Fertilisation

Question 1

When must sperm enter the vagina for pregnancy to occur?

Answer 1

Between 5 days before and 1 day after ovulation. Sperm can fertilise an egg for up to 4-6 days. Ovulated eggs are only viable for 24-48 hours.

Question 2

What structure allows the egg to move through the fallopian tube?

Answer 2

Cilia

Question 3

How many days does it take for the egg to be beaten to the uterus?

Answer 3

4

Question 4

Give 2 reasons why sperm have high mortality (large death rate).

Answer 4

1. Vaginal environment is acidic
2. Length and energy requirement is very large

This is why the ejaculate contains so much sperm to increase likelihood of fertilisation.

Question 5

What is capacitation?

Answer 5

Final maturation stage of spermatozoa in the female genital tract

Question 6

What are the effects of capacitation?

Answer 6

1. Sperm tail action is whiplike to propel sperm more strongly
2. Sperm plasma membrane is altered to fuse with surface membrane of egg

Question 7

Where does fertilisation occur?

Answer 7

Ampulla of fallopian tube

Question 8

Which layer must the sperms acrosomal enzymes break through in order to fuse with the egg?

Answer 8

Zona pellucida

Question 9

What is a fertilised egg called?

Answer 9

Zygote

Question 10

What is polyspermy?

Answer 10

More than one sperm fertilising an egg

Question 11

Which reaction prevents polyspermy? What occurs during this reaction?

Answer 11

The cortical reaction.

Enzymes cause hardening of the zona pellucida, preventing additional sperm from advancing through

Question 12

How long after fertilisation does the zygote complete meiosis 2?

Answer 12

4-7 hours

Question 13

What is cleavage?

Answer 13

Mitotic cell divisions that do not result in cell growth and occur 24 hours after fertilisation. Successive cleavages increases cell numbers.

Question 14

What does it mean for a cell to be totipotent?

Answer 14

Totipotent cells are stem cells with the capacity of differentiating into any cell type.

Question 15

How do twins arise?

Answer 15

During cleavage, the dividing cells become completely separated into two independently growing cell masses.

Question 16

What is a blastocyst?

Answer 16

A mass of 80+ cells which have begun to differentiate. Forms at day 5.

Question 17

When does the embryo hatch from the zona pellucida?

Answer 17

Blastocyst expands to embryo. Day 6+

Question 18

What is secreted to prevent antigenic rejection of the embryo once implanted in the uterus?

Answer 18

Interleukin-2

Question 19

How does the early embryo receive nutrients?

Answer 19

Via endometrial cells

Question 20

Which structure takes over in providing nutrition for the embryo?

Answer 20

Placenta. Forms after implantation.

Question 21

What does the placenta synthesise?

Answer 21

Glycogen, cholesterol, fatty acids

Question 22

What does the placenta transport to the embryo/foetus?

Answer 22

O2, water, glucose, vitamins, amino acids (active transport), steroid hormones, electrolytes, maternal antibody IgG

Also drugs (can result in foetal drug addiction) and infectious agents.

Question 23

What does the placenta transport away from the embryo/foetus?

Answer 23

CO2, urea, uric acid, bilirubin

Question 24

Give the layers through which substances have to be transported through from mother to foetus.

Answer 24

Maternal endothelial 
Maternal connective tissue
Endometrial epithelial 
Chorionic epithelial
Fetal connective
Fetal endothelial

Question 25

When does the foetal heart begun to pump blood?

Answer 25

At 5 weeks

Question 26

What attaches the foetus to the placenta?

Answer 26

Umbilical cord

Question 27

What is the function of amniotic fluid?

Answer 27

Buffers temperature variations and mechanical disturbances

Question 28

What happens in the embryo after embryonic genome activation and before blastocyst formation?

Answer 28

Compaction

Question 29

After fertilisation, male and female pronucleuses are unified. What is this process called?

Answer 29

Syngamy

Question 30

Which genes confer self renewal and pluripotency in embryonic stem cells?

Answer 30

OCT4 and Nanog