Meiosis Flashcards
(34 cards)
what is meiosis
- single round of DNA replication
- 2 consecutive rounds of cell division (end up with 1/2 chromosome complement of parent)
meiosis result in females
each original 2N oogonia entering meiosis gives rise to only one 1N oocyte
meiosis result in males
2 meiotic divisions –> 4 daughter cells each being 1N 1C (half chromosomal content of the parent)
why does meiosis in females only give rise to 1 oocyte
cytokinesis is uneven –> nearly all cytoplasm goes to one of the cells at each division –> smaller remnant cells are polar bodies –> done to preserve oocyte products needed for early embryo development
arrest of meiosis in females
- first meiotic division continues up to diplotene stage of prophase
- arrested there until birth (arrested in diplotene of first meiotic prophase)
female reinitiation of first meiosis
- occurs after puberty
- result of a preovulatory LH surge
action of LH on reinitiation of first female meiosis
-limited to large graafian folicles because only in these do the granulosa cells have sufficient LH receptors
what happens when oocyte completes this meiosis
- first polar body is expelled
- enters 2nd meiotic division and is again arrested
when does the second female meiosis block occur
at the metaphase stage of the second meiosis –> state that oocytes are ovulated in most species
when does completion of second female meiotic division occur
when the oocyte is reactivated by a penetrating sperm at the time of fertilization
what is the process of CL formation called
luteinization
when does lutenization begin
following LH surge but prior to ovulation, when follicles begin to secrete less estrogen and more progesterone
what are the initial stages of lutenization in all species due to
LH surge
what happens to follicles following oculation
- collapsed follicle reorganizes
- granulosa cells and theca cells respectively form large and small luteal cells
what do large and small luteal cells do with LH
- large: responsible for most of the baseline progesterone secretion but do not respond to LH by increasing progesterone secretion
- small: respond to LH with increased progesterone secretion
functions of CL
- secretion of progesterone to prepare uterus for ensuing pregnancy
- prevents sexual receptivity
- suppresses gonadotropin release
LH in luteotropic complex
- luteotropic in all species
- responsible for early stages of lutenization
- “universal luteotropin”
prolactin in luteotropic complex
- from anterior pituitary
- luteotropin in carnivores, mice, rats, hamsters (many species)
estradiol in luteotropic complex
vital luteotropin in rabbit, may be luteolytic in other species
PGF2a in luteotropic complex
- luteolytic hormone in all mammals
- other prostaglandins may have luteotropic functions (PGI2, PGE2)
what must happen for a new cycle to commence in species with short cycles
influence of the CL must be removed –> CL is actively killed off (luteolysis)
what do sustained high levels of progesterone throughout luteal phase cause
down-regulation of the progesterone receptor in both the hypothalamus and uterine endometrium –> progesterone has less influence at the tissue level, small amounts of estrogen from developing follicles have more influence
results of the effective increase in the radio of estrogen/progesterone
- receptors for ocytocin are up regulated in the uterine endometrium
- activity of the central oxytocin pulse generator is increased
what does increased oxytocin release and the increase in its receptors on the uterine endometrium cause
PGF2a release –> acts on CL to cause luteolysis
