Embryology 2

Question 1

Define ploidy.

Answer 1

number of copies of each chromosome in a nucleus

Question 2

What is the ploidy of somatic cells?

Answer 2

2n

Question 3

What is the ploidy of germ cells/gametes?

Answer 3

1n

Question 4

What does the letter “c” refer to?

Answer 4

total number of copies of each unique DNA molecule

Question 5

What is the “c” of resting somatic cells?

Answer 5

2c

Question 6

What is the “c” of definitive gametes?

Answer 6

1c

Question 7

What is the (#,n,c) of gamete precursor cells?

Answer 7

46, 2n, 2c

Question 8

What is the name of the diploid precursor cells?

Answer 8

spermatogonium/oogonium

Question 9

How does the name of the gamete precursor cells change through meiosis?

Answer 9

Question 10

What is the (#,n,c) configuration for cells immediately prior to meiosis?

Answer 10

46, 2n, 4c

Question 11

What is the (#,n,c) result of meiosis I?

Answer 11

(23, 1n, 2c) = secondary spermatocytes/oocytes

Question 12

What is the (#,n,c) result of meiosis II?

Answer 12

(23, 1n, 1c) = spermatozoon/oocyte

Question 13

Where does spermatogenesis take place?

Answer 13

seminiferous tubules of testes

Question 14

Which cells support spermatogenesis?

Answer 14

Sertoli cells

Question 15

Describe the movement of developing sperm cells in the seminiferous tubules.

Answer 15

developing cells gradually move from basal compartment to lumen via adluminal compartment

Question 16

How are the terms “primary spermatocyte,” “spermatid” and “spermatozoa” related?

Answer 16

a primary spermatocyte undergoes two rounds of meiosis to become 4 spermatids; these 4 spermatids mature (i.e. tail growth) into spermatozoa

Question 17

Where are spermatozoa released?

Answer 17

released into lumen of seminiferous tubules

Question 18

In humans, how long does the production of spermatozoa take?

Answer 18

spermatogonium to spermatozoon takes 65 days

Question 19

When does oogenesis begin in females?

Answer 19

prenatally

Question 20

When exactly do oogonia, the female gamete precursor cells, start to undergo meiosis prenatally?

Answer 20

start to undergo meiosis I in 5th month of fetal life, but become arrested in meiosis I until girl reaches puberty

Question 21

Describe what happens in the uterus on a monthly basis in terms of female definite oocyte production. (3)

Answer 21

1 primary oocyte made available for fertilization each month; developing oocyte embedded in follicle of uterus and produces estrogen; estrogen stimulates growth of endometrium

Question 22

What happens to a primary oocyte right before ovulation?

Answer 22

primary oocyte, which until now was arrested in meiosis I, completes meiosis I and enters meiosis II

Question 23

In females, meiosis I is completed right before ovulation. When is meiosis II completed?

Answer 23

only after fertilization

Question 24

How is cell division different between spermatogenesis and oogenesis?

Answer 24

in oogenesis, cytoplasm division is unequal — only one secondary oocyte receives all cytoplasm whereas other is called a polar body and degenerates

Question 25

What happens to the oocyte upon ovulation?

Answer 25

follicle ruptures and releases oocyte + surrounding cells

Question 26

Define corona radiata.

Answer 26

structure composed of oocyte + surrounding cells released upon ovulation

Question 27

Define corpus luteum.

Answer 27

residual tissue of follicle after ovulation that secretes progesterone

Question 28

What is the function of the progesterone secreted by the corpus luteum?

Answer 28

prepares endometrium for implantation by increasing vascularization and stimulating glands to produce nutrients

Question 29

Where does fertilization take place?

Answer 29

the ampulla, which is the intermediate part of the uterine tube

Question 30

Describe how sperm interact with the corona radiata and zona pellucida.

Answer 30

several sperm can penetrate the corona radiata, but only one sperm can penetrate the zona pellucida, and once it does, chemical processes prevent other sperm from interacting with the zona pellucida

Question 31

What is the sequence of events in fertilization?

Answer 31

sperm penetrates zona pellucida; plamsa membranes of oocyte and sperm fuse and sperm enters cytoplasm of oocyte; oocyte completes meiosis II; (23, 1n) sperm and (23, 1n) oocyte form diploid (46, 2n) zygote

Question 32

Cleavage occurs how many days after fertilization?

Answer 32

1-3 days after fertilization

Question 33

Define blastomeres.

Answer 33

The new cells that result from rapid mitotic division of the zygote as it travels along the uterine tube towards the uterus

Question 34

What is notable about the size of the zygote during cleavage?

Answer 34

the size of the zygote remains the same because the blastomeres formed by mitotic division do not grow, meaning the cells become smaller with each division to maintain the same size

Question 35

After undergoing several mitotic divisions, the zygote is now called

Answer 35

a morula

Question 36

When does the morula enter the uterus?

Answer 36

4 days after fertilization

Question 37

Describe the toti/pluri/multipotency of the zygote.

Answer 37

The zygote, up until the division that creates 16 cells, is totipotent, meaning it can differentiate into any embryonic or extraembryonic cell

Question 38

When does formation of the blastocyst occur?

Answer 38

4-6 days after fertilization

Question 39

As the morula hollows out, it is called

Answer 39

a blastocyst

Question 40

What are the components of the blastocyst?

Answer 40

outer layer - trophoblast; inner cell mass - embryoblast; blastocystic cavity

Question 41

The trophoblast develops into

Answer 41

part of the placenta

Question 42

The embryoblast develops into

Answer 42

the embryo

Question 43

The blastocystic cavity develops into

Answer 43

the yolk sac

Question 44

What is the significance of the blastocyst's development in relation to the dorsal-ventral axis?

Answer 44

the side of the inner cell mass facing the blastocystic cavity will become the ventral surface of the embryo

Question 45

When does implantation in the uterus occur?

Answer 45

7-12 days after fertilization (begins 7 days after, complete 12 days after)

Question 46

What two hormones are critical for implantation?

Answer 46

estrogen, which thickens the endometrium, and progesterone, which stimulates production of nutrients

Question 47

What happens to the trophoblast upon implantation?

Answer 47

proliferates significantly and differentiates into two portions: inner cytotrophoblast and outer syncytiotrophoblast

Question 48

The trophoblast differentiates into

Answer 48

inner cytotrophoblast and outer syncytiotrophoblast

Question 49

Define syncytium.

Answer 49

large, multinucleated mass of cytoplasm

Question 50

Describe how the cytotrophoblast and syncytiotrophoblast develop.

Answer 50

as cytotrophoblast proliferates, its outer layer cells fuse to form syncytiotrophoblast

Question 51

What is the purpose of the syncytiotrophoblast?

Answer 51

to invade endometrium and erode maternal blood vessels, which forms in blood-filled lacunae that provides embryo access to O2 and nutrients

Question 52

What structure produces hCG?

Answer 52

syncytiotrophoblast

Question 53

What is the function of hCG?

Answer 53

maintain progesterone production in corpus luteum

Question 54

When can hCG levels be reliably detected in maternal blood or urine?

Answer 54

maternal blood - 2-3 days after implantation; maternal urine - 6-8 days after implantation

Question 55

Why are the first two weeks after conception referred to as the "all or nothing" period?

Answer 55

because only healthy morulas and blastocysts will survive — all others will spontaneously abort

Question 56

What percentage of pregnancies result in early, spontaneous abortion?

Answer 56

10-15%

Question 57

Where do most ectopic implantations occur?

Answer 57

uterine tube

Question 58

Describe the hypoblast.

Answer 58

forms on ventral surface of embryoblast

Question 59

Describe the amniotic cavity.

Answer 59

forms between dorsal trophoblast and embryoblast

Question 60

Describe how the amnion forms.

Answer 60

result of some embryoblast cells differentiating

Question 61

The epiblast layer originates from

Answer 61

the upper layer of the embryoblast

Question 62

The epiblast layer consists of

Answer 62

columnar cells

Question 63

The hypoblast layer consists of

Answer 63

cuboid cells

Question 64

The embryonic disc results from

Answer 64

the hypoblast and epiblast layers forming a bilaminar plate of cells

Question 65

The exocoelomic membrane results from

Answer 65

cells from the hypoblast surrounding the blastocytic cavity

Question 66

Following formation of the exocoelomic membrane, the blastocytic cavity is now called

Answer 66

the exocoelomic cavity a.k.a. primary yolk sac

Question 67

What are the two associated cavities of the embryonic disc?

Answer 67

amniotic cavity and primary yolk sac

Question 68

When hypoblast cells surround the embryonic disc and proliferate, what tissue forms?

Answer 68

extraembryonic mesoderm

Question 69

The extraembryonic mesoderm, as a result of gaps appearing, becomes

Answer 69

the extraembryonic coelom

Question 70

The extraembryonic mesoderm splits into

Answer 70

extraembryonic splanchic mesoderm; outer extraembryonic somatic mesoderm

Question 71

What makes up the chorion?

Answer 71

extraembryonic somatic mesoderm + cytotrophoblast + syncytiotrophoblast

Question 72

What makes up the placenta?

Answer 72

chorion + parts of maternal endometrium

Question 73

The secondary yolk sac originates from

Answer 73

the primary yolk sac

Question 74

What is the function of the secondary yolk sac?

Answer 74

its blood vessels form vitelline arteries/veins; portions of secondary yolk sac contribute to gut tube

Question 75

What is the fate of the primary yolk sac?

Answer 75

disintegrates within a few days

Question 76

What connects the developing embryo to the developing placenta?

Answer 76

connecting stalk

Question 77

What is the significance of the prechordal plate?

Answer 77

primordium of the mouth; defines the cranial pole of the embryo

Question 78

What gives rise to the prechordal plate?

Answer 78

hypoblast cells in the embryonic disc becoming more columnar in a specific circular area gives rise to prechordal plate

Question 79

Draw out a diagram illustrating gamete cell naming conventions.

Answer 79

Question 80

Draw out a diagram showing how a zygote differentiates.

Answer 80