Development- Chapter 43
gestation in humans lasts about
266 days or 9 months
cleavage is followed by rapid ______ ________ and ___________ without cell growth
DNA replication, mitosis
control development along the anterior-posterior axis
Hox genes
different segments of the embryo receive different combinations of Hox gene products which will serve as ___________ ___________
RESULT, transcription factors
fusion of sperm and egg accomplishes several things: +sets up blocks to the entry of _______ _________ +stimulates ______ ______ across egg membrane +changes the eggs _________ +increases egg __________ and stimulates _______ ___________ +initiates the rapid series of ________ _________ necessary for development of an _________
additional sperm ion fluxes pH metabolism, protein synthesis cell divisions, embryo
outgrowth of the extra embryonic endoderm plus mesoderm
allantoic membrane
the allantoic membrane forms the __________- a sac for storage of metabolic wastes
allantois
_______ then forms and encloses the embryo in fluid filled amniotic cavity
amnion
surrounds the embryo
amnion
secretes fluid
amniotic cavity
ball of cells forms a _____________ - embryo now called a _____________
blastocoel, blastula
trophoblast cells secrete fluid creating the blastocoel- embryo now called a __________
blastocyst
________ become determined at different times in different species
blastomeres
opening created by invagination during gastrulation is called the
blastopore
pattern of cleavage in different species influences the form of their __________
blastulas
induces the overlying ectoderm to form the nervous system by expressing signaling molecules
chordamesoderm
forms a continuous membrane under the eggshell- prevents water loss and exchanges respiratory gases
chorion
transformation of the diploid zygote into a mass of cells occurs through a series of cell divisions called
cleavage
in most eggs with little yolk- early cleavage furrows divide the egg completely and daughter cells are all similar in size (sea urchin)
complete cleavage
positions of mitotic spindles during cleavage are defined by ___________ _______ from mother stored in egg; orientation of mitotic spindles determines planes of cleavage and ________________ of daughter cells
cytoplasmic factors, arrangement
rearrangements of egg cytoplasm prepare cells for _____________
determination
common in fishes, reptiles, birds- embryo forms a disc of cells called a blastodisc that sits on top of yolk mass
discoidal cleavage
outer germ layer, gives rise to the nervous system, epidermal layer of skin and structures derived from skin
ectoderm
regulative development: pluripotent cells of the blastocyst are the __________ _____ __________
embryonic stem cells
innermost germ layer, gives rise to the lining of the digestive tract, respiratory tract, pancreas, liver
endoderm
during gastrulation three germ layers form
endoderm, ectoderm, mesoderm
embryos in reptiles, birds, mammals are surrounded by several __________-_____________ membranes which originate from the embryo but are not a part of it
extra- embryonic
function in nutrition, gas exchange, waste removal
extra- embryonic membranes
joining of sperm and egg to generate diploid zygote
fertilization
embryo becomes a ______ in the first trimester
fetus
during second trimester the fetus grows rapidly: + limbs elongate, fingers, toes, and facial features become well _______ + fetal _______ are first felt by mother + ________ ________ undergoes rapid development
formed movements nervous system
_______ families of Hox genes control differentiation along this axis: + each resides on a _________ ___________ + Hox genes closest to the 3' end of each gene grouping are expressed ________ and in the _________ of the embryo + Hox genes closer to the 5' end of the gene grouping are expressed ________ and in a more ___________ part of the embryo
four different chromosome first, anterior later, posterior
when two separate eggs are fertilized by two separate sperm
fraternal twins
the process where the blastula is transformed by massive movements of cells into an embryo with multiple tissue layers and visible body axes
gastrulation
in many species where egg contains a lot of yolk, cleavage furrows do not penetrate completely
incomplete cleavage
fetus continues to grow during third trimester: +________ _______ mature + ___________ _________ begins to function, liver stores __________, kidneys produce ________, brain undergoes _____ and ______ cycles +infant is born when last of the vital organs (_________) mature
internal organs digestive system, glycogen, urine, sleep, wake lungs
middle germ layer, contributes tissues to many organs, heart, blood vessels, muscles, bone
mesoderm
if blastomeres at early blastula formation are physically separated into two groups both groups produce complete embryos
monozygotic twins
each blastomere contributes a specific set of "tiles" to the final organism
mosaic development
break loose from the neural tube after fusing and contribute to development of the peripheral nerves which grow out to the body tissues and back to the spinal cord
neural crest cells
neurulation involves the formation of a ______ ______ from an external sheet of cells
neural tube
thickening continues and forms fold that deepen and fuse creating the ______ _____
neural tube
body segmentation develops during
neurulation
initiation of the nervous system
neurulation
positions of mitotic spindles during cleavage are...
not random
gives structure support to the developing embryo and is eventually replaced by the vertebral column
notochord
cleavage results in the differential differentiation of ___________ and cytoplasmic _____________
nutrients, determinants
process of development of many organ and organ systems simultaneously and in coordination with each other
organogenesis
somites help to guide the _______ ________ that connect the brain and spinal cord with tissues and organs of the body
peripheral nerves
exchanges nutrients, respiratory gases, metabolic wastes between mother and embryo
placenta
extra embryonic membranes in mammals form the
placenta
extra- embryonic membranes in mammals..... interact with tissues of the mother to form the ________
placenta
yolk sac in mammals contributes mesodermal tissue that with the tissues of the uterine wall produce the
placenta
first trimester: + implantation, gastrulation, tissues differentiate, ______ forms, organs begin to ________ + heart begins to beat during week ______ + limbs form by week ______ + a time of rapid cell division and tissue ___________ + embryo most sensitive to damage from ______, drugs, chemicals, __________
placenta 4 8 differentiation radiation, pathogens
loss of some cells during cleavage does not affect the developing embryo (remaining cells compensate for loss)
regulative development
pattern of cleavage is _________- first cell division is parallel to the vertical axis and yields two blastomeres +subsequent divisions of blastomeres occur at _______ angles to each other + products of genes expressed at this time play roles in __________ + at 8-cell stage the blastomeres change ________ to maximize surface contact with each other + at 16-32 cell stage the ccells separate into _______ groups (_________ ______ _________- will become embryo) + outer cells beome encompassing sac- ________________
rotational right cleavage shape two, inner cell mass trophoblast
mosaic development: if one of the blastomeres is removed you will fail to have development of a portion of the embryo (____________)
roundworms
fetus grows and matures during
second and third trimesters
as neural tube forms, mesodermal tissues gather along the sides of the notochord to form separate segmented blocks of cells called
somites
produce cells that will become the vertebrae, ribs, muscles fo the trunk and limbs, and lower layer of the skin
somites
expressed in the mammalian notochord and induces cells in the neural tube to have fates characteristic of ventral motor nerves
sonic hedgehog
other genes provide information about dorsal-ventral positioning such as
sonic hedgehog
early in development, cycles of mitosis occur without cell division producing _________ ( a single cell with multiple nuclei)
superficial cleavage, syncytium
ectoderm and mesoderm grow out from the embryo to form two layers of cells that extend along the inside of the eggshell. they meet and fuse forming two membranes-
the inner amnion and outer chorion
portion of the mesoderm called the chordamesoderm produces a rod of connective tissue-
the notochord
first sign of formation of neural tube
thickened area of the ectoderm forming the neural plate
events of gestation can be divided into three periods called
trimesters
first extra embryonic membrane to form is the __________- interacts directly with the endometrium in the uterus and allows attachment and burrowing into the uterine wall
trophoblast
in mammals cleavage is ________
unique
first to form, extension of the endodermal tissue. grows to enclose the entire body of the yolk in the egg
yolk sac
four membranes in the chick that form
yolk sac, allantoic membrane, amnion, chorion
superficial cleavage; nuclei migrate to the periphery of the egg and after further mitosis the plasma membrane of the egg grows inward separating the nuclei into individual cells surrounding a core of ______- (ie: ___________)
yolk, Drosophila