Fertilization

Question 1

What is fertilization?

Answer 1

The fusion of male and female gametes

Question 2

What percentage of sperm deposited in the vagina enter the cervix

Answer 2

1%

Question 3

How is movement of sperm from the cervix to the oviduct achieved?

Answer 3

Movement of sperm from the cervix to the oviduct is achieved mainly by their own propulsion, but may be assisted by movements of fluids created by uterine cilia.

Question 4

Movement of sperm from the cervix to the oviduct requires a minimum of …………hours

Answer 4

2-7 hours

Question 5

After reaching the ……………, sperm become less motile & cease their migration.

Answer 5

Isthmus

Question 6

Chemo-attractants that may be responsible for the motility of sperm cells at ovulations are produced by …………

Answer 6

Cumulus cells

Question 7

What are two reactions sperms must undergo to be able to fertilise oocyte?

Answer 7

– Capacitation and acrosome reaction

Question 8

Capacitation lasts for ……….. hours

Answer 8

Seven

Question 9

Where does most of the capacitation process occur?

Answer 9

Uterine tube

Question 10

What is meant by acrosome reaction?

Answer 10

the exocytosis of the acrosome, or the fusion of the acrosomal membrane with the sperm’s plasma membrane

Question 11

Describe the process of capacitation

Answer 11

• It entails epithelial interactions between the sperm and mucosal surface of the tube.

• It involves removal of the glycoprotein coat and seminal plasma proteins of the plasma membrane that overlies the acrosomal region of the spermatozoa.

• Only capacitated sperm can pass through the corona cells and undergo the acrosome reaction

Question 12

Acrosome reaction is induced by …………..

Answer 12

Zona proteins

Question 13

Enzymes required for the penetration of the zona pellucida include;

Answer 13

Acrosin and trypsin-like substances

Question 14

……………… sperm pass freely through corona cells

Answer 14

Capacitated

Question 15

Maintenance of sperm binding and acrosome reaction are mediated by …………..

Answer 15

Zona protein (ligand ZP3)

Question 16

……………….. allows sperm to penetrate the zona

Answer 16

Release of acrosomal enzymes (acrosin)

Question 17

How does the permeability of the zona pellucida change when the head of the sperm comes in contact with the oocyte surface?

Answer 17

The contact results in release of lysosomal enzymes from cortical granules lining the plasma membrane of the oocyte. These enzymes alter properties of the zona pellucida (zona reaction) to prevent sperm penetration and inactivate species-specific receptor sites for spermatozoa on the zona surface.

Question 18

The initial adhesion of sperm to the oocyte is mediated in part by …………..

Answer 18

the interaction of integrins on the oocyte and their ligands or disintegrins on sperm.

Question 19

The fusion of gametes is accomplished between ………………

Answer 19

the oocyte membrane and the membrane that covers the posterior region of the sperm head

Question 20

What part of the spermatozoon is left behind on the oocyte surface?

Answer 20

the plasma membrane

Question 21

Outline the phases of fertilization

Answer 21

Phase 1: penetration of the corona radiata
Phase 2: penetration of the zona pellucida
Phase 3: fusion of the oocyte & sperm cell membranes

Question 22

The chromosomes of the definitive oocyte (22+X) arrange themselves in a vesicular nucleus called ……………..

Answer 22

Female pronucleus

Question 23

What are the 3 ways the ovum responds as soon as the spermatozoon enters the oocyte?

Answer 23

Cortical and zona reactions.
– The oocyte membrane becomes impenetrable to other
spermatozoa
– The zona pellucida alters its structure and composition to prevent sperm binding and penetration, thus preventing polyspermy

Resumption of the second meiotic division.
– The oocyte finishes its second meiotic division immediately after the entry of the spermatozoon.
– One of the daughter cells, becomes second polar body and the other the definitive oocyte.
– Its chromosomes (22+X) arrange themselves in a vesicular nucleus called female pronucleus

Metabolic activation of the egg
– The activating factor is probably carried by the spermatozoon.
- The spermatozoon, moves forward until it lies close to the female pronucleus.
- Its nucleus becomes swollen and forms the male pronucleus
- Morphologically, the male and female pronuclei are indistinguishable, and eventually, they come into close contact and lose their nuclear envelopes
- During growth of male & female pronuclei (both haploid), each pronucleus must replicate its DNA.
- The 23 maternal & 23 paternal (double) chromosomes split longitudinally at the centromere, and sister chromatids move to opposite poles, providing each cell of the zygote with the normal diploid number of chromosomes and DNA

Question 24

Morphologically, the male and female pronuclei are distinguishable, true or false

Answer 24

False

Question 25

What are the barriers between the sperm and oocyte?

Answer 25

Corona radiata cells
Zona pellucida and
The cell membrane of the oocyte

Question 26

What are the factors that come into play to overcome the barriers between the sperm and the oocyte?

Answer 26

1. Secretion of certain enzymes in the fallopian tube to dispel the granulosa cells of the corona radiata.
2. Capacitation occurs at the acrosomal cap of the sperm to enable the sperm pierce the zona pellucida
3. Acrosome reaction which involves the release of enzymes from the acrosomal cap to enable the sperm pierce the oocyte.
4. Zona reaction : Entry of one sperm into the oocyte prevents the entry of others by making the zona pellucida impregnable.

Question 27

Mention the events that occur after fertilization

Answer 27

1. Completion of second meiotic division of the secondary oocyte into mature oocyte.
2. The diploid number of chromosome is restored
3. The sex of the zygote is restored
4. The cleavage commences and zygote is formed
5. Zygote contains a new combination of chromosomes that are different from the cells of either parents

Question 28

The clinical manifestation of ovarian tumours include;

Answer 28

Women with ovarian tumors may have abdominal pain and masses that can be felt in the abdomen.

Question 29

A note on ovarian cysts

Answer 29

Ovarian cysts are non-cancerous sacs filled with fluid or semi-solid material. Large cysts may push on surrounding organs, causing abdominal pain. In most cases, cysts will pass or disappear on their own and treatment is not necessary. If the cysts are painful and occur frequently, birth control pills can alter their growth and occurrences. Surgery is also an option if they need to be removed.

Question 30

………………… is a hormone disorder in which too many hormones are produced by the ovaries.

Answer 30

Polycystic ovary syndrome

Question 31

What is the effect of polycystic ovary syndrome?

Answer 31

This condition causes the ovaries to become enlarged and develop many fluid filled sacs or cysts. It often first appears during the teen years.

Question 32

In some women, sudden constant pain is felt ……………. in abdomen

Answer 32

inferolaterally in abdomen

Question 33

What is the cause of mid cycle pain?

Answer 33

This is due to slight bleeding in the abdomen during ovulation.

Question 34

How is the suppression of ovulation achieved by the use of contraceptives?

Answer 34

the estrogen in the birth control pill inhibits the secretion of FSH and LH which is essential for ovulation.

Question 35

What is the full meaning of IVF-ET?

Answer 35

in-vitro fertilization embryo transfer

Question 36

The male gamete has to reach the …………… part of the fallopian tube to meet the oocyte for fertilization.

Answer 36

ampullated