Conception

Question 1

gametes

What is a similarity between the ovum and spermatozoa?

Answer 1

They are both haploid cells (contain 23 chromosomes)

Question 1

Fertilisation

At ovulation, why does the cervical mucus change consistency?

Answer 1

To allow easier sperm transport

Question 2

fertilisation

What do fimbriae do when the ends of the uterine tube ocme into close contat with the ovary during ovulation?

Answer 2

Fimbriae ”sweep” the ovulated ovum into the fallopian tube

Question 3

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

Answer 3

1. spermatozoa enter uterine tube and “wait” for oocyte (become immotile and temporarily bind to epithelial cells
2. After ovulation occurs, spermatozoa become active again, and travel to ampullary-isthmic junction once there is chemoattractant release by the oocyte.

Question 4

capacitation - Preparing the spermatozoa

True or False? Newly ejaculated spermatozoa can fertilise an ovum.

Briefly Justify your answer

Answer 4

False, newly ejaculated spermatozoa cannot fertilise ovum because capacitation has not occurred yet

Question 5

capacitation - preparing the spermatozoa

What is capacitation?

Answer 5

When glycoproteins are removed from plasma membrane of the head of sperm cell

Question 6

capacitation - Preparing the spermatozoa

how long does capacitation take?

Answer 6

5-7 hours

Question 7

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

Answer 7

• Leads to increased calcium permeability of sperm and egg cells, increasing motility of sperm cell
• occurs when sperm enter uterine tube

Question 8

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

Answer 8

capacitated sperm have hyperactived motility, which increases strength and amplitude of flagellar (tail) beats (movement)

Question 9

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.

Answer 9

Penetration of Corona Radiata and zona pellucida:

1. Flagellar action and release of enzymes form acrosome aids corona radiata penetration
2. Chemical changes occur in the acrosome of the spermatozoa when it comes into contact with the Zona pellucida of the oocyte (Acrosomal reaction)
3. Hyaluronidase enzymes in acrosome are exposed and then release from the sperm, digesting the extracellular matrix around the corona radiata cells

Question 10

Fertilisation - Stage 1

What ligand faciliatates binding of sperm and the acrosomal reaction?

Answer 10

ZP3

Question 11

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

Answer 11

1. cortical reaction occurs
2. increased calcium levels causes cortical granules in oocyte to fuse with oocyte membrane and release their contents
3. this does 2 things:
   - enzymes destroy ZP receptors
   - zona becomes non-dissolvable by proteolytic enzyme

Question 12

fertilisation - Stage 2

what do the cortical granules in oocytes fusing with the oocyte membrane prevent?

Answer 12

prevents polyspermy
(dispermy = 2)
(triploidy = 3)

Question 13

fertilisation stage 2

what is the cortical reaction

think cortical vesicles and what they are released by

Answer 13

release of cortical vesicles from oocyte plasma membrane after fusion

Question 14

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.

Answer 14

1. head and tail of sperm enter the cytoplasm of oocyte, while plasma membrane of sperm cell remains on oocyte surface
2. 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

Question 15

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

Answer 15

1. Two pronuclei each contain 23 chromosomes (haploid) and are indistinguishable
2. membranes of pronuclei break down and chromosomes become arranged from mitotic cell division (first cleavage division)
3. fertilisation is complete when pronuclei fuse, forming a Zygote

Question 16

results of fertilisation

what are the results of fertilisation?

think chromosome number

think sex of individual

think cleavage

Answer 16

• restoration of diploid chromosome number (46)
• Determination of chromosomal sex of new individual (XX or XY)
• initiation of cell cleavage

Question 17

initiation of cell cleavage

How does the zygote divide to form smaller cells and what are these known as?

Answer 17

• divides via mitosis
• known as blastomeres

Question 18

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

Answer 18

• Topipotent stem cells (can become any embryonic cell tissue)
• Have potential to form an entire embryo

Question 19

initiation of cell cleavage

When do blastomeres become compacted?

Answer 19

At the 8 cell stage (when there are 8 blastomeres)

Question 20

formation of the blastocyst

how is a blastocyst formed?

Answer 20

Aroud day 4, morula (16 cell stage) becomes a blastocyst when a blastocele (fluid-filled cavity) forms.

Question 21

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

Answer 21

Inner cell mass/embryoblast:
- forms embryo

outer cell mass/ trophoblast:
- forms placenta

Question 22

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

Answer 22

• Blastocyst loses its zona pellucida, meaning it can now implant on the uterine endometrium

Question 23

first week of embryonic life

When is a zygote called an embryo?

Answer 23

when it has undergone mitosis to form 2 smaller cells after fertilisation is complete