REP - L3 - Beginnings of life

Question 1

Are primordial germ cells haploid or diploid?

Answer 1

Diploid.

Question 2

What cells undergo meiosis to form germ cells?

Answer 2

Primordial germ cells.

Question 3

When do eggs go through 1^st meiosis?

Answer 3

Ovulation.

Question 4

What happens during the zygotic stage?

Answer 4

• Sperm enters oocyte.
• Zona pellucida becomes impenetrable.
• Change from haploid to diploid.
• Cell division is initiated.

Question 5

What happens during the cleavage stage?

Answer 5

• Blastomere’s look like blackberries in contact with zona pellucida.
• Asynchronous cell division (mammals).

Question 6

What is a blastomere?

Answer 6

Cells produced during cleavage of a zygote.

Question 7

What is a blast?

Answer 7

Primitive or precursor cell.

Question 8

What are the cells called at the 16 cell stage?

Answer 8

Morula.

Question 9

What happens during the Morula stage?

Answer 9

Cells divide but do not grow.

Question 10

What happens at the blastocyst stage?

Answer 10

• First differentiation event - Inner cell mass (ICM) formed.
• Cells on outside pump fluid into embryo to form blastocyst cavity.

Question 11

In a blastocyst what are the inner cells called?

Answer 11

Inner cell mass.

Question 12

In a blastocyst what are the outer cells called?

Answer 12

Trophoblast.

Question 13

What has to happen before the embryo can grow?

Answer 13

It has to hatch out of zona pellucida.

Question 14

How does the hatching happen?

Answer 14

Enzymes are produced to degrade protein of zona pellucida.

Question 15

How does normal pregnancy occur?

Answer 15

• Embryo developes as it moves along the oviduct.
• Implantation occurs in uterus.

Question 16

How does ectopic pregnancy occur?

Answer 16

• Narrowing of oviduct caused by infection impedes movement.
• Extra-uterine implantation (90% in oviduct).
• Oviduct can rupture.

Question 17

What’s the other name for the oviduct?

Answer 17

Follopian tubes.

Question 18

Why can’t the embryo survive implantation in the oviduct?

Answer 18

• Not enough space.
• Nutrition deficient.

Question 19

How are ectopic pregnancy’s treated?

Answer 19

Surgery.

Question 20

What happens during the implantation stage?

Answer 20

• Hatched blastocyst implants into uterine wall.
• Trophoblast are induced to divide and invade endometrium (uterus lining).
• Invading trophoblasts loose cell membranes and become multi-nucleated.

Question 21

Why does the blastocyst implant itself into uterine wall?

Answer 21

To gain nutrition and excrete waste - uterine wall is blood vessel rich.

Question 22

What are the 2 types of trophoblasts seen at implantation?

Answer 22

• Syncytiotrophoblasts - group of cells acting as one.
• Cytotrophoblasts - retain individual membranes.

Question 23

When is the cut off point for studying embryos in a dish?

Answer 23

When the embryo must bury itself in the endometrium.

Question 24

What 2 layers does the Inner cell mass form?

Answer 24

• Epiblast - columnar cells.
• Hypoblast - cuboidal cells.

Question 25

What does **totipotency** mean?

Answer 25

**Differentiating** ability.

Question 26

What's the fate of the **epiblast** (inner cell mass)?

Answer 26

* Ectoderm. * Mesoderm. * Endoderm.

Question 27

What's the fate of the **hypoblast**?

Answer 27

No adult tissue.

Question 28

What's the main **function** of the **outside of blastocyst**?

Answer 28

Communication.