Embryology Flashcards
which steps occur during the first week of pregnancy
ovulation
fertilisation
implantation
what is a zygote
fertilised ovum
what is a morula
what the zygote becomes once it has completed its first cell divisions - a solid mass of cells
after how many days does the morula form
4-6
what is a blastocyst
this is what the morula develops into during days 6-10 of pregnancy and is a hollow ball of cells
what is contained within the blastocyst
inner cell mass and trophoblast
what replenishes the baby’s blood
the mother’s blood
do the circulations of the embryo and mother mix
no
what separates the circulations of the embryo and mother
a thin barrier, permeable to most molecules but not cells
what occurs at 10-12 days of pregnancy
the implanted trophoblast contains an embryo with two cell layers
what are the two layers to the bilaminar embryo
epiblast and hypoblast
what is the function of the epiblast
gives rise to the embryonic ectoderm, mesoderm and endoderm
what does the hypoblast layer of the bilaminar embryo do
participates in the formation of the endoderm and the extraembryonic mesoderm
describe the shape of the bilaminer embryo
a disc with no distinct orientation or axis
what happens during gastrulation
the embryo develops an axis and the three embrionic cell layer
what is the key stage of gastrulation
the formation of a groove called the primitive streak
why does the bilaminar embryo develop an axis during gastrulation
to become bilaterally symmetrical
what are the mesoderm
the ectodermal cells that are induced to differentiate and migrate through the primitive streak toward the hypoblast
what forms the endoderm
interaction between the newly formed mesoderm and the hypoblast
how do the mesodermal cells form a third layer
by pushing through the primitive streak and spreading out
what occurs during weeks 3-8
organogenesis
what is organogenesis
formation of major organs from the three basic germ cell layers
what is the one of the first organs to be developed
the central nervous system
what is the neural tube
forerunner of the central nervous system
what is spina bifida
defect of the neural tube where it persists
what is the ectomesenchyme
a population of cells produced from the neural crest
what is the neural crest derived from
the ectoderm
what happens at around 25 days of pregnancy
the embryo folds around the yolk sac and some important organs appear like the heart, liver and lungs
what are stem cells
unspecialised cells that can develop into more specialised cells
what are the types of stem cells
embryonic and adult stem cells
describe embryonic stem cells
the inner cell mass is totipotent and has potential to differentiate into many cell types. stem cells found in the three germ layers are pluripotent as they are more restricted in potential
describe adult stem cells
generally committed cell lines like bone marrow stem cells
what does stem cell development involve
genes and various signalling molecules
what are all body tissues developed from
the three primary embryonic layers
what are the three primary embryonic layers
ectoderm
mesoderm
endoderm
what is the ectoderm
the outer covering
what is the mesoderm
the middle
what is the endoderm
the inner lining
what does the ectoderm develop into
skin
mucous membranes of the mouth and anus
brain
spinal cord
tooth enamel
what does the mesoderm develop into
most connective tissues
most muscle
blood vessels
kidney and urinary system
reproductive system
serous membranes
what does the endoderm develop into
the alimentary canal
respiratory system
parts of the urogenital system
what is the ectomesenchyme
the fourth germ layer
what does the ectomesenchyme develop into
- sensory and autonomic nerves
- melanocytes
- adrenal medulla
- most of the head mesenchyme
what are the connective tissues formed from the mesoderm
dermis
tendons
cartilage
bone
what parts of the mesenchyme of the head are developed from the ectomesenchyme
muscles
connective tissues
dentine
cementum
pulp
periodontal ligament
jaw bones
when do developmental abnormalities occur
during critical or sensitive periods of development
what can occur during the first two weeks of pregnancy
spontaneous abortion
what can occur during weeks 3-12
this is the period of greatest sensitivity ie likelihood of miscarriage
what is the first trimester
3-12 weeks
whane do most developmental defects occur
during the first trimester
what is the period of functional maturity of the foetus
weeks 13-39
when does the central nervous system first develop
week 3
what happens in week one of pregnancy
the zygote becomes the morula becomes the blastocyst which is implanted
in which weeks of pregnancy can spontaneous abortion occur
1-2
do ears develop before or after the eyes
before
which limbs form first
upper
when does the heart form
mid way through week 3
when do teeth form
mid way through week 6
when do external genitalia form
week 7
what is ovulation
release of the egg
what is the endometrium
innermost layer of the uterus composed of epithelial layer and lamina propria. has two layers
what are the two layers of the endometrium
basal and functional
describe the basal layer of the endometrium
composed of stem cells that serve to regenerate the functional layer
describe the functional layer
adjacent to the uterine cavity, lined by a single layer of columnar epithelium . hosts the embryo during pregnancy or is shed during menstruation.
what happens to the endometrium when pregnancy occurs
it becomes a thick blood vessel rich glandular tissue layer
what is the function of the endometrium
provide the optimal environment for the implementation of the embryo and maintain the patency of the uterus
what is the menstrual cycle
loss of the endometrial tissue
what is the placenta
temporary organ of pregnancy found in the uterus. functions to interchange between the mother and uterus - supply of oxygen and nutrients and removal of waste material and carbon dioxide
what is responsible for the embryo’s life support
the placenta
why can the circulatory systems of the foetus and the mother be described as closed
becuse they do not interact
what is rhesus factor
a protein found on the surface of red blood cells
what is Rh compatibility
this is when the pregnant woman is Rh negative and the baby is Rh positive, causing the mother’s immune system to produce antibodies that attack the baby’s blood cells, leading to anaemia and jaudince in the baby of the next pregnancy
what can happen if the circulations of the baby and mother mix
Rh incompatibility can occur
why can medication have an impact on the baby
it can pass through the placenta into the circulation of the child
what does the epiblast layer of the bilaminar embryo give rise to
embryonic cells to form the embryp
when is left and right handedness established
week three
what happens to the bilaminar embryo in gastrulation
it acquires a third layer to become the trilaminar disc, and it develops axial inclination.
how does gastrulation begin
linear region of cells of the epiblast layer becomes thicker at the caudal (posterior) aspect of the embryo. this becomes the primitive streak, and it develops as the epiblast cells replicate and migrate to the midline of the bilaminar disc
what is nodal
transformation growth factor protein that initiates and maintains the primitive streak
what comprises the primitive streak
totipotent stem cells from the epiblast
what forms the primitive node
when cells are added to the posterior end of the primitive streak, the cranial end begins to englarge and form the primitive node
what maintains the primitive node and streak
hepatocyte nuclear factor
what is FGF8
fibroblast growth factor 8
what is produced by the cells of the primitve streak
FGF*
where is the ectoderm located on the embryo
dorsal surface
what can the ectoderm be divided into
the neural ectoderm and the surface ectoderm
what does the neural ectoderm give rise to
the sensory organs like the eyes and the internal ears
what does the neural ectoderm subdivide into
the neural tube and the neural crest
what does the neural tube develop into
brain and spinal cord
what does the neural crest develop into
head mesenchyme and the peripheral nervous system
what are the three divisions of the mesoderm
paraxial
intermediate
lateral plate
what does the lateral plate mesoderm develop into
spleen
lymphatics
adipose tissue
what does the intermediate mesoderm develop into
urinary tract
kidneys
reproductive system
what does the paraxial mesoderm develop into
bone
ligaments
tendons
cartilage
skeletal muscle
dermis
what does the zygote develop into
inner cell mass and trophoblast
what does the inner cell mass contain
the epiblast and hypoblast
what does the epiblast develop into
the primitive streak and the ectoderm
what does the primitive streak become
the mesoderm and endoderm
what does the surface ectoderm develop into
epidermis
what does the endoderm develop into
the gut tube
what develops from the gut tube
thyroid
liver
gi tract
prostate
pancreas
lung
thymus
what is the function of the hypoblast
formation of the endoderm
when does division of the embryo occur for identical twins
after fertilisation
when does division of the embryo occur for fraternal twins
there is no division as two separate eggs are fertilised by different sperms
how many placentas do identical twins have
one
how many placentas do fraternal twins have
two
what happens at 16-18 days of pregnancy
rearrangement of the primitive streak to organise itself to the neural tube
what are somites
cells responsible for the formation of muscle
when do muscles form in relation to nerves
at the same time
what forms the dorsal root ganglia
the neural crest
what causes spina difida
persistence of the neural groove - it is associated with the non closure of the neural groove that usually forms the neural tube
what is the cardiac structure formed through
the heart tube
what are the areas of the trilaminar embryo
head and tail
what happens to the neural tube at 4 weeks
parts of tissue from the sides of the tube move forward to form the face
what forms the face at 4 weeks of pregnancy
migration of cells from posterior region to anterior region
what happens between 4-7 weeks to the face
migration of cells from the posterior region to the anterior region occurs which begins to resemble the face
when do legs begin to form
week 9
what happens between 9 and 14 weeks of pregnancy
maturation of organs
when does formation of organs begin
week 7
when does the embryo become the foetus
week 9
what is found within the embryonic stem cells
the inner cell mass for forming the three germs
what are totipotent cells
cells that differentiate into anything
why are the three germ layers described as pluripotent
more restricted in potential
which stem cells have the most limited potential
adult stem cells
what do all body tissues come from
primary embryonic cell layers
which germ layer develops into tooth enamel
ectoderm
what is the ectomesenchyme
the fourth layer that gives rise to sensory and autonomic nerves
which teeth finish developing first
the permanent teeth
which teeth finish maturing first
deciduous
what is gastrulation characterised by
extensive movements of the cells
what forms the three primary germ layers
morphogenic movements of the embryo cells
what is gastrulation centred around
the primitive streak - transient midline that serves as conduit through which epiblast cells fated to become mesoderm and endoderm ingress to establish the germ layers
what specifies cell fate
the primitive streak
what are the sources of the endoderm
epiblast
caudolateral region of the blastoderm
yolky cells
what is the yolk sac
this is the umbilical vesicle that is a small membranous structure outside the embryo.
what is the innermost tissue found in the embryo
the endoderm
what gives rise to epithelial cells that line the respiratory and digestive systems
endoderm
what do endodermally derived organs in the human body include
thyroid
thymus
liver
lungs
biliary system
pancreas
what are the functions of the endodermally derived organs
gas exchange
digestion
nutrient absorption
glucose homeostasis
detoxification
blood clotting
what does the mesoderm surround
the gut tube
which pregnancy period is the least prone to having defects of development
weeks 13-9
what is the pre embryonic period
1-2 weeks
when are the regions of the gut tube
foregut midgut and hindgut
how can the domains of the gut tube be observed at a molecular level
restricted gene expression patterns
what does the foregut give rise to
esophagus, trachea, stomach, lungs, thyroid, liver, biliary system and the pancreas
what does the midgut form
the small intestine
what does the hindgut form
the large intestine
in what process are the germ layers generated
gastrulation
what is the timeline of organ formation
endoderm formation
endoderm patterning
organ specification
organ buds
proliferation
differentiation
what is mesenchyme
loosely organised embryonic connective tissue of undifferentiated cells that gives rise to most tissues, like skin blood and bone. the interactions between mesenchyme and epithelium help to form nearly every organ in the developing embryo
