Conception Flashcards
gametes
What is a similarity between the ovum and spermatozoa?
They are both haploid cells (contain 23 chromosomes)
Fertilisation
At ovulation, why does the cervical mucus change consistency?
To allow easier sperm transport
fertilisation
What do fimbriae do when the ends of the uterine tube ocme into close contat with the ovary during ovulation?
Fimbriae ”sweep” the ovulated ovum into the fallopian tube
Gamete transport - Spermatozoa
Outline the 2 steps of Gamete transport for spermatozoa
think uterine tube and epithelial cells, for first step
for second step, think ovulation, ampullary-isthmic junction and chemoattractants
- spermatozoa enter uterine tube and “wait” for oocyte (become immotile and temporarily bind to epithelial cells
- After ovulation occurs, spermatozoa become active again, and travel to ampullary-isthmic junction once there is chemoattractant release by the oocyte.
capacitation - Preparing the spermatozoa
True or False? Newly ejaculated spermatozoa can fertilise an ovum.
Briefly Justify your answer
False, newly ejaculated spermatozoa cannot fertilise ovum because capacitation has not occurred yet
capacitation - preparing the spermatozoa
What is capacitation?
When glycoproteins are removed from plasma membrane of the head of sperm cell
capacitation - Preparing the spermatozoa
how long does capacitation take?
5-7 hours
Capacitation - preparing the spermatozoa
What does the increased cytoplasmic pH in ovum and sperm due to the capacitation of spermatozoa lead to and when does capacitation occur?
think calcium permeability and motility for first part
for second part think tubes
- Leads to increased calcium permeability of sperm and egg cells, increasing motility of sperm cell
- occurs when sperm enter uterine tube
capacitation - preparing the sperm
Give a reason why capcitated sperm can pass through the corona radiata cells surrounding the oocyte
think motility, strength and amplitude
capacitated sperm have hyperactived motility, which increases strength and amplitude of flagellar (tail) beats (movement)
Fertilisation - Stage 1
What are the 3 steps in Phase 1 of fertilisation?
think penetration of surface of oocyte and name this surface
for step 1 think flagella action, release of enzymes and what form they are released in.
for step 2, think what happens in the acrosome of the sperm when it comes in contact with a specific layer (“zone” layer) of the oocyte
for step 3, think enzymes in the acrosome that are exposed and what happens to them and waht they do to the oocyte.
Penetration of Corona Radiata and zona pellucida:
- Flagellar action and release of enzymes form acrosome aids corona radiata penetration
- Chemical changes occur in the acrosome of the spermatozoa when it comes into contact with the Zona pellucida of the oocyte (Acrosomal reaction)
- Hyaluronidase enzymes in acrosome are exposed and then release from the sperm, digesting the extracellular matrix around the corona radiata cells
Fertilisation - Stage 1
What ligand faciliatates binding of sperm and the acrosomal reaction?
ZP3
Fertilisation - Stage 2
what happens in phase 2 of fertilisation?
think about the type of reaction, what increased calcium levels cause and what 2 things this leads to
- cortical reaction occurs
- increased calcium levels causes cortical granules in oocyte to fuse with oocyte membrane and release their contents
- this does 2 things:
- enzymes destroy ZP receptors
- zona becomes non-dissolvable by proteolytic enzyme
fertilisation - Stage 2
what do the cortical granules in oocytes fusing with the oocyte membrane prevent?
prevents polyspermy
(dispermy = 2)
(triploidy = 3)
fertilisation stage 2
what is the cortical reaction
think cortical vesicles and what they are released by
release of cortical vesicles from oocyte plasma membrane after fusion
fertilisation stage 3
waht happens in phase 3 of fertilisation
for first step, think what in the sperm enters the cytoplasm of the oocyte and what remains on the surface of the oocyte
for the second step, think about what the oocyte was “arrested” in and what it immediately does after the entry of sperm cell and then what 2 things this then forms.
- head and tail of sperm enter the cytoplasm of oocyte, while plasma membrane of sperm cell remains on oocyte surface
- oocyte that was arrested in metaphase of 2nd meiotic division immediately completes meiosis after entry of sperm cell to form mature oocyte and 2nd polar body
fertilisation stage 4
outline the final stage of fetilisation
for step 1, think pronuclei and what they contain and what they are compared to one another
for step 2, think what on the pronuclei break down, and what happens to chromosomes after
for step 3, think about how fertilisation is complete and what the pronuclei form as a result
- Two pronuclei each contain 23 chromosomes (haploid) and are indistinguishable
- membranes of pronuclei break down and chromosomes become arranged from mitotic cell division (first cleavage division)
- fertilisation is complete when pronuclei fuse, forming a Zygote
results of fertilisation
what are the results of fertilisation?
think chromosome number
think sex of individual
think cleavage
- restoration of diploid chromosome number (46)
- Determination of chromosomal sex of new individual (XX or XY)
- initiation of cell cleavage
initiation of cell cleavage
How does the zygote divide to form smaller cells and what are these known as?
- divides via mitosis
- known as blastomeres
initiation of cell cleavage
What are blastomeres and what do they have the potential to form?
think stem cells for first part
for second part think embryo
- Topipotent stem cells (can become any embryonic cell tissue)
- Have potential to form an entire embryo
initiation of cell cleavage
When do blastomeres become compacted?
At the 8 cell stage (when there are 8 blastomeres)
formation of the blastocyst
how is a blastocyst formed?
Aroud day 4, morula (16 cell stage) becomes a blastocyst when a blastocele (fluid-filled cavity) forms.
formation of the blastocyst
what are the 2 separate groups of cells in a blastocyst and what do each form
think embryo cell mass and what this will form for first group
think tropism and waht this will form for the second group
Inner cell mass/embryoblast:
- forms embryo
outer cell mass/ trophoblast:
- forms placenta
formation of the blastocyst
what happens to the blastocyst at day 6 of embryonic life and what does this mean for implantation
think what blastocyst loses and what this means for implantaton and where it would implant
- Blastocyst loses its zona pellucida, meaning it can now implant on the uterine endometrium
first week of embryonic life
When is a zygote called an embryo?
when it has undergone mitosis to form 2 smaller cells after fertilisation is complete