Chapter 18- Developmental Biology Flashcards
what does cleavage result in
progressively smaller cells with an increasing ratio of nuclei to cytoplasm and the surface area to volume of each cell
how long after fertilization is the first cleavage completed
32 hours
how long after fertilization is the second cleavage completed
72 hours
what is the result after the second cleavage
a morula
what is blastulation
when the morula develops a fluid-filled cavity called the blastocoel
what does the blastocoel become
the blastula
what is the order of “embryonic development”?
morula-> blastocoel-> blastula-> gastrula
what is the outer layer of cells of the blastula called
the trophoblast
what does the trophoblast do
- plays a role in the implantation of the blastula in the uterus
- provides nutrients to the embryo and develops into part of the placenta
what is the amnion
a thin, tough membrane containing a watery fluid called amniotic fluid
what is the purpose of the amnion
is acts as a shock absorber of external pressure during gestation and localized pressure from uterine contractions during labor
what does placenta formation begin with
the chorion
what is the chorion
a membrane that completely surrounds the amnion
what does the chorion do
assists with transfer of nutrients from the mother to the fetus
what is the allantois
an outpocketing of the gut
what is the purpose of the allantois
the blood vessels of the allantoic wall enlarge and become the umbilical vessels, which will connect the fetus to the placenta
what does the yolk sac do
comes associated with the umbilical vessels
when is the gastrula formed
after week two
what does the ectoderm differentiate into
integumentary system, lens of the eye, the retina, the nervous system
what does the mesoderm differentiate into
musculoskeletal system, circulatory system, excretory system, gonads, connective tissue throughout the body, and portions of digestive and respiratory systems
what does the endoderm differentiate into
epithelial linings of the digestive and respiratory tracts and parts of the liver, pancreas, thyroids, and bladder lining
what is neurulation
regions of the germ layer begin to develop into rudimentary nervous system at the end of gastrulation
what do neural crest cells give rise to
sensory ganglia, autonomic ganglia, adrenal medulla, and schwann cells
what are the three final stages of development
organogenesis, growth, gametogenesis
what happens in organogenesis
the body organs begin to form
what happens in growth phase
organs increase in size which is a continual process from infancy to adulthood
what happens in gametogenesis
eggs develop in women and sperm develop in men which permits reproduction to occur
what happens during the first weeks of fertilization
major organs begin to develop, the heart starts to beat at 22 days
describe the embryo at the end of the first trimester
most of the organs have developed, the embryo is referred to as a fetus, it is 9 cm long
describe the fetus at the end of the second trimester
its face appears human, its toes and fingers elongate, the fetus is 30-36 cm long
what happens during the ninth month of pregnancy
antibodies are transported from the mother to the fetus
what occurs in the first phase of labor
cervix thins and dilates, the amniotic sac ruptures and contractions are relatively mild
what occurs in the second phase of labor
rapid contractions, resulting in the birth of the baby
what occurs in the third phase of labor
uterus contracts, expelling the placenta and the umbilical chord
what are teratogens
congenital disorders from chemical and biological agents
what is vertical transmission
when a mother passes on an infection directly to her developing offspring
what process occurs in angiosperms
double fertilization
what are the components in a seed embryo
epicotyl, cotyledons, hypocotyl, endosperm, seed coat
what is the epicotyl
precursor of the upper stem and leaves
what is the cotyledons
seed leaves, dicots have two seed leaves, while monocots have only one
what is the hypocotyl
the lower stem and root
what is the endosperm
feeds the embryo in angiosperms. in dicots the cotyledon absorbs the endosperm
what is the seed coat
develops from the outer covering of the ovule, the embryo and its seed coat together comprise the seed
what is seed germination
the process of a seed sprouting into a seedling
what are meristem cells
they determine how tall a plant can grow
where is the apical meristem found and what occurs here
found at the tips of roots and stems and growth in length only occurs at these points
where is the lateral meristem located
between the xylem and phloem
what is the purpose of the lateral meristem
permits growth in diameter and can differentiate into new xylem and phloem cells
