Embryology (complete) Flashcards
how many in 1000 children have distinct anatomical alterations at birth
30
About what percent of birth defects are of known causes
50
What are environmental factors that cause birth defects
maternal disease
infections
mechanical
drugs or chemicals
What is a teratogen
anything that causes a birth defect
What is teratology
the science that seeks to understand causes of birth defects
What are the two factors that influence how likely and how serious a birth defect will be when exposed to a teratogen
- the dose of exposure to the teratogen
2. the period of exposure to the teratogen
What is the leading cause of mental retardation in america
fetal alcohol syndrome
What is thalidomide, and what does it cause
it is an anti-nausea agent that inhibits vessel development and can lead to lack of limb formation
When is the worst time for an embryo to be exposed to teratogens
from 3 - 8 weeks
What are two periods of a pregnancy
embryonic period
fetal period
when is the embryonic period
from conception to 8 weeks
what happens in the embryonic period
a lot, but specifically the formation of all organs
when is the fetal period
from week 9 through term
what happens in the fetal period
the organs that were already formed grow and develop
What are the 5 steps of human development
- pregenesis
- blastogenesis
- organogenesis
- metamorphosis
- phenogenesis
What is pregenesis
developmental pre-conditions in parents that enable successful reproduction. (the creation of the sperm and egg cell that became you)
What are the four parts of pregenesis
- formation and migration of parental primordial germ cells
- differentiation and creation of gonads (testis and ovaries)
- mitosis to increase number of primordial germ cells
- gametogenesis, maturation of gametes (meiosis)
What are primordial germ cells
the cells that will eventually become the sperm and egg cells
From which germ layer do the primordial germ cells come from
the ectoderm
What is the path the primordial germ cells take starting with the ectoderm and ending in the gonads
- they leave the ectoderm right away and go into the yolk sac
- they re-enter the embryo at 4 weeks and enter the gonads
What is a teratoma
when germ cells migrate to locations other than the gonads and begin to proliferate rapidly. they create a large tumor
can Teratomas have traces back to all three germ cells
yes
What is meiosis
a special form a cell division that leads to the formation of 4 haploid cells.
what are haploid cells
cells with half of the DNA of a regular (diploid) cell
What are the steps of meiosis
1, prophase 1 2. metaphase 1 3, anaphase 1 4. telophase 1 5. metaphase2 6. anaphase 2 7. telophase 2
What happens in meiosis prophase 1
- nuclear membrane dissolves
- chromosomes condense
- mitotic spindle develops
What happens in meiosis metaphase 1
homologous chromasomes line up on the metaphase plate
what happens in meiosis anaphase 1
the homologous chromosomes are pulled apart by the mitotic spindle
what happens in meiosis telophase 1
the cell divides in half with one of each of the homologous chromosomes in each cell
what happens in metaphase 2 of meiosis
The chromosomes line up on the metaphase plate
What happens in anaphase 2 of meiosis
the chromosomes are pulled in half by the mitotic spindle
what happens in telophase 2 of meiosis
the cells then divide in half again, making 4 total haploid cells from 1 diploid parental cell
from where do the 2 homologous chromosomes come from
one from each parent
What is recombination
when the homologous chromosomes that are lined up on the metaphase plate trade a portion of their DNA
when does recombination occur
at metaphase 1 of meiosis
what is crossing over
the same thing as recombination
what is a result of recombination
increased genetic variability
What is non disjunction
when the chromosomes don’t separate correctly during either anaphase step of meiosis
When does non-disjunction happen
in either meiosis 1 or 2
what results from non-disjunction in meiosis 1
4 cells
two of which have twice as much DNA as normal
two of which have no DNA
What results from non-disjunction in meiosis 2
4 cells
two of which are normal (haploid)
one that has no DNA
one that has twice as much DNA as normal
What is monoploidy
when a zygote only has one copy of a chromosome (usually they have 2)
what usually results from monoploidy
it is fatal to the embryo
what is trisomy
when a zygote has three copies of a chromosome (usually they have 2)
what usually results from trisomy
it isn’t always fatal to the embryo
what causes monoploidy and trisomy
non disjunction
When does meiosis begin and end in males
it starts and goes to completion at puberty
when does meiosis begin and end in females
it starts as an embryo, then freezes until puberty
What is spermatogenesis
the creation of sperm
what is oogenesis
the creation of eggs
What is the leading cause of death of our species
nondisjunction
What does the sticky cumulus do
moves the egg down the fallopian tube
What is fertilization
the fusing of an egg and a sperm cell
What is capacitation
obtaining the capacity to do work (speaking of a sperms ability to do its works)
What does it take for a sperm to have reached capacitation
- obtains motility
- obtains directionaliity
- becomes energetically efficient
What are the three layers that the sperm has to penetrate to fertilize the egg
- zona pellucida
- corona radiata
- eggs plasma membrane
What are the two reactions that need to occur for the sperm to fertalize the egg
- acrosome reaction
2. cortical reaction
what generates the acrosome reaction
the sperm
what does the acrosome reaction cause to happen
breaks down the zona pellucida
what generates the cortical reaction
the egg
what does the cortical reaction cause to happen
prevents additional sperm from entering the egg
What do you call a fertilized egg
a zygote
what is a zygote
a single cellular fertilized egg
what is cleavage
specialized mitoses, cell division accompanied by a reduction in cell size. (more cells, but the same size as the initial single cell)
how do you get fraternal twins
two eggs fertilized by two spermies
how do you get identical twins
a single fertilized egg that divides and becomes two embryos
What is compaction
when the outer cells of the embryo flatten out and form tight junctions
what happens to the inner cells of the embryo during compaction
gap junctions form between them
What do the outer cells from compaction of the embryo develop into
the placenta
what do the inner cells from compaction of the embryo develop into
the fetus
What is a morula
a filled ball of cells (usually around 32-64 cells) not hollow
What is a blastocyst
a hollow ball of cells, with a mass of cells inside
What are the parts of the blastocyst
- Inner cell mass
2. trophoblast
at what point does the embryo enter the uterus
3-4 post fertilization
What happens after the embryo enters the uterus as a blastocyst
the blastocyst hatches
what does it mean that the blastocyst hatches
it sheds the zona pellucida and remaining corona radiata
why does the blastocyst hatch
so that it can implant into the uterine wall
so that it can grow
what is the blastocoel
the hollow space in the blastocyst
what are the events of the first week
- fertilization
- cleavage
- compaction
- becomes a morula
- becomes a blastocyst
- enters the uterus
- hatches
- implants into the uterine wall
Why do we call the second week of embryology the week of 2’s
- its the second week
- the blastocyst has two different cell masses
- those cell masses give rise to two different cell masses each
- there are two cavities in the blastocyst
What are the two cell masses of the blastocyst
- trophoblast
2. inner cell mass
What two cell masses does the trophoblast become
- sycytiotrophoblast
2. cytotrophoblast
what does the syncytiotrophoblast do
the cells lose their shape and seep deep into the uterine wall and mesh with the uterine wall
what does the cytotrophoblast do
houses the inner cell mass
What two cell masses does the inner cell mass develop into
- epiblasts
2. hypoblasts
what does the epiblasts develop into
the fetus
they also surround the amniotic cavity
what does the hypoblasts do
form the yolk sac
What kind of tissue is the yolk sac
hypoblastic tissue
what are the two cavities formed during the week of two’s’
the amniotic cavity and the yolk sac
what is the purpose of the yolk sac
(giver of life)
it houses blood cell precursors and primordial germ cells
What makes up a component of the umbilicus
the yolk sac
what is the purpose of the amniotic cavity
excercise and cushion room for the fetus
What is the chorion
outermost sac of the placenta
what does the chorion do
place of exchange between maternal and fetal circulation
What is the starting point and ending point of 2nd week of embryology
start : when it implants into the uterus
Ends: with gastrulation
What is a trilaminar embryo
an embryo that has developed the three flat layers
what are the three germ layers formed during gastrulation
- ectoderm
- mesoderm
- endoderm
What is gastrulation
the creation of a trilaminar embryo which happens when epiblasts become mesencyhmal and fall through the primitive streak and differentiate into three layers
What marks the beginning of gastrulation
the creation of the primitive streak
what are the parts of the primitive streak
- primitive node
- primitive pit
- primitive groove
What is the primitive streak
a linear opening down the center of the epiblast layer, through which mesenchymal epiblast cells will pass to create the three germ layers
What is a mesenchymal cell
a cell that loses polarity and is highly migratory
What are the two places that no mesenchymal cells will set up, and where ectoderm and endoderm contact eachother
the buccopharyngeal membrane
the cloacal membrane
what does the buccopharyngeal membrane become
the place where the mouth forms
What does the cloacal membrane become
the place where the anus forms
What is re-epithelialization
when cells go from being mesenchymal, back to being epithelial cells
When does re-epithelialization occur
when cells have migrated to their desired locations and have differentiated into the three germ layers
Which germ layer comes from cells that replace the hypoblast
endoderm
which germ layer forms from the remaining epiblast cells that didn’t migrate through the primitive streak
ectoderm
which germ layer forms between the other two layers
the mesoderm
What does the ectoderm develop into
epidermis hair nails sweat glands nevous tissue sensory organs enamel epithelium of mouth and anus salivary glands
what does the mesoderm develop into
Dermis connective tissue muscle heart internal reproductive organs
what does the endoderm develop into
epithelium of respiratory tract and digestive tract liver pancreas thymus thyroid
What is the notocord
a specific rod like group of cells in the mesoderm
where does the notocord form
right below the primitive streak in the mesoderm layer
What does the notocord do
It is a potent molecular signaling machine that signals the neural plate to form
What is the neural plate
the portion of the ectoderm above the notocord. that develops when the notocord signals to it
What is a placode
a thickened portion of the ectoderm, signaled by the inner layer of ectoderm. These then develop into specific things
what happens to the neural plate
it folds up on itself and eventually becomes the neural tube, which becomes the brain and spinal cord
What are the bodies of cells at the periphery of the neural plate that fuse together to create the neural tube
neural crest cells
what happens to the ectoderm right next to the neural plate
when the neural pate fuses to become the neural tube, this ectoderm fuses and seals the neural tube inside
What are the three types of mesoderm that develop from closest to neural tube, to most distant
somites (paraxial mesoderm)
Intermediate mesoderm
lateral plate mesoderm
What are the two plates of the lateral plate mesoderm
splanctic (near endoderm)
somatic (near ectoderm)
What does the paraxial mesoderm (somites) do
becomes the muscle, bone, and connective tissue of most of the body
What does the intermediate mesoderm do
becomes the urogenital system
what does the lateral plate mesoderm do
becomes the muscle of the body wall, the digestive tract, and the proximal part of limbs
What is embryonic folding
a set of folds that transition the embryo from a flat 3 layered disk, into a 3d embryo
what are the two types of embryonic folding
- cephalocaudal
2. transverse or lateral
What is transverse or lateral folding
the folding of the embryo down its long axis to create a cylinder. left and right sides of the embryo curve toward the midline
what happens to the yolk sac during folding
it is pinched off, and the portion that remains inside the embryo goes on to form the body’s internal cavities
What drives transverse folding
the interaction between the mesoderm and the endoderm
What is cephalocaudal folding
the “head” and “tail” fold anteriorly towards each other, making a cresent moon shape of sorts
How does the neural tube affect cephalocaudal folding
when the neural tube closes it does so like a zipper, from one end to another, this helps drive cephalocaudal folding
where does closure of the neural tube begin
midway along the neural plate
how does closure of the neural tube go
it begins midway along the neural plate, and moves cranially and caudally
which end of the neural tube closes first
the cranial end
what are neuropores
the openings at the ends of the neural tube, before they close completely
What is cardiogeneic mesoderm
the mesoderm that will become the heart
What kind of mesoderm gives rise to cardiogenic mesoderm
splanchnic
What does the constriction due to folding look like when considering the yolk sac
it looks like a purse string
What lines the gut tube from mouth to anus
the endoderm
what drives the formation of respiratory, digestive, and endocrine organs and glands
interaction between endo and mesoderm
What outlines week 3
gastrulation
what outlines week 4
completion of gastrulation (beginning) neural tube formation body folding organ and limbs begin to form embryonic folding Pharyngeal arches form (end)
