Human Embryogenesis Flashcards
the development of a human embryo, which occurs during the early stages of prenatal development
human embryogenesis
occurs between fertilization and birth
prenatal development
what are the three periods of prenatal development
pre-implantation period
embryonic period
fetal period
what time frame does the pre-implantation period occur in
1st week
what time frame does the embryonic period occur in
2nd to 8th week
what time frame does the fetal period occur in
3rd to 9th month
in the pre-implantation period, the zygote forms into a __________
blastocyst
in the embryonic period, the blastocyst forms into an _________
embryo
in the fetal period, the embryo forms into a _________
fetus
disturbances in prenatal development can produce _______ ________
birth defects
structural or functional disorders that are present at birth
congenital malformations
when do most congenital malformations occur
during embryogenesis
when looking at teratogenic sensitivity, if exposure is very early (up to 4 weeks), what happens
death of the conceptus
when looking at teratogenic sensitivity, if exposure is between 4 and 8 weeks, what happens
significant structural anomalies
when looking at teratogenic sensitivity, if exposure happens after 10 weeks, what happens
the effect may be unnoticed
what happens during fertilization
egg and sperm unite
what is another name for egg and sperm
gametes
gametes contain _______ the complement of chromosomes found in other human cells
half
a cell has half the number of chromosomes
haploid
DNA is divided into _________
chromosomes
each chromosome contains _________
genes
a segment of DNA that provides instructions for making a cell
gene
different versions of the same gene
alleles
chromosomes 1-22
autosomes
members of each pair of chromosome are __________
homologous
which chromosome is the sex chromosome
chromosome 23
somatic cells are produced by _________
mitosis
duplicated chromosomes pack and the spindle preps
prophase
chromosomes meet in the middle of the cell
metaphase
duplicated chromosomes split apart and move to opposite ends of the cell
anaphase
two new nuclei form
telophase
cytoplasm divides to form two new cells
cytokinesis
gametes are haploid and form by _______
meiosis
homologous pairs of duplicated chromosomes meet up and then split up during the first division, duplicated chromosomes split apart in the second division
extra division
does mitosis or meiosis have extra division
meiosis
how is genetic material exchanged in meiosis
crossing over
when step of meiosis is occurring when homologous chromosome pairs meet up and exchange genetic material through crossing over
prophase 1
does mitosis or meiosis create genetic variance
meiosis
how many daughter cells are created in mitosis
2
how many daughter cells are created in meiosis
4
meiosis in female gametes does not complete until __________
fertilization
in females, meiosis pauses at ___________
metaphase II
in order for fertilization to occur, what must the sperm do
reach the egg in the ampulla and penetrate the zone pellucida
an extracellular matrix surrounding the ovum
zona pelluicda
sperm releases enzymes that break down some of the ________ _________, making a path for the sperm
zona pellucida
after fertilization, the zona pellucida remains around the ________ until it hatches before implantation
zygote
what are the genetic factors that may affect development
aneuploidy, genetic mutations, and structural chromosomal anomalies
individual inherits an extra or missing chromosome
aneuploidy
individual may inherit an allele with a disease causing mutation from one or both parents
genetic mutations
what is an example of an aneuploidy
Down syndrome
what is an example of a genetic mutation
apert syndrome
caused by errors in DNA replication or environmental factors including DNA damage
structural chromosomal anomalies
fertilized egg
zygote
are zygotes diploid or haploid
diploid
zygote undergoes mitosis and quickly splits into more and more cells without stopping to grow
cleavage
when does cleavage occur
preimplantation
in preimplantation, the zygote starts to travel to the _________, where it will hatch from the zona pellucida and embed in the cell wall of the uterus
uterus
cells in the morula continue to divide, but also start to differentiate and secrete fluid
differentiation
the process by which a cell becomes a specific type of cell and specialized in certain functions
differentiation
cleavage gives rise to a ball of cells
morula
as a result of further division and differentiation, the morula developed into a ________
blastocyst
small cluster of cells in blastocysts
embryoblast
blastocysts consists of:
embryoblast
blastocoel
trophoblasts
a fluid filled space inside of a blastocyst
blastocoel
a layer of cells in blastocysts
trophoblasts
when does implantation occur
around day 7
at the end of the first week, the blastocyst hatches out of the _________ _________
zona pellucida
when do trophoblasts attach and invade the lining of the uterine wall
implantation
when does the formation of the bilaminar embryo occur
second week
when does the embryoblast reorganize into a flat, bilayered disc with the amniotic cavity and yolk sac on either side
during the formation of the bilaminar embryo
what are the two cell layers of the bilayered disc
epiblast layer and hypoblast layer
tall columnar cells lining facing the amniotic cavity
epiblast layer
flat/cuboidal layer facing the yolk sac
hypoblast layer
the process by which the bilaminar embryo is converted into a 3-layered trilaminar embryo
gastulation
gastrulation involves the migration of some cells in the __________ layer toward the __________ layer
epiblast
hypoblast
extends from the caudal end of the developing embryo to about half way toward the cephalic end and ends in the primitive node
primitive streak
during gastrulation, cells continue to migrate below the ________ layer
epiblast
as a result of gastrulation, the migratory epiblast cells displace the hypoblast layer and form what two layers
mesoderm and endoderm
the cells that do not displace to the hypoblast layer and remain in the epiblast become what
the ectoderm
what will the ectoderm form
epidermis, salivary glands, and nervous system
what will the mesoderm form
bones, cartilage, muscles, connective tissues, lymphatic system, blood cells and cardiovascular system,
what will the endoderm form
lining of the digestive tract and respiratory system
two areas where there is not a middle layer of mesoderm
oropharyngeal membrane and cloacal membrane
what will the oropharyngeal membrane eventually form
mouth
what will the cloacal membrane eventually form
anus
where in the embryo is the oropharyngeal membrane located
cephalic end
where in the embryo is the cloacal membrane located
caudal end
in the areas surround the oropharyngeal membrane and cloacal membrane, what happens
ectoderm and endoderm fuse to prevent growth of mesoderm in between
some ectoderm cells also migrate from the primitive node towards the cranial end of the developing embryo to form a rod structure called __________
the notochord
what is the notochord important for
inducing the formation of a structure called the neural tube in the next stage of embryogenesis
when does the formation of the trilaminar embryo take place
around the 4th to 6th week
what major events take place after the formation of the trilaminar embryo
the neural tube forms
appearance and migration of neural crest cells
lateral and cephalocaudal folding of embryo
formation of the neural tube
neurulation
the notochord induces thickening of the __________
ectoderm
the neural plate moves down towards the notochord to form the ________ ___________
neural groove
margins of groove are raised and are called ________
neural folds
neural folds fuse to form a tube beneath the ectoderm called the ________
neural tube
the neural tube will give rise to the _________
spinal chord and brain
what is a result of the failure of the posterior neural tube closing
spina bifida
what is the process that the special cells at the edges of the neural plate undergo called
epithelial to mesenchymal transition
what are the cells at the edges of the neural plate called
neural crest cells
where do neural crest cells migrate to
mesoderm
while the neural tube is forming, the mesoderm is differentiating into what
paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm
paraxial mesoderm adjacent to the neural tube will become _______
somites
