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Reproduction > Oogenesis > Flashcards

Oogenesis Flashcards

1
Q

Oogenesis

A

Formation of female gamete

Starts from undifferentiated primordial germ cells

Starts during early embryonic life and completed in adulthood

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2
Q

Spermatogenesis

A

Formation of male gamete

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3
Q

Miosis

A

Primordial gem cell- diploid

Diploid, 2n have two copies (homologs) of each chromosome, one from mother and one from father

Prior to fertilization the number of chromosomes needs to be reduced because haploid gametes must be produced

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4
Q

Mitosis

A

Cell division, diploid to diploid cell because replication occurs before division, still have 2 chromosomes and 2 chromatids- identical cells produced

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5
Q

Miosis cell division

A

Diploid cell to haploid cell

Number of chromosomes reduced- resulting cells only have 1 copy of one homolog each- DNA synthesis after mitosis and then division where the two chromosomes are separated results in haploid cells.

Later becomes 1 chromosome per chromatid

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6
Q

1st meiotic division

A

Separates homologous chromosomes- each daughter cell has only one copy of each homolog

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7
Q

2nd meiotic division

A

Separates the two sister chromatids from each other

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8
Q

1St meiotic division

A

Synthesis phase and prophase

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9
Q

Synthesis phase

A

Results in two chromatids chromosomes

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10
Q

Prophase

A

Takes a long time

Subdivided into 5 stages- leptotene, zygotene, pachytene, diplotene, diakinesis

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11
Q

Leptotene

A

Chromosomes appear as

Thin as threads

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12
Q

Zygotene

A

Condensation of the thinly stretched out chromatin

Homologous chromosomes pair- synapses directed by synaptonemal complex

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13
Q

Pachytene

A

Condensation proceeds

Formation of tetrads

Crossing over- genetic recombination

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14
Q

Diplotene

A

Synaptonemal complex breaks down

Homologs start to separate

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15
Q

Diakinesis

A

Centromers move away from each other

Nuclear membrane breaks down

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16
Q

Metaphase I

A

Homologs align equidistant to each (metaphase plate)

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17
Q

Anaphase I

A

Homologs are separated from each other

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18
Q

Telophase I

A

Two daughter cells formed

Each daughter cell contains one copy of the homologous chromosome

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19
Q

2nd meiotic division

A

Separates the two sister chromatids from each other

1n, 1c

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20
Q

Meiosis

A

Two divisions

21
Q

Primordial germ cells

A

Stem cell of oogenesis

Migrate from yolk sac to the genital ridge (chemotaxis)

PGC- oogonia

22
Q

Oogonia

A

Interconnected by cytoplasmic bridges

Lose motility

Multiply by mitosis

23
Q

Oogenesis process

A

Oogonium (in gonadal ridge ) my multiplication by mitosis to an oogonia man which is diploid as well 2n, 2c

Then initiation of meiosis to primary oocyte which is the primordial follicle (2n 4c)

24
Q

Primary oocytes

A

Initiation by meiosis (independent of stimulus)

Intercellular bridges disappear

During embryonic life (in ,cattle ~140 days gestation)

25
Q

1st meiotic arrest(block) of meiosis

A

Primary oocyte enters meiosis but does not finish the first meiotic division immediately

Meiosis is arrested iN the late diplotene stage (dictyate)

Arrest occurs prenatally and is kept through the adulthood until activation of th oocyte in response to ovulatory gonadotropic stimulus (sexual maturity)

Oocyte grows

Zone pellucida formed

Follicular development proceeds

26
Q

Anisogamy

A

Difference in size of male and female gametes

27
Q

Oogenesis stages

A

1st meiotic arrest- oocyte growth and follicular development

Does not divide and polar body and 2ndary oocyte not produced until out of arrest and go through first meiotic division

28
Q

Resumption of meiosis and 2nd meiotic arrest (block)

A

Resumption of meiosis occurs in response to the ovulatory gonadotropic stimulus

First meiotic division ends with extrusion of the first polar body

2nd meiotic division initiated- also arrested at metaphase 2

Second arrest terminated upon fertilization and ends with extrusion of the 2nd polar body

29
Q

Oogenesis

A

Secondary oocyte ovulation and fertilization

LH primary oocyte

In secondary have zone pellucida and end up with two polar bodies one from each oocyte (primary and secondary) and ends with ovum

30
Q

Meiotic events

A

Before birth oogonium
Then primary oocyte via meiosis initiation and then arrest while develop and grow

Before puberty ovary inactive

After puberty primary oocyte still arrested in prophase (2n 4c)
Then LH surge and meiosis 1 resumed

Once meiosis 1 completed- first polar body and secondary oocyte arrested in metaphase 2 (1n, 2c)
Meiosis 2 completed only if sperm penetration occurs- ovum and second polar body

31
Q

Oogenesis new idea

A

Females like males have the capacity to renew their germ cell pool during adult life

Old dogma- cease production of oocytes shortly after birth

32
Q

Folliculogenesis

A

Interwoven with oogenesis

Formation of an antral follicle starting from a primordial follicle

Follicle- oocyte surrounded by somatic cells

Different stages of development- primordial, primary, secondary, and tertiary follicle

Primary and secondary follicles develop independent of gonadotropins

Development beyond secondary follicle relies heavily on gonadotropins

33
Q

Hormonal regulation

A

GnRH
FSH and LH

FSH- stimulates follicular growth

LH- maturation of oocyte, triggers ovulation

34
Q

Anterior pituitary

A

LH and FSH

35
Q

FSH receptors

A

Exclusively located on granulosa cells

36
Q

LH receptors

A

Early stages- only on thecal cells

Later stages- also on granulosa cells

37
Q

Hormonal regulation

A

Two cell two gonadotropin hypothesis

LH on theca cell- androgens from cholesterol
Androgens diffuse to granulosa cells
Granulosa cells androgens via aromatase converts estrogen

38
Q

Negative feedback

A

Estrogen from ovary has negative feedback on ant. Pituitary and hypothalamus

+ feedback on hypothalamus as well

39
Q

Ovulation

A

Estrogen feedback

Negative feedback on GnRH, FSH, LH at low levels

Positive once reaches threshold- burst of GnRH release, surge of LH, follicular maturation and ovulation

40
Q

Ovulation LH surge

A

Surge of LH necessary for ovulation

LH pulse is short lived in most species, except mares

LH surge post estrus, on last day 0-21?

41
Q

Follicular maturation

A

LH surge

Resumption of meiosis- meiotic inhibitors removed at LH surge

Meiosis resumes

1st meiotic division occurs- 1st polar body extruded

Meiotic arrest occurs (metaphase II) and remains until fertilization or atresia

42
Q

Preovulatory luteinization

A

Following LH surge, theca cells begin to produce low levels of progesterone

Stimulation of collagenase

Degradation of connective tissue and follicle weakens

43
Q

Ovulation

A

Results from weakening of follicular wall

Not increased follicular pressure/bursting

44
Q

Corpus luteum formation

A

Collapsed follicle fills with blood- corpus hemorrhagicum

Rapid remodeling of follicle- theca cells- small literal cells
Granulosa cells- large luteal cells

Progesterone production slowly increases over first few days

45
Q

Corpus luteum roles

A

Secretion of progesterone

Progesterone required for maintenance of pregnancy

46
Q

Corpus luteum-luteolysis

A

Non pregnant females must regress their corpus luteum in order to initiate another cycle

Prostaglandin F2a produced by the endometrium of the uterus, causes the CL to regress in large animals

Destruction of the corpus luteum results in formation of the nonfunctional corpus albicans

CA does not produce progesterone

47
Q

Luteolysis

A

PGF2a

Ruminants- unilateral pathway (counter current diffusion mechanism)

Mares- systemic uterine ovarian pathway

Ewe=local exchange via ovarian artery

48
Q

Cow

A

Countercurrent diffusion mechanism for PGF2a

Reproduction (22 decks)

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