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