Fertilisation

Question 1

What process of cell division applies to gametes?

Answer 1

Meiosis

Question 2

How long can an unfertilised oocyte survive?

Answer 2

12-72 hours

Question 3

How many sperm does each ejaculation contain and what percent reaches the ovum?

Answer 3

Around 300 million sperm
Around 15%

Question 4

What is fertilisation?

Answer 4

The fusion of the nucleus of a male gamete with the nucleus of a female gamete to produce a new cell called a zygote

Question 5

What enzyme does the sperm release to allow penetration through the zona pellucida?

Answer 5

Hyaluronidase

Question 6

What is the process that sperm are required to go through to enable it to fertilise an oocyte?

Answer 6

Capacitation

Question 7

Where does capacitation of the sperm take place?

Answer 7

In the uterine tubes

Question 8

What does the acrosome of the sperm react with when it reaches the ovum?

Answer 8

The zona pellucida

Question 9

Outline what happens when the sperm reaches the egg in regard to the chemical reactions

Answer 9

• The entry of the acrosome into the egg surface causes a cortical reaction or change
• Chemical reactions cause the ovum to swell, altering the zona pellucida making it impermeable to other sperm
• The sperm nucleus reaches the cytoplasm, where the tail will detach
• The cortical granules within the cytoplasm fuse with the plasma membrane to make the vitelline layer impenetrable to other sperm

Question 10

What is polyspermy?

Answer 10

This is a condition where more than one sperm nucleus interacts with the female nucleus, creating an unviable zygote

Question 11

What does fertilisation result in?

Answer 11

A new nuclei containing genetic material from both the sperm and ovum resulting in a diploid cell

Question 12

How long does the process of fertilisation within the uterine tube take place

Answer 12

24 hours

Question 13

Name the three developmental periods of the zygote with timescales

Answer 13

Pre-embryonic period week 0-2
Embryonic period weeks 2-8
Fetal period 8 weeks until birth

Question 14

What happens within the first week of the pre-embryonic stage?

Answer 14

Within the first week, the zygote travels along the uterine tubes towards the uterus, during this travel the zygote goes through cleavage

Question 15

Outline what happens day 1-3 of the pre-embryonic stage

Answer 15

Day 1- the zygote splits into 2 cells
Day 2- the zygote has split into 4 cells
Day 2.5- the zygote has split into 8 cells
Day 3- the zygote has split into 16 cells and then 32 cells and is now known as the morula

Question 16

What does the morula develop into when a fluid filled cavity appears?

Answer 16

A blastocyst

Question 17

What surrounds the outside of the blastocyst?

Answer 17

The trophoblast (this is a single layer of cells)

Question 18

What is the inner cell mass within the blastocyst called?

Answer 18

The embryoblast

Question 19

What is the fluid filled cavity of the blastocyst called?

Answer 19

The blastocoele

Question 20

Outline what happens to the blastocyst when it enters the uterus

Answer 20

It lies free for approximately 2-3 days
On around day 6, it embeds into the endometrium
The trophoblasts become sticky and secrete substances that digest the endometrium

Question 21

Outline of implantation

Answer 21

Villi make their way into the decidua where they branch and contain blood vessels of the developing embryo to allow gaseous exchange between the mother and embryo
By day 12, the conceptus is completely embedded in the compact layer of the endometrium and is covered by the overlying uttering epithelium

Question 22

At implantation, what formations take place?

Answer 22

Trophoblasts become the placenta and chorion
Embryoblast becomes the embryo, amnion, and umbilical cord
The trophoblasts differentiate into two distinct layers, the inner cytotrophoblasts and the outer syncytiotrophoblasts
Syncytiotrophoblasts are formed from the outer layer of trophoblasts
Cytotrophoblasts are trophoblasts that haven’t formed synctiotrophoblasts

Question 23

What two types of cells does the embryoblast differentiate into?

Answer 23

Embryonic epiblast- this is closest to the trophoblast and becomes the embryo and amniotic cavity
Hypoblast- this is closest to the blastocyst cavity and becomes the yolk sac

Question 24

What process are the three layers of epiblast cells developed through?

Answer 24

Gastrulation

Question 25

Name the three layers of epiblast cells and what they form

Answer 25

Ectoderm- This forms the epidermis later of the skin, hair, and nails. It also forms the nervous system
Mesoderm- This forms the muscle, skeleton, dermis of skin, connective tissues, urogenital glands, blood vessels, and blood and lymph cells
Endoderm- This forms the epithelia lining of the digestive, respiratory, and urinary systems, and glandular cells

Question 26

What is the role of the corpus luteum in fertilisation?

Answer 26

Human chronic gonadotrophin is secreted into the maternal blood stream
It releases progesterone and oestrogen
The release of progesterone suppresses menstruation