Coitus, Fertilisation & Preimplantation

Question 1

What are the 4 phases of human sexual response? (EPOR)

Answer 1

Excitement
Plateau
Orgasm
Resolution

Question 2

When must coitus occur in order for fertilisation to occur?

Answer 2

No longer than 3-5 days before ovulation and no longer than 1 day after

Question 3

How long are sperm viable?

Answer 3

24-72 hours

Question 4

How long are oocytes viable for?

Answer 4

12-48 hours

Question 5

When is the 2nd trimester?

Answer 5

13-28 weeks

Question 6

Why does sperm DNA show high rates of mutation?

Answer 6

Lack DNA repair system

Question 7

When is the embryonic period?

Answer 7

First 8 weeks

Question 8

When is the foetal period?

Answer 8

8-40 weeks

Question 9

Which type of cells aid transport of oocyte from ovary to fallopian tube?

Answer 9

Cumulus cells cling to the ciliated surface of the fimbriae

Question 10

How do sperm move through uterus and fallopian tubes?

Answer 10

Own propulsions

Uterine contraction

Question 11

Why is there such a large number of sperm in ejaculate?

Answer 11

Vagina is acidic
Length and energy required for trip
High sperm mortality

Question 12

What is the consistency of cervical mucus at ovulation?

Answer 12

High oestrogen results in thin, serous and alkaline mucus which is hospitable to sperm

Question 13

What is the effect of progesterone on cervical mucus?

Answer 13

Makes it thick and acidic “infertile sperm”

Also prevents pathogens entering uterus when pregnancy has occurred

Question 14

What results from capacitation of sperm?

Answer 14

Change in wavelike beats of sperm tail to whip-like action to propel sperm forward
Acrosome reaction allows the sperm to fuse with the oocyte

Question 15

What is the point in capacitation of sperm?

Answer 15

Makes sperm capable of fertilisation

Question 16

Where does fertilisation normally occur?

Answer 16

Ampulla of uterine tube

Question 17

What triggers the acrosome reaction?

Answer 17

Rise in intracellular Ca2+ inside the sperm cell when it binds to the zona pellucida

Question 18

Describe the acrosome reaction

Answer 18

Sperm head contacts with zona pellucida and binds to glycoproteins
Acrosome PM fuses and releases contents, resulting in more Ca2+ entry
Sperm then digest a path through the zona pellucida

Question 19

What happens in the cortical reaction?

Answer 19

Release of cortical granules that lay beneath the PM, causing the zona pellucida to harden, preventing entry of other sperm

Question 20

What induces the completion of the second meiotic division of the oocyte?

Answer 20

Rise in intracellular calcium

Question 21

What happens the sperm head when inside the oocyte?

Answer 21

It enlarges and becomes the male pronucleus

Question 22

What happens when the male and female pronuclei fuse?

Answer 22

Sperm contributes nuclear material and centrioles
All other organelles are present in the oocyte cytoplasm
Mitochondrial DNA inherited via maternal route

Question 23

What causes conceptus to remain the the fallopian tube until it reaches 32 cells?

Answer 23

Oestrogen maintains smooth muscle contractions near where fallopian tube enters wall of uterus

Question 24

What is unusual about cell division from zygote to morula?

Answer 24

Cells increase in number but decrease in size, meaning conceptus reaching the uterus is the same size as the original fertilised egg

Question 25

What type of cells are the cells reaching the uterus?

Answer 25

Totipotent

Question 26

When does the conceptus pass into the uterus and why?

Answer 26

Progesterone levels rise 3-4 days after fertilisation allowing the smooth muscle relaxes and conceptus passes into uterus

Question 27

Which cells give rise to the placenta?

Answer 27

Trophoblast

Question 28

What cells form the embryo?

Answer 28

Inner cell mass

Question 29

What do the trophoblast cells differentiate into?

Answer 29

Inner cytotrophoblast

Outer syncytiotrophoblast

Question 30

What does totipotent mean?

Answer 30

Can divide into any cell type in body, plus extra embryonic or placental cells

Question 31

What does pluripotent mean?

Answer 31

Can give rise to all cells in the body