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Embryology > Embryology > Flashcards

Embryology Flashcards

1
Q

what does the embryonic period encompass

A

all of
organogenesis

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2
Q

what period of development is most susceptible to disruption and disorder?

A

organogenesis

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3
Q

development of the CNS entails several coordinated _________ and ________ ______

A

molecular and anatomical changes

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4
Q

what entails several molecular and anatomical changes

A

development of the CNS

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5
Q

embryology definition

A

study of initial development of an embryo

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6
Q

study of initial development of an embryo is

A

embryology

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7
Q

all organ systems are developed by how many weeks?

A

8 weeks

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8
Q

what happens by week 8 of development?

A

all organ systems are developed

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9
Q

after 8 weeks the remainder of gestation is referred to as

A

the fetal period

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10
Q

what is the fetal period?

A

after 8 weeks of development

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11
Q

Describe the first 5 initial events

A

fertilisation - zygote is formed
division of the early embryo - cleavage
after around 3 days embryo is now MORULA
by 4 days - BLASTOCOEL develops and the embryo is now a blastocyte
5 Days - EMBRYOBLAST/inner cell mass is distinct

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12
Q

describe events 6-10

A

hatching occurs day 6/7 - from ZONA PELLUCIDA
day 8-9 blastocyte IMPLANTATION
HYPOPLAST and EPIBLAST cells divide into 2 growing lumens (amniotic cavity and YOLK SAC)
Interface of 2 cell tyes is called - BILAMINAR GERMINAL DISC and becomes the fetus
GERMIAL DISC is where GASTRULATION OCCURS

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13
Q

where does gastrulation occur

A

germinal disc

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14
Q

what is the interface between 2 cell types called?

A

bilaminar germinal disc

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15
Q

what is the bilaminar germinal disc

A

interface between 2 cell types

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16
Q

what is gastrulation

A

generation of the 3 germ layers which derive all embryonic structures

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17
Q

what is the generation of the 3 germ layers that derive all embryonic structures called?

A

gastrulation

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18
Q

describe initial events 11-14

A

Gastrulation occurs along PRIMITIVE STREAK in a caudal to cranial orientation
cells from epiblast invaginate into primitive streak to form ENDODERM and MESODERM - 3 layers form
Led by primitive node
Primitive node also allows for formation of Notochord that orchestrates formation of neural tube

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19
Q

what does primitive node determine

A

anterior-posterior access

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20
Q

where does gastrulation occur

A

along primitive streak in caudal to cranial direction

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21
Q

What does notochord orchestrate

A

formation of neural tube

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22
Q

what orchestrates formation of the neural tube

A

notochord

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23
Q

what are the 3 germ layers

A

ectoderm, mesoderm and endoderm

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24
Q

what does ectoderm form

A

epidermis, epithelial lining of mouth and anus, cornea and lens of eye, nervous system, adrenal medulla

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25
Q

what does meso derm form

A

notochord, skeletal system, muscular system, excretory system, reproductive system, dermis of skin

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26
Q

what does endoderm form

A

epithelial lining of digestive tract and respiratory system, lining of urethra urinary bladder and reproductive system, liver, pancreas, thymus, thyroid

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27
Q

what foes notochord form in line with

A

primitive node

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28
Q

what is the notochord in vertebrates

A

transient but essential

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29
Q

what does notochord do

A

organises surrounding tissues and provides structural support

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30
Q

what does notochord secrete

A

factors which control CNS development from overlying ectoderm

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31
Q

what does notochord regulate

A

left/right asymmetry
arterial/venous identity in major vessels
aids in the specification of forming somites

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32
Q

notochord secretes:

A

signalling factors which induce specification of the overlying ectoderm to form the neural plate (starts day 18)

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33
Q

uneven proliferation causes the formation of:

A

neural groove and neural folds

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34
Q

_____ converge at _____ to form the neural tube

A

neural folds at the neural plate border

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35
Q

neural folds converge at neural plate border to form

A

neural tube

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36
Q

final closures of the neural tube at the ________

A

caudal and cranial neuropores

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37
Q

when does the cranial neuropore close

A

day 24 of development

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38
Q

when does the caudal neuropore close

A

day 28 of development

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39
Q

what gives sheets of cells the ability to specify and develop multiple organ systems, many cell types and all in the correct orientation and order

A

morphogens and also via a cell’s competence for that morphogen signal (external and internal control)

40
Q

what do morphogens do

A

specifying and developing multiple organ systems, many cell types and all in the correct orientation and order

41
Q

what does notochord induce and via what

A

induces the floor plate via Sonic HedgeHog

42
Q

what does induction of notochord by SHH allow for

A

a switch in cadherin expression (E to N) and initiation of inward folding

43
Q

what signals are required for notochord to switch in cadherin expression

A

Chordin, Noggin and SHH

44
Q

where are the morphogens Chordin and Noggin expressed

A

in the node at the cranial end of the primitive streak

45
Q

what are Chordin and Noggin morphogens key for

A

setting the midline of the embryo - determining dorsal/ventral AND left/right axes both of which are required for future brain segmentation

46
Q

after initiation of initial folding, what does the surrounding ectoderm express

A

opposing morphogens BMPs (4 and 7) and WNTs

47
Q

what doe the opposing morphogens after initial folding allow for

A

orientation of the roof plate and closure of the neural tube. aid in specification of the now overlying ectoderm - epithelium

48
Q

what population of cells are specified after the closure of the neural tube

A

neural crest cells

49
Q

what happens after closure of the neural tube

A

neural crest cells detach from the neural folds and sit dorsal to the roof plate of the neural tube

50
Q

neural crest cells migrate and differentiate into what key structures

A

Neurons and glia of the PNS
Adrenal Medulla
Melanocytes
Facial cartilage and bone
Corneal epithelium
Endothelial lining of the aortic arches, endocardial cushion and aorticopulmonary septum

51
Q

as the neural tube starts to close, distinct structures are specified at the _____ end

A

cranial

52
Q

as the neural tube starts to close, what distinct structures are specified at the cranial end

A

primary vesicles (week 4)

53
Q

what are the primary vesicles

A

prosencephalon
mesencephalon
rhomboencephalon

54
Q

primary vesicles after further specification form:

A

secondary vesicles

55
Q

what are the secondary vesicles

A

telencephalon
diencephalon
mesencephalon
metencephalon
myelencephalon

56
Q

describe initial formation of vesicles

A

via tightly orchestrated proliferation events
cranial end of the neural tube proliferates before closure even occurs to crease the 3 primary vesicles
proliferation of neural tube occurs in restricted space creates 3 bends of neural tube to allow for further specification

57
Q

3 bends in the neural tube called:

A

Cephalic flexure (ventral) - midway through the mesencephalon
Pontine flexure (dorsal) - at the base of metencephalon
Cervical flexure (ventral) - separates the myelencephalon from the spinal core

58
Q

when do the flexures in neural tube develop

A

between primary and secondary vesicle formation - present by week 5

59
Q

what does the telencephalon become

A

cerebrum

60
Q

neurogenesis meaning

A

process by which neurons and glia proliferate, migrate and are specified to form the mature brain

61
Q

what is synaptogenesis

A

synapse formation and organisation occurs

62
Q

what is neural pruning

A

orchestrated apoptosis

63
Q

what is orchestrated apoptosis known as

A

neural pruning

64
Q

where is myelination initiated

A

starts in the cerebellum and the brain stem

65
Q

what is deemed a multipotent neuroepithelial population

A

neural stem cells

66
Q

what initiates proliferation in the embryonic brain

A

neural stem cells

67
Q

what doe neural stem cells produce and what do they develop

A

radial glia that develop into both glia and neurons

68
Q

what are radial glia essential for

A

development of the embryonic neural network - comprise the ventricular zone

69
Q

what do NSCs divide by to continue what

A

NSCs divide by both asymmetric and symmetric division to continue self-propagation during development

70
Q

what do NSCs primarily divide into

A

neurons, astrocytes and oligodendrocytes

71
Q

what is cell specification determined by

A

spatial patterning (dorsal/ventral)
time/chronological
local signalling (microenvironment/morphogens)

72
Q

what is a key requirement of the developing brain

A

migration

73
Q

what are the 2 types of migration

A

glial mediated - use of radial glia framework
somal translocation 0- self propelled

74
Q

what are the 2 directions of migration

A

radial - radiates out from the centre
tangential - moves around or along the neural tube

75
Q

when does formation of synapses start

A

during fetal life (mid-second trimester) and is intensely built in the first few years of life

76
Q

when does axonal myelination start

A

late in gestation and is continued throughout adolescence and into adulthood

77
Q

at 12 weeks gestation

A

brain structures similar to the adolescent/adult brain
lack of gyri and sulci in the cerebral cortex

78
Q

what increases cortical volume

A

sulcation and gyrification

79
Q

what is sulcation and gyrification essential for

A

increasing cortical volume and allowing for increased cognitive fucntion/processing

80
Q

when are primary sulci initiated and formed

A

week 12- 28
vast majority of gyri and sulci are formed and defined in second and third trimester

81
Q

how much does grey matter increase per week from week 29

A

15ml/week

82
Q

how are preterm infants kept

A

in conditions which prevent overstimulation/ can impact neural development as a result

83
Q

what is one of the most essential pieces of embryology

A

closure of the neural tube

84
Q

what occurs if neural tube is not closed

A

neural tube defects

85
Q

what is anencephaly

A

failure of the cranial neuropore to close

86
Q

what occurs when cranial neuropore fails to close

A

anencephaly

87
Q

what is telencephalon

A

absence of major aspects of the brain and skull

88
Q

what is the most common neural tube defect

A

spinal bifida

89
Q

how does spina bifida occur

A

when the caudal neuropore fails to close

90
Q

what are neural tube defects linked to

A

folic acid metabolism

91
Q

mechanism of folic acid preventing neural tube defects?

A

not fully understood
possible role in epigenetic reprogramming which coincides with the time of neural tube formation

92
Q

what is the most severe neural tube defect

A

craniorachischisis

93
Q

what is Craniorachischisis

A

both brain and spinal cord are exposed

94
Q

what causes craniorachischisis

A

multi factorial cause - genetic and environmental disruption.
linked with genetic disruption of the folate metabolism pathway
seen in cases of trisomy 18

95
Q

describe microcephaly

A

smaller than normal head circumference due to lack of brain development
associated with many exposures to teratogens (ZIKA)
genetic links - trisomies
usually lack of cerebral cortex development
poor neurogeneis, loss of neural stem cells or uncontrolled apoptosis

96
Q

describe holoprocencephaly (HPE)

A

defect whereby the procencephalon fails segment at the midline
failure of segmentation at week 5-6
detected by ultrasound
poor prognosis

97
Q

describe variances of holoproencephaly

A

classifications - lobar, semi-lobar, alobar
reflected in facial patterning of fetus- most severe is cyclopia
less severe- cleft lip

Embryology (1 decks)

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