gamete interaction Flashcards
when does the semen coagulate?
rapidly during or immediately after deposition
the coagulation of semen may become…
gelinatous (human, pig, horse)
fibrous (guinae pig)
cancerous (mouse)
how does the semen coagulate in humans?
enzymes from the prostate interact with fibrinogen like substrates derived from the seminal vesicle.
why does coagulation of semen happen?
to retain spermatozoa in the vagina or buffer it against the hostile acidity of the vaginal fluids
how long does it take for the coagulum to dissolve in the female tract?
20- 60 minutes
what percentage of sperm does not enter the cervix?
99%
how long for and where are the sperm stored in the cervix?
humans 3-4 days
mice 0.5-1 days
deep in the cervical crypts of the mucus membrane
what are the sperm nourished by in the cervix?
mucoid secretions
what does the profession of the sperm to the uterus depend on?
the absence of progesterone domination (only in the absence does the mucus permit sperm penetration)
abnormal sperm are prevented from passing further up the reproductive tract
in humans what aids sperm movement through the uterus?
probably aided and directed by peristaltic contractions
how do the sperm travel across the uterotubule junction and enter the oviduct?
by their own propulsion
however the uterotubal junction regulated entry to the oviduct by its action as an intermitted sphincter
what happens when the sperm reach the isthmus of the oviduct ?
they linger and bind temporarily to oviductal epithelial cells.
what happens as a result of the sperm binding to the oviductal epithelial cells ?
the oviductal cells are stimulated secrete factors that serve to maintain the stored sperm in a viable state.
when do the sperm detach from the oviductal epithelial cells? where do they swim?
only at ovulation
they swim to the ampillary isthmus junction at the site of fertilisation
in vitro studies suggest that this process may depend on the release of chemo-attractants by both the oocyte and the cumulus mass.
what is the process called when sperm gain full fertilising capacity?
Capacitation
what are two characteristics a fully capacitated sperm can be distinguished by?
1) hyperactive motility -> the flagellar beats are stronger with a wider amplitude or whiplash beats.
2) A change in surface membrane proteins that leave the sperm responsive to signals encountered when close to the oocyte.
What changes are needed for a sperm to be a full capacitated state?
- oestrogen primed uterus/oviductal isthmus
- critical features of secretions of female reproductive tract (proteolytic enzymes, cholesterol binding sinks, higher ionic strength compared with seminal plasma)
- when ejaculate is exposed to atmospheric oxygen, reactive oxygen species form and stimulate the production of H2O2 a potent capacitating agent.
what is a physiological changes in the sperm during the process of capacitation?
stripping from and/ or modification of many of the glycoproteins that coat the sperm surface during passage through the epididymis and in the seminal plasma. (associated with change to the surface charge and macromolecular organization and lipid structure of the sperm membrane, especially loss of cholesterol.
What are the first steps of capacitation?
Where may they commence?
What are they followed by?
removal of glycoproteins and cholesterol efflux
may commence in the cervix
followed by an increased pH and calcium entry, generation of cAMP, activation of protein kinase A and the phosphorylation of tyrosines on a number of proteins
which part of the oviduct helps to stabilise the capacitated sperm?
the isthmic region
when does the sperm move to the ampullary-isthmic junction?
when an egg has been ovulated
what does the sperm need to penetrate before contact with the oocyte can occur?
zona pellucida
cumulus of granulose cells
what is hyaluronidase?
it is the enzyme that digests the matrix of the cumulus cells causing them to fall apart.
the sperm acrosome is a rich source of hyaluronidase
what happens during the acrosome reaction?
the acrosome swells
its membrane fuses with the overlong plasma membrane
a vesiculated appearance is created
the contents of the acrosomal vesicle and the inner acrosomal membrane both become exteriorised in a process of exocytosis
what is the terminal phase of capacitation?
acrosome reaction
what is located on the inner acrosmal membrane which digest a path through the zona pellucida?
proteolytic enzymes such as across
(a path with the acrosome reacted sperm pass through aided by the whiplash forward propulsion of the hyper activated tail)
how long does penetration on the zona take?
between 5 and 20 minuted
why is it though to be important that the acrosome reaction occurs close to the oocyte?
because acrosome reacted sperm have a very short life span
what is between the zona pellucida and the oocyte membrane?
perivitelline space
what is the oocyte membrane called?
oolema
where do the sperm lie after penetrating the zona pellucida?
perivitelline space
what happens to sperm once fusion has occurred?
they stop moving
its nucleus passes into the ooplasm
what chemical change happens in the oocyte after fusion?
1-5 minutes after fusion there is a dramatic increase in the level of intracellular calcium in the egg (due largely to the relates of calcium from internal stores.
how long does the first calcium rise in the egg last for?
2-3 minutes
what happens to calcium levels after the initial rise?
calcium spikes every 3-15 minutes for several hours
how is calcium release in the egg activated?
through a sperm enzyme passing into the oocyte after fusion . (spermatozoal-specific phospholipase zeta)
after fusion what is the sperm and oocyte called?
zygote
what four transitions must the penetrated oocyte undergo for the successful completion of fertilization?
1) diploidy
2) cytoplasmic constitution of the oocyte is secured
3) syngamy
4) developmental programme is initiated
what does diploidy require?
- only one haploid sperm to fertilise the egg
(or if two did it would cause triploidy) - the oocyte to complete the second meiotic division dispatching one set of chromosomes to the second polar body.
what happens if the oocyte fails to complete second meiotic devision?
gynogenetic triploidy
what chemical change plays a key role in achieving diploidy?
calcium pulsations resulting from gamete fusion.
What does elevated calcium do to the zygotic subcortical cortical granules?
mobilisation and fusion of them
fusion leads to the release of their contents into the perivitelline space (the cortical reaction).
what is in the contents of the zygote cortical granules?
enzymes which act on the zona pellucida to preventer impair the further binding and penetration by sperm (the zona reaction)
they remove spermatozoal-binding properties
what does the arrest of oocytes in the second meiotic metaphase depend on?
the balance of maturation promoting factor (MPF) and the cytostatic factor (CSF).
MPF stabilises m-phase and sin turn stabilised by CSFD
does the centriole come from the sperm or egg?
sperm
what makes up the centrosome
centriole (comes from sperm) pericentriolar material (sperm and egg contribute)
what does the centrosome play a role in regulating?
karyokinesis and cytokinesis at mitosis
without it early development is compromised and eventually fails
what does the oocyte provide to the zygote?
cell membrane, cytoplasm, cell organelles and macromolecular matrix in which the two sets of chromosomes operate (the maternal cytoplasmic inheritence)
what happens to the contents of the sperm cell membrane during fusion?
the pass into the oocyte cytoplasm
the nuclear membrane breaks down and the highly condensed chromatin swell, releasing filamentous strands of chromatin into the cytoplasm.
what happens between 4 and 7 hours after fusion?
the two sets of haploid chromosomes each become surrounded by distinct membranes and are now known as pronuclei.
when does the first mitotic devision occur
18-24 hours after gamete fusion
what happens when syngamy occurs
the pronuclear membranes around the reduplicated sets of parental chromosomes break down, the mitotic metaphase spiel forms and the chromosome assume their position at its equator.
what is syngamy
coming together of the gametic chromosomes
what happens after syngamy occurs?
the first mitotic anaphase and telophase are completed, the cleavage furrow forms and the one cell zygote becomes a two cell conceptus
what is aneuploidy?
abnormal number of chromosomes
what happens if aneuploidy occurs?
embryonic abnormality and loss in most
hydatidiform mole (a benign trophoblastic tumour)
choriocarcinoma (malignant derivative of hydaitiform mole
what two things are responsible for sperm transport in the FRT?
sperm motility and female reproductive tract movement
when was capacitation first discovered and who by?
1950
chang and austin
what are extracellular vesicles
spherical particles enclosed by a phospholipid biller and have a diameter ranging from 30nm up t 5um
what are the extracellular vesicle subtypes?
exosomes
microvesicles
membrane particles
apoptotic vesicles
what two types of signals is the peri-conception environment modulated by?
short rage signals (local responses to gametes and embryos)
long rage signals (environmental factors, nutrition and hormonal status)
why is it important to study maternal communication with gametes and embryos? (preconception environment)
- improve efficiency of modern livestock production
- promote embryo production
- improve implantation and maintenance of pregnancy
- improve artificial insemination practice
- improving genetic selection for fertilities
- improving offspring health and welfare
