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Embryology > Fertilization--Week 1 > Flashcards

Fertilization--Week 1 Flashcards

1
Q

How many chromosomes do humans have?

A

46; 44 autosomal and 2 sex chromosomes

22 pairs of autosomes, and 2 sex chromosomes or 1 X 1 Y

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2
Q

One member of each pair of chromosomes comes from _____ and the other from _____. Thus, each gene is represented _____ times and the ____ copies may be different, affecting the individuals phenotype

A

maternal origin; paternal origin;

two times; two copies

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3
Q

What is the point of the cell cycle?

A

replication of the chromosomes for cell division

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4
Q

How many chromosomes in G1?

A

2n (46 pairs)

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5
Q

What happens in the S phase of the cell cycle?

A

all of the DNA in a cell is replicated (chromatid = copy of chromosome)

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6
Q

How many chromosomes in S?

A

4n (46 chromosomes made of 2 sister chromatids each)

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7
Q

How many chromosomes in G2?

A

4n (each chromosomes = 2n, aka 2 chromatids)

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8
Q

What is the point of mitosis?

A

Somatic cell division;

chromosomes align on a spindle and each chromatid is moved to the opposite pole as the cell divides

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9
Q

Briefly describe the number of copies of DNA through the process of mitosis:

A

2n –> 4n –> 2n

  • New cells have 2 copies of each chromosome (2n) and each chromosome has ONE chromatid
  • At S phase, all of the DNA is copied so each chromosome in a pair has 2 chromatids (4n)
  • After M phase, each new cell inherits one copy (chromatid) of each chromosome (2n)
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10
Q

What is the purpose of gametogenesis?

A

differentiation of germ cells into sperm or egg (oocyte), specialized cells for sexual reproduction

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11
Q

How is meiosis different from mitosis:

A

sperm/egg (product of meiosis) only contribute 1n (one copy) of the human genome to the embryo
Mitosis = somatic cells have two copies (2n) of the human genome that are inherited from sperm and egg

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12
Q

In meiosis, after the initial S phase, the cell divides _____ times without another intervening S phase

A

twice!

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13
Q

Briefly describe the number of copies of DNA through the process of meiosis:

A

2n–> 4n –> 2n –> 1n

diploid germ cell becomes a haploid gamete

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14
Q

What is meiosis I referred to as?

A

reductional division (4n –> 2n)

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15
Q

What is unique to Meiosis I:

A

During prophase I, the chromosome pairs align, cohere, and exchange segments of DNA (Crossing over … unique homologous chromatids)

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16
Q

when does crossing over occur? what happens? what is the results?

A

in prophase I of meiosis I;

DNA exchanges between homologous chromosomes; each homologous chromatid becomes unique

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17
Q

What is the result of Meiosis I?

A

separation of the homologous chromosome pairs, each with 2 chromatids (2n)

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18
Q

What is Meiosis II commonly referred to?

A

equatorial division (2n –> 1 n)

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19
Q

what is the result of meiosis II?

A

chromatids separate as in mitosis, leaving daughter cells with a haploid set of chromosomes, each containing a single chromatid
-DNA of the 4 daughter cells is non-identical due to crossing over from prophase I

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20
Q

what is different in sperm and oocyte in meiosis?

A

-Mature sperm at fertilization complete meiosis
-Mature oocyte at fertilization is arrested at Metaphase II
(meiosis does not resume in oocyte until fertilization)

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21
Q

Where does oogenesis take place?

A

in the follicles of the ovary cortex (in primordial, primary, antral, and Graafian stages)

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22
Q

What stages of meiosis are arrested in oocyte development?

A
  • prophase I (primary oocyte) until puberty

- metaphase II (mature oocyte) until fertilzation

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23
Q

when does the first oocyte meiotic division occur?

A

by birth

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24
Q

when does profession of the oocyte to the diplotene stage of prophase I occur?

A

at puberty

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25
Q

When does oogenesis and follicular development continues (get out of the diplotene arrest)? in what structure does meiosis resume from?

A

at puberty; resumes from the primordial follicles

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26
Q

what stage and how many chromosomes are are the majority of the oocytes in a woman’s ovary?

A

in prophase I, and dipoloid

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27
Q

What happens with regards to oogenesis every month?

A

10-12 follicles are recruited to develop, and one will ovulate into a mature oocyte

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28
Q

what is the function of the ovaries (what processes take place there?)

A

gametogenesis and steriodogenesis

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29
Q

what tissues are found in the medulla of the ovary?

A

connective tissue, blood vessels, neves, lympatic vessels

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30
Q

what tissues are found in the cortex of the ovary?

A

follicles and connective tissue with an outer layer of germinal epithelium

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31
Q

what structures are found within a developing follicle?

A
  • oocyte
  • zona pellucida
  • cumulus mass
  • granulosa
  • theca interna
  • theca externa
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32
Q

How many oocytes are found in a primordial follicle?

A

1

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33
Q

While the primary oocyte enlarges, _____ grows to form a zona pellucida.

A

primordial follicle

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34
Q

Briefly describe what happens in folliculogenesis/oogenesis

A
  1. primary oocytes ENTER the first meiotic division (stuck in diplotene stage of prophase I) by birth
  2. At puberty, follicular/oogenesis proceed in primordial follicles (one oocyte, surrounded by one layer of flat granulosum cells)
  3. Primordial follicle matures into primary follicle which is surrounded by granulosa cells (early and late primary follicle)
  4. FSH stimulates the production of a zona pellucida to separate oocyte from the granulosa
  5. Primary follicle matures into secondary follicle; has theca cells surrounding it (external and internal layers form)
  6. Fluid accumulates in the follicle to form an antrum (cavity) and the granulosa cells sit on basal lamina of follicle
  7. Granulosa cells near oocyte form cumulus mass; the innermost cumulus cells = corona radiata
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35
Q

what is the corona radiata?

A

granulosa cells in the innermost layer of the cumulus mass

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36
Q

What is special about the theca interna

A

it is steroidogenic

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37
Q

What tissue type is the theca externa ? what does is structure say about its function?

A

elastic connective tissue; allows it to expand with the antrum (cavity that forms due to fluid filling the follicle)

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38
Q

what part of the follicle makes contact with the oocyte?

A

microvilli from the corona radiata; they extend through the zona pellucida

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39
Q

how do the microvilli of the corona radiata communicate with the oocyte?

A

via intracellular gap junctions

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40
Q

what is the role of cyclic AMP (c-AMP) in folliculogenesis/oogenesis?

A

it moves through the gap junction (between the corona radiata and oocyte) and maintains oocyte meiotic arrest (so that the oocyte cannot mature past the primary oocyte)

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41
Q

In which cells is is c-AMP formed in oogenesis?

A

granulosa cells

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42
Q

Describe the hormonal control of follicular growth and maturation?

A

ALL OCCURS ONCE C-AMP IS NOT PRESENT (PRIMARY TO SECONDARY OOCYTE)

  1. LH from the anterior pituitary stimulates theca interna to secrete testosterone
  2. Testosterone is converted by granulosa cells into estrogen (E2) via aromatase that accumulates due to stimulation by FSH
  3. E2 stimulates granulosa proliferation and oocyte maturation (and production of more FSH and LH)
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43
Q

____ from the anterior pituitary stimulates ______ to secrete testosterone

A

LH; theca interna

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44
Q

_______ is converted by granulosa cells into estrogen (E2) via ________ that accumulates due to stimulation by _____

A

Testosterone; aromatase; FSH

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45
Q

what does estrogen (E2) production stimulate?

A

E2 stimulates granulosa proliferation and oocyte maturation (and production of more FSH and LH)

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46
Q

on what cells are FSH receptors found on?

A

granulosa cell

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47
Q

on what cells are LH receptors found on?

A

Theca cells (interna) at first, then later in development, granulosa start having LH receptors dur to increased production of FSH

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48
Q

When does meiosis I resume in oogenesis?

A

in Graafian follicle

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49
Q

what happens when the granulosa retract from the oocyte, stopping c-AMP delivery?

A

end of meiotic arrest; the chromosomes partition between extruded polar body and secondary oocyte, meiosis I completes and meiosis II starts; and the secondary oocyte arrests at metaphase II.

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50
Q

what follicle does ovulation begin at?

A

late graafian follicle

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51
Q

what happens to the theca externa during ovulation?

A

it stretches and ruptures, releasing the cumulus oocyte complex

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52
Q

what is cells secrete hyaluonic acid? what does HA help with?

A

secreted by cumulus cells; helps to stick to fimbriae at the end of uterine tube

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53
Q

what helps move the cumulus mass into the infundibulum?

A

ciliated epithelia

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54
Q

what is the course of travel of the released cumulus-oocyte complex?

A

released at fimbriae at end of uterine tube, moves into infundibulum and up to ampulla via ciliated epithelia

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55
Q

what helps facilitate dispersal of the cumulus mass?

A

hyaluronidase in the oviductal fluid and released by sperm

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56
Q

what forms from the empty follicle (after the cumulus-oocyte complex is released)

A

corpus luteum

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57
Q

What cells can make progesterone? what is progesterone derived from?

A

granulosa and theca cells; derived from cholesterol (which is derived from LH)

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58
Q

what cells can make testosterone? what is testosterone derived from?

A

Theca ONLY (granulosa can make progesterone, what T is derived from)

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59
Q

what cells can make estradiol? what is estradiol derived from?

A

ONLY granulosa cells; from testosterone

60
Q

explain LH production and the corpus luteum

A

increasing FSH signaling induces LH production, which positively feeds back on the pituitary by progesterone to further stimulate LH production

61
Q

what is the infundibulum

A

where the oocyte enters; has finger like fimbrae

62
Q

what occurs in the ampulla

A

site of fertilization

63
Q

what is the isthmus

A

extension of the uterine tube into the uterus

64
Q

what is the uterus fundus

A

the rounded, upper region of the uterus

65
Q

what is the copus uteri?

A

the lower region of the uterus tapering toward the cevix

66
Q

Is the uterine cavity a potential space?

A

Yes! It’s normally collapsed

67
Q

what is the endometrium?

A

a multilayer lining of the uterus

68
Q

what cells line both of the uterus and the oviduct:

A

cilated epithelium

69
Q

what do the secretory cells in both of the uterus and the oviduct form

A

glands

70
Q

what type of tissue encircles both the uterus and the oviduct?

A

smooth muscle (myometrium)

71
Q

What phases of the menstrual cycle take place in the endometrium?

A
  • menstrual phase
  • proliferative phase
  • secretory phase
  • ischemic phase
72
Q

what phases of the menstrual cycle take place in the ovary?

A
  • follicle recruitment
  • follicular phase
  • luteal phase
  • degenerative corpus luteum
73
Q

when does the menstrual phase of the endometrial cycle take place? What occurs during this phase?

A

Day 1 of the cycle; begins at the onset of menstruation

the endometrium is sloughed over 4-6 days

74
Q

when does the proliferative phase of the endometrial cycle take place? What occurs during this phase?

A

days 5-14
the endometrium is regenerated and the follicles grow and mature in the ovary (follicular phase)
ovulation occurs at day 14.

75
Q

what day does ovulation take place at?

A

day 14

76
Q

when does the secretory phase of the endometrial cycle take place? What occurs during this phase?

A

days 15-26;

  • characterized by increased secretion from glands, stroma decidualizes (fibroblasts that differentiate);spiral arteries become more toruous (more twists/turns)
  • The post ovulatory follicle gives rise to the corpus luteum (luteal phase)
77
Q

what is the luteal phase? when does it take place?

A

when the post-ovulatory follicle turns into the corpus luteum; occurs in the secretory phase (days 15-26)

78
Q

when does the ischemic phase of the endometrial cycle take place? What occurs during this phase?

A

day 27-28
If no viable embryo is produced:
the corpus luteum degenerates as LH (lutenizing hormone) levels decrease; this causes: corpus luteum to stop producing progesterone, spiral arteries constrict, cutting off blood supply to the endometrium; Menses is initiated and the cycle repeats

79
Q

what does a decrease in LH during the endometrial cycle cause?

A

corpus luteum to stop producing progesterone, spiral arteries constrict, cutting off blood supply to the endometrium

80
Q

when does the pregancy phase of the endometrial cycle occur?

A

when a viable embryo is produced (at the very end of a menstrual cycle)

81
Q

when does the oocyte develop into a blastocyst and implant?

A

day 20-22

82
Q

what is human chorionic gonadotropin (hCG) produced by? what is its function?

A

produced by the embryo (similar to LH) it maintains the corpus luteum (which makes progesterone)

83
Q

what is the function of the corpus luteum?

A

makes progesterone

84
Q

what is the function of progesterone?

A

maintains endometrium

85
Q

During pregnancy, how are the muscle of myometrium affected by progesterone?

A

they relax to allow uterine expansion

86
Q

what produces progesterone?

A

from 0-4 months: corpus luteum

From 10 weeks - birth: placenta takes over

87
Q

What is the function of RU 486

A

to block progesterone receptors, allowing the endometrium to be shed

88
Q

what do pregnancy tests detect? when do they start being effective/detect?

A
  • detect hCG in maternal urine or serum

- can detect pregnancy 10-14 days after fertilization

89
Q

what is the function of the cervical mucus?

A

barrier and facilitator (optimal conditions for sperm penetration; sperm is separated from inhibitors in the seminal plasma)

90
Q

How does the cervical mucus change during the endometrial cycle?

A

thicker barrier during non-receptive phases, mucus is thinner during ovulation;

91
Q

What moves the semen from the uterus to the ampulla?

A 
ciliary movement and muscular contractions in the oviduct and uterus;
sperm motility (swimming) = minor role in the transport through the female reproductive tract
92
Q

How long is sperm fertile/viable for? how long is an oocyte fertile/viable for?

A

sperm: 2-4 days
oocyte: less than 24 hours

93
Q

what is capacitation?

A

the required change in the sperm that occurs in the uterus of a female in order for coitus to occur;

“biochemical changes necessary for sperm to be able to bind to the zona pellucida and undergo the acrosome reaction”

94
Q

how is sperm motility altered after semen enters the female uterus?

A

increased lateral head movement is produced, which promotes penetration of oocyte and its vestments

95
Q

how is capacitation achieved artificially?

A

semen is centrifuged and washed out to remove seminal plasma

96
Q

what is the point of the acrosome reaction?

A

release of enzymes to remove barriers to the egg

97
Q

what is the acrosomal reaction triggered by?

A

Upon contact with:

  1. Uterine epithelium (uterine tube or uterus)
  2. Cumulus mass
  3. Zona pellucida
98
Q

what is defined by an “acrosomal reacted” sperm?

A

the outer plasma membrane is removed, the acrosomal membrane is exposed and can bind to the zona pellucida

99
Q

Explain the acrosomal reaction

A

the outer acrosomal membrane fuses with the egg, forms vesicles that release contents and exposes receptors; the contents are discharged and the inner acrosomal membrane becomes apical surface of anterior portion of the sperm headq

100
Q

what are the contents of the vesicles formed by the acrosomal reaction?

A

hyaluronidase, acrosin (protease)

101
Q

What 4 glycoproteins does the zona pellucida consist of?

A

ZP1, ZP2, ZP3, ZP4

102
Q

where is the zona pellucida formed?

A

by the oocyte in the primary follicle stage

103
Q

what is the function of the zona peullcida

A

to induce the acrosome reaction allowing capacitated sperm to penetrate its structure

104
Q

Describe the morphology of the zona pellucida and why its structure is significant for its function

A

Zona Pellucida is a thick, porous ECM with a spongey appearance; the pores are large enough for sperm to pass through using primarily their motility

105
Q

what digestive enzyme assists sperm in their “swimming” movement? Where is located on the sperm cell?

A

acrosin; it remains bound to inner acrosomal membrane

106
Q

During the acrosomal reaction, hyaluronidase is released. What is it’s function?

A

hyaluronidase; to break up the cumulus mass so that the sperm can pass through the corona radiata to reach the zona

107
Q

During the acrosomal reaction, acrosin is released; what is its function?

A

to disrupt the zona pellucida so that sperm can enter

108
Q

why is it important that the sperm and oocyte plasma membranes fuse?

A

in order to activate the oocyte and decondense the sperm nucleus; also, it blocks polspermy

109
Q

Fusion of the oocyte and sperm beings with the _____ region of the sperm

A

postacrosomal

110
Q

Fusion of the oocyte and sperm continues until the ___________________ are contained within the oocyte cytoplasm

A

sperm nuclei and other organelles

111
Q

Describe the signal cascade steps for oocyte activation following sperm/oocyte fusion

A
  1. membrane depolarization: Na/H exchange across the PM, “shocks away” other sperm about to fuse and is the initial block to polyspermy
  2. Ca2+ wave
  3. Cortical reaction: exocytosis of cortical granules which modify zona and oocyte surface; second block to polyspermy
  4. Rise in intracellular pH: activates proteins that restart meiosis and initiates decondensation of sperm nucleus
112
Q

what is the initial block to polyspermy?

A

depolarization of the oocyte membrane via Na/H+ exchange across the PM

113
Q

where does the Ca2+ wave initiate?

A

at the site of sperm contact

114
Q

what is the secondary block to polyspermy?

A

the release of cortical granules in the oocyte (modifies the zona and oocyte surface)

115
Q

what is the function of the cortical granules that are released in the oocyte after oocyte/sperm fusion?

A

they remodel the zona and oocyte… add a new PM!

Act as a secondary block to polyspermy

116
Q

what causes the restart of meiosis after oocyte/sperm fusion?

A

rise in intracellular pH

117
Q

what is the result of meiosis after the oocyte/sperm fuse?

A
  1. second polar body is produced
  2. female pronucleus formed (1N; haploid)
    male pronucleus is formed (1N;haploid)
118
Q

what forms the male pronucleus?

A

the decondensed sperm nucleus

119
Q

Where do the cortical granules form?

A

throughout the oocyte cytoplasm

120
Q

where are the cortical granules found during oocyte maturation?

A

the oocyte cortex, adjacent to the plasma membrane

121
Q

where are the cortical granules absent?

A

the apical bulge, near the metaphase plate

122
Q

what triggers the fusion of the cortical granules and the plasma membrane?

A

elevated intracellular Ca2+

123
Q

where are the contents of the cortical granules released into?

A

the perivitelline space

124
Q

How do the cortical granules modify the zona pellucida?

A
  1. Zp2 is cleaved, preventing binding or penetration of the zona by sperm
  2. Zona hardening; the zona proteins become cross linked and make it difficult to dissolve zona
125
Q

What is a zygote? How is the DNA arranged?

A

fertilized egg; contains both parental genomes, but the male and female genomes remain separate in their respective pronuclei for 24 hours

126
Q

Do the pronuclei fuse?

A

NO

127
Q

when do the membranes of the pronuclei in the zygote dissociate? what happens to the DNA at this point? When does the first cleavage occur?

A

during the first mitosis; the dna is intermingled, combining maternal and paternal DNA for the first time in the two-cell embryo; first cleavage occurs 24 hours after fertilization

128
Q

What happens at the first cleavage?

A

the 2 parental genomes unite for the first time!

-occurs during mitosis of first cleavage division; forming 2 cells (blastomeres)

129
Q

where do the first few cleavages occur? (what part of the female reproductive organ)

A

uterine tube

130
Q

how often do the cleavages occur after the first cleavage?

A

every 12 hours

131
Q

what happens to the overall size of the zygote after the first few cleavages?

A

nothing! it stays relatively the same size because the cytoplasm is just being divided so the blastomeres keep getting smaller without any overall increase in the diameter or mass of the ovum

132
Q

What is totipotency?

A

the ability of each blastomere to develop into an entire blastocyst

133
Q

how long is totipotency retained?

A

2-3 divisions

134
Q

what is embryonic genome activation?

A

for the first few cleavages, mRNA and proteins are produced by the oocyte and used for embryo development; then the embryonic genome is activated = new transcripts produced by the embryonic genome are made and used for the remainder of the development. Occurs around 8-cell stage in humans

135
Q

when does compaction occur?

A

after the third cleavage (8 cell stage)

136
Q

what happens during the compaction stage?

A

the blastomere adhere tightly to each other, and individual blastomeres are no longer visible… looks like a “glob” no distinct boundary and this allows the fluid to accumulate.

morula = ball of cells

137
Q

what happens during cavitation

A

the blastocyst cavity/ blastocoel forms

  1. tight junctions seal the outer cells of morula
  2. osmotic gradient forms by inward Na pumping
  3. fluid filled pockets coalesce to form a single large cavity
138
Q

What happens during trophectoderm differentiation?

A

• Outside cells of morula form tight junctions
• Responsible for cavitation
• 1st transporting epithelium
its the progenitor of trophoblast

139
Q

what makes up the blastocyst?

A

inner cell mass + trophoblast

140
Q

In what form down the embryo enter the uterus? At what day post-fertilization does this occur?

A

the blastocyst is the embryo that enters the uterus; around day 4

141
Q

What is another name for the embryoblast?

A

inner cell mass

142
Q

what defines the inner cell mass?

A

pluripotent mass of cells; it can be cultured to produce pluripotent embryonic stem cells

143
Q

from what cells is the inner cell mass derived from?

A

the inside cells of the morula

144
Q

what constitutes a pluripotent cell

A

it can form all fetal cell types

145
Q

what is the function of the trophoblast? where is it located?

A

it is the outer layer of the blastocyst; it mediates implantation of the embryo in the uterine wall by facilitating the binding and invasion into the uterine tissue
It forms the PLACENTA and FETAL MEMBRANES and EXTRAEMBRYONIC MESODERM

Embryology (16 decks)

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