Embryology 2

Question 1

what is the first thing that happens during week 3

Answer 1

a groove/dip forms in the middle of the epiblast region called the primitive streak

Question 2

what does the formation of the primitive streak signal the start of?

Answer 2

the axis of the embryo

Question 3

What happens to the cells that start to divide when primitive streak is formed?

Answer 3

these newly formed cells are going to sink down from epiblast and invaginate/ migrate in between the epiblast and hypoblast

Question 4

what do the cells do once they migrate from the epiblast?

Answer 4

they displace the hypoblast

and form 3 germ layers.

Question 5

what are the 3 germ layers that are formed from the epiblast

Answer 5

ectoderm
mesoderm
endoderm

Question 6

what happens when a cell commits to being ecto, meso or endoderm?

Answer 6

cannot reverse this- they are somewhat specialised now- have to progress down that pathway

Question 7

what does an ectodermal cell form

Answer 7

part of the skin

neural tube

Question 8

what does a mesodermal cell form

Answer 8

cardiovascular system
muscles
bone

Question 9

what does an endodermal cell form

Answer 9

certain organs/systems

Question 10

what happens during gastrulation

Answer 10

formation of the germ layers

Question 11

how is a notochord formed

Answer 11

cells haven’t stopped dividing at the primitive streak- after forming the 3 germ layers, they continue to divide to form a solid tube (not neurul tube) downwards
they soon lose contact with the ectoderm and form a solid rod of cells called the ‘notochord’

Question 12

what is a notochord?

Answer 12

a solid rod of cells that sits below the primitive streak in the mesoderm

Question 13

what happens after the notochord is formed

Answer 13

neurulation (neural tube formation)

Question 14

what happens after notochord formation

Answer 14

notochord induces ectodermal cells in the midline to form a neural plate that sinks down to forn neural tube that sits between the ectodermal and mesodermal layers

Question 15

what does the neural tube do to the mesoderm layer first?

Answer 15

it induces it to thicken it

Question 16

what are the 3 parts called that the mesodermal layer splits into?

Answer 16

paraxial mesoderm
intermediate plate mesoderm
lateral plate mesoderm

Question 17

what does the paraxial mesoderm separate into?

Answer 17

somites

Question 18

what does the intermediate plate mesoderm separate into?

Answer 18

urogenital system (kidneys + repro)

Question 19

what does the lateral plate mesoderm separate into?

Answer 19

body cavity and coverings

Question 20

what is the 4th-8th weeks period called

Answer 20

embryonic/ organogenetic period

Question 21

what is the term ‘lateral folds’ describing?

Answer 21

folding of ectodermal layer into a tube - starts in week 3

Question 22

when are lateral folds are complete

Answer 22

in the 4th-8th week period

Question 23

what develops from the neural tube

Answer 23

forebrain, midbrain, hindbrain and spinal cord

Question 24

when does the heart start to beat?

Answer 24

day 24

Question 25

from which part does the gut form?

Answer 25

the endoderm

Question 26

how many pairs of somites form in the paraxial mesoderm?

Answer 26

43- these differentiate further

Question 27

what does a dermatome give rise to

Answer 27

dermis of the skin

Question 28

what does a myotome give rise to

Answer 28

muscles

Question 29

what does sclerotome give rise to

Answer 29

bones including vertebrae

Question 30

somites develop further into which 3 things?

Answer 30

dermatome myotome sclerotome

Question 31

define teratology

Answer 31

Study of when things go wrong during development

Question 32

what are teratogens

Answer 32

environmental factors that cause abnormal development

Question 33

what is congenital rubella syndrome caused by

Answer 33

contraction of german measles whilst pregnant

Question 34

what can malformed limbs be due to

Answer 34

use of thalidomide by mother whilst pregnant

Question 35

TRUE or FALSE | the majority of caused of abnormal development are of unknown aetiology

Answer 35

TRUE

Question 36

Environmental causes for abnormal development

Answer 36

drugs- prescription/ recreational/ other alcohol/tobacco infectious agents radiation

Question 37

examples of infectious agents that can transfer through placenta and affect developing embryo

Answer 37

ToRCH | Toxoplasma, Rubella, Cytomegalovirus, Herpes

Question 38

genetic factors causing abnormal development

Answer 38

Too many/too few chromosomes | Structural changes - deletions of genes, segments of chromosomes

Question 39

Turner's syndrome

Answer 39

45 chromosomes single X

Question 40

Down's syndrome

Answer 40

47 chromosomes trisomy 21

Question 41

what does the risk posed by a teratogen depend on? (3)

Answer 41

exposure during critical periods of development dosage of drug/chemical/factor genetic constitution of embryo ie some more susceptible than others at equivalent doses

Question 42

when is your risk of teratogenesis highest

Answer 42

weeks 3-8

Question 43

when is your highest risk of death during development

Answer 43

weeks 1-2 but low risk from teratogens

Question 44

how do you diagnose malformations/ check baby is alright PRENATAL?

Answer 44

Blood - AFP alpha-fetoprotein Ultrasound scan – 12 week anomaly scan Invasive tests: chorionic villus sampling and amniocentesis

Question 45

how do you diagnose malformations/ check baby is alright POSTNATAL? (4)

Answer 45

Hip stability Testes (descent) Fingers and toes Hearing