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BRS Year 2 > Early foetal development + disorders > Flashcards

Early foetal development + disorders Flashcards

1
Q

what is fertilisation age?

A

measured from the time of fertilisation (assumed +1 day drom last ovulation)
often difficult to measure unless IVF

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2
Q

what is gestational age?

A

calculated from the time of the beginning of the last menstrual period
determined by fertilisation date (+14 days) or early obstetric ultrasound and comparison to embryo size charts

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3
Q

what are carnegie stages?

A

23 stages of embryo development based on embryo features (not time)
allows comparison of developmental rates between species
covers window of 0-60 days fertilisation age in humans

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4
Q

when is the embryogenic stage of pregnancy?

A

14-16 days post fertilisation

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5
Q

what occurs within the embryogenic stage of pregnancy?

A

establishing the early embryo from the fertilised oocyte

pluripotent embryonic and extraembryonic cells established

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6
Q

what is the embryonic stage of pregnancy?

A

16-~50 days post fertilisation

establishing germ layers

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7
Q

what occurs within the embryonic stage of pregnancy?

A

establishment of germ layers, body plan and differentiation of tissue types

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8
Q

how long is the first trimester and what stages make this up?

A

~12wks

embryogenic and embryonic stages

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9
Q

what is the fetal stage of pregnancy?

A

~8wks to ~38wks post fertilisation

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10
Q

what occurs within the fetal stage of pregnancy?

A

major organ systems now present
migration of some organ systems to final location
extensive growth and acquisition of fetal vitality (survival outside the womb)

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11
Q

what cell cluster occurs after zygotic cleavage?

A

cleavage stage embryos (2-8 cells)

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12
Q

what cell cluster occurs after cleavage stage embryos?

A

morula (16 cells)

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13
Q

what cell cluster occurs after a morula?

A

blastocyst (200-300 cells)

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14
Q

when does the maternal-to-zygotic transition occur?

A

4-8 cell stage aka as a morula
this is zygotic genome activation

around 2 days after fertilisation

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15
Q

what is zygotic genome activation?

A

where the embryo transitions from being dependent upon maternal mRNAs and proteins to transcription of embryonic genes

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16
Q

what occurs during maternal-to-zygotic transition?

A

transcription of embryonic genes, increased protein synthesis, organelle maturation

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17
Q

what occurs around the 8 cell stage after maternal to zygotic transition? as a morula

A

compaction

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18
Q

what is embryo compaction?

A

outer cells become pressed against zona, changing mass from spherical to wedge shaped
outer cells polarised, connect to form tight junctions&desmosomes
forms barrier to diffusion between inner and outer embryo

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19
Q

what occurs after compaction?

A

blastocyst formation

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20
Q

what is the structure of a blastocyst?

A

2 distinct cell types (inner cell mass, trophoectoderm)
blastocoel cavity
zona pellucida

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21
Q

what does the inner cell mass contribute to?

A

pluripotent embryonic cells (form final organism)

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22
Q

what does the trophoectoderm contribute to?

A

extra-embryonic cells - make extraembryonic structures to support development e.g placenta

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23
Q

what occurs after blastocyst formation?

A

hatching

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24
Q

what is hatching?

A

the blastocyst enzymatically digests the zona pellucida and the cell contracts to escape it
(5-6 days post F)

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25
Q

what occurs to the trophoblastic cell lineage during peri implantation events?

A

days 7-9
fuse to form syncitiotrophoblast which invades and destroys local maternal cells in endometrium
creates interface between embryo & maternal blood supply
cytotrophoblast cells remain individually to provide source of syncitiotrophoblast cells

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26
Q

what does the inner cell mass separate into during peri implantation events?

A

days 7-9
epiblast - foetal tissues derive from here
hypoblast - forms yolk sac

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27
Q

what occurs at day 12+ to aid pregnancy detection?

A

syncitiotrophoblast secretes hCG (basis of pregnancy tests)

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28
Q

what is bilaminar embryonic disc formation?

A

new amniotic cavity forms between epiblast cells

leaves two layer disc of epiblast & hypoblast cells sandwiched between cavities

epiblast cells separated from hypoblast form amnion cells (will form extraembryonic structures)

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29
Q

what occurs after the bilaminar embryonic disc has formed?

A

gastrulation

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30
Q

what does the endoderm form?

A

GI tract
liver, pancreas
lung
thyroid

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31
Q

what does the ectoderm form?

A

CNS and neural crest
skin epithelia
tooth enamel

32
Q

what does the mesoderm form?

A 
blood
muscle
heart
gonads
kidneys
adrenal cortex
bone, cartilage
33
Q

when does notochord formation occur in foetal development?

A

day 13 onwards

34
Q

what is the notochord?

A

rod like tube of cartilage-like cells formed along embryo midline under the ectoderm
key organising centre for neurulation and mesoderm development

35
Q

what is neurulation?

A

transformation of neural plate into a tube by folding

36
Q

how is neurulation initiated?

A

notochord signals direct the neural plate ectoderm to invaginate forming neural groove
neural folds form along cranio-caudal axis

37
Q

how does the neural tube form?

A

neural folds formed by invagination of neural plate ectoderm eventually fuse to form a hollow tube
neural tube then overlaid with epidermis (ectoderm)
neural crest cells migrate from folds downwards

38
Q

what is gastrulation?

A

formation of body plan via primitive groove invagination
formation of 3 germ layers
(important for forming the body’s axis)

39
Q

what is the first step of gastrulation?

A

formation of primitive groove:
primitive streak (thickened structure along epiblast midline) forms from caudal-cranial
expands to create primitive node and primitive pit
continues to form primitive groove

40
Q

what is the second stage of gastrulation?

A

invagination:
epiblast cells migrate inward to streak, detach from epiblast and move to interior of embryo
fall into space between epi and hypoblast
cells invade and displace the hypoblast

41
Q

what is the final stage of gastrulation

A

formation of germ layers:
definitive endoderm - as cells invaginate, hypoblast cells are displaced forming the layer of endoderm (first cells to invaginate)
mesoderm - cells that invaginated thorough primitive groove are between the new endoderm and old epiblast
ectoderm - old epiblast layer, have not invaginated

42
Q

what closes first in the neural tube

A

head then tail

43
Q

pathologies related to neural tube development

A

anencephaly - partial skull and brain

spina bifida - open tube at birth usually lower spine

44
Q

from which end does the primitive streak develop from?

A

caudal to cranial (tail to head)

45
Q

what are neural crest cells all derived from

A

ectoderm

migrate away from ectoderm during neurulation

46
Q

what is the neural plate?

A

thickened layer of ectoderm on top

location of neurulation, forms neural groove/folds

47
Q

key cells derived from neural crest

A

pigment cells - melanocytes
cranial bones
cardiac - musculoconnective tissue
trunk neurons, sympathetic, parasympathetic and enteric NS

48
Q

disorders of neural crest migration defects

A 
pigmentation disorders
deafness
cardiac defects
facial defects
failure of gut innervation
49
Q

what two tissues do somites originally form

A

dermomyotome (subsequent dermatome and myotome)

sclerotome

50
Q

what is the dermomyotome

A

somite derived tissue
dermatome - dermis of skin, connective tissues of neck and trunk
myotome - muscles of embryo

51
Q

what is the sclerotome

A

vertebrae and rib cartilage from somite derived embryonic tissue

52
Q

what are somites

A

structures arising from paired blocks of paraxial mesoderm to the sides of neural tube/notochord

53
Q

describe the process of formation of the gut tube

A

primitive gut forms from ventral and lateral folding and pinching off part of the yolk sac

primitive gut then patterned into foregut midgut hindgut

54
Q

what is the heart derived from

A

mesoderm
foetal heartbeat detectable around week 6
starts pumping around day 22

55
Q

what are the lungs derived from

A

lung bud of endoderm in 4th week of development

splits into two at end of 4th week

56
Q

what are the gonads derived from

A

mesoderm

57
Q

how are gonads differentiated in the mesoderm

A

presence or absence of SRY gene on Y chromosome
present - sertoli cells form from gonad cells, testis develop
absent - granulosa cells form from gonad cells, ovaries, needs FOXL2 to continue

58
Q

what is early pregnancy loss

A

miscarriage before 23 weeks

59
Q

causes of early pregnancy loss

A

errors in development
failure of implantation
inability to sustain foetus

60
Q

what is a miscarriage before 12 weeks

A

early clinical pregnancy loss

61
Q

biggest cause of early pregnancy loss? esp older women

A

aneuploidy

associated with cohesin loss in ageing oocytes (chromatids not held together)

62
Q

what signalling pathways are indicated in recurrent miscarriages

A

Lif-deficiency - reduced Lif levels in uterine secretions of subfertile women (leukaemia inhibitory factor)
non selective uterus hypothesis - uterus permits implantation of poor embryo, changes in mucin expression

63
Q

what is genomic imprinting

A

epigenetics of gene expression based upon whether the gene was inherited from mother or father

64
Q

what is a parthenogenic embryo

A

embryo without fertilisation - all maternal DNA

large embryo, small placenta (so that mother can go on to have other pregnancies)

65
Q

what is an androgenic embryo?

A

embryo with only paternal DNA

small embryo, large placenta

66
Q

what is a hydatidiform mole?

A

mass of cells that will not grow into a baby due to overwhelming paternal DNA

67
Q

what is a complete hydatidiform mole

A

empty egg fertilised by sperm (duplicated) or 2 sperm

68
Q

what is a partial hydatidiform mole

A

normal egg fertilised by sperm (duplicated genome) or 2 sperm

69
Q

what predisposes some females to recurrent molar pregnancies

A

NLRP-7 mutations

70
Q

what is a gestational trophoblastic neoplasia

A

invasive, malignant hydatidiform mole

71
Q

what is an ectopic pregnancy

A

implantation of embryo at site other than uterine endometrium

72
Q

treatment of ectopic pregnancy

A

chemotherapy
surgery to remove trophoblast
tube removal

73
Q

risk factors for ectopic pregnancy

A

age
previous EP
smoking cigarettes or marijuana
STDs

74
Q

how does smoking cigarettes increase risk of EP?

A

conitine downregulates expression of PROKR1 which regulates fallopian smooth muscle contractility and also induces pro-apoptosis in fallopian tube epithelium
tobacco smoke inhibits ciliary function

75
Q

how does cannabis increase risk of ectopic pregnancy (possibly)

A

CB1 receptor responsible for embryo migration down tube
endocannabinoid signalling higher in all ectopic pregnancies

potential use of exogenous cannabinoids overwhelms/disrupts cannabinoid signalling by either: disrupting receptors, reducing endocannabinoid production or breakdown of endocannabinoids

BRS Year 2 (67 decks)

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