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Embryology > Embryogenesis > Flashcards

Embryogenesis Flashcards

1
Q

When does embryogenesis occur?

A

From 2-8 weeks post fertilisation

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2
Q

When is the fetal period?

A

From 9 weeks till term

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3
Q

When and where does fertilisation usually occur?

A

At the ampulla of the Fallopian tube, 12 hours post ovulation

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4
Q

What is a zygote?

A

A fertilised ovum

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5
Q

Describe the 1st week after fertilisation

A

1st meiotic division occurs directly after fertilisation
Day 2 (zygote) and 1st mitotic division occurs 30 hours post fertilisation
Day 3 (16 cells)- morula (blackberry)- uterine cornu
Day 4 blastocyst enters the uterine cavity
Day 6 implantation begins

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6
Q

What is a blastocyst?

A

The blastocyst forms by day 4 after fertilisation, composed of 70-100 cells, once the embryo has reached the uterine cavity. It is formed of an inner cell mass (the embryoblast) and the outer cell mass (the trophoblast) and a fluid filled cavity called the blastocoele

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7
Q

What is the trophoblast?

A

The outer cell mass that forms the placenta, it is composed of 2 cell lines- the outer syncytium and the inner cytotrophoblast

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8
Q

What is the embryoblast?

A

It is the inner cell mass of the blastocyst which forms embryonic tissues

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9
Q

When does decidualisation occur?

A

Day 8 after fertilisation

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10
Q

What is the bilaminar disc and when does it form?

A

The bilaminar disc forms from the embryoblast (inner cell mass of the blastocyst) on day 8, it is formed of the epiblast (the dorsal germinal later) and the hypo last (the ventral germinal layer)

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11
Q

Where does the amniotic cavity come from?

A

The amniotic cavity starts to form on day 8 from the epiblast (the dorsal germinal layer in the bilaminar disc which is formed from the embryoblast)

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12
Q

When does implantation start and when is it complete

A

Implantation begins on day 6 and is complete on day 13

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13
Q

First heart beat

A

Day 21

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14
Q

What does the ectoderm form?

A

Integumentary system (Epidermis, nails, hair) and nervous system (brain and spinal cord), pituitary gland

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15
Q

What does the mesoderm form?

A 
Muscles (cardiac/smooth muscle/striated muscle)
Skeletal system
blood vessels
Connective tissues
excretory system
reproductive system
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16
Q

What does the endoderm form?

A

Epithelial layer of the gastrointestinal tract, lungs, pancreas, bladder, endocrine glands, auditory system, urinary system

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17
Q

What are somites, when do they start to form and what do they eventually form?

A

Somites are formed by the mesoderm, they develop on the embryos dorsum starting on day 20, they develop on either side of the neural tube and develop at a rate of three pairs a day, they form muscle and connective tissue (dermomyotomes) and bones (sclerotomes)

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18
Q

How does the blastocyst get its nutrients?

A

From the zona pellucida in the blastocoele

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19
Q

What is the trilaminar disc, when does it form and how is it different from the bilaminar disc?

A

The trilaminar disc forms in the 3rd week (the bilaminar disc forms in the 2nd week) the trilaminar disc is formed of the ectoderm, endoderm, and mesoderm (the bilaminar disc is formed from the embryoblast and is composed of two layers- the epiblast and hypo last)

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20
Q

When does birth usually occur?

A

37-42 weeks

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21
Q

When does fertilisation have to occur?

A

Within 1 day of ovulation

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22
Q

What is the difference between embryological and gestational timing?

A

Embryological timing starts at fertilisation, whereas,
Gestational timing is a clinical estimate and starts at the last menstrual period and ends at 9 months+7 days, it is usually 2 weeks longer than embryological timing i.e. 8 weeks embryonic age is 12 weeks gestation

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23
Q

Preterm and post term dates

A

<37 weeks and >42 weeks gestation

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24
Q

What are the three germ layers?

A

Endoderm, ectoderm, mesoderm

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25
Q

What do the hypoblast cells form?

A

The endoderm and yolk sac (umbilical vessicle)

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26
Q

What do the epiblast cells form?

A

The ectoderm and amniotic cavity

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27
Q

What does the yolk sac develop into?

A

The umbilical cord

28
Q

When does the primitive streak develop?

A

day 15

29
Q

What end of the embryo does the primitive streak develop?

A

The caudal end

30
Q

Which end of the embryo does the primitive node develop?

A

The cephalic end

31
Q

What is the primitive streak?

A

An invagination of the ectoderm, where ectodermal cells migrate between the ectoderm and endoderm to form the intra-embryonic mesoderm

32
Q

How is the mesoderm formed?

A

Invagination of the ectoderm forming the primitive streak at day 15, ectodermal cells migrate outwards forming the intra-embryonic mesoderm between the endoderm and ectoderm - these then migrate outwards to form the extraembryonic mesoderm

33
Q

What is the chorionic sac?

A

Another term for the gestational sac

34
Q

What is the clinical significance of the gestational sac?

A

The mean sac diameter can be used to estimate gestational age

35
Q

In relation to the gestational sac, when should the yolk sac be seen on ultrasound?

A

When the gestational sac is 20mm

36
Q

In relation to the gestational sac, when should the fetal pole be seen on ultrasound?

A

When the gestational sac is 25mm

37
Q

When do the germ layers form?

A

at 3 weeks

38
Q

When does embryo folding occur?

A

day 21-24

39
Q

What does the allantois become?

A

The allantois forms on day 16. It is a diverticulum of the yolk sac (umbilical vesicle). It goes on to form the urachus - bridging at the urogenital sinus between the yolk sac and the fetal bladder. It is also involved in early fetal blood formation

40
Q

What is gastrulation?

A

The formation of the 3 germ layers (endoderm, ectoderm, mesoderm) at week 3 of embryo development

41
Q

When does neurulation begin?

A

3rd week of development

42
Q

Where does the notchord form?

A

In the intraembryonic mesoderm

43
Q

When is the neural plate formed?

A

By day 18

44
Q

When are the neural folds formed?

A

By day 20

45
Q

When is the neural tube formed?

A

By day 22

46
Q

When does the anterior neuropore close?

A

Day 24

47
Q

When does the posterior neuropore close?

A

Day 26

48
Q

What is the neural plate?

A

A thickening of the ectoderm lying below the notochord of the intra-embryonic mesoderm, it forms on day 18

49
Q

What does the neural tube form?

A

The brain and the spinal cord (central nervous system)

50
Q

What eventually gives rise to the peripheral nervous system?

A

The neural crests (ganglia)

51
Q

What does the paraxial mesoderm form?

A

It lies beside the neural tube and forms the somites which eventually form muscles, connective tissue and dermis -

52
Q

When do the first pair of somites form?

A

Day 20

53
Q

What rate do the somites form?

A

The somites are formed from paraxial mesoderm, the first pair form on day 20 and they form at a rate of 3/day

54
Q

What does the intermediate mesoderm form?

A

The gonads and the kidneys

55
Q

What does the somatic mesoderm do?

A

It arises from the lateral mesoderm and lines the amnion

56
Q

What does the splanchnic mesoderm do?

A

It arises from the lateral mesoderm and lines the yolk sac

57
Q

What is the maximum number of somites?

A

42-44 pairs

58
Q

What are the three parts of the embryonic brain?

A

Prosencephalon (forebrain), mesencephalon (midbrain) and rhombencephalon (hindbrain)

59
Q

What does the telencephalon form from and what does it become?

A

The telecephalon forms from the prosencephalon and it becomes the right and left hemispheres of the brain (cerebral cortex)

60
Q

What does the diencephalon form from and what does it become?

A

The diecenphalon forms from the prosencephalon (forebrain) to form the thalamus, hypothalamus and eptithalamus

61
Q

What does the metencephalon form from and what does it become?

A

The metencephalon forms from the rhombencephalon (hindbrain) and forms the pons and cerebellum

62
Q

What does the myencephalon form from and what does it become?

A

The myencephalon forms from the rhombencephalon (hindbrain) and forms the medulla oblongata

63
Q

Which cranial nerve comes from the telencephalon?

A

The olfactory nerve

64
Q

Which cranial nerve develops from the diecephalon?

A

The optic nerve

65
Q

Which cranial nerves develop from the mesencephalon?

A

III and IV

66
Q

Which cranial nerves develop form the metencephalon?

A

Trigeminal, abducens, facial, vestibulocochlear,

67
Q

Which cranial nerves develop from the myencephalon?

A

glossopharyngeal, vagus, accessory and hypoglossal

Embryology (4 decks)

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