Embryology - Overview and Terminology/Fertilization
when should you have sex to make fertilization most likely to occur?
1-2 days before or on day of ovulation
what are the two subperiods of the embryonic period?
1. early development (0 -3) 2. organogenesis (4 - 8 weeks) - most suspectible to teratogens, especially 4 - 6 wks
what are the three ways to estimate the duration of pregnancy?
1. fertilization age - (0 - 38 wks), goes from 14 days after last menstrual period 2. mesntrual age (0-40) - after LMP 3. Trimesters (3 three month periods)
ways to guess gestational age?
1. gestational sac diameter 2. crown rump length (0 - 14 wks) 3. head size
what are the contents of the sperm acrosome and what do they do?
1. hyaluronidase - breaks down hyaluronic acid in cumulus mass 2. acrosin - protease that breaks down zona pellucida glycoproteins (ZP 1 - 4)
what are the stages of egg activation?
1. membrane depolarization after sperm and egg fuse - shocks away other sperm 2. Ca2+ wave - sperm phospholipase C generates IP3, which releases Ca from sER 3. cortical reaction triggered by Ca release - release of cortical granules, which cause cleavage of ZP2 and zona hardening 4. Juno is shed from the egg, binding to other sperm and blocking them from binding the egg 5. intracellular pH rises, which restarts meiosis and the decondensation of the sperm nucleus 6. female and male pronucleus formed (also 2nd polar body)
what are the four phases of the menstrual cycle?
1. menstrual phase - endometrium sloughs off 2. proliferative/follicular phase - endo bulids up 3. secretory/luteal phase - endo is maintained 4. ischemic phase - LH declines and spiral arteries constrict, cutting off endometrial blood supply
what are the steps of the acrosome reaction?
1. outer acrosomal membrane fuses w/ sperm plasma membrane 2. acrosome contents released 3. inner acrosomal membrane now apical surface of sperm head
what are the four follicular stages?
1. primordial 2. primary 3. antral 4. graafian (mature)
what are the polyspermy blocks?
1. zona hardening (by cortical granule release into perivitelline space) 2. juno blebbing - binds to izumo on other sperm 3. Na shockwave - shocks off excess sperm
how many primordial follicles are released every month?
10 - 20 into ovary cortex
at what point in pregnancy does the placenta become the major source of progesterone?
10 weeks
when does meosis I resume in the oocyte?
12 hr before ovulation
what percentage of births have minor anomalies?
15%
what enzyme do theca interna cells use to convert progesterone to testosterone?
17 beta
how long are sperm viable and how long is the egg viable?
2 - 4 days for sperm 24 hrs or less for egg
how big is a mature graafian follicle?
20 mm
what does the first cleavage occur?
24 hr after fertilization
what enzyme do theca and granulosa cells use to convert cholesterol into testosterone?
3 beta
what percentage of births have major anomalies?
4 - 6%
what are the stages of the cell cycle in order?
G1, S, G2, M
what protein on the sperm inner acrosome is exposed by the acrosome reaction?
Izumo1
what two proteins are invovled in sperm/egg binding?
Izumo1 (sperm) and Juno (egg)
is Meosis I or II long?
Meiosis I because of crossing over
does izumo and juno affect gamete fusion?
NO - only binding
do the pronuclei ever fuse?
NO - they disassociate and then mom/dad's DNA can intermingle
does the primary oocyte have a zona pellucida?
YES
what can a pluripotent cell differentiate into?
all fetal cells
what is embryonic genome activation?
basically, mRNA and proteins leftover from oogeneisis are used by the embryo until after the 8 cell stage, and then the embryo begins producing its own mRNA transcripts
where is the perivitelline space?
below zona pellucida in oocyte
what is the major cause of infant death?
birth defects - 21%
what is compactation and what does it form?
blastomeres adhere tightly together w/ tight junctions and form the morula
what cells in the corpus luteum make progesterone?
both theca interna and granulosa cells
what is required for the acrosome reaction to happen?
capacitiation
what is the function of FSH on the granulosa cells?
causes them to convert testosterone to estrogen w/ aromatase
what is the antrum?
cavity in a follicle - think antral follicle
where is the mucus plug located?
cervix
what compound can theca and granulosa cells convert into progesterone?
cholesterol
what moves semen to the ampulla?
ciliary movement (in uterine tubes) and muscular contraction
what kind of epithelium does the endometrium have?
ciliated epithelium
what follicular cells pass through the zona pellucida and contact the oocyte through gap junctions?
corona radiata - innermost cumulus mass (granulosa) cells
does the cortex or the medulla of the ovary function in steroidogenesis?
cortex
where are eggs formed?
cortex of ovary
when the theca externa ruptures during ovulation, what structures remain w/ the oocyte?
cumulus mass, zona pellucida
what days of the menstrual cycle correlate with the menstrual phase?
days 1 - 4
what days of the menstrual cycle correlate with the secretory phase?
days 15 - 26
what days of the menstrual cycle correlate with the ischemic phase?
days 27 - 28
what days of the menstrual cycle correlate with the proliferative phase?
days 5 - 14
what stage does the egg get arrested at by birth?
diplotene of prophase I
what stage of meosis I are oocytes stuck at (until 12 hr before ovulation)?
diplotene stage of meoisis I - after crossing over
where is the infindibulum located?
distal end of uterine tube - has fimbrae
what is the inner cell mass?
embryoblast
what forms the corpus luteum?
empty follicle after ovulation - theca interna and granulosa cells
what does RU 486 do?
ends pregnancy by causing the endometrium to be shed - inhibits progesterone receptors in the endometrium
how often does the cell divide during the 2 - 8 cell stage?
every 12 hours
when do the pronuclei membrane disassociate?
first mitosis
where are sperm formed and stored?
formed: seminferous epithelium of testes stored: vas deferens
what is another name for a coronal plane?
frontal plane
what is the corpus uteri vs the fundus?
fundus = superior fat portion of uterus corpus uteri = tapering portion of uterus
what changes about the cervical mucus plug during ovulation?
gets thinner - allows sperm to get through to feritilize egg
what forms the corpus luteum?
granulosa and theca cells
what cells in the follicle convert testosterone to estrogen?
granulosa cells - use aromatase
what is the cumulus mass?
granulosa cells near the oocyte in the follicle
what does the embryo secrete in order to maintain the CL (which maintains the endometrium via progesterone)?
hCG
what does crossing over occur between?
homologous chromosomes - creates unique chromatids
is the theca interna or externa steroidogenic?
interna
what portion of the uterine tube are the 1 - 8 cell embryo's located in?
isthmus
what does a pregnancy test measure and when can it detect pregnancy?
levels of hCG - 10 to 14 days after fertilization
where is testosterone produced?
leydig cells in the testes
what can a multipotent cell differentiate into?
limited number of cells ie myeloid stem cells
what stops the LH surge?
massive progesterone creation by corpus luteum in reaction to the LH surge
what is the significance of pronuclei in IVF?
means that feritilization worked
what is the point of cAMP release by corona radiata cells on the oocyte?
meiotic arrest in prophase I
what stage of meosis is the mature oocyte arrested at?
metaphase II
the fundamental cause of how many birth defects is known?
only 40 - 60%
what are primordial follicles?
oocytes arrested in meiosis I
what can a totipotent cell differentiate into?
placenta and fetus
are the inner cell mass cells totipotent, pluripotent or multipotent?
pluripotent - can become all embryo cells (but not placenta)
is the acrosome reaction biochemical or mechanical?
probably mechanical - pores in zona pellucida
when does crossing over occur?
prophase I
how does progesterone affect the myometrium?
relaxes it - staves off contractions and allows uterus to expand during pregnancy
what did the rabbit experiment show?
sperm capacitation - sperm undergo changes in the uterus that allow them to bind the zona pellucida and cause the acrosome reaction
which stage of meosis is a reductional division?
stage I
what are granulosa and theca externa cells?
steroid secreting cells that produce estrogen during follicle development - surround oocyte
what is the function of LH on the theca interna?
stimulates it to secrete testosterone - which can be converted to estrogen so that the follicle will mature
what cells in the follicle secrete testosterone?
theca interna
what cells can convert progesterone into testoterone in the corpus luteum?
theca interna cells
what is cavitation and what does it form?
tight junctions between blastomeres allow Na to be pumped into cell, which pulls in fluid - fluid pockets coalesce to form blastocoel
are blastomere cells totipotent, pluripotent, or multipotent?
totipotent - become embryo and placenta
where do the 2 - 8 cell divisions occur?
uterine tube
what part of the oocyte induces the acrosome reaction?
zona pellucida
what is another name for the 1 cell embryo?
zygote
what occurs during the secretory phase?
- corpus luteum secretes progesterone - increased secretion from endometrium - stroma cells in endometrium keep expressing progesterone receptors so that the endometrium is maintained (deacidualizes) - spiral arteries are more tortuous
what day of the menstrual cycle does the egg usually begin to implant and what stage of development is it at?
- day 20 - 22 - blastocyst
what occurs during the proliferative phase?
- endometrium regenerated - follicle matures - ovulation on day 14
what day of development does the blastocyst enter the uterus at and what day does it implant?
- enters on day 4 - 6 - implants on day 6 - 8
what is the trophoectoderm and what does it form?
- first transporting epithelium - forms the trophoblast
what do the cumulus mass cells secrete and what is the function of this substance?
- hyaluronic acid - helps oocyte stick to fimbrae
what does sperm capacitation do?
- increased lateral head movement - membrane and metabolic changes
what events are caused by the conversion of testosterone to estrogen by the granulosa cells?
- oocyte matures - granulosa proliferates - endometrium regrows (proliferative phase) - LH surge - increased expression of LH receptors in theca and granulosa cells
how can you identify a mature graafian follicle histologically?
- polar body - chromosomes lined up at metaphase plate
what occurs during the ischemic phase?
- spiral arteries constrict (no blood flow to endometrium) - corpus luteum stops producing progesterone - LH declines and CL degenerates