Fertilization and Embryo Development Flashcards
What species have sperm deposition in the uterus?
Rodents, dog, pig, horse
What species have sperm deposition in the cervix?
Cat and pig
What species have sperm deposition in the vagina?
Cat, rabbit, sheep, cattle, human
What is the shift of pH in the upper vagina once sperm is deposited?
4.3-> 7.2 in 10 seconds
What is deposited in the upper vagina during copulation?
Seminal fluid
What is the purpose of seminal fluid?
Its composition and buffering capability protect spermatozoa from the acidity of the upper vagina
How long does the buffering effect last in the reproductive tract, and what is its significance?
The buffering effect lasts only a few minutes, which is enough for sperm to approach the cervix in a pH range of 6 to 6.5, optimal for sperm motility.
What role does the cervix play in spermatozoal transport?
The cervix is a major barrier to spermatozoal transport and serves as a spermatozoal reservoir.
What happens to mucus production in the cervix during estrus?
Copious mucus is produced under the influence of estrogen, regulating the transport of spermatozoa.
How does the composition and viscosity of cervical mucus change?
It varies throughout the menstrual cycle; during days 9-16, its water content increases, facilitating sperm passage at ovulation.
3 functions of the cervix
a) it is receptive to sperm penetration and inhibits sperm migration during other phases of estrus cycle
b) It protects sperm from hostile environment in the vagina
c) it filters defective and immotile spermatozoa
What are the two types of sperm transport?
Rapid transport
Slow release and transport
What occurs immediately after insemination/ejaculation regarding sperm transport?
Spermatozoa penetrate the cervical mucus and some are quickly transported through the cervical canal to the uterine tubes within one hour of ejaculation
What facilitates the rapid transport of spermatozoa?
Muscular movements of the female reproductive tract.
Is it clear whether the first spermatozoa entering the oviduct participate in fertilization?
It is still unclear whether the first spermatozoa entering the oviduct participate in the fertilization of the ovum.
What is the swimming speed of spermatozoa through cervical mucus?
Spermatozoa swim through cervical mucus at a rate of 2-3 mm/hr.
How are spermatozoa stored and released in the cervix?
They are stored in cervical crypts and released sequentially for a prolonged period, allowing passage through the cervical canal for as long as 3-4 days after ejaculation.
What is the significance of slow sperm release from the cervix?
It ensures the continued availability of spermatozoa for entry into the oviduct to effect fertilization.
What is the role of anatomical and physiological barriers in the female reproductive tract?
They help prevent polyspermy
Where does fertilization usually occur?
Ampullary part of the uterine tube
What is fertilization?
Series of processes beginning with the spermatozoa penetrating the corona radiata and ending with the intermingling of maternal and paternal chromosomes after the spermatozoon entered the egg
How many spermatozoa typically surround the corona radiata?
12
What enzyme from the sperm head might assist in penetrating the corona radiata?
Hyaluronidase, emanating from the acrosome of the sperm head.
What role does sperm motility play in relation to the corona radiata?
Major role in penetration of the corona radiata
What is the primary function of the zona pellucida regarding sperm entry?
It allows only sperm of the same species to enter the egg.
What happens to sperm entry after fertilization?
The zona pellucida prevents any other spermatozoon from entering the egg.
What does the zona pellucida act as during the first cleavage divisions?
It acts as a filter, allowing substances from the uterine tubes to enter the egg.
What part of the oocyte plays a role in preventing premature implantation?
zona pellucida
What is the acrosomal reaction?
It is the orderly fusion of the spermatozoal plasma membrane and the outer acrosomal membrane
What is released during the acrosomal reaction that aids in penetrating the zona pellucida?
Acrosomal enzymes (Hyaluronidase and acrosin) that allow the spermatozoon to digest its way through the zona pellucida.
Where is the trigger for the acrosome reaction in several species?
zona pellucida
What is the state of the membranes of the sperm head before the acrosomal reaction?
All membranes of the head are intact
What occurs during the acrosomal reaction regarding the membranes?
The plasma membrane begins to fuse with the outer acrosomal membrane, creating pores
What is the significance of the pores created during the acrosomal reaction?
They allow acrosomal enzymes to pass through, enabling sperm to penetrate the zona pellucida
What remains intact after the acrosomal reaction?
The inner acrosomal membrane and nuclear cap remain intact, while vesicles are sloughed off
What happens when sperm completely penetrates the zona pellucida?
The sperm reaches the perivitelline space, and cortical granules migrate to the periphery of the oocyte
What occurs when the plasma membrane of the oocyte fuses with the sperm?
The plasma membrane fuses with the equatorial segment, and the fertilizing sperm is engulfed
What happens to the cortical granules during fertilization?
Cortical granules are released into the perivitelline space
What occurs after the fusion of the oocyte’s plasma membrane with the sperm’s equatorial segment?
The sperm nuclear membrane disappears, and the nucleus of the sperm decondenses
What must happen once sperm-egg fusion occurs?
entry of other
spermatozoa into the egg must be avoided to prevent
abnormal development
What happens during the fast block?
Rapid depolarization of the egg
plasma membrane.
*Occurs 2-3 seconds after fusion
What happens during the slow block?
Its the cortical reaction
Granules fuse with the PM of the oocyte, release content that eats all ZP protein on ZP so it kills the receptor which prevents any more sperm from entering
What happens after sperm-egg fusion regarding calcium?
There is a propagation of a Ca²⁺ wave from the site of sperm-egg fusion
What occurs when cortical granules fuse with the plasma membrane?
They release hydrolytic enzymes and polysaccharides into the perivitelline space
What is the effect of the contents of cortical granules on sperm receptors?
The contents hydrolyze the sperm receptor molecules in the zona, creating the “zona block.”
What is the first event that occurs ~ 24 hours after fertilization?
Cleavage
What is cleavage in embryonic development?
Rapid cell divisions that convert the unicellular zygote into a multicellular embryo.
How does the timing of cell divisions in cleavage affect the embryo?
The divisions are not synchronous, leading to embryos with an odd number of cells.
How long does it typically take between each cell division during cleavage?
Approximately 12-24 hours
What is the total size of the embryo during cleavage?
The total embryo size remains approximately 0.1 mm in diameter.
How does the number of cells in the embryo change during cleavage?
It increases exponentially
What characterizes the initial divisions of the zygote?
Rapid mitotic divisions with no growth phases.
What are the resulting daughter cells from the cleavage called?
Blastomeres
How does the size of blastomeres change with each division?
Blastomeres become smaller with each division since there is no overall growth
What stage is reached with blastomeres up to 8 cells? When is it important?
They are totipotent, which is important in twinning
What occurs when a cavity appears within the morula?
It converts the morula into a cystic structure called the blastocyst.
what happenes to the arrangement of cells in a blastocyst/what layers do they form?
- Inner mass (embryoblast) which will form all the tissues of the embryo
- Outer layer called trophoblast which invade the uterine wall
What is the inner cell mass of the blastocyst called?
Embryoblast
What is the outer cell mass of the blastocyst called?
Trophoblast
What does the trophoblast contribute to?
It becomes the fetal contribution to the placenta.
What are the two poles of the blastocyst?
Embryonic pole and abembryonic pole.
Where is the inner cell mass located in relation to the blastocyst?
The inner cell mass is located at the embryonic pole.
When does blastocyst hatching occur?
Just before implantation
What are some reasons for not hatching that can lead to infertility?
-Altered ZP
-Absense of proteases
-Embryos lacking ZP protein leading to premature hatching
How does the embryo break through the zona pellucida (ZP)?
It breaks through due to proteases secreted by the blastocyst
3 steps in preimplantation embryo development?
-Translation of maternal mRNA transcripts
-Activation of embryonic transcription
-Morphogenetic events
What point should all embryos reach post fertilization?
At least reach the 8-cell stage
