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