Embryology Flashcards
embryology
the study of the development of a unicellular zygote into a complete multicelluar organism
Fertilization of vertebrates
an egg can be fertilized within 12-24 hours following ovulation. Occurs in the fallopian tube
faternal twins
if more than one egg is fertilized
Cleavage
early embryonic development is characterized by a series of rapid miotic divisions known as cleavage. results in progressively smaller cells with an increasing ratio of nuclear to cytoplasmic material.
indeterminate cleavage
is one that results in cells that maintain the ability to develop into a complete organism.
Identical twins
are the result of an indeterminate cleavage.
determinate cleavage
results in cells whose future differentiation pathways are determined at an early developmental stage.
differentiation
is the specialization of cells that occurs during development
morula
a solid ball of embryonic cells
Blastulation
begins when the morula develops a fluid filled cavity called the blastocoel. which by the fourth day becomes a hollow sphere of cells call the blastula.
Gastrulation
once the blastula is implanted in the uterus cell migrations transform the single cell layer of the blastula into a three layerd strucutre called gastrula
Gastrula
composed of three primary germ layers that are responsible for the differential development of the tissues, organs and systems of the body at later stages of growth. ectoderm, endoderm and mesoderm
Ectoderm
itegument (including the epidermis,hair , nails, and epithelium of the nose, mouth, and anal canal), the lens of the eye, the retina and the nervous system
Endoderm
epithelial linings of the digestive and respiratory tracts and parts of the liver, pancreas, thyroid and bladder lining
Mesoderm
musculoskeletal system, circulatory system, excretory system, gonads, connective tissues throughout the body and portions of the respiratory organs.
External development
the early development of many animals occurs outside of the mothers body, on land or in the water.
Egg shells
provide protection for the developing embryo outside the mothers body. Consisting of chorion, allantois, amnion and yolk sac
Chorion of egg shells
lines the inside of the shell, it is the moist membrane that permits gas exchange
Allantois of egg shells
saclike structure that is involved in respiration and excretion and it contains numerous blood vessels to transport O2, CO2, water, salt and nitrogenous wastes
Amnion of egg shells
this membrane encloses the amniotic fluid which keeps the embryo safe from shock
Yolk sac
encloses the yolk. Blood vessels in the yolk sac transfer food to the developing embryo
Nonplacental internal development
marsupials and some tropical fish develop in the mother without a placenta. Without a placenta exchange of food and oxygen between the young and the mother is limited.
Placental internal development
the growing fetus receives oxygen directly from its mother through a specialized circulatory system. which also supplies nutrients and removes waste. key component is the placenta and the umbilical cord
The placenta and the umbilical cord are out growths of _
four extra-embryonic membranes formed during development: the amnion, chorion, allantois and yolk sac
The amnion in humans
is a thin tough membrane containing a watery fluid called amniotic fluid. Amniotic fluid acts as a shock absorber of external pressure and localized pressure from uterine contractions
the chorion in humans
the placenta formation begins with the chorion, a membrane that completely surrounds the amnion
allantois of the human
develops as an out-pocketing of the gut. blood vessels of the allantoic wall enlarge and become the umbilical vessels, which connect the fetus to the developing placenta
yolk sac of humans
the site of early development of the blood vessels becomes associated with the umbilical vessels
labor
a series of strong uterine contractions. three distinct stages. first stage the cervix thins and dilates and the amniotic sac ruptures releasing fluids. second stage is characterized by rapid contractions resulting in birth. third is followed by expelling of the placenta and umbilical cord
embryo parts of seed formation
epicotyl, cotyledons, hypocotyl, endosperm, and seed coat
epicotyl
this is the precursor of the upper stem and leaves
cotyledons
these are the seed leaves. Dicots have two seed leaves while monocots have only one.
hypocotyl
this develops into the lower stem and root
endosperm
the endosperm grows and feeds the embryo. In dicots the cotyledon absorbs the endosperm
seed coat
develops from the outer covering of the ovule. the embryo and its seed coat together comprise the seed
Seed dispersal
the fruit is formed from the ovary walls and other parts of the plant is the means of seed dispersal. it enables to the seed to be carried more frequently and effectivley
meristem cells
these tissues undergo active cell reproduction. gradually the cells elongate and differentiate into cell types characteristic of the species
apical meristem
found in the tips of roots and stems. growth and length only occurs at these points
lateral meristem
the lateral meristem or cambium is located between the xylem and pholem. this tissue permits growth in the diameter and can differentiate into xylem and pholem cells. predominant in woody dicots
Embryonic development stages
1) fertilization
2) cleavage
3. Morula
4. Blastula
5. Gastrula
6. Extra embryonic development
7. Organogenesis
Notochord
Cells of dorsal surface of mesoderm germ layer, form this stiff Rod that provides support
Neural tube
In Ectoderm layer above the notochord, a layer of cells forms the neural plate the plate indents forming a neural grove which becomes a neural tube (encasing CNS) and neural crest creating teeth bones and more
Blastocyst
Consists if two parts- outer ring trophoblast and inner cell mass called embryonic disc
Trophoblast
Outer ring the embeds into the endometrium, and produces HCG, then becomes the chorion
Embryonic disc
Inner cell mass that clusters at one pole and flattens into embryonic disk. A primaries streak occurs, gastrulation follow and then extraembryonic membranes form (except chorion)
