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1st Year Med > Embryology/Pregnancy (W1 KPH) > Flashcards

Embryology/Pregnancy (W1 KPH) Flashcards

1
Q

what are the 3 stages of life before birth?

A

preimplantation stage (week 1)
embryonic stage: organogenesis (weeks 2-8)
fetal stage: growth/development (weeks 9-38)

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2
Q

what is embryological cleavage and what does it allow?

A

mitotic divisions of the fertilised oocyte (egg)
allows passage down narrowest part of the uterine tube (isthmus)

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3
Q

what cell specialisation does the oocyte have and what is its purpose?

A

surrounded by tough glycoprotein coat (zona pellucida) to prevent premature implantation

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4
Q

explain the process of morula formation

A

around day 4 after fertilisation, cells maximise contact with eachother, forming a cluster of cells held together by tight junctions
it then enters the uterus

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5
Q

what are the first signs of cellular differenciation?

A

blastocyst formation

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6
Q

what occurs during blastocyst formation?

A

inner cell mass - forms embryo and extraembryonic tissues
outer cells (trophoblasts) - contributes to placenta
fluid filled blastocyst cavity also forms

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7
Q

explain the process of blastocyst hatching

A

ICM cells undergo proliferation and fluid fills up in the cavity, resulting in the blastocyst hatching from the zona pellucida to facilitate implantation

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8
Q

explain the process of decidualisation

A

occurs in uteral stromal cells, is the process of several endometrium (part of uterus) changes in preparation for pregnancy

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9
Q

what happens to trophoblasts during decidualisation?

A

they become invasive and begin to differenciate

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10
Q

what are the 2 differenciated trophoblast layers called and which one is invasive?

A

inner - cytotrophoblast
outer - syncytiotrophoblast (invasive)

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11
Q

what do implanting syncytiotrophoblasts do at the end of week 2?

A

communication with maternal placenta side to establish a connection
enables diffusion of oxygen, nutrients and waste through blood supply

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12
Q

what hormone does syncytiotrophoblasts produce?
where is it secreted?

A

human chorionic gonadotrophin (hCG)
secreted into urine

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13
Q

what is an ectopic implantation?

A

where zygote implantation occurs in the wrong place

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14
Q

what could cause an ectopic pregnancy?

A

slow transit through uterine tube or premature blastocyst hatching

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15
Q

where can ectopic implantations implant?

A

uterine tube, peritoneal cavity or ovary surface

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16
Q

name the 4 extra-embryonic membranes

A

amnion
chorion
yolk sac
allantois

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17
Q

describe the key features of the amnion

A

continuous with epiblasts on bilaminar disc
lines amniotic cavity which is filled with fluid and protects the embryo
presents up until birth

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18
Q

describe the key features of the chorion

A

doubled layered membrane formed by trophoblasts/extraembryonic mesoderm (EEM)
lines chorionic cavity, seen in early pregnancy but disappears due to amniotic cavity
forms fetal component of placenta

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19
Q

describe the key features of the yolk sac

A

continuous with hypoblasts on bilaminar disc
important in week 2-3 nutrient transfer, dissapears by week 20
important in blood cell and gut formation

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20
Q

describe the key features of the allantois

A

outgrowth of yolk sac
contributes to umbilical arteries and connects to fetal bladder

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21
Q

define gastrulation

A

a process of cell division and migration resulting in the formation of 3 germ layers

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22
Q

what forms from the bilaminar epiblast in week 3?

A

trilaminar embryo

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23
Q

what are the 3 germ layers called?

A

ectoderm, mesoderm and endoderm

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24
Q

what additional structures are important in week 3 development?

A

primitive streak, notochord, neural tube

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25
Q

what is the primitive streak?

A

a thickened area of cells originating from the embryo’s tail end

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26
Q

what growth factor is made by the primitive streak?

A

fibroblast GF 8

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27
Q

describe some of the structures the ectoderm forms

A

generally outer structures:
epidermis, hair follicles, epithelial lining of mouth/anus, cornea, adrenal medulla, nervous system

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28
Q

describe the structures formed by the mesoderm

A

generally central structures:
MSK, circulatory/lymphatic systems, dermis of skin, adrenal cortex

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29
Q

describe the structures formed by the endoderm

A

generally inner linings and organs:
liver, pancreas, epithelial digestive tract lining, thyroid/parathyroid glands

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30
Q

what does the mesoderm layer divide into once formed?

A

notochord
paraxial mesoderm
intermediate mesoderm
lateral mesoderm
extraembryonic mesoderm

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31
Q

what are the 2 areas of the early embryo without mesoderm?

A

oropharyngeal membrane and cloacal membrane

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32
Q

what days are the paraxial, intermediate and later plate mesoderm formed between?

A

17-21

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33
Q

describe the formation, location and differenciations of the paraxial mesoderm

A

forms from cells moving bilaterally and cranially from primitive streak
lies adjacent to notochord and neural tube
forms somites in the embryo

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34
Q

what does the intermediate mesoderm form?

A

GU system

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35
Q

what 2 layers is the lateral plate mesoderm split into and what splits it?

A

split by cavity (intraembryonic coelom)
forms somatic (parietal) and splanchnic (visceral) layer

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36
Q

which mesoderm layer does each muscle type arise from?

A

skeletal - paraxial
smooth/cardiac - visceral lateral plate

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37
Q

explain the formation of somites from paraxial mesoderm

A

paraxial mesoderm arranged into somites (segments)
forms alongside neural tube in a craniocaudal sequence
somites appear 3 pairs a day from day 20 until 5 weeks

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38
Q

what happens to unsegmented mesoderm?

A

called pre-somitic mesoderm
gets ‘patterned’

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39
Q

explain the gene regulation of somite formation

A

as somites form, gene notch is high and it moves down the embryo from the bottom
FGF8 gene washes up somites
the overlapping gradients control somite formation

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40
Q

what happens when somites lose their epithelial characteristics?

A

segmented paraxial mesoderm is transformed into spheres forming an epithelial cell lumen
occurs in week 4 when cells undergo epithelial-mesenchymal transition

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41
Q

what happens to cells in the ventral half of a somite?

A

they undergo epithelial-mesenchymal transition
the become the sclerotome and form the vertebrae and ribs

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42
Q

what happens to cells in the dorsal half of somites?

A

they become the dermomyotome
this splits into the dermatome (dermis of the back) and myotome (muscles)

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43
Q

what does the parietal layer of the lateral plate mesoderm form?

A

body wall, CT and bones

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44
Q

what does the visceral layer of the lateral plate mesoderm form?

A

the tube of gut wall and serous membranes

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45
Q

what occurs when myoblasts align with chains and fuse?
what mediates this?

A

cell membranes disappear creating multinucleated myotubules (primary tubules)
myogenin mediates this differenciation

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46
Q

explain the role of muscle specific gene activator transcription factors (with examples)

A

enables differenciation of myogenic precursor cells in the dermomyotome of myoblasts
converts non-muscle cells (fibroblasts/adipocytes) into cells expressing muscle proteins (essentially muscle cells)
e.g MYOD and MYF5

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47
Q

how is MYOD and MYF5 expressed in the neural tube?

A

WNT proteins (activating) and BMP proteins (inhibitory) combine to activate MYOD in the dermomyotome
this creates muscle cell precursors which express MYF5

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48
Q

what induces sclerotome formation in the notochord?

A

sonic hedgehog and noggin

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49
Q

name the 2 locations MYOD and MYF5 can be expressed?

A

neural tube and lateral plate mesoderm

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50
Q

explain the process of embryonic folding and when it occurs

A

split into lateral folding (by somites) and cephalocaudal folding (by CNS)
occur simultaneously and closes body wall of embryo creating a tube structure
occurs days 18-21

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51
Q

explain mesenchymal stem cells role in intramembranous ossification

A

begins with condensation of mesenchymal cells which proliferate and differenciate into osteoprogenitor cells which turn into osteoblasts (allowing cartilage step to be skipped)

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52
Q

explain the characteristics of the notochord

A

transient patterning structure
role in molecular signalling
controls embryonic folding direction
flexible rod-shaped structure ventral to neural tube
inductive relationship with overlying ectoderm

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53
Q

what does the notochord become after birth?

A

nucleus puplosus of the intervertebral disc

54
Q

what do the signals arising from the notochord do?

A

induce development in neural plate and overlying ectoderm

55
Q

what are the 2 important notochord signals and what do they do?

A

noggin and chordin
negative regulators - presence activates inhibition of other molecules
they inactivate BMPs (BMP4) which allows patterning of neural tube and somites

56
Q

explain the formation of the neural plate

A

appearance of the notochord and mesoderm induces overlying ectoderm to thicken (forming neural plate)
cells of the plate make up the neuroectoderm (the initial event of neurulation)

57
Q

explain how the neural tube is formed from the neural plate

A

neural plate lengthens and lateral edges elevate
the elevation makes 2 neural folds and the depression in the centre creates the neural groove
the folds move towards eachother and fuses in the middle creating the tube

58
Q

what happens to the neural tube after formation and what will it go on to form?

A

neural tube sinks into embryo body
surface ectoderm repairs over the top of tube
will go on to form the brain and spinal cord

59
Q

what mechanisms control the bending of the neural plate?

A

cell wedging - microtubules/microfilaments change cell shape
hinge points - median and dorsolateral
extrinsic forces - pushing of surface ectoderm, adhesion point with notochord

60
Q

what are neural crest cells?

A

migratory cells forming during neurulation
move through embryo body forming various structures (e.g dorsal root ganglia and teeth)

61
Q

explain the closure of the neural tube

A

cervical fusion occurs in caudal and cephalic directions
open tube ends form anterior and posterior neuropores (connect with overlying amniotic cavity)
occurs in week 4 (anterior day 25, posterior day 27)

62
Q

name the 3 known causes of congenital issues

A

environmental
chromosomal
multifactorial genetic predisposition (with environment correct for expression)

63
Q

name some minor congenital defects

A

pigmented spots
small ears

64
Q

what is a teratogen?

A

an agent/substance that can disturb the development of an embryo/fetus

65
Q

what will occur during teratogen exposure in weeks 1-2 of development?

A

either nothing or spontaneous abortion

66
Q

what will occur during teratogen exposure from weeks 3-8?

A

teratogens highly effective
defect seen depends on which organ system is most vunerable at time of development when teratogen acts

67
Q

what will occur during teratogen exposure from weeks 9-38?

A

functional deficits and minor abnormalities as susceptibility is reduced

68
Q

what 2 organ systems remain vunerable to teratogen exposure through all weeks of gestation?

A

GU and CNS

69
Q

explain the effect of sonic hedgehog from the notochord on the neural tube

A

notochord presents SHH to adjacent neural tube, where the ventral-most cells respond, creating the neural tube floorplate
floorplate now makes its own SHH which develops motor neurones on each side of the tube

70
Q

describe the characteristics of sonic hedgehog (SHH)

A

powerful and widespread
works at short range
critical role in development/patterning of the brain and spinal cord
also has roles in somite patterning and limb bud development

71
Q

what can SHH signal in ventral somite sclerotome?

A

signals it to undergo epithelio-mesenchymal transformation

72
Q

how are dorsolateral hinge points only seen in some regions of the spine?

A

upper spine - DLHPs absent due to BMP2 inhibition, SHH expression is strong inhibiting noggin
lower spine - SHH is reduced so noggin is uninhibited, it antagonises BMP2 which allows DLHPs to form

73
Q

what are the 5 classifications of teratogens?

A

drugs/chemicals
industrial pollutants
hormones
infectious agents
mechanical factors

74
Q

name different types of drug that can be teratogenic and an example of each

A

antibiotics - streptomycin
non-prescription painkillers - paracetamol
DMARDs - methotrexate

75
Q

name which hormones can be teratogenic and what they defect

A

androgens - masculinisation of female genitalia
endocrine disruptors (synthetic oestrogens) - increased carcinoma

76
Q

explain the mechanism of fetal alcohol syndrome development

A

alcohol crosses placenta -> fetal liver cant metabolise alcohol -> high blood alcohol conc. in fetus -> lack of o2 and nutrients -> white matter development affected

77
Q

how does the embryo receive nutrition before the placenta develops?

A

diffusion

78
Q

what are trophoblastic lacunae?

A

spaces where syncytiotrophoblastic activity has eroded

79
Q

what happens to the enlarged blood vessels in the embryonic implantation?

A

they fill the spaces in the syncytiotrophoblast layer merging the maternal and fetal blood supply

80
Q

what are villi on the zygote?

A

stalks of cytotrophoblast that appear at day 13

81
Q

what occurs to villi at around day 16?

A

extra-embryonic mesoderm (chorionic) invades the primary villi core
they become secondary villi that line the surface of the chorion

82
Q

what occurs to secondary villi?

A

blood vessels develop in mesenchyme (they become tertiary villi)
they connect to umbilical vessels of embryo

83
Q

what is the placental barrier?

A

partition between maternal and fetal circulation
it is initially 4 layers thick (reduces to 3 in month 4)

84
Q

what are the 4 layers of the placental barrier?

A

fetal capillary endothelium
CT of villi
cytotrophoblast
syncytiotrophoblast

85
Q

what are the main functions of the placenta?

A

metabolism - synthesises glycogen, cholestorol, fatty acids, nutrients
transfer - o2, co2, urea, uric acid, bilirubin
amino acid transfer by carrier mechanism
vitamins B/C/D cross readily

86
Q

name all the blood vessels present in the placenta

A

maternal artery, maternal vein, 2x umbilical arteries, umbilical vein, chorionic vessels

87
Q

what are the basic functions of the placental membrane?

A

separates maternal and fetal blood, allows substance diffusion

88
Q

what is present in the intervillous spaces in the placenta?

A

pools of maternal blood

89
Q

what is the function of wharton’s jelly?

A

protects umbilical vessels from damage

90
Q

what enters the trophoblastic lacunae to support the developing placenta?

A

glandular secretions and spiral arteries

91
Q

what are interstitial extravillous trophoblasts?

A

cytotrophoblast cells that have left the trophoblast
they invade the endometrial blood vessels, blocking them

92
Q

explain what extravillous trophoblast cells do after invading the spiral arteries

A

remodel the coiled vessels from low flow-high resistance to wider high flow-low resistance channels
this allows sufficient blood flow to fetus

93
Q

explain the process of maternal blood flow through the placenta

A

blood enters the villous trees and enter the intervillous space coming in close contact with fetal blood without mixing

94
Q

how does maternal blood supply nutrients?

A

flows from uterine arteries into large blood sinuses surrounding villi, then back into uterine veins

95
Q

how does fetal blood transfer nutrients?

A

flows through umbilical arteries to capillaries in villi and returns through umbilical vein to fetus

96
Q

what are the 4 mechanisms in which nutrients travel across the placenta?

A

diffusion
paracellular diffusion
transporter-mediated transfer
endocytosis/exocytosis

97
Q

name molecules that travel across the placenta

A

O2, CO2, H2O, HCO3, glucose, amino acids, lipids, fatty acids, vitamins B/C
immunoglobulins (IgG not IgM)

98
Q

what does human chorionic gonadotrophin do?

A

maintains corpus luteum in ovary
allows oestrogen, placental lactogen and progestorone production in corpus lutem before placenta develops

99
Q

name pathogens that can cross the placenta that would cause harm

A

bacteria - listeria
protozoa - plasmodium falciparum (causes malaria) and toxoplasma gondii (cat feces produces it)
viruses - zika, rubella, cytomegalovirus

100
Q

define miscarriage and stillbirth

A

loss of a pregnancy during the first 23 weeks of pregnancy
(after 13 weeks = late miscarriage)
stillbirth is the death of a baby after 24 weeks of gestation

101
Q

what is fetal growth restriction?

A

failure to reach genetically pre-determined growth potential
birth weight before 5th percentile of growth charts

102
Q

what is the cause and risks of fetal growth restriction?

A

cause - placental dysfunction
risks - childhood morbility, stillbirth, adult disease

103
Q

explain the basics of the barker hypothesis

A

assesses the correlation of prenatal nutrition and fetal environment to adulthood disease

104
Q

what is pre-eclampsia?

A

new onset hypertension (above 140/90) and proteinuria occuring after 20 weeks gestation
if left untreated = elcampsia (maternal seizures)

105
Q

explain the pathophysiological result of pre-eclampsia

A

vessels remain narrow and blood supply is reduced
ischaemia-reperfusion injury
impaired nutrient delivery

106
Q

explain the maturation of the lungs during pregnancy

A

lungs are filled with fluid which is expulsed during breathing movements into the amniotic sac via the trachea

107
Q

explain the function of pulmonary surfactant in lung maturation

A

secretes by type 2 pheumocytes at 24 weeks gestation
facilitates lung expansion at birth and reduces surface tension
enough produced to support gas exchange after 35 weeks

108
Q

explain the mechanisms of the renal system maturation

A

new nephrons formed until 36 weeks gestation
kidneys produce dilute urine but placenta fulfils most of their role

109
Q

how much amniotic fluid does a fetus swallow?

A

7ml per hour

110
Q

how much urine does a fetus produce?

A

300ml/kg per day

111
Q

what is associated with poor renal function in fetuses?

A

oligohydraminos (too little amniotic fluid)

112
Q

what is produced in the process of digestive tract maturation?

A

maturation of enzymes for digestion and absorption occurs
crypts and villi develop from weeks 8-24 gestation that elongate with time

113
Q

what is meconium?

A

greenish mixture of shed intestinal cells, lanugo, mucous and amniotic fluid
baby’s first poo

114
Q

explain the physiological features of fetal circulation maturation

A

haemopoiesis in the fetal liver becomes dominant from the second trimester
most erythrocytes contain fetal haemoglobin (hbF) which has a greater affinity for oxygen than adult haemoglobin

115
Q

why is the adrenal cortex in a fetus very large?

A

adrenal gland produces steriod precursor for oestrogen biosynthesis by the placenta

116
Q

explain the role of the fetal posterior pituitary gland

A

secretes oxytocin from second trimester onwards
levels rise during labour to initiate contractions

117
Q

what maternal adaptations occur to support a pregnancy?

A

RR and tidal volume increase - increase gas exchange
maternal blood volume increases by 50%
nutrient requirements increase
glomerular filtrartion increases by 50%

118
Q

explain how the maternal blood volume increases during pregnancy

A

placenta removes blood from systemic circulation
erythropoetin and renin production induced to increase blood volume

119
Q

explain how oestrogen is produced and maintains pregnancy

A

stimulates labour/birth
produced by fetus and placenta cooperation
fetal adrenal gland secretes androgens which are converted to oestrogen by placenta

120
Q

what is the functions of human placental lactogen (hPL) in maintaining pregnancy?

A

promotes growth/differenciation of mammary glands (lactation tissues)

stimulates maternal tissues to ensure glucose and protein available to fetus

121
Q

what is the function of relaxin in supporting a pregnancy?

A

increases pubic symphysis flexibility and cervix dilation
suppresses oxytocin by hypothalamus delaying labour contractions

122
Q

what is the functions of placental growth hormone in maintaining a pregnancy?

A

suppresses/replaces maternal GH

enhances nutrient availability to fetus by stimulating lipolysis and gluconeogenesis

123
Q

what is partuition and how does it occur?

A

childbirth
series of strong rhythmic uterine contractions (labour)

124
Q

what fetal and maternal endocrine changes occur during labour?

A

progestorone levels reduced
fetal pituitary secretes oxytocin entering maternal blood stream
maternal pituitary secretes oxytocin
prostoglandin produced by fetal membranes (as well as oestrogen and oxytocin)

125
Q

explain labour contractions and how it is a positive feedback system

A

contractions begin at superior uterus towards cervix and increase in force and frequency
stretching of cervix further stimulates oxytocin release

126
Q

explain the first step of parturition

A

dilation:
cervical softening and dilation
myometrial contractions increase frequency
amniochorionic membrane ruptures
cervix dilates to ~10cm

127
Q

explain the second stage of parturition

A

expulsion:
contractions strong/frequent
urge to push baby out
may need episiotomy (peritoneum cut to avoid tearing)

128
Q

how is neonatal health assessed and what is assessed?

A

APGAR score
A - appearance (colour)
P - pulse (HR)
G - grimace (reflex irritability)
A - activity (muscle tone)
R - respiratory effort

129
Q

explain the third stage of parturition

A

placental:
can either be removed by midwife using oxytocin injection (active) or delivered postpartum using contractions (physiological)

130
Q

what are some of the common terminologies used in describing embryological defects?

A

atresia - absense or narrowing of an opening
agenesis - failure of an organ part to develop

131
Q

what are the defects of babies with VACTERL?

A

V - vertebrae/ribe
A - anorectal
C - cardiac
T - tracheo-oesophageal fistula
A - esophageal atresia
R - renal anomaly
L - limb anomaly

1st Year Med (52 decks)

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