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Oogenesis Flashcards

(48 cards)

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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

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A

Two divisions

21
Q

Primordial germ cells

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A

Stem cell of oogenesis

Migrate from yolk sac to the genital ridge (chemotaxis)

PGC- oogonia

22
Q

Oogonia

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A

Interconnected by cytoplasmic bridges

Lose motility

Multiply by mitosis

23
Q

Oogenesis process

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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

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A

Initiation by meiosis (independent of stimulus)

Intercellular bridges disappear

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

25
1st meiotic arrest(block) of meiosis
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
Anisogamy
Difference in size of male and female gametes
27
Oogenesis stages
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
Resumption of meiosis and 2nd meiotic arrest (block)
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
Oogenesis
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
Meiotic events
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
Oogenesis new idea
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
Folliculogenesis
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
Hormonal regulation
GnRH FSH and LH FSH- stimulates follicular growth LH- maturation of oocyte, triggers ovulation
34
Anterior pituitary
LH and FSH
35
FSH receptors
Exclusively located on granulosa cells
36
LH receptors
Early stages- only on thecal cells | Later stages- also on granulosa cells
37
Hormonal regulation
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
Negative feedback
Estrogen from ovary has negative feedback on ant. Pituitary and hypothalamus + feedback on hypothalamus as well
39
Ovulation
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
Ovulation LH surge
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
Follicular maturation
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
Preovulatory luteinization
Following LH surge, theca cells begin to produce low levels of progesterone Stimulation of collagenase Degradation of connective tissue and follicle weakens
43
Ovulation
Results from weakening of follicular wall Not increased follicular pressure/bursting
44
Corpus luteum formation
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
Corpus luteum roles
Secretion of progesterone Progesterone required for maintenance of pregnancy
46
Corpus luteum-luteolysis
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
Luteolysis
PGF2a Ruminants- unilateral pathway (counter current diffusion mechanism) Mares- systemic uterine ovarian pathway Ewe=local exchange via ovarian artery
48
Cow
Countercurrent diffusion mechanism for PGF2a

Reproduction (22 decks)

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