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96 Cards in this Set
- Front
- Back
2 reasons to study embryology
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understand normal anatomy & dev. of birth defects
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what is the leading cause of neonatal death
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birth defects
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% of newborns with birth defects
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3%
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% of birth defects recognized in early childhood
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another 3%
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somatic cell karyotype is what normally?
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22 prs autosomes, 1 pr. sex chrom. (46 chromosomes)
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failure of chromosomes to distribute normally during meiosis leads to ?
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gametes with abnormal numbers of chromosomes because of non-disjunction
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abnormal number of chromosomes called?
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aneuploidy
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% of non-disjunction w/in sperm cells?
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2 3%
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% of non disjunction in oocytes in women approaching menopause?
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20%
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what happens with most aneuploid embryos?
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dont come to term spontaneously abort
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most common trisomy?
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21: down syndrome
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effect of monosomy?
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usually lethal. In sex chromosome usually results in early death & range of problems
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% of sperm which may be abnormal?
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10-15% (above 20% = infertility)
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% of abnormal forms above which may cause infertility?
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20%
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define gametogenesis
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production of a population of cells specialized for fertilization
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2 events of gametogenesis?
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1: gametes acquire structural and functional characteristics nec. for successful union 2: meiosis occurs (only occurs in gametes) = half the number of chromosomes
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# of chromosomes in somatic cells
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46N
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number of chromosomes in gametes
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23N
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non-disjunction
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failure of chromosomes to distribute normally during meiosis = embryo with abnormal number of chromosomes (aneuploid).
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spermatogenesis begins when?
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puberty
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spermatogenesis occurs where?
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seminiferous tubules of the testis
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phases in spermatogenesis, & their results?
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two phases: phase 1 spermatogonia undergo meiosis 1 & 2 to create spermatids. phase 2: spermatids mature, undergoing morphogenesis/spermiogenesis creating spermatozoa
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how many sperm are created every day?
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between 50 and 150 million
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central part of head of sperm and its purpose
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nucleus, contains chromosomes
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outer covering of head of sperm called? purpose?
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cell membrane contains binding sites for sperm receptors on zona pellucida and on oocyte membrane
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portion of head of sperm covering nucleus called what, purpose
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acrosome contains hydrolytic emzymes to digest pathway to egg
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how long does spermatogenesis take?
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about 9 weeks
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three parts of the head of the sperm(diagram p 1-3 in notes)
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cell membrane, nucleus, acrosome
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three parts of the tail of the sperm
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middle piece (nearest sperm head), principle piece, end piece
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what structures create seminal fluid and in what percentages? (How many structures?)
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2 seminal vesicles (60%),1 prostate gland (30%), 2 bulbourethral glands (10%)=5 structures total
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When is seminal fluid added to spermatozoa?
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at time of ejaculation, to constitute semen
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three purposes of seminal fluid?
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nutrients (simple sugars) for spermatozoa, neutralize vaginal acidity, promote sperm motility (need slightly alkaline environment to swim well.
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what is considered a normal concentration of spermatozoa per ml of semen?
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40 200 million
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spermatozoa live how long in female reproductive tract?
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5 days or more
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How long do oocytes live for?
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24 hours
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normal site of fertilization?
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ampulla of uterine tube
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what carries some spermatozoa to ampulla of uterine tube within minutes of ejaculation?
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contractions of uterus and tubal musculature
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where are spermatozoa that are not carried to ampulla?
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colonize crypts of the cervix majority of sperm
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why so many sperm?
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50% chance of going to the wrong ampulla, as ovaries take turns ovulating
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why dont fertilization and ovulation have to coincide?
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sperm can live within the cervix and then swim to the ampulla by tail beat
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what occurs to create fully functional spermatozoa?
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capacitation (after 4 6hrs in fem. rep. tract) increases motility & metabolism, nec. for sperm-egg attachment & acrosome reaction
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acrosome reaction
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acrosome perforates, releasing enzymes, which allow sperm to digest a path through the zona pellucida
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internal os
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constricted opening of cervical canal: communicates with uterus. (external os communicates w/ vagina)
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probability of conception near day of ovulation
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within 5 days of ovulation, probability still exists, with highest probability of conception on day of ovulation.
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24 36 hrs before ovulation what occurs?
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hormonal changes: spike in leutinizing hormone:- triggers follicular cells to disassemble gap junction- releases oocyte from meiotic inhibition, causing oocyte to undergo meiosis I- oocyte floats freely in antrum
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when does oogenesis begin/end?
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begins: during fetal life in fetal ovary, ends: menopause
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what occurs in the ovary during the first phase of oogenesis?
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Meiosis I begins, but does not complete until just before ovulation à this creates 2ndary oocyte from primary oo.
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what occurs just before ovulation?
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meiosis II begins, but does not complete unless egg is fertilized. beginning of Meiosis II creates an ovum from a secondary oocyte.
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what is the name given to the cellular units in the ovary that contain the developing egg?
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follicles
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an oocyte develops from what? 2 main characteristics
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primordial follicle: primary oocyte arrested in prophase of Meiosis I, enclosed by a layer of cells.
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# primary follicles (approx) do females have at birth?
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abt. 2 million.
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primordial follicle develops into?
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primary follicle
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Summarize 4 stages primordial primary follicle
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growth, follicular cells à granulosa, tissue around granulosa à thica (thickens: theca=thicker!), zona pellucida forms
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connections between granulosa and oocyte
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gap junctions transfer of nutrients, etc
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theca produces what/why?
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androgens- substrate for granulosa to produce estrogen
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zona pellucida is?
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extracellular matrix between primary oocyte and innermost follicular layer
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name of thick vascularized outer coating of granulosa
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theca
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follicular cells do what for primary oocyte
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metabolic support, and suspension in meiosis. Are connected to prim.ooc. via gap junctions, so transfers nutrients, plus chemicals which keep oocyte suspended.
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follicular cells secrete what
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OMI: Oocyte maturation inhibitor- follicle:Meiosis I
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after primary follicles, what forms?
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secondary follicles
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differences between primary and secondary follicles?
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- increased size + appearance of antrum (fluid-filled spaces eventually enlarge - coalesce into large space)
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follicular cells forming walls of antrum are called?
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mural follicular cells (like a mural on a wall)
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secondary follicle matures to become what/how?
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graffian follicle cumulus oophorus forms around oocyte, projects into antrum
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mural follicular cells do what to form what?
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stay in ovary after ovulation to form the granulosa lutein cells of the corpus luteum
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structure projects into antrum? formed by?
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cumulus oophorus, formed by oocyte & follicles around
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what is a graffian follicle?
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very large secondary follicle these grow to about 2.5cm in size, and can be seen as a bulge on the side of the ovary.
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graffian follicles grow large what happens to ovary
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white avascular spot seen there: stigma
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avascularity why, causes what on ovary surface
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Proteolytic enzymes secreted by follicular cell: break down tissue for oocyte escape. Ovary tissue becomes pale because avascular: called stigma.
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length of time for a primary follicle to develop into a mature, pre-ovulatory secondary follicle?
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about 3 mos.
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OMI is what and what does it do?
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OOcyte maturation inhibitor, secreted from follicular cells to keep follicle in Meiosis I. Removal of follicular cells removes OMI, and causes continuation of meiosis.
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what is released when from the ovary during ovulation?
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secondary oocyte, first polar body, zonal pellucida, corona radiata
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what happens to the primary oocyte before ovulation?
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a few hours before, it completes meiosis I.
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characteristic of completion of primary oocyte meiosis I?
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both daughter cells still within zona pellucida, but cytoplasm division unequal during cytokinesis, so one large secondary oocyte, one small polar body.
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After oocyte completes meiosis I
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oocyte begins meiosis II, but only completes if fertilized
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what happens to the secondary oocyte etc. at ovulation
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released through surface of ovary, into peritoneal cavity, to enter the ostium (mouth) of the uterine tube at ovum pick-up.
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cumulus oophorus becomes?
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corona radiata
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cells covering the secondary oocyte at ovum pick-up?
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corona radiata no longer connected firmly to oocyte by gap junctions fall away easily
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3 purposes of corona radiata?
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Assist 2ndary oocyte into uterine tube: easier for the cilia of the fimbria of ampulla to grab onto the ova; larger target size for sperm; helps trap sperm cells and direct them to surface of egg
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What happens (at this point) if the egg is fertilized?
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completes meiosis II, but division is again unequal, so a second polar body is created, which then degenerates.
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What does the corpus luteum become after ovulation?
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a secretory body that secretes hormones to prepare uterus for implantation
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corpus luteum become if no implantation?
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corpus albicans a scar
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how does the sperm bind with the egg?
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species-specific interaction. zona binding sites on sperm cell membrane bind with sperm receptor on zona pellucida (ZP3)
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sperm-zona binding trigger?
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acrosome reaction sperm cell membrane fuses with acrosome, disappears- enzymes released: zona pellucida breaks down: pathway eaten through for sperm.
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main 2 acrosomal enzymes facilitate zona penetration?
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hyaluronidase and acrosin
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which is species specific, zona sperm interaction, or sperm-egg binding?
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zona-sperm interaction, NOT sperm-oocyte interaction.
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sperm crosses what to reach oocyte membrane
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perivitelline space betw. zona pellucida & oocyte memb.
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after the sperm has crossed perivitelline space - ?
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sperm head crosses the space to bind with sperm receptors on the oocyte membrane. (sperm-egg binding)
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sperm-oocyte binders?
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integrin receptor on oocyte membrane +fertilin on sperm cell membrane = fusion of membranes
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3 events triggered following binding?
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meiosis completes, other polar body cast off, cortical granules released = zona reaction.
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zona reaction is?
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chemistry change to zona pellucida because of cortical granule release
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zona reaction occurs why?
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block to polyspermy
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name for cortical granule release
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exocytosis
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What are formed in the oocyte following fertilization?
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male and female pronuclei in the oocyte. (All other parts of the sperm body/tail are taken up into the egg cytoplasm and incorporated into the egg membrane, meaning that only the paternal chromosomes survive.)
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mechanisms in place to prevent polyspermy?
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zona reaction caused by cortical granule exocytosis changes modify receptors on zona no more sperm can bind with
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why prevent polyspermy?
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maintain equal genetic contributions, restore diploid chromosome value.
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what events occur in the first 12 hours of fertilization to form the zygote?
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nucleus of sperm decondenses, forms male pronucleus; secondary oocyte completes Meiosis II, casts off 2nd polar body remaining oocyte nucleus now female pronucleus; DNA replication occurs in both male and female pronuclei; pronuclear membranes break down, chromosomes co-mingle, joining on a mitotic spindle for the first cleavage division of the zygote --> this restores the chromosomes to 46 or 2N = zygote
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