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Flashcards in Embryology Deck (119):
1

What takes place on day 0 of development?

Fertilisation

2

Where does fertilisation initially take place?

Ampulla

3

How long does fertilisation take?

Around 20 hours

4

What is a zygote?

A fertilised oocyte containing the DNA of the ovum and the spermatocyte

5

What happens around 24 hours after fertilisation?

The zygote begins to increase its number of cells by rapid mitosis, though the actual size doesn't increase

6

What is a blastomere?

A type of cell produced by the cleavage (cell division) of the zygote after fertilisation

7

What is a morula?

An embryo at the early stage of development, consisting of cells (called blastomeres) in a solid ball

8

What is the morula contained within?

Zona pellucida

9

What are the cells inside the morula called?

The inner cell mass (embryoblast)

10

What are the cells on the outside of the morula called?

Outer cell mass (trophoblast)

11

What will the outer cell mass become?

Supporting structures for the embryo

12

What does the zone pellucida do?

Protects the zygote from any more sperm

13

What occurs around 4 days after fertilisation?

Morula passes into uterus

14

What do the trophoblast cells do to the luminal fluid in the uterine cavity?

Pull it into the centre of the morula

15

What is a blastocoele?

A fluid filled region of the blastocyst

16

What happens to the inner cell mass as the blastocoele forms and what is become known as?

Inner cell mass is pushed to one end
Becomes known as embryonic pole

17

What is a blastocyst?

Structure formed around 5 days after fertilisation and possesses an inner and outer cell mass and a blastocoele

18

What happens to the zone pellucida around 5 days after fertilisation?
What does this allow?

Blastocyst loses zona pellucida
Allows it to grow in size and interact with uterine wall

19

What is triggered when the blastocyst attaches to the endometrial epithelial lining of the uterus?

Changes in the trophoblast cells
Changes to the endometrium in preparation for implantation

20

What are the three phases of the menstrual cycle?

Proliferative phase
Secretory phase
Menstrual phase

21

When is the proliferative phase of the menstrual cycle and what happens during it?

Day 5-13 of menstruation, prior to ovulation.
Increased thickness of endometrium and increase in vascularisation

22

What happens in the secretary phase of the menstrual cycle?

Arteries and glands become coiled and secretions increase, helping to maintain thickness of endometrium

23

Why does implantation occur?

Allow developing embryo to take oxygen and nutrients from mother

24

When does implantation of the blastocyst begin?

6-7 days after fertilisation

25

When the blastocyst 'sticks' to the uterine wall, where is the embryonic pole?

Closest to endometrium
If it isn't it rotates till aligned with the decidua

26

What is the entire surface of the endometrium covered with and what happens if fertilisation doesn't occur?

It's covered with decidual cells, which shed, along with the spongy and compact layers if fertilisation does not occur

27

What is the decidual reaction?

Endometrial decidua react to contact of blastocyst by increasing secretory functions of endometrium at area of implantation

28

At implantation what do the cells accumulate?

Fats and glycogen

29

What is a syncytium?

Multinucleated barrier that form the interface with the maternal blood stream

30

What is the syncytiotrophoblast?

Epithelial covering of highly vascular embryonic placental villi, which invade the wall of the uterus to establish nutrient circulation between the embryo and mother

31

What part of the trophoblast forms the syncytiotrophoblast?

Trophoblast cells that are in contact with the endometrium

32

What do the trophoblast cells that are not in contact with the endometrium become?

Cytotrophoblast

33

What happens to cells that become the cytotrophoblast?

Spread out and become thinner

34

What is the bilaminar disc?

Where cells of embryoblast have differentiated and become two layers: epiblast and hypoblast

35

What forms as a space above the epiblast?

Amniotic cavity

36

What are the cells that line the amniotic cavity called and what do they do?

Amnioblasts
Secrete amniotic fluid

37

What space appears below the hypoblast on day 9 and what does it do?

Primary yolk sac
Provides nutrients for the embryo until placenta is formed

38

On day 12 what begins to form from the syncytiotrophoblast?

Lacunae

39

What do the lacunae of the syncytiotrophoblast do?

Join up and meet with the maternal blood vessels to become the maternal/foetal blood interface

40

What does the chorionic cavity form from?

Extra-embryonic coelom

41

By which day post-fertilsation has the endothelium of the endometrium completely closed over the blastocyst?

Day 12

42

What happens to the primary yolk sac after day 13?

It becomes known as the secondary yolk sac

43

What is the connecting stalk?

A yolk sac diverticulum, derived from extra-embryonic mesoderm
Goes on to form umbilical cord

44

What do decidual cells have a high capacity to secrete?
What is their main functional quality?

Laminin and fibronectin
Have high adhesive qualities

45

What happens in gastrulation?

Single-layered blastula is reorganised into a trilaminar structure known as the gastrula

46

What are the three germ layers?

Ectoderm
Mesoderm
Endoderm

47

When is gastrulation initiated?

14 to 15 days after fertilisation

48

What is the primitive streak?

A depression that runs on the epiblastic surface of the bilaminar disc
Is restricted to caudal half of embryo

49

What is the primitive node?

A round mass of cells at the cephalic end surrounding the primitive pit

50

How are the germ layers formed in gastrulation?

Epiblastic cells migrate towards the primitive streak and slip under (invaginate) the epiblast later to form new layers

51

What happens to the first cells that invaginate in gastrulation?

They replace the hypoblast later and become the endodermal layer

52

From what is the mesodermal layer formed?

Epiblast cells that sit between the epiblast and endodermal layer

53

From what is the ectodermal layer formed?

Remaining epiblast layer

54

What will the ectoderm form? Give examples.

External layer of the embryo:
Epidermis of skin
Neural crest cells (go on to form nervous system)

55

What will the mesoderm form? Give examples.

Major contributor to embryo and cells:
Bones
Cartilage
Muscle
Cardiovascular and respiratory system
Kidneys
Spleen
Dermis of skin

56

What will the endoderm form? Give examples.

Epithelia that line passages exposed to external substances:
GI tract
Lungs
Epithelia of urethra and bladder
Thymus
Thyroid

57

What is the embryonic period?

First 8 weeks after fertilisation

58

What happens during the embryonic period?

Major structures of the embryo formed

59

What happens in the foetal period?

Rapidly grows in size, mass and complexity

60

What is the difference in embryologists and clinicians timings?
And why?

14 days
Embryologists measure from fertilisation
Clinicians measure from LMP

61

What is the gestational period according the embryologists and clinicians?

38 weeks or 9.5 lunar months to embryologists
40 weeks or 10 lunar months to clinicians (equal to 9 months and 7 days)

62

By what three ways can growth occur?

Proliferation
Hypertrophy
Accretion

63

What is proliferation?

An increase in cell number by cells dividing to produce daughter cells

64

What is hypertrophy?

An increase in cell size

65

What is accretion?

An increase in tissue by cells increasing the amount of extracellular matrix

66

What is differentiation?

Proces by which cells and tissues become specialised

67

How do cells know where and what part of the body they will become?

Through signalling proteins and connections between neighbouring cells

68

What is morphogenesis?

Formation of a shape during development

69

How does morphogenesis occur?

Through migration and adhesion of cells

70

When does the development of the digestive system occur?

During the fourth week of development

71

What is the primitive gut?

A cavity formed by the endodermal cells, which is the forerunner of the GI tract

72

What is the cranial end of the primitive gut covered by?

Bucopharyngeal membrane

73

What is the caudal end of the primitive gut covered by?

Cloacal membrane

74

What does the bucopharyngeal membrane separate?

Foregut from stomodeum

75

What will the stomodeum develop into?

Oral cavity

76

What does the cloacal membrane separate?

Hindgut from proctodeum

77

What will the proctodeum develop into?

Anus

78

How is the gut tube separated?

Into anterior foregut, intermediate midgut and posterior hindgut.
Divided by region of the rube that remains attached to the yolk sac and the the branches of the aorta that supply each part

79

What happens to the yolk sac at the 5th week?

Constricts and detaches from the midgut and the midgut seals

80

How does the stomach develop from the primitive gut tube?

A part of the foregut begins to dilate at week 4
Dorsal side grows faster than ventral
Then rotates to bring left side around to become ventral surface

81

What does the rotate of the stomach do to the duodenum?

Moves it into its adult C-shaped position

82

What does the rotation of the stomach do to the bile ducts?

Moves the entry of the bile ducts into the duodenum posteriorly

83

What happens to the midgut at approximately week 6?

Has grown so quickly it cannot be contained in abdominal cavity and so herniates into umbilical cord

84

How does the midgut rotate?
What does this do to the caecum?

270 degrees counter-clockwise
Brings caecum from inferior abdomen to left of developing small intestine, to top of abdomen and then descends into right lower quadrant

85

When does the midgut re-enter the abdomen?

About week 10

86

Name the factors that affect re-entry of the midgut into the abdomen.

Growth of the abdomen
Regression of the mesonephric kidney
Reduced rate of liver growth

87

What does the urorectal septum divide the cloaca into?

Primitive urogenital sinus anteriorly
Anorectal canal posteriorly

88

What is the ventral mesentery derived from?

Septum transversum

89

What will the dorsal mesentery form?

Greater omentum
Mesenteries of small and larger intestine

90

What will the ventral mesentery form?

Lesser omentum
Falciform ligament

91

What is the main embryological function of the liver?

Haematopoiesis

92

In what week does the liver start forming bile?

Week 12

93

What is the period of respiratory development?

Day 28 after fertilisation continuing to childhood

94

What are the five stages of lung development?

Embryonic stage
Pseudoglandular stage
Canalicular stage
Saccular stage
Alveolar stage

95

When and what happens in the embryonic stage of lung development?

Upto week 5
Initial bud and branching

96

When and what happens in the pseudoglandular stage of lung development?

Week 6-16
Complete branching

97

When and what happens in the canalicular stage of lung development?

Week 17-24
Terminal bronchioles

98

When and what happens in the saccular stage of lung development?

Week 25 to birth
Terminal sacs and capillaries come into close contact

99

When and what happens in the alveolar stage of lung development?

Week 36 onwards
Well-developed blood-air barrier

100

How does the development of the respiratory system begin?

Growth of an endodermal bud from the ventral wall of the developing gut tube in week 4

101

What splits the dorsal foregut and ventral lung bud?

Tracheoesophageal septum

102

Which cells produce surfactant?

Lung-specific type II alveolar cells (pneumocytes)

103

What are the cells of gaseous exchange?

Type I alveolar cells (pneumocytes)

104

What is respiratory distress syndrome caused by?

A lack of surfactant resulting in lung collapse

105

How many alveoli are there at birth compared to an adult lung?

Around 20-50 million at birth
Increasing to 400 million in an adult lung

106

What is neurulation?

Transformation of the neural tube into the neural plate

107

What starts off neurulation in the ectoderm?

Signals from the notochord

108

What are the primary brain vesicles?

Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)

109

What happens in primary neurulation?

Neural plate creases inward until the edges come in contact and fuse

110

What signal induces formation of the floor plate of the incipient neural tube?

Sonic Hedgehog (SHH) signal

111

By what day after fertilisation has the notochord formed?

Day 22

112

At the beginning of neural tube formation, what are the openings at either end called?

Cranial and caudal neuropores

113

What day does the cranial neuropore close?

Day 24

114

What day does the caudal neuropore close?

Day 26

115

Where would neural crest cells be found on the neural plate?

At the border between the neural plate and the epidermis

116

As the neural tube forms, what happens to neural crest cells?

Leave neural tube and migrate to other parts of the embryo

117

Where do spinal defects in the embryo normally arise and why?

In the cranial or caudal end as the neuropores are the last bit to close

118

What are the subdivisions of the embryonic forebrain and what do they form?

Telencephalon - cerebral hemispheres
Diencephalon - Pituitary, hypothalamus, thalamus

119

What are the subdivisions of the embryonic hindbrain and what do they form?

Myelencephalon - medulla oblongata
Metencephalon - cerebellum, pons