fertilisation and contraception

Question 1

Where does fertilisation occur

Answer 1

Ampulla (most dilated area of Fallopian tube)

Question 2

What re granulose cells in oocyte suspended in and what does it produce

Answer 2

Hyaluron rich matrix - produces progesterone and chemo-attractants

Question 3

How many chromosomes does the secondary oocyte have

Answer 3

23 (haploid)

Question 4

How does the secondary oocyte obtain nutrients

Answer 4

From cytoplasm

Question 5

What acts as a protective shell of oocyte

Answer 5

ZOna pellucida

Question 6

Features of the plasma membrane of sperm head

-what can it secrete

Answer 6

Odorant receptors can react to chemo-attractants from oocyte

3 surface binding molecules- ADAM (a disintegrin and metalloproteinase domain) family; Fertilin alpha, beta and cyritestin

Can secrete Hyaluronidase

Question 7

Acrosome of sperm

Answer 7

Surrounds head and contains the enzyme acrosin

Question 8

What do the sperm have ti undergo to attain full fertilisation capacity

Answer 8

Capacitation

Question 9

What happens when sperm gets to isthmus of Fallopian tube

Answer 9

Waits for egg to be released into the ampulla and send out chemoattractins so the sperm can swim to it

Question 10

What is capacitation

Answer 10

1) Changes in movement characteristics

2) Changes in spermatozoal surface by stripping of glycoproteins

Question 11

How is movement changed in capacitation

Answer 11

regular wave like (from vagina to oviduct) changes to wide amplitude whiplash beats needed to swim upstream from isthmus to ampulla

Question 12

What direction do ciliated cells of oviduct flow and why

Answer 12

Against the sperm so sperm has to swim against the tie. This introduces selective pressure

Question 13

What changes are there in spermatozoal surface in capacitation

Answer 13

• Changes in surface charge, macromolecular organisation, loss of cholesterol
• Reduced stability of plasma membrane and enhances fusibility
• Increased permeability to calcium

Question 14

How does penetration of the corona radiate occur

Answer 14

Secretion of hyaluronidase

Digestion of extra cellular matrix

Active movement to reach zona pellucida

Question 15

How does sperm attach to zona pellucida

Answer 15

Receptors for ZP proteins (ZP2R and zP3R) are present on different membrane components of the spermatozoa

the receptor for ZP3, ZP3R is on the surface of the sperm head

the receptor for ZP2, ZP2r, is on the inner acromosal membrane

Question 16

Where is the receptor for ZP3, ZP3R

Answer 16

surface of sperm head

Question 17

where isreceptor for ZP2, ZP2r

Answer 17

inner acromosal membrane

Question 18

What does binding of ZP3 to its receptor on sperm head plasma membrane lead to

Answer 18

Calcium influx which causes depolymerization of the F-actin present between the acrosome and sperm-head plasma membrane. Acrosome now has room to expand and does so.
Increased calcium also leads to  cAMP and increase in pH

Question 19

Consequence of acrosome binding

Answer 19

1. Acrosome swelling
2. Acrosome fusion with overlying surface plasma membrane. Gives a vesiculated appearance.
3. Exteriorisation of contents and inner acrosomal membrane (IAM) by exocytosis. to outside. This leads to exposure of inner ZP2 receptor.
4. The revealed ZP2 Receptor on inner acrosomal membrane can now bind to ZP2 on zona pellucida.
5. Mechanical propulsion along ZP2 filaments until oocyte plasma membrane surface is reached
6. Release of acrosin aids digestion of a pathway through the zona pellucida

Question 20

How does the intern layout of the oocyte prevent triploidy

Answer 20

Specific areas on egg surface are rich in interns to allow binding in correct areas

Question 21

What happens post fusion

Answer 21

. At fertilisation, the oocyte is still arrested in second meiotic metaphase (M phase).

2. A rise in Ca++ after fusion leads to exit from M phase.
3. One set of chromosomes is dispatched as the 2nd polar body
4. The other half set of 23 unpaired chromosomes remain behind in the female pronucleus and can unite with the 23 paternal chromosomes of the penetrating sperm

Question 22

How Is gynogenetic triploidy avoided

Answer 22

Dispatching the second polar body

Question 23

What is another way that triploidy can happen

How can this be avoided

Answer 23

If the exiting second polar body encounters the entering sperm there can be interference and all 3 haploid sets of chromosomes remain inside, this results in fetal death

Spermatozoa do not bind to oocyte membrane immediately overlying the second metaphase spindle. (This region doesn’t have binding proteins like integrins, CD9, and of microvilli).
This ensures avoidance of encounter between the exiting second polar body and the entering spermatozoa

Question 24

How is polyspermy/ androgenetic triploidy avoided

Answer 24

Changes in electrical activity of zygote leads to Ca2+ wave from point of sperm entry . There are Ca2+ spikes.

this leads to cortical reaction which is release of cortical granules into perivitelline space. enzymes cleaves ZP2 and hydrolyses binding region of ZP3 so ZP2 and 3 are no t available anymore for more sperm binding

Question 25

What does sperm contribute to in cytoplasmic inheritance

Answer 25

Centriole- essential for Karyo- and cytokinesis

Question 26

What does the oocyte contribute to cytoplasmic inheritance

Answer 26

Cell membrane, cytoplasm, cell organelles and mitochondria (maternal cytoplasmic inheritance)

Question 27

how does silencing of gene occur

Answer 27

Through addition of methyl groups

Question 28

How does the combined oral contraceptive pill work

Answer 28

Oestrogen: inhibits FSH release and therefore development of follicle

Progesterone: inhibits LH release, prevents ovulation, alters cervical mucus, motility in Fallopian tube