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Y3 repro > applied embryology > Flashcards

applied embryology Flashcards

1
Q

What are the pre-requisits for a pregnancy to occur

A

functioning gametes - viable sperm and mature egg

patent reproductive pathway - vagina, cervix, uterus and fallopian tubes

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2
Q

release of the egg for fertilisation

A

ovulation - can survive for 1 day once released

picked up by the fimbrial end of the fallopian tube where it waits to meet the sperm

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3
Q

sperm reaching the egg for fertilisation

A

sperm released into the vagina

has to travel up through the cervix, uterine canal and fallopian tube to reach the egg in order to fertilise it

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4
Q

what happens during fertilisation

A

sperm enters the egg and unites with its nucleus

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5
Q

what follows fertilisation

A

organised series of cell division

cell numbers increase and form an early blastocysts ~day 5

embryo then implants into the womb

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6
Q

what is the outer layer surrounding the egg called

A

zona pellucida

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7
Q

what helps the sperm get into the egg

A

cap on the sperm head (acrosome) releases hydrolytic enzymes

helps it dissolve the zona pellucida and fet into the perivitelline space

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8
Q

what is the perivitelline space

A

the space between the egg and the zona pelludica

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9
Q

what occurs in the perivitelline space during fertilisation

A

sperm binds to the protein receptos an the plasma membrane of the egg and sperm fuse

sperm then releases its nucleus whih enters the egg

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10
Q

what happens once a sperm has released its nucleus into the egg

A

cortical reaction - egg plasma membrane becomes a tough wall and doesn’t let any more sperm in

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11
Q

what happens if multiple sperm enter the egg

A

abnormal fertilisation

these eggs aren’t capable of further cell division or pregnancy

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12
Q

what is the first stage in the egg following fertilisation called

A

pronuclei stage

2 nuclei in the fertilised egg (1 from egg and 1 from sperm)

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13
Q

what stages occur during day 1-5 following fertilisation

A 
day 1 - pronuclei forms 
2 - 1st cell division 
3 - cell division continues
4 - formation of Morula 
5 - blastocyst forms
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14
Q

what is a morula

A

cells continue to divide and numbers increase rapidly until you cannot count them but they form into a ball of cells - morula

this then organises into a blastocyst embryo

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15
Q

organisation of cells in the blastocyst

A

2 cell groups:
outer layer - trophoblast, placenta forms from this
inner layer - inner cell mass, this is where the embryo develops

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16
Q

what layer of the blastocyst invades the maternal endometrium

A

trophoblast

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17
Q

what are the 4 steps for implantation to occur

A

hatching
apposition
adhesion
invation

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18
Q

what is hatching

A

blastocyst has to come out of the zona

trophoectoderm cells produce protease to dissolve the zona in preparation for implantation

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19
Q

what is apposition

A

first connection between blastocyst and endometrium

apposes to microvilli like structure (pinopodes) expressed on receptive endometrium

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20
Q

how does the maternal endometrium become receptive

A

under hormonal preparation which happens in every monthly cycle

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21
Q

what is adhesion

A

earliest implantation sign

trophoblast of the blastocyst adheres to the epithelial layer of the maternal endometrium
embyronic tissue starts to actively secrete hCG

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22
Q

what is invasion

A

trophoblast proliferation and differentiation
crossing of the epithelial BM and invasion of endometrial stroma to form the placenta

uterine spiral arteries remodelled by the invasive trophoblast - placentation starts

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23
Q

what happens with inability to hatch

A

infertility

premature hatching can result in abnormal implantation in the uterine tube - ectopic

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24
Q

what regulates apposition and adherence

A

a number of growth factors and cytokines

this all has to happen in sync as well as with hormones for the implantation to happen

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25
Q

decidualisation prior to invasion

A

pre-requisite for trophoblast invasion and placentation

involves transformation of stromal cells of maternal endometrium every month under the effect of progesterone

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26
Q

what changes occur to the endometrium under the effect of progesterone prior to invasion

A

stromal cell differentiation - elongated fibroblast cells converted into decidual (rounded epithelial cells)

angiogenesis - increased vascular permeability

increased macrophages, lymphocytes and decidual leukocytes (uterine natural killer cells) for maternal immune tolerance

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27
Q

why are the changed in the endometrium important for invasion

A

transform the endometrium into a vascular receptive tissue for blastocyst invasion

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28
Q

describe placentation

A

invading trophoblast forms 1y chorionic villi
with infiltration of extra-embryonic mesoderm these become 2y villi
when capillaries form they become 3y villi
invasion of cytotrophoblast remodels spiral arteries to increase blood flow

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29
Q

what are the 2 cell layers of the trophoblast

A

inner part close to the inner cell mass = cytotrophoblast
outer part = syncytiotrophoblast

these are the parts which will develop into villi

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30
Q

placentation - what is the main function of villi

A

establish the connection with the maternal circuation

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31
Q

what is the mature placenta formed from

A

chorionic villi
intervillous space
placental septae
cotyledons - subunits of the placenta

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32
Q

what are the functions of the placenta

A 
immunological barrier
gas exchange 
nutrient exchange 
waste excretion 
endocrine functions - secreted hCG
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33
Q

what is embryogenesis

A

first 8wks of embyro development post-fertilisation

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34
Q

embryoblast development

A

wk2-3 - formation of bilaminar disc and development of amniotic sac, yolk sac, extraembryonic mesoderm and chorionic cavity

wk3-4 - differentiation of bilaminar disc into trilaminar structure - 3 germ layers (endoderm, mesoderm, ectoderm), through gastrulation and neural tube formation

wk5-8 - organogenesis

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35
Q

what are the different parts of the blastocyst and what are the cell types

A

inner cell mass (embryoblast) - pluripotent cells

bilaminar disc - epiblast (undergoes gastrulation) and hypoblast (forms extraembryonic mesoderm)

blastocele - fluid filled cavity

inner layer cytotrophoblast forms chorionic villi

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36
Q

inner cell mass differentiation

A

inner cell mass differentiates into bilaminar epiblast (columnar epithelial cells) and hypoblast

2 cavities form - yolk sac on side of hypoblast and amniotic cavity on side of epiblast

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37
Q

epiblast differentiation/gastulation

A

3 germ layers form - ectoderm, mesoderm, endoderm (day 13-16)

gastrulation starts with a groove appearing in the caudal end of epiblast (primitive streak)

newly formed trilaminar disc w/ 3 layers is called gastrula and forms the different organ systems

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38
Q

how is the endoderm formed

A

epiblast cells migrate into the hypoblast layer displacing them

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39
Q

how is the mesoderm formed

A

further epiblast cells migrate through primitive streak between the epiblast and the hypoplast/endoderm to form the mesoderm

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40
Q

how is the ectoderm formed

A

remaining epiblast becomes the ectoderm

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41
Q

what forms from the ectoderm

A 
epidermis 
CNS
PNS
hair and nails 
neuroendocrine organs (adrenal medulla, pituitary)
enamel of teeth
42
Q

what forms from the mesoderm

A 
dermis 
MSK structures
CVS
kidneys
ureters
trigone of bladder
gonads (not germ cells)
adrenal cortex
visceral and parietal linings (pleura, pericardium, peritoneum)
43
Q

what forms from the endoderm

A 
lining of GI tract 
parenchyma of liver 
pancreas
thyroid 
parathyroid 
tonsils and thymus
bladder (not trigone)
44
Q

what are the 3 major subunits of the mesoderm

A

paraxial - forms MSK structures
intermediate - forms kidney, ureter and gonads
lateral plate

45
Q

what is a dizygotic pregnancy

A

≥2 eggs fertilising and implanting

non-idential

46
Q

what is a monozygotic pregnancy

A

1 embryo splitting
timing of embryo splitting determines nature of pregnancy
identical twins

47
Q

what type of twins are more common

A

non-identical

48
Q

what is the risk of multiple pregnancy

A

natural conception - 1-2%

fertility treatments have increased the rates, target to keep <10%

49
Q

DCDA twins

A

division day 1-4 post fertilisation

20%

50
Q

MCDA twins

A

division day 5-8 post fertilisation
75%
seen in fertility treatment

51
Q

MCMA twins

A

division day 7-14 post-fertilisation
5%
high risk twins - shared placenta, higher incidence of fetal death

52
Q

conjoined twins

A

division >14 days post fertilisation

<1%

53
Q

how is the urinary system linked to the gonads

A

kidney and ureter and repro system develop from the urogenital ridge in the intermediate mesoderm (same origin)

urogenital ridge differentiates into gonadal ridge medially which gives rise to gonad and nephrogenic cord laterally (forms kidney and ureter)

urinary system develops ahead of repro system from wk4

54
Q

development of urinary system

A

kidney, ureter, bladder and urethra
kidney and ureter develop from 3 overlapping system in nephrogenic cord portion of urogenital ridge (pronephros, mesonephros and metanephros)

kidney develop in pelvis and then ascend into abdo with final position by wk12

bladder and urethra formed from urogenital sinus (part of cloaca) which also gives rise to parts of female and male repro tract

55
Q

what are the 3 stages of development of the kidneys and ureter

A

pronephros - non-functional
mesonephros - functional but transient
metanephros - kidneys

56
Q

where does the kidney form from

A

metanephric mesenchyme

57
Q

what forms the ureter

A

ureteric duct

58
Q

what is the cloaca

A

common temporary outlet for digestive, urinary and genital tract in embryonic life

nephric duct drains into this

59
Q

what is the nephric duct

A

connects pronephros, mesonephros and metanephros

60
Q

what are 6 examples of renal anomalies

A 
renal agenesis
horseshoe kidney 
pelvic kidney 
duplex kidney 
duplex ureter and calyceal system
61
Q

what is renal agenesis

A

no kidney
one of the metanephric ducts or none develop
gives rise to a unilateral kidney system
complete renal agenesis = no kidney

62
Q

what is a pelvic kidney

A

kidneys have failed to ascend from the pelvis to the abdomen

63
Q

what is a horseshoe kidney

A

fusion of the kidneys during ascent

get stuck so cannot ascend any further

64
Q

where is the cloaca located and what are its coverings

A

caudal end of the enfolded yolk sac

covered in cloacal membrane which is formed by the fusion of the ectoderm and endoderm

65
Q

what does the urorectal septum form

A

cloaca is divided by the urorectal septum to form:
urogenital sinus
anal canal

66
Q

what does the urogenital sinus form

A

bladder and urethra

67
Q

what forms the trigone of the bladder

A

mesonephric duct below the ureteric bud is incorporated into the bladder as the trigone

68
Q

where does the indifferent gonad develop

A

in the gonadal ridge

69
Q

what is the gonadal ridge related to

A

closely related to the mesonephros

70
Q

where do the primordial germ cells originate from

A

do not originate in the gonadal ridge

they migrate to the gonads from the endoderm lining of the yolk sac via the hindgut at wk6

71
Q

what forms the primitive sex cords

A

epithelium of gonadal ridge

72
Q

what forms the indifferent gonad

A

combination of germ cells and primitive sex cords

indifferent gonad is capable of developing into a testis/ovary

73
Q

what determines whether the indifferent gonad becomes a testis/ovary

A

Y chromosome contains SRY gene
SRY produces testis determining factor
protein acts on the indifferent gonad to promote the formation of the testis

in rare cases following a translocation error, a male can be born w/ 46 XX karyotype

74
Q

development of the ovary

A

migrating germ cells enter the ovary
primitive sex cords extends into the medulla but degenerate
2y sex cords (cortical cords) develop and surround the germ cells –> ovarian primordial follicles
ovarian follicle pool established at 20wks gestation

75
Q

development of the testis

A

migrating germ cells enter the testis
primitive sex cords extend into medulla and forms testis cords which transform into future seminiferous tubules and rete testis

sertoli cells are derived from surface epithelium under effect of AMH

Leydig cells are produced from intermediate mesoderm and produce testosterone from wk8 onwards

76
Q

where do the testis develop

A

posterior abdo wall and then descend through the deep inguinal ring ~7mths into the scrotal sac

77
Q

why do the testis have to descend

A

scrotal sac temp is lower than body temp

required for proper spermatogenesis

78
Q

what % have undescended testis

A

2-3%

can be in the abdo area or somewhere in the inguinal canal

79
Q

what is cryptochordism

when is it checked for

what is the management

A

undescended testis

checked for in all male infants

early corrective surgery to prevent effects on fertility later on

79
Q

what is cryptochordism

when is it checked for

what is the management

A

undescended testis

checked for in all male infants

early corrective surgery to prevent effects on fertility later on

80
Q

what are the 2 sets of genital ducts

A

mesonephric duct next to the gonad

paramesonephric duct laterally

81
Q

what is AMH and why is it important

A

Anti-Mullerian hormone

presence/abscence determines which of the genital ducts develops and which regresses

males - presence of AMH causes paramesonephric ducts to regress and these don’t form any part of the adult

82
Q

where do the mesonephric duct and paramesonephric duct open into

A

urogenital sinus

83
Q

which ducts remain in males and females

A

Mesonephric - Male

paramesonephric - female

84
Q

what do the mesonephric ducts drian

A

aka Wolffian ducts

drain mesonephros into the cloaca

85
Q

what does the mesonephric duct form

A

in both males and females it forms the trigone part of the bladder?

86
Q

persistence of mesonephric duct in males

A

persists under the effect of testosterone

forms epididyms, vas deferens and seminal vesicles

87
Q

regression of mesonephric duct in females

A

remnants might remain as epophoron, paraophoron (small cysitc structures lateral to ovary) and gartners duct cyst

88
Q

what is gartner’s duct cyst

A

benign lesions on lateral vaginal wall

89
Q

female reproductive tract development

A

absence of AMH
paramesonephric ducts continue to develop, mesonephric ducts regress

paramesonephric ducts grow medially and fuse - fused portions canalises to form uterus and upper 2/3 of vagina

unfused portions give rise to fallopian tubes

paramesonephric ducts fuse w/ urogenital sinus at the sinus tubercle, point of fusion –> hymen

90
Q

what forms the lower 1/3 of the vagina

A

urogenital sinus

91
Q

development of external genitalia

A

on either side of the cloacal membrane folds develop - urogenital folds

these fuse anteriorly –> genital tubercle

lateral to this are the labioscrotal swellings

as the cloaca is split by the urorectal septum the anus is separated off

92
Q

male external genitalia development

A

genital tubercle elongates to form the penis

labioscrotal swelling folds fuse posteriorly - form scrotum

urogenital folds fuse posterior to anteriorly to form penile urethra (spongy urethra)

glans penis will canulate at the tip to form the final part of the urethra

93
Q

female external genitalia

A

urogenital folds form labia minora
labioscrotal folds form labia majora
genital tubercle forms clitoris

94
Q

male repro tract anomalies

A

penile - micropenis, hypospadia
testicular - absence, undescended (cryptochordism)
absence of vas deferens - CF
absence of seminal vesicles

95
Q

how does a micropenis occur

A

tubercle doesn’t elongate fully

96
Q

what is hypospadias

A

development problem causing urethral opening to be abnormally located e.g. undersurface of penis

97
Q

female repro tract anomalies

A

common - 4-7%
no one agreed classification system (ASRM, ESHRE/ESGE)

association w/ renal tract anomalies

uterine
vaginal
MKRH syndrome

98
Q

uterine anomalies

A

underdevelopment - uterine agenesis, unocornuate uterus
fusion - didelphys uterus, bicornuate
resorption - septate uterus, arcuate uterus

99
Q

how do uterine anomalies occur

A

paramesonephric ducts on one or either side don’t develop properly - agenesis or unicornuate

ducts don’t fuse correctly in the middle (no fusion - didelphys, part fusion - bicornuate)

fused part of ducts doesn’t undergo canalisation, remains as fibromuscular band (uterine septum), septation can be partial or complete

100
Q

vaginal anomalies

A

vaginal septa - longitudinal or transverse

imperforate hymen
vaginal agenesis - absent or underdeveloped uterus and vagina

101
Q

MKRH syndrome

A

Mayer Rokitansky Küster Hause

aka Mulleria agenesis syndrome

failure of paramesonephric ducts to develop normally - absence of all female repro tract

Y3 repro (47 decks)

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