Embryology-01-Fertilization

Front 1

2 reasons to study embryology

Back 1

understand normal anatomy & dev. of birth defects

Front 2

what is the leading cause of neonatal death

Back 2

birth defects

Front 3

% of newborns with birth defects

Back 3

3%

Front 4

% of birth defects recognized in early childhood

Back 4

another 3%

Front 5

somatic cell karyotype is what normally?

Back 5

22 prs autosomes, 1 pr. sex chrom. (46 chromosomes)

Front 6

failure of chromosomes to distribute normally during meiosis leads to ?

Back 6

gametes with abnormal numbers of chromosomes because of non-disjunction

Front 7

abnormal number of chromosomes called?

Back 7

aneuploidy

Front 8

% of non-disjunction w/in sperm cells?

Back 8

2 – 3%

Front 9

% of non disjunction in oocytes in women approaching menopause?

Back 9

20%

Front 10

what happens with most aneuploid embryos?

Back 10

don’t come to term – spontaneously abort

Front 11

most common trisomy?

Back 11

21: down syndrome

Front 12

effect of monosomy?

Back 12

usually lethal. In sex chromosome usually results in early death & range of problems

Front 13

% of sperm which may be abnormal?

Back 13

10-15% (above 20% = infertility)

Front 14

% of abnormal forms above which may cause infertility?

Back 14

20%

Front 15

define gametogenesis

Back 15

production of a population of cells specialized for fertilization

Front 16

2 events of gametogenesis?

Back 16

1: gametes acquire structural and functional characteristics nec. for successful union 2: meiosis occurs (only occurs in gametes) = half the number of chromosomes

Front 17

# of chromosomes in somatic cells

Back 17

46N

Front 18

number of chromosomes in gametes

Back 18

23N

Front 19

non-disjunction

Back 19

failure of chromosomes to distribute normally during meiosis = embryo with abnormal number of chromosomes (aneuploid).

Front 20

spermatogenesis begins when?

Back 20

puberty

Front 21

spermatogenesis occurs where?

Back 21

seminiferous tubules of the testis

Front 22

phases in spermatogenesis, & their results?

Back 22

two phases: phase 1 spermatogonia undergo meiosis 1 & 2 to create spermatids. phase 2: spermatids mature, undergoing morphogenesis/spermiogenesis creating spermatozoa

Front 23

how many sperm are created every day?

Back 23

between 50 and 150 million

Front 24

central part of head of sperm and its purpose

Back 24

nucleus, contains chromosomes

Front 25

outer covering of head of sperm called? purpose?

Back 25

cell membrane – contains binding sites for sperm receptors on zona pellucida and on oocyte membrane

Front 26

portion of head of sperm covering nucleus called what, purpose

Back 26

acrosome – contains hydrolytic emzymes to digest pathway to egg

Front 27

how long does spermatogenesis take?

Back 27

about 9 weeks

Front 28

three parts of the head of the sperm(diagram p 1-3 in notes)

Back 28

cell membrane, nucleus, acrosome

Front 29

three parts of the tail of the sperm

Back 29

middle piece (nearest sperm head), principle piece, end piece

Front 30

what structures create seminal fluid and in what percentages? (How many structures?)

Back 30

2 seminal vesicles (60%),1 prostate gland (30%), 2 bulbourethral glands (10%)=5 structures total

Front 31

When is seminal fluid added to spermatozoa?

Back 31

at time of ejaculation, to constitute semen

Front 32

three purposes of seminal fluid?

Back 32

nutrients (simple sugars) for spermatozoa, neutralize vaginal acidity, promote sperm motility (need slightly alkaline environment to swim well.

Front 33

what is considered a normal concentration of spermatozoa per ml of semen?

Back 33

40 – 200 million

Front 34

spermatozoa live how long in female reproductive tract?

Back 34

5 days or more

Front 35

How long do oocytes live for?

Back 35

24 hours

Front 36

normal site of fertilization?

Back 36

ampulla of uterine tube

Front 37

what carries some spermatozoa to ampulla of uterine tube within minutes of ejaculation?

Back 37

contractions of uterus and tubal musculature

Front 38

where are spermatozoa that are not carried to ampulla?

Back 38

colonize crypts of the cervix – majority of sperm

Front 39

why so many sperm?

Back 39

50% chance of going to the wrong ampulla, as ovaries take turns ovulating

Front 40

why don’t fertilization and ovulation have to coincide?

Back 40

sperm can live within the cervix and then swim to the ampulla by tail beat

Front 41

what occurs to create fully functional spermatozoa?

Back 41

capacitation (after 4 – 6hrs in fem. rep. tract) increases motility & metabolism, nec. for sperm-egg attachment & acrosome reaction

Front 42

acrosome reaction

Back 42

acrosome perforates, releasing enzymes, which allow sperm to digest a path through the zona pellucida

Front 43

internal os

Back 43

constricted opening of cervical canal: communicates with uterus. (external os communicates w/ vagina)

Front 44

probability of conception near day of ovulation

Back 44

within 5 days of ovulation, probability still exists, with highest probability of conception on day of ovulation.

Front 45

24 – 36 hrs before ovulation – what occurs?

Back 45

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

Front 46

when does oogenesis begin/end?

Back 46

begins: during fetal life in fetal ovary, ends: menopause

Front 47

what occurs in the ovary during the first phase of oogenesis?

Back 47

Meiosis I begins, but does not complete until just before ovulation à this creates 2ndary oocyte from primary oo.

Front 48

what occurs just before ovulation?

Back 48

meiosis II begins, but does not complete unless egg is fertilized. beginning of Meiosis II creates an “ovum” from a secondary oocyte.

Front 49

what is the name given to the cellular units in the ovary that contain the developing egg?

Back 49

follicles

Front 50

an oocyte develops from what? 2 main characteristics

Back 50

primordial follicle: primary oocyte arrested in prophase of Meiosis I, enclosed by a layer of cells.

Front 51

# primary follicles (approx) do females have at birth?

Back 51

abt. 2 million.

Front 52

primordial follicle develops into?

Back 52

primary follicle

Front 53

Summarize 4 stages primordial – primary follicle

Back 53

growth, follicular cells à granulosa, tissue around granulosa à thica (thickens: theca=thicker!), zona pellucida forms

Front 54

connections between granulosa and oocyte

Back 54

gap junctions – transfer of nutrients, etc

Front 55

theca produces what/why?

Back 55

androgens- substrate for granulosa to produce estrogen

Front 56

zona pellucida is?

Back 56

extracellular matrix between primary oocyte and innermost follicular layer

Front 57

name of thick vascularized outer coating of granulosa

Back 57

theca

Front 58

follicular cells do what for primary oocyte

Back 58

metabolic support, and suspension in meiosis. Are connected to prim.ooc. via gap junctions, so transfers nutrients, plus chemicals which keep oocyte suspended.

Front 59

follicular cells secrete what

Back 59

OMI: Oocyte maturation inhibitor- follicle:Meiosis I

Front 60

after primary follicles, what forms?

Back 60

secondary follicles

Front 61

differences between primary and secondary follicles?

Back 61

- increased size + appearance of antrum (fluid-filled spaces eventually enlarge - coalesce into large space)

Front 62

follicular cells forming walls of antrum are called?

Back 62

mural follicular cells (like a mural on a wall)

Front 63

secondary follicle matures to become what/how?

Back 63

graffian follicle – cumulus oophorus forms around oocyte, projects into antrum

Front 64

mural follicular cells do what to form what?

Back 64

stay in ovary after ovulation to form the granulosa lutein cells of the corpus luteum

Front 65

structure projects into antrum? formed by?

Back 65

cumulus oophorus, formed by oocyte & follicles around

Front 66

what is a graffian follicle?

Back 66

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.

Front 67

graffian follicles grow large – what happens to ovary

Back 67

white avascular spot seen there: stigma

Front 68

avascularity why, causes what on ovary surface

Back 68

Proteolytic enzymes secreted by follicular cell: break down tissue for oocyte escape. Ovary tissue becomes pale because avascular: called stigma.

Front 69

length of time for a primary follicle to develop into a mature, pre-ovulatory secondary follicle?

Back 69

about 3 mos.

Front 70

OMI is what and what does it do?

Back 70

OOcyte maturation inhibitor, secreted from follicular cells to keep follicle in Meiosis I. Removal of follicular cells removes OMI, and causes continuation of meiosis.

Front 71

what is released when from the ovary during ovulation?

Back 71

secondary oocyte, first polar body, zonal pellucida, corona radiata

Front 72

what happens to the primary oocyte before ovulation?

Back 72

a few hours before, it completes meiosis I.

Front 73

characteristic of completion of primary oocyte meiosis I?

Back 73

both daughter cells still within zona pellucida, but cytoplasm division unequal during cytokinesis, so one large secondary oocyte, one small polar body.

Front 74

After oocyte completes meiosis I

Back 74

oocyte begins meiosis II, but only completes if fertilized

Front 75

what happens to the secondary oocyte etc. at ovulation

Back 75

released through surface of ovary, into peritoneal cavity, to enter the ostium (mouth) of the uterine tube at “ovum pick-up”.

Front 76

cumulus oophorus becomes?

Back 76

corona radiata

Front 77

cells covering the secondary oocyte at ovum pick-up?

Back 77

corona radiata – no longer connected firmly to oocyte by gap junctions – fall away easily

Front 78

3 purposes of corona radiata?

Back 78

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

Front 79

What happens (at this point) if the egg is fertilized?

Back 79

completes meiosis II, but division is again unequal, so a second polar body is created, which then degenerates.

Front 80

What does the corpus luteum become after ovulation?

Back 80

a secretory body that secretes hormones to prepare uterus for implantation

Front 81

corpus luteum become if no implantation?

Back 81

corpus albicans – a scar

Front 82

how does the sperm bind with the egg?

Back 82

species-specific interaction. zona binding sites on sperm cell membrane bind with sperm receptor on zona pellucida (ZP3)

Front 83

sperm-zona binding trigger?

Back 83

acrosome reaction – sperm cell membrane fuses with acrosome, disappears- enzymes released: zona pellucida breaks down: pathway “eaten” through for sperm.

Front 84

main 2 acrosomal enzymes facilitate zona penetration?

Back 84

hyaluronidase and acrosin

Front 85

which is species specific, zona –sperm interaction, or sperm-egg binding?

Back 85

zona-sperm interaction, NOT sperm-oocyte interaction.

Front 86

sperm crosses what to reach oocyte membrane

Back 86

perivitelline space betw. zona pellucida & oocyte memb.

Front 87

after the sperm has crossed perivitelline space - ?

Back 87

sperm head crosses the space to bind with sperm receptors on the oocyte membrane. (sperm-egg binding)

Front 88

sperm-oocyte binders?

Back 88

integrin receptor on oocyte membrane +fertilin on sperm cell membrane = fusion of membranes

Front 89

3 events triggered following binding?

Back 89

meiosis completes, other polar body cast off, cortical granules released = zona reaction.

Front 90

zona reaction is?

Back 90

chemistry change to zona pellucida because of cortical granule release

Front 91

zona reaction occurs why?

Back 91

block to polyspermy

Front 92

name for cortical granule release

Back 92

exocytosis

Front 93

What are formed in the oocyte following fertilization?

Back 93

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.)

Front 94

mechanisms in place to prevent polyspermy?

Back 94

zona reaction – caused by cortical granule exocytosis changes – modify receptors on zona – no more sperm can bind with

Front 95

why prevent polyspermy?

Back 95

maintain equal genetic contributions, restore diploid chromosome value.

Front 96

what events occur in the first 12 hours of fertilization to form the zygote?

Back 96

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