12. Embryology

Question 1

What stage is the primary oocyte arrested in until puberty?

Answer 1

Prophase 1 of meiosis 1

Question 2

When does the primary oocyte complete meiosis 1?

Answer 2

Puberty - secondary oocyte is released every month

Question 3

What is produced from oogenesis?

Answer 3

1 ovum

3 polar bodies

Question 4

What is produced from spermatogenesis?

Answer 4

4 spermatozoa

Question 5

Where does fertilisation usually take place?

Answer 5

Ampullary region of fallopian tube

Question 6

What happens in ovulation?

Answer 6

Secondary oocyte is released from the ovary and swept into the fallopian tube by the frimbriae.

Question 7

How long are sperm viable for?

Answer 7

5 days

Question 8

How long is a secondary oocyte viable for?

Answer 8

12-24 hours

Question 9

What changes occur to sperm in order to enable fertilisation?

Answer 9

1. Capacitation

2. Acrosome reaction

Question 10

What is capacitation?

Answer 10

When the sperm comes into contact with vaginal secretions, they undergo changes to their cell membane and become hypermobile to allow fertilisation.

Question 11

What is the acrosome reaction and when does it occur?

Answer 11

When sperm binds to the zona pellucida, it releases enzymes that break down the glycoprotein and allow penetration of the egg.

Question 12

Once a sperm enters the egg, what structural change occurs?

Answer 12

Zona pellucida hardens to prevent any other sperm from entering.

Question 13

What process occurs within the oocyte once it has been fertilised?

Answer 13

Meiosis II is completed to form a female pronucleus which fuses with the male pronucleus to form a zygote.

Question 14

Outline the structures which surround the secondary oocyte.

Answer 14

Surrounded by:
Zona pellucida - glycoprotein
Zona radiata

Question 15

Outline what happens after zygote formation in order to produce a blastocyst.

Answer 15

Cell division to eventually form a 16-cell morula which comprises of an inner cell mass and an outer cell mass.

Question 16

Outline how a morula develops into a blastocyst.

Answer 16

Inner cell mass becomes the embryoblast.
Outer cell mass becomes the trophoblast.
Cavity is formed beneath the embryo blast.
Zone pellucida degenerates “hatching”.

Question 17

When does implantation take place?

Answer 17

Day 6

Question 18

What happens during implantation?

Answer 18

Blastocyst is implanted into endometrium wall

Question 19

What is the function of the zona pellucid, why does “hatching” take place?

Answer 19

Zone pellucida prevents the morula/blastocyst adhering to the fallopian tube.
ZP stops the morula enlarging so degenerates to allow blastocyst formation.

Question 20

What is the most common location for implantation to happen?

Answer 20

Upper past of uterus body, in the posterior wall.

Question 21

Outline what happens to the blastocyst in week 2, following implantation.

Answer 21

1. Trophoblast differentiates into 2 layers
2. Embryoblast differentiated into 2 layers
3. 2 cavities are formed

Question 22

What 2 layers does the trophoblast differentiated into?

Answer 22

Inner - cytotrophoblast

Outer- synctiotrophoblast

Question 23

What 2 layers does the embryoblast differentiated into?

Answer 23

Epiblast

Hypoblast

Question 24

What 2 cavities are formed during week 2?

Answer 24

Yolk sac

Chorionic cavity

Question 25

What is placenta previa, what are the implications of this?

Answer 25

Placenta develops unusually low, covering the cervix. Cesarean section is necessary.

Question 26

What is histiotrophic nutrition and when is it most important?

Answer 26

Nutrition provided to the embryo which is not from the maternal blood.
Important up to 12th week.

Question 27

What is haemotrophic nutrition and when is it important?

Answer 27

Nutrition provided from the mothers blood, important 12th week onwards.

Question 28

What is the embryonic age?

Answer 28

Time since fertilisation

Question 29

What is the gestational age?

Answer 29

Time since last menstruation (embryonic age + 2 weeks usually)

Question 30

When is the embryonic period?

Answer 30

Weeks 3-8

Question 31

When is the foetal period?

Answer 31

Week 9 - birth at 38 weeks embryonic age/ 40 weeks gestational age.