Exam 2 Flashcards
(79 cards)
1
Q
What is fertilization?
A
The union of two haploid (1n) gametes, the spermatozoa and the oocyte
2
Q
1 haploid oocyte + 1 haploid sperm
A
= 1 diploid zygote
3
Q
How many sperm do you need to fertilize 1 oocyte?
A
1 sperm
4
Q
What are the mechanisms sperm use to get to the oocyte?
A
Hyperactivation
Acrosome Reaction
5
Q
Hyperactivation
A
push to reach the oocyte
6
Q
Acrosome reaction
A
Get through the zona pellucida
7
Q
What mechanisms do oocytes use to limit fertilization to one sperm?
A
Cortical reaction
8
Q
Cortical reaction
A
prevent other sperm from fusing with the oocyte
9
Q
What happens after the sperm reach the infundibulum?
A
they bind to epithelial cells forming the sperm reservoir
10
Q
How long can sperm be stored?
A
Days to months
11
Q
How long are oocytes viable for?
A
about one day
12
Q
Where does the sperm reservoir form after mating?
A
oviduct
13
Q
When do species mate prior to ovulation?
A
- species that undergo estrus cycles typically mate 12-24 hours prior to ovulation
- dogs can mate several times prior to ovulation (superfecundation)
- Species that experience menstrual cycles have a fertile mating a week before ovulation
14
Q
What hormone causes sperm hyperactivation?
A
progesterone from granulosa cells
15
Q
Where do sperm become hyperactivated?
A
oviduct
16
Q
What effect does hyperactivation have on sperm?
A
it slows sperm movement but increases force
17
Q
3 important functions of hyperactivation
A
- release sperm from oviductal epithelium
- pushes sperm through thick secretion in the oviduct
- pushes sperm against oocyte, facilitating fertilization
18
Q
What surrounds the oocyte?
A
Zona pellucida
19
Q
What is the zona pellucida?
A
-specialized protein coat
- zona proteins are part of the zona pellucida and important for fertilization
20
Q
Zona proteins
A
ZP1, ZP2, ZP3, ZP4 (only expressed in mice)
21
Q
Acrosome
A
- sperms specialized organelle
- each sperm contains 1 acrosome at anterior end
- contains enzymes (proteases) that are important in fertilizaiton
22
Q
What triggers acrosome reactions?
A
Sperm binding to oocyte
1. sperm bind to ZP proteins around oocytes
2. Acrosome fuses with plasma membrane of sperm
3. enzymes are released
4. ZP starts to breakdown
5. plasma membrane of sperm and oocyte fuse
23
Q
How do oocytes prevent 2nd sperm from fusing with plasma membrane?
A
- polyspermy is lethal in most animals
- oocyte stops 2nd sperm from fusing with plasma membrane
- 1st sperm triggers the cortical reaction
24
Q
How does the oocyte prevent polyspermy?
A
cortical granules
-a specialized type of secretory granule
-contain enzymes that crosslink proteins in zona pellucida
25
Cortical reaction
1. plasma membrane of sperm and oocyte fuse
2. cortical granules fuse with the oocyte plasma membrane
3. enzymes are released into perivitelline space
4. proteins in ZP crosslink
5. more sperm cannot fuse with ZP4 proteins
26
Blocking polyspermy
Fast block: due to changes in electrical potential across membrane, only in species with external fertilization
Slow block: cortical reaction, happens in all animals
27
After fusion, the pronucleus of the sperm and egg fuse
- organelles from sperm are released into oocyte
- pronuclei from oocyte and sperm fuse
- other organelles in sperm degenerate
- left with 1 diploid oocyte
28
Results of polyspermy
- results in triploidy
- birds, reptiles, and amphibians
- rare and pathologic in mammals (usually lethal)
29
In vitro fertilization
- culture 1 oocyte and hundreds of sperm in a dish
- allow sperm to fertilize oocyte "naturally"
30
Why use IVF in livestock?
- increase number of offspring from elite animals
- enhance genetics of livestock
- genetically alter livestock
- understand IVF and human fertilization better
31
How do we bypass natural fertilization?
Intracytoplasmic sperm injection
- oocyte and sperm are retrieved from patients
- sperm are aspirated into micropipette
- oocyte is held in place with slight vacuum
- sperm is injected into oocyte
32
Parthenogenesis
an egg can develop into an embryo without being fertilized by a sperm
33
Some animals reproduce without fertilization
worms, snails, insects, crustaceans, sharks
34
Embryo definition
developing offspring that hasn't acquired full anatomical form
35
Fetus definition
a potential offspring within the uterus, generally recognizable as a member of a given species
36
Conceptus
all the products of conception
- embryo/ fetus+ placenta
37
Stem cells make other cell types, what are they?
totipotent, pluripotent, multipotent
38
totipotent
a cell that can give rise to a complete organism
39
pluripotent
cell that can differentiate into most cells of an organism
40
multipotent
a cell type that can differentiate into several related types of cells
41
zygote
-the male and female pronuclei have fused (syngamy)
- 2n cell
- very large cytoplasm
- surrounded by ZP
42
Cleavage development
cell number increases but total mass of embryo does not
43
totipotent cells
zygote, 2-cell, 4-cell, 8-cell
44
Where does most of cleavage development occur?
Oviduct
- occurs in ampulla of oviduct
- embryo enters uterus at about the morula
45
what types of cells line the oviduct?
secretory and ciliated epithelium
46
Secretory epithelium
-secrete growth factors and nutrients into the lumen
-supports the embryo as it develops
47
ciliated epithelium
- fingerlike projection that moves sperm, oocyte, embryo
48
At what stage do cells compact and start to differentiate?
Morula
- compaction: cells attach and squish
- gap junctions: create channels between cells. Communication
- tight junctions: pull cells together, create and outer "shell" around embryo
49
What results in blastocyst formation?
pumping ions into the center of the embryo
50
what cells will form the placenta in the future?
trophoblasts
51
what cells will form the embryo in the future?
intracellular mass (ICM)
52
In humans, when are embryos transferred? (IVF and ICSI)
During the 4-cell, 8-cell, morula
53
In cattle, when are embryos transferred?
Once the cell becomes a blastocyst
54
How many embryos should be transferred?
Women with high fertility, 1 embryo
3 embryos max
55
Hatching
embryo sheds the zona pellucida
56
Gastrulation
this is when the ICM differentiates further
57
Epiblast
embryo proper
58
hypoblast-> yolk sac
forms primitive blood
circulates nutrients in early embryo
source of PGC's
59
Three types of epiblasts
Ectoderm: skin, neurons
Mesoderm: muscle, RBC
Endoderm: GI tract, lungs
60
Embryo shapes
spherical or elongated
61
species that have an elongated conceptus
sheep
cow
pig
62
species that have a spherical conceptus
horse
human
63
the uterus is lined with?
secretory epithelium
64
Preimplantation embryos are dependent on what?
Histotroph: secretions epithelium lining the oviduct and uterus that contain growth factors and nutrients necessary for implantation growth
65
Growth factors
proteins that help regulate embryo development
66
Nutrients
only source of nutrients available to support embryo development
67
Preimplantation has to alter female to its presence
embryo must stop luteolysis
- maternal recognition of pregnancy
68
Placenta forms...
exchanges nutrients and wastes with maternal circulation
69
Maternal recognition of pregnancy
the requirement for the conceptus to produce a hormone that acts on the uterus and or CL to ensure maintenance of a functional CL
70
the luteal phase prepared the body for...
potential pregnancy
71
Luteolysis is triggered by PGF 2a in these species
sheep, horse, cow, pig
72
How does PGF2a effect livestock?
1. PGF2a is produced by the uterus and enters through the uterine vein
2. PGF2a is transferred to ovarian artery via counter exchange
3. sufficient PGF2 a reaches ovary to trigger luteolysis
73
MRP in sheep and cows
1. embryo produce interferon T (no effect directly on ovary)
2. Interferon T blocks expression of oxytocin receptor in endometrium
3. lack of oxytocin signaling. prevents PGF2a production
4. without PGF2a CL remains functional
74
what is thought to be a major cause of pregnancy loss?
Luteolysis
- elongated conceptus necessary to prevent luteolysis in ovary
- preventing PGF2a production is inhibited in both horns
- insufficient elongation may contribute to pregnancy loss
75
MRP in pigs
1. embryo produces estradiol
2. estradiol redirects PGF2a secretions of uterine vein to uterine lumen
3. without reaching the blood PGF2a cannot reach the ovary
4. if PGF2a doesn't reach the blood, CL will remain functional
76
What is required for MRP?
sufficient embryos and spacing
- estradiol contributes to embryo spacing
- embryos in both uterine horns protect CL in both ovaries
- requires min 2 embryos per horn to prevent luteolysis
77
MRP in horses
horse embryo moves from horn to horn
about 12 times per day to prevent PGF2a in both horns
78
Human CL produces PGF2a
- cl makes small amounts
- PGF2a acts locally to cause regression of CL
79
The embryo produces a lot of ___ during early pregnancy
hCG
- embryo produces a lot during first trimester
- hCG binds to LH receptor
- continues to stimulate progesterone production
- prevents luteolysis
