Animal Development Flashcards
a series of mitotic divisions and cell migrations that transform the zygote into a blastula
cleavage
blastula
“hollow ball” of cells
hallow center of blastula
blastocoel
there is little increase in the overall volume during cleavage because the – become progressively smaller
blastomeres
the cells of a blastula
blastomeres
the amount of – influences cleavage
yolk
fertilization stimulates – across the egg membrane
ion fluxes
fertilization sets up blocks to the entry of – into the egg
additional sperm
fertilization changes the –of egg cytoplasm
pH
fertilization increases egg – and stimulate protein synthesis
metabolism
fertilization initiates the rapid series of – that produce a multicellular embryo
cell divisions
– is well stocked with organelles, nutrients, transcription factors, and mRNA
egg cytoplasm
sperm contributes –
DNA (haploid nucleus) and centriole (origin of primary cilia)
centriole becomes the zygote’s –
centrosome which organizes the mitotic spindles for subsequent cell divisions
molecules in the cytoplasm of amphibian egg are – distributed
not homogenously
sperm entry establishes – of the zygote
polarity
the nutrients in an unfertilized frog egg are dense yolk granules that are concentrated by gravity in the lower half of the egg called
vegetal pole
the haploid nucleus of egg is located at
animal pole
the animal cortical cytoplasm is
pigmented
frog egg is – symmetrical
radially
when a sperm binds to and enters a frog’s egg the radial symmetry turns into a – symmetry
bilateral
cortical cytoplasm rotates toward
the site of sperm entry
in amphibian eggs, cortical rotation and rearrangement of the cytoplasm after fertilization create the – opposite the point of sperm entry
gray crescent
gray crescent marks the location of
important developmental events
the centriole from sperm initiates
cytoplasmic reorganization (causes microtubules in vegetal pole to form a parallel array that guides movement of the cortical cytoplasm)
sequence of early cell divisions that transform the diploid zygote into a mass of undifferentiated cells that will develop as the embryo
cleavage
occurs in most eggs that have little yolk
complete cleavage
frogs undergo – complete cleavage
unequal
occurs in species in which the egg contains a lot of yolk and the cleavage furrows do not penetrate it all
incomplete cleavage
is a type of incomplete cleavage common in fishes and birds in which the embryo forms a disc of cells (blastodisc) that sits on top of the dense yolk mass
discoidal cleavage
variation of incomplete cleavage that occurs in fruit flies
superficial cleavage
a single cell with many nuclei
syncytium
the nuclei eventually migrate to the periphery of the egg, after which the plasma membrane grows inward, creating a – by partitioning the nuclei into individual cells surrounding a core of yolk
blastoderm
what influences the pattern of cleavage
amount of yolk and orientation of mitotic spindle (determined by maternal genome)
– cleavage occurs in mammals
rotational
mammalian cleavage is slow and asynchronous because
blastomeres do not undergo mitosis at the same time
when the zygote reaches the 8-cell stage, the blastomeres change shape to maximize their surface contact with each other forming – and become a compact mass of cells
tight junctions
At the 32-cell stage, cells separate into two groups:
inner mass and trophoblast
will become embryo
inner mass
surrounding outer cells become an encompassing sac that secretes fluids to create the blastocoel cavity with the inner cell mass at one end
trophoblast
at the 32-cell stage the embryo is called a
blastocyst
specific blastomeres generate specific
tissues and organs
loss of blastomeres results in loss of later structures
mosaic (determinate) development
loss of blastomeres doesn’t deleteriously affect the development because the remaining cells compensate for loss
regulated (undeterminate) development
cells move to new positions adn form the three germ layers from which differenitated tissues develop
gastrulation
inner most germ layer, digestive tract, respiratory tract, pancreas, thyroid, liver
endoderm
outer germ layer, nervous system and epidermis of skin
ectoderm
middle layer, skeletal muscle, circulatory system, kidneys, gonads, blood cells, dermis of skin
mesoderm
embryonic or unspecialized cells that migrate to other tissue layers
mesenchyme cells
sea urchin gastrulation, some cells change shape and move inward to form the – other cells break free becoming primary –
archenteron, mesenchyme
opening created by the invagination of the vegetal pole
blastopore
blastopore becomes anus
deuterostomes (sea urchins and vertebrates)
blastopore becomes mouth
protostomes (earthworm and insects)
the embryo develops only partially in the uterus then finishes outside in a pouch (marsupium)
non Eutherian mammals
nutrient and waste exchange in eutherian mammals occur via the
placenta
surround the vertebrate embryo
extraembryonic membranes
encloses yolk within egg
yolk sac
yolk is – by cells of the yolk sac and the nutrients are transported to the embryo
digested
a sac for waste storage
allantois
surrounds the embryo, forming the fluid-filled amniotic cavity that protects the embryo
amnion
forms a continuous membrane just under the eggshell; reduces water loss and exchanges gases
chorion
the amniotic egg provides an – environment for development of the embryo
aqueous
the yolk sac is the – and – layers that surround the yolk to absorb its nutrients
mesoderm and endoderm
the – forms the umbilical cord in eutherian mammals
allantois
chorion layers
ectoderm and mesoderm
amnion layers
mesoderm and ectoderm
allantois layers
mesoderm and endoderm
in placental mammals, the first extraembryonic membrane to form is the –
trophoblast
the inner cell mass consists of – and –
hypoblast and epiblast
trophoblast cells interact with the – and adhesion molecules and adhesion molecules attach them to the –
endometrium, uterine wall
the trophoblast – into the uterine wall and sends out – to increase contact with maternal blood
burrows, villi
hypoblast cells form the
chorion
the placenta develops from the – and – tissues
chorion and uterine
the epiblast produces the –
amnion
rupturing of the amnion and chorion and loss of the – = water break
amniotic fluid
the process of embryonic/fetal development from fertilization to birth (parturition)
gestation or pregnancy
first trimester =
“embryonic” development
in the first trimester the embryo becomes a –
fetus
heart begins to beat by week
four
limbs form by week
eight
first trimester is a time of – cell division and tissue differentiation
rapid
second trimester
limbs elongate
fingers, toes, and facial features form
nervous system develops rapidly
first fetal movements are felt
third trimester
internal organs mature
brain goes through sleep-wake cycles
birth occurs when lungs are mature
increased ratio of – to – at the end of 3rd trimester
estrogen to progesterone
human chorionic gonadotropin is produced by the chorion during
first trimester
During the first trimester, hCG keeps the – functional which keeps producing high E and P levels to prevent ovulation from occuring
corpus luteum
Due to its highly negative chard, hCG may repel the – of the mother, protecting the fetus during the first trimester
immune cells
hormonal changes during the first trimester cause
“morning sickness”
rapid fetal development occurs during the – trimester
second
during the second trimester, the placenta produces lots of E and P from – (eg the steroid biosynthetic pathway) which continues to inhibit ovulation and menstruation
circulating androgens
during the third trimester the – ratio increases
E/P
amniotic fluid is withdrawn
amniocentesis
amniocentesis - chromosomal abnormalities, sex determination, week –, risk 0.5% miscarriage
14-16
not as invasive as amniocentesis during week – risk 0.5-1% miscarriage
chorionic villus sampling, 10-12
ultrasound early week 6-10 = / week 10-13 =
vaginal, belly
ultrasound measures
nuchal translucency
an accumulation of fluid at the base of the baby’s neck that is expected to be seen in all pregnancies
nuchal translucency
a nuchal translucency measurement above – is considered abnormal
3.0 - 3.5mm
an increased nuchal translucency is associated with a higher risk for –
chromosome abnormality or structural defect
absence of testosterone and MIH –>
mullerian duct system (fallopian tubes and uterus)
presence of testosterone and MIH –>
wolffian duct system (epididymis and vas deferens)
during the first trimester in humans, embryonic gonadal tissue (the mesoderm) develops into – due to the expression of the gene on the Y chromosome
testes
5-alpha DHT promotes the development of – into male genitalia
undifferentiated external genitalia
XY gonads produce androgen –>
male
XX no androgen –>
female
XY but androgen receptor defect –>
inside testes outside female
XY 5-alpha reductase deficient –>
internal male, external micropenis
XY no androgen –>
fertile female
XX androgen production
oversized clitoris and fused labia
XY androgen/no-androgen
fertile male, micropenis
Later in fetus XY no androgen
baby boy with micropenis
a general term used for a variety of conditions in which a person is born with a reproductive or sexual anatomy that doesn’t seem to fit the typical definitions of female or male
intersex
consequences of normalizing procedures
loss of sensory tissue, memories of child sexual trauma, surgeries intensify the feeling of shame and alienation they are meant to eliminate