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30 Cards in this Set
- Front
- Back
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Where is the site of ejaculation in different species?
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Vagina - ruminants, humans, rabbits
Cervix - horse, dog, pig, rodents |
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What happens to the sperm once it enters the uterine tube?
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Binds to epithelium in caudal part of isthmus - can preserve its fertility for 2 days or more
Once ovulation has occured, sperm travels up to meet oocyte in ampulla |
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How long is an oocyte viable for after ovulation?
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6-24 hours
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How is a large percentage of sperm lost before meeting the oocyte?
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Physical stress (ejaculation and female contractions)
Oxidative damage Female immune system (mucus, macrophages) |
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Where does sperm undergo capacitation reaction?
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In isthmus region, decapacitation factors are removed
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What is the mechanism behind sperm capacitation?
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Influx of calcium -> increase in cAMP and pH
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What are the effects of capacitation?
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Increase in cytoplasmic enzyme activity
Changes to plasma and acrosome membrane Hyperactivation of flagellum |
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What is the acrosome?
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Cap-like structure from Golgi apparatus that contains digestive enzymes
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What is involved in the acrosome reaction?
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Fusion of plasma membrane to acrosome membrane and release of acrosome enzymes
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Describe what happens in the first stage of fertilisation
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Sperm bind to zp3 (zona pellucida protein)
Outer acrosome membrane is lost, inner membrane binds to zp2 protein Acrosome enzymes begin to break down zona pellucida |
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What is the next stage?
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Sperm binds to oocyte membrane and enters oocyte cytoplasm
Calcium is released from intracellular oocyte stores in pulsatile manner |
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What do calcium oscillations result in?
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Formation of pronuclei - decondensation and expansion of nuclei
Resumption of oocyte meiosis Cortical reaction - fusion of cortical granules to oocyte membrane -> release of contents into perivitelline region -> modifies zona pellucida -> prevents acrosome reaction by other sperm |
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What is the final step of fertilisation?
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Breakdown of each pronucleus membrane during metaphase of first mitotic division -> diploid cell
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What is the resumption of meiosis called?
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Germinal vesicle breakdown
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What is it caused by?
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LH surge
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Which stage does it resume from?
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Prophase 1 - primary oocyte - 4N
Arrested again at metaphase 2 - secondary oocyte -2N |
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What happens at metaphase 2 stage and the last stage of meiosis?
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Two polar bodies are discarded
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Which stage of oocyte is ovulated?
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Secondary oocyte - 2N
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After hatching, what does the blastocyst need to do?
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Find enough uterine space for adequate nutrition
Signal the uterus not to produce PGF2a -> luteolysis |
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How are these achieved?
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Blastocyst migration and/or elongation
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In which species does migration and/or elongation occur?
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Migration - horse, dog and pig
Elongation - cow, sheep and pig |
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Describe the embryo development in the horse
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Before hatching, glycoprotein layer between trophoblast and zona pellucida forms called the capsule
At day 15, increased size of embryo restricts embryo's movement, fixation occurs and attachment initiation |
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What is the function of the capsule?
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Protects the embryo from mechanical pressure by uterine contractions
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What is formed at day 35 of pregnancy?
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Endometrial cups in placenta which secrete eCG
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What is histotroph?
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Secreted from uterine glands in response to progesterone:
Provides nutrients for embryo Factors for embryo attachment Antibacterials |
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How does the embryo prevent luteolysis?
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Secretes anti-luteolysins
In humans, CL rescued by high levels of chorionic gonadotropin |
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Describe the antiluteolytic mechanism in ruminants
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IFN-T:
Stabilizes progesterone receptor Downregulates oestrogen receptors Inhibits PG synthesis Synthesises PGE2 - luteotropic |
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Describe the antiluteolytic mechanism in pigs
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Embryonic oestrogen:
Changes PGF2a to exocrine from endocrine which stops it from reaching ovary Synthesises PGE2 - luteotropic |
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Describe the antiluteolytic mechanism in horses
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Also blocks PGF2 synthesis
Has to be blocked from two uterine horns - high embryonic motility |
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How is the paternal antigen of the embryo accepted by the mother?
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Embryonic antigenicty reduced - restricted antigen expression in placenta - antigen binds to pregnancy-associated glycoproteins
Placental and endometrial factors inhibit lymphocyte proliferation |
