hardens zona pellucida at fertilisation

65
Q

describe depolarisation in polyspermy blocking in detail

A
  • when plasma membrane of sperm binds w plasma membrane of egg
  • sodium rushes into egg (sodium influx)
  • causes egg to depolarise (electrical signal change)
  • [electronically] repels any sperm that might be part way thru zona pellucida
66
Q

describe cortical granule reaction in polyspermy blocking in detail

A
  • very edge of oocyte underneath plasma membrane (ie/ within oocyte) contains little spheres - cortical granules
  • when fertilisation occurs, calcium influxes into egg causing cortical granular reaction
  • when fertilisation occurs, cortical granules move to surface & release granular material into space between zona pellucida and oocyte
  • cortical granular material binds to zona pellucida -> changes way proteins interact within zona pellucida (composition) -> hardens zona pellucida
  • sperm that part way through zona pellucida find it impossible to burrow through ie/ progress to meet egg stops
  • zona pellucida was soft and jellylike -> now very hard
67
Q

when is second polar body ejected

A

fertilisation - where meiosis II continues

68
Q

cell progression at fertilisation

A

sperm and egg pronuclei -> become 1 cell (zygote)
- 2 haploid gametes form to make 1 diploid zygote
1 cell -> 2 cells
2 cells -> 4 cells
(undergoing mitotic divisions to lead to formation of an embyro)

69
Q

what is cleavage

A
  • cell division of fertilised egg into two cells -> four cells -> eight cells -> etc
70
Q

what level of oocyte is ovulated

A

secondary oocyte
(in tertiary follicle)

71
Q

what occurs at day 0 of fertilisation

A
  • ovulated secondary oocyte in oviduct plasma membrane is met by plasma membrane of sperm that has travelled into oviduct = fertilisation
  • sperm travels into oocyte
  • formation of zygote (fertilised egg) (2 haploid pronuclei join to form diploid single cell)
72
Q

what occurs day 1 (24hrs) fertilisation. what is this known as

A
  • zygote divides into 2 cells
  • part of cleavage
73
Q

what occurs day 2 (48hrs) fertilisation. what is this known as

A
  • 2 cells divide again into 4 cells
  • part of cleavage
74
Q

what happens 3 days (72hrs) fertilisation. what is this known as

A
  • 4 cells divide again into 8 cells
  • part of cleavage
75
Q

timeframe that cleavage occurs

A

cell division in first three days after fertilisation

76
Q

what happens at day 4 of fertilisation

A
  • cells still divide
  • ball of cells - ‘morula’
77
Q

what is still present from day 0 to day 4 after fertilisation

A

zona pellucida still present around dividing cells

78
Q

as the days pass after fertilisation, and the morula forms where is this occuring

A
  • moving down oviduct toward uterus
  • dividing cells in morula are still within oviduct
  • morula enters into uterus
79
Q

where don’t we want implantation to occur & what would be the result

A
  • don’t want implantation to occur in oviduct
  • would cause ectopic pregnancy - dangerous
80
Q

what is the significance of the zona pellucida surrounding the dividing cells after fertilisation in regard to implantation

A
  • zona pellucida stops these embryonic cells from binding to wall of oviduct
  • so that implantation does not occur here
81
Q

what occurs day 5 after fertilisation

A
  • blastocyst
  • that is within uterus
  • zona pellucida has dissolved
82
Q

why would the zona pellucida dissolving by day 5 be appropriate

A
  • by day 5 the embryonic cells are located (as a blastocyst) in the uterus
  • want implantation to occur in uterus
  • zona pellucida would block this
83
Q

what is the difference between blastocyst and morula

A
  • morula was solid ball of cells
  • blastocyst structure has fluid-filled space in centre
84
Q

what happens day 6 after fertilisation

A
  • blastocyst implant into wall of uterus => implantation occurs
85
Q

explain which part of blastocyst implants into wall of uterus in regards to structure

A
  • one side of blastocyst will contain cluster of cells - this implants into uterine wall / wall of endometrium
  • other side blastocyst only has one layer of cells
  • fluid-filled space in middle / toward emptier cell side
86
Q

endometrium is which layer of uterine wall

A

innermost

87
Q

what is above the endometrium

A

lumen
centre of uterus

88
Q

what are the outer cells of the blastocyst called and what do they become

A
  • trophoblast cells
  • will become foetal part of placenta
89
Q

what is the placenta

A
  • structure that supports and protects embryo and then focetus
90
Q

what is placenta made from

A
  • partly from blastocyst trophoblast cells
  • partly made from mother
91
Q

what are the cluster of cells in the blastocyst (side that implants into endometrium) called and what do they become

A
  • embryoblast cells
  • become embryo itself
    (note: cluster of same cells)
92
Q

what happens in early days after implantation

A
  • embryoblast cells begin to differentiate (they not all same)
  • trophoblast cells at base where blastocyst implants into wall of endometrium begin to differentiate into 2 populations - cytotrophoblast cells that continue to become part of foetal placenta (smaller than trophoblast cells); new layer of cells emerge (from trophoblast cells) called syncitotrophoblast cells that secrete digestive enzymes that digest a space into endometrium of uterus for blastocyst to actually implant in (hence blastocyst burrowed into wall of endometrium) & secrete hCG (human chorionic gonadotropin) hormone that only found in blastocysts => only found in pregnancy - keeps corpus luteum alive within ovary
93
Q

what hormone keeps corpus luteum alive beyond 14 days

A

hCG that made by syncitotrophic cells of blastocyst

94
Q

how does keeping corpus luteum alive prevent uterine wall from shedding during menstruation

A
  • corpus luteum produces progesterone
  • which prepares uterine wall for implantation
  • if corpus luteum turns into corpus albicans and progesterone level drop (+ oestrogen drop), which would lead to endometrial lining shedding
95
Q

what are the 2 requirements that result in hCG being produced

A
  • fertilisation and implantation occurring
96
Q

what hormone is looked for in a pregnancy test to confirm pregnancy - both urine and blood

A

hCG

97
Q

what does positive hCG reading indicate and why

A
  • pregnancy
  • that a fertilised egg has implanted into wall of uterus
98
Q

blastocyst ends up completely within wall of endometrium after burrowing into it during implantation process. true or false. what allows this to happen

A

true
- digestive enzymes of syncitotrophic cells create space for it

Reproductive System (21 decks)

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