13. Gametogenesis, Implantation, Foetal Membranes

Question 1

What are gametes derived from?

Answer 1

Primordial Germ Cells formed in epiblast during the second week

Question 2

Where do PGCs migrate during gastrulation?

Female

Answer 2

Through the primitive streak to the wall of the yolk sac

Question 3

Where do PGCs move to during week 4?

Female

Answer 3

Towards developing gonads

Question 4

What is a teratoma?

Answer 4

Tumours containing a variety of tissues

Arise from pluripotent stem cells that strayed from normal migratory paths

Question 5

What is oogenesis?

Answer 5

Process where oogonia mature into oocytes

Question 6

What happens once PGCs arrive in the gonads in females?

Answer 6

Differentiate into oogonia
Undergo mitotic divisions
Arrange in clusters surrounded by a layer of flat epithelial cells

Question 7

Where do the flat epithelial cells (follicular cells) surrounding oogonia come from?

Answer 7

Surface epithelium covering the ovary

Question 8

How are primary oocytes formed?

Answer 8

Some oogonia arrest their cell division in prophase of meiosis 1

Question 9

What happens at 5 months during oogenesis?

Answer 9

Cell death begins

Many oogonia and primary oocytes degenerate and become atretic

Question 10

What happens at 7 months during oogenesis?

Answer 10

Majority of oogonia have degenerated except for a few near the surface
All surviving primary oocytes have entered prophase
Now known as a primordial follicle

Question 11

What do oocytes do instead of entering metaphase?

Answer 11

Enter the diplotene stage

Question 12

What is the diplotene stage?

Answer 12

Resting stage
Characterised by a lacy network of chromatin
Induced by oocyte maturation inhibitor

Question 13

What happens so that oocytes can enter the antral or vesicular phase?

Answer 13

Follicles accumulate fluid in a space called the antrum

Question 14

What happens to follicles immediately before ovulation?

Answer 14

Follicles are swollen and are called mature vesicular or graafian follicles

Question 15

What happens to the surrounding follicular cells of the graafian follicle?

Answer 15

Change from flat to cuboidal
proliferate
Form a stratified epithelium of granulosa cells

Question 16

What is the function of granulosa cells?

Answer 16

Secrete a layer of glycoproteins which form the zona pellucida

Question 17

What is the graafian follicle called after fluid-filled spaces form between granulosa cells?

Answer 17

Vesicular or antral follicle

fluid-filled spaces join to form the antrum

Question 18

What do granulosa cells form in the vesicular or antral follicle?

Answer 18

Cumulus oophorus

Question 19

What induces meiosis of the antral follicle?

What happens?

Answer 19

LH

2 daughter cells are formed: one with all the cytoplasm (secondary oocyte) other gets none (first polar body)

Question 20

What happens to sex cords shortly before puberty?

Answer 20

Aquire a lumen and become seminiferous tubules

Question 21

What are the steps between PGCs to spermatids?

Answer 21

Spermatogonial stem cells
Become type A spermatogonia
Mitosis to form type B spermatogonia
Divide to form primary spermatocytes
Meiosis 1 to form secondary spermatocytes
Form haploid spermatids during 2nd division

Question 22

What are the functions of sertoli cells?

Answer 22

Participate in nutrition and assist in release

Question 23

What happens in spermiogenesis?

Answer 23

Formation of acrosome
Condensation of nucleus
Formation of neck, middle piece and tail
Shedding of most of cytoplasm

Question 24

What does an abrupt increase of LH cause in the female?

Answer 24

Primary oocyte completes meiosis 1

Follicle enters the preovulatory mature vesicular phase

Question 25

What happens during the preovulatory mature vesicular phase?

Answer 25

Surface of the ovary begins to bulge
Stigma appears at the apex
Collagen surrounding follicle are digested

Question 26

How is ovulation carried out?

Answer 26

Prostaglandins cause local muscular contractions in the wall of the ovary
Oocyte breaks free and floats out of the ovary
Fimbriae of the fallopian tube sweep over the ovary to . pick up the ovum

Question 27

Where does fertilisation usually occur?

Answer 27

Ampullary region of uterine tube

Question 28

How is a blastocyte formed?

Answer 28

Fluid penetrates the zona pellucida into the intracellular spaces of the inner cell mass
Single cavity called the blastocele forms
(embryo is now a blastocyst)

Question 29

What is the inner cell mass of the blastocyst now called?

Answer 29

Embryoblast

Question 30

What is the outer cell mass of the blastocyst now called?

Answer 30

Trophoblast

Question 31

What does the trophoblast layer differentiate into?

Answer 31

Syncythiotrophoblastic cells

Cytotrophoblast

Question 32

What are the layers of the foetal membrane?

Answer 32

Chorion
Amnion
Allantois
Yolk sac

Question 33

Which layers of the foetal membrane contribute to the placenta?

Answer 33

Amnion
Allantois
Yolk sac

Question 34

What are the functions of the placenta?

Answer 34

Contain and protect embryo
Nutrition and waste collection
Blood and oxygen supply
Signally between maternal decidua and foetus

Question 35

Describe the development of the placenta

Answer 35

Syncythiotrophoblast layer develops projections into the endometrium
Small spaces called lacunae develop, become filled with blood and secretions
Lacunae join together to form primitive maternofoetal circulation

Question 36

What is the umbilical cord made up of?

Answer 36

2 arteries
1 vein
Contained in Wharton’s jelly

Question 37

Name 3 problems that can arise from the placenta

Answer 37

Placenta praevia
Placenta accretia
Hydatiform mole

Question 38

what is a hydatiform mole?

Answer 38

Placenta forms a mass with little or no foetal tissue
Secretes hCG
May become carcinogenic