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Flashcards in Embryology 1 Deck (98):
1

Primordial Germ Cells (PGC)

precursors to the developement of gametes in males and females

2

Epiblast

where primordial germ cells arise from

3

Where do PGCs migrate in the fourth week of development?

yolk sac

4

T or F yolk sac serves as nutritional support in development?

false

5

What happens to PGCs during the 4th and 6th weeks of developement?

migration of PGCs from yolk sac to populate gonads

6

Where do gonads develope weeks 4-6?

urogenital ridge on posterior abd. wall

7

What happens to PGCs on their way to gonads?

rapid MITOSIS

8

When do PGCs begin gametogenesis?

when they enter testis/ovary and begin meiosis

9

If primordial germ cells fail to migrate to urogenital crest what will happen?

No gonad will develop at that site

10

what two major events occcur in meiosis 1 but not in meiosis 2?

crossover and synapsis

11

What is the foundation for most genetic variability from person to person?

crossover

12

Crossover

segmental exchange of DNA from part of one chromosome to another

13

What happens to male primordial cells when they populate the future testis?

they go dormant until puberty

14

When does male spermatogensis begin?

puberty

15

What happens to male PGCs at puberty?

they diffentiate into type A and B spermatogonia

16

What do type A spermatogonia do?

remain in seminiferous tubules for life and go through mitotic divisions to keep a constant supply of type B. (funct. as stem cells)

17

What do type B spermatogonia do?

undergo meiosis 1 and 2 to from haploid spermatozoa (birth to death)

18

Primary spermatocyte

cells in meiosis I

19

secondary spermatocyte

cells in meiosis II

20

In males is there interphase between meiosis I and II?

NO

21

what does a secondary spermatocyte split to form?

spermatids

22

What happens when PGC's in females migrate to the urogenital region from the yolk sac?

immediate differentiation to primary oocyte

23

When does Oogenesis and meiosis one begin in females?

5th month of development

24

What happens in females at puberty to oocytes?

exit the arrest of prophase of meiosis 1

25

How many gametes are produced from one spermatogonia?

4

26

How many gametes from one oogonia

1 and 2 polar bodies

27

Where does fertilization generally take place?

ampulla (distal in of fallopian)

28

capacitation reaction

takes 7-8 hours, rearrangement of proteins in acrosome to allow it to drill a hole through the zona pellucida

29

acrosome reaction

initiates on sperm contact with zona pellucida, pore in head opens up and releases proteolytic enzymes to bore through zona pellucida (much faster than capacitation)

30

What part of sperm actually enters the oocyte?

head- mitochondria left behind

31

cortical/zonal reaction

makes oocyte impermeable to other sperm

32

Male pronucleus

induces oocyte to unarrest

33

zygote

single cell resulting from fertilization

34

Graffin follicle

develops ~day14

oocyte becomes unarrested and quickly forms secondary oocyte (before arresting again)

35

Event after zygote formation is...

cleavage

36

When does cleavage take place?

days 1-4 initiated by fusion of male and female pronuclei

37

What happens during cleavage

cell divisions (1,4,8,16, 32)

38

What prevents the mass of cells from growing during cleavage?

zona pellucida encapsulates cells and prevents growth

39

When does morula form?

Day 5 (16-32 cell) when zona pellucida breaks down

40

when the morula undergoes reorganization it becomes the...

blastocyst

41

3 parts of the blastocyst

embryoblast (embryo), trophoblast (placenta), Blastocyst cavity

42

Where does implantation normally take place?

inner wall of the uterine cavity

43

What does the trophoblast layer do to aid in implanation?

differentiates into two cells lines cytotrophoblasts and syncyiotrophoblasts

44

What is the cytotrophoblast?

layer that remains in the postion of the trophoblast after trophoblast differentiation

45

What is the syncyiotrophoblast?

portion of trophoblast that differntiates into projections that release enzymes that erode uterine lining (allow adherance of embryo)

46

where is morula found?

in ampulla

47

how is morula moved?

moved to uterine cavity using cilia, fluid movement, and muscular contraction

48

What marks the beginning of week 2?

completion of implantation and uteroplacental blood flow
w2

49

What happens to the embryoblast at the beginning of week 2?

it has reorganized into a bilaminar disc
w2

50

What composes the bilaminar disc?

epiblast cells (dorsal surface), hypoblast cells (ventral surface)
w2

51

Which tissue is more important between epiblast and hypoblast?

all tissues making up humans derived from epiblast
w2

52

What is the role of the hypoblast?

lays extraembryonic mesoderm (plays role in placenta and umbilical cord developement)
w2

53

how long does the hypoblast persist?

1 week

w2

54

What happens to cytotrophoblast cells in week 2?

grow and push into syncytiotrophoblast until they lose membranes and become part of the mass
w2

55

What second fluid filled space besides blastocyst arises in week 2?

amnion
w2

56

Where does amnion arise?

in epiblast layer as a cleft
w2

57

What are the epiblast cells that form the roof of the amnion?

amnioblasts
w2

58

Polyhydramnios

amniotic fluid levels that are too high

59

oligohydramnios

amniotic fluid levels are too low

60

what is the primary yolk sac?

its what the blastocyst is referred to once Heuser's (exocoelomic) membrane forms

w2

61

What happens after after exocoelomic membrane?

extraembyonic mesoderm forms

w2

62

How is chorionic space formed?

extraembyonic layer forms vacuoles that fuse

w2

63

How is the definitive yolk sac different than the primary yolk sac?

definitive yolk sac is directly against the hypoblast, while cells off hypoblast push the primary yolk sac away

w2

64

What is the purpose of the definitive yolk sac?

houses primordial germ cells early in development and hematopoiesis

w2

65

What gives rise to the umbilical cord?

the connecting stalk - arises dorsal to amnion where chorionic cavity doesn't separate the layers

w2

66

The chorion is made of what 3 layers?

(int --> ext) extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast (THESE GIVE RISE TO FETUS)

w2

67

T or F it is important to have rudimentary circulation in developing embryo by end of week 2?

T

w2

68

What are lacunar networks?

Lakes of blood formed by syncytiotrophoblasts penetrating multiple vessels

w2

69

What does the prechordal plate give rise to?

marks future mouth

w2

70

What major 4 events occur in week 2 of development?

trophoblast divides into 2 layers (cytotrophoblast and syncytiotrophoblast)
embryoblast forms 2 layers (epiblast and hypoblast)
extraembryonic mesoderm splits to 2 layers (somatic and splanchnic)
two fluid filled spaces for (amnion and yolk sac)

71

Syncytiotrophoblasts secrete which important hormone for maintaining pregnancy?

hCG-secretion begins in week 2

w2

72

What important events occur during the first 3 and a half days of the third week?

1. Formation of the primitive streak and node
2. Migration of epiblast cells through the primitive streak and subsequent development of 3 germ layers

73

What begins in the second half of the third week of pregnancy?

organogenesis (continues through 8th week)

74

What is the first step in gastrulation?

formation of primitive streak and primitive node

w3

75

What covers the definitive yolk sac?

extraembryonic mesoderm

w3

76

What axis is the primitive streak formed along?

cranial-caudal axis

w3

77

What forms the future mouth?

prechordal plate - marks cranial end

w3

78

What marks the caudal end during gastrulation?

cloacal membrane - future anus
marks caudal end

w3

79

Where does the primative streak form?

in the caudal end during gastrulation

w3

80

What is the elevated disc formed by thickening of epiblast cells?

Primitive groove (streak)

w3

81

What happens after primitive groove formation?

epiblast cells migrate from all directions and fall into the streak (groove)

w3

82

Define gastrulation?

migration of epiblast cells to the primitive streak

w3

83

T or F: the primitive streak extends to the cranial end

False

w3

84

What is located at the end of the primitive streak?

Primitive node

w3

85

What is the center point of the primitive node called?

primitive pit

w3

86

What happens to the first wave of epiblast cells to move through the primitive streak?

1. They move ventrally to become adjacent to hypoblast cells
2. They move hypoblast cells out
3. These cells make up the endoderm

w3

87

What happens to the second wave epiblast cells that move through the primitive streak?

1. they move between 1st layer of epiblast cells and hypoblast
2. they form the mesoderm

w3

88

What happens to the third wave of epiblast cells that in gastrulation?

1. They do not move through primitive streak
2. they form the ectoderm

w3

89

What is the trilaminar disc?

3 layered disc formed by gastrulation of epiblast cells to form endoderm, mesoderm, and ectoderm

w3

90

What is sarcococcygeal teratoma?

Tumor made of tissue from all three germ layers (hair, bone, and nerve)

91

T or F sarcococcygeal teratomas usually become malignant.

True

92

What is the cause of sarcococcygeal teratoma?

failure of primative streak to fully regress after gastrulation

93

T or F: sarcococcygeal teratoma is most common in males

False

94

What is a mature male gamete called?

Spermatozoa

95

What are three parts of a spermatozoa?

Head Piece (contains acrosome), Middle piece (mitochondria), Tail (microtubules)

96

What is the zona pelluida?

Very dense PROTEIN coat surrounding the secondary oocyte

97

What is the corona radiata?

A network of follicular cells outside of the corona radiata

98

What are the zona pellucida and corona radiata derived from?

the graffian follicle