Fertility and Early Development Flashcards
(95 cards)
1
Q
What are the two sites of sperm deposition?
A
- fornix
- Cervix
2
Q
What is seminal plasma used for?
A
- Vehicle for transport
- Energy, motility and pH
3
Q
What do vaginal secretions do to sperm?
A
they immobilize sperm within 1-2 hours
4
Q
How do sperm achieve rapid transport?
A
Through contractile activity of the myometrium
5
Q
How long does it take sperm to reach the site of fertilization?
A
About 15 minutes
6
Q
Where are sperm reservoirs?
A
- In the cervical crypts
- In the utero-tubal junction
7
Q
What happens in sperm reservoirs over time?
A
- Phagocytosis and loss of sperm cells
- Slow release of sperm cells
8
Q
What prevents excessive numbers of sperm from descending on the site of fertilization?
A
Anatomic and Physiologic barriers
9
Q
What increases the chances of fertilization?
A
The slow release of sperm from the reservoirs
10
Q
What causes opposite direction transport of sperm?
A
- Peristalsis and anti-peristalsis
- Complex nervous control
11
Q
How long do sperm survive?
A
normally a maximum of 24 hours
12
Q
How are sperm killed off?
A
- Loss by phagocytosis and physical barriers
13
Q
Where do sperm cells mature?
A
epididymis
14
Q
How do sperm mature in the epididymis?
A
- Gain motility
- Loose cytoplasmic droplet
15
Q
When does capacitation start?
A
In the uterus, but mainly in the isthmus
16
Q
Where does the acrosome reaction occur?
A
in the oviduct before fertilization
17
Q
What is Capacitation?
A
sperm surface components are modified or removed by genital tract secretions causing the phospholipid bilayer to become destabilized, permitting acrosomal activation
- makes the sperm capable of attaching to and penetrating the ovum
18
Q
What does capacitation function to prevent?
A
premature acrosome activation until the sperm reach the site of fertilization and come in contact with the ovum.
19
Q
What changes do the sperm undergo during capacitation?
A
- depletion of sperm cholesterol at sperm surface
- alteration in glycosaminoglycans
- changes in ions as sperm traverse the genital tract
20
Q
What modifications happen on the surface of the spermatozoa?
A
- Cholesterol efflux along with PKA-dependent phosphorylation
21
Q
What modifications happen to the surface of the mitochondria?
A
- loosely wraped around the axoneme or distended
22
Q
What does looser wrapping of the mitochondria allow?
A
Faster moving sperm –> the sprint before the finish
23
Q
What surface components are modified or removed (not including mitochondria or spermatozoa)
A
- Secretions and accessory gland fluids
- Phospholipid layer destabilized
- Acrosome activation
24
Q
Where does capacitation usually occur and why?
A
in the lower segment of the isthmus where fertilizing sperm are stored
25
What is capacitation facillitated by?
rubbing off of sperm surface-absorbed materials against the cervical mucus
26
What happens during the acrosome reaction?
- Sperm plasma membrane fuses with outer acrosomal membrane
- Vesiculation of acrosome
- Release of hydrolytic enzymes
27
What are the functions of the acrosome reaction?
- Eggs are surrounded by glycoprotein coats which the sperm have to travel through.
- Acrosome-reacted sperm dissolve coat locally to produce a hole through which the sperm swim
- outer acrosomal membrane overlying plasma membrane destroyed or becomes detached from the main body of the sperm.
28
What is required for freshly ovulated eggs to be picked up into the oviduct?
- characteristics of fimbriae of infundibulum and relationship to the surface of the ovary at the time of ovulation
- Pattern of release of cumulus cells and egg
- Biophysical properties of follicular fluid released
- coordinated contraction of the fimbriae and the utero-ovarian ligaments
29
What is the average transport time of the ova?
72-96 hours in cattle swine and sheep
| - months in mares
30
what is the fertile life of the egg?
12-24 hours after ovulation
31
What happens if the egg is delayed?
increased chance for polyspermy
32
At ovulation, what phase in the ovum in?
metaphase 2
33
When is maturation of the ovum completed?
after fertilization and zygote formation
34
what happens when the male and female pronuclei fuse?
- happens in the center of the ovum
- nuclear envelope disperses
- Intermixing of chromosome
- 1st cleavage division
- Zygote is formed
35
What is parthenogenesis?
the development of a zygote without a sperm
36
What are two types of twinning?
- monozygotic
| - dizygotic
37
What is monozygotic?
Zygote division
38
What is dizygotic?
double ovulation
39
What changes in the egg immediately after fertilization?
The surface of the ova
40
What happens if blocking polyspermy fails?
- Polispermic fertilization occurs which then results in polyploid embryos that undergo embryonic death or abnormal development
41
Where is the polyspermic block performed?
at the zona
42
How is the block performed?
- sperm are allowed to penetrate but corticle granules released into peri-vitelline space (Ca++) causing a reorganization of zona or vitelline surface
43
What is a zygote?
the cell produced by the union of two gametes (egg and sperm), before it undergoes cleavage.
44
What do sperm maturational changes depend on?
epididymal secretions and transport time
45
What roles do hyaluronidase and acrosin play?
Aid in the penetration of the ovum during the acrosome reaction
46
What does the true acrosome reaction involve?
The fusion of the sperm plasma membrane with the outer acrosomal membrane followed by extensive vesiculation over the anterior segment of the acrosome
47
When do high conception rates occur?
when sperm are present in the oviduct shortly before ovulation
48
How is sperm fertilizability evaluated?
- sperm's ability to fertilize zona-free hampster eggs
- motility patterns
- surface characteristics
- structural stability of head/tail
49
What is capacitation controlled by?
autonomic nerve and hormonal controls
50
How is capacitation achieved?
sperm-surface absorbed materials are rubbed off by the cervical mucus of the isthmus
51
Low numbers of sperm in the oviduct are the result of what?
- controlled movement into the ampulla by the utero-tubal junction and lower isthmus (Pigs) as well as from their movement from the vagina and cervix into the uterus (Ruminants)
52
What does the low numbers of sperm in the oviduct prevent/allow/regulate?
- regulates the number of sperm at the fertilization site (preventing polyspermy)
- providing a sperm reservoir to ensure that capacitated sperm are present until ovulation
53
What may assist in maintaining adequate numbers of sperm at the site of fertilization?
The ability of the sperm to adhere and release from the epithelial lining of the ampulla
54
When do sperm become hyperactivated?
In the ampulla
55
What does hyperactivation of sperm increase the probability of?
increases the probability that they will make contact with the ovum
56
What three critical events are required for fertilization in mammals?
1. Sperm migration between cumulus cells (if present)
2. Sperm attachment and migration through the zona pellucida
3. Fusion of sperm and the ovum plasma membranes
57
What do peristalic contractions in the ampulla increase?
chance of ovum-sperm contact
58
What is the attachment of the sperm head to the zona pellucida regulated by?
receptor sites on the suface of the zona pellucida
59
What do antibodies to sperm or the zona pellucida do?
block or mask sperm receptor sites on sperm and zona surfaces
60
What is acrosome organization required for?
to insure release of acrosome components in precise order to sperm traverse the egg vestments
61
Why is the acrosome reaction an indicator of capacitation?
cause sperm do not undergo AR either spontaneously or mediated by ligands unless they become capacitated
62
What happens chemically during the acrosome reaction? (what is massively influxed?)
Massive influx of Ca2+
63
What does the glycoprotein layer of the inner surface of the outer acrosomal membrane do?
holds vesiculated plasma/outer acrosomal membranes together during AR
64
What is essential for sperm attachment to the zona pellucida?
An intact acrosome
65
What is required for the passage of sperm through the zona?
- enzymes exposed during the AR
| - Sperm motility
66
What does binding with the ZP3 allow?
interactions with other zona components that stimulate acrosome activation
67
What does the ZP2 serve as?
may serve as a secondary sperm receptor to maintain sperm attachment during passage through the zona
68
What is the acrosome reaction a prerequisite for?
fusion between the ova and spermatozoa plasma membranes
69
What is the ZP3?
sperm receptor to which only sperm with an intact acrosome can bind
70
What happens once sperm has traveled through the zona pellucida?
the head moved into the vitelline space and contracts the vitelline membrane. Sperm tail propells sperm into vitelline space, rotating the vitelline membrane within the zona pellucida
71
What is the vitelline membrane covered with?
dense microvilli
72
What happens to the surface of the equatorial region of the sperm head?
it is incorporated into the plasma membrane of the ovum
73
What happens when the cortical granules release their content?
causes extensive reorganization of zona pellucida and/or vitelline surface
74
What does the cortical reaction result in?
release of enzymes that cause hardening of zona pellucida/inactivation of sperm receptors
75
How do zygotes attain a ratio (nuclear to cytoplasmic) similar to somatic cells?
Through cleavage: cell divisions occur without increasing the mass
76
What happens to the nucleus and cytoplasm during cleavage?
Cytoplasm amount decreases and the nucleus amount increases
77
How does the egg receive metabolic support during early pregnancy?
By oviductal and uterine secretions
78
What are the daughter cells of cleavage called?
blastomeres
79
What sequence does cleavage follow in terms of the number of blastomeres?
A doubling sequence
80
What type of division is cleavage?
Mitotic division with each daughter cell receiving the full assortment of chromosomes
81
What does totipotent mean?
the cell can give rise to anything
82
What is a morula?
When the embryo has formed 9-16 blastomeres
83
What is compaction?
The combined process of flattening of the blastomeres and polarization
84
When do tight junctions form between the blastomeres?
when the blostomeres are in close apposition during the process of compaction
85
What do the tight junctions allow?
- provides a permeability seal that allows fluid to move from the outside to the inside of the blastocyst without substantial leakage
- important role in separating cells from contact with the maternal environment, thereby allowing the blastocyst to positionally differentiate into two populations of cells
86
What do the two populations of a blastocyst give rise to?
- Inner cell mass gives rise to the embryo proper
| - outer cell mass gives rise to the trophectoderm or trophoblast which forms the chorion
87
What forms during gastrulation?
The ectoderm, mesoderm and endoderm
88
What do the microvilli on the outside of the trophoblast do?
contact and adhere to the maternal uterine epithelium for placental attachment and nutrient uptake
89
Following the hatching from the zona pellucida, the trophectoderm will become lined with what? why?
mesoderm which expands out from the inner cell mass to form the outer membrane of the placenta
90
What is the chorion?
the outer membrane of the placenta formed by the mesoderm
91
When does bloastocyst hatching occur? Where?
Where: uterine lumen
When: 4-8 days post-ovulation
92
What stretches the zona of the blastocyst during hatching?
physical and enzymatic actions in the form of rhythmic expansion and contraction of the blastocyst causing the zona to stretch. Involves cellular hyperplasia and increased fluid accumulation in the blastocoele
93
What does hatching and fluid movement within the blastocyst seem to involve?
prostaglandin synthesis (Especially prostaglandin E)
94
What causes softening of the zona matrix?
activation of enzymes such as plasmin and trypsin
95
What is the conceptus?
embryo and its extraembryonic membranes
