Chapter 4 - Vertebrate Embryology Flashcards
Embryology
study of development of a unicellular zygote into complete multicellular organism
in course of nine months, a unicellular human zygote undergoes ___ in preparation for life outside uterus
(human embryology)
cell division
cellular differentiation
morphogenesis
mammalian development studied in
sea urchins
frogs
Early Developmental Stages
(5)
Fertilization
Cleavage
Gastrulation
Development
Birth and Maturation
- Fertilization
(developmental stages)
can begin within ___
12-24 hours following ovulation
fertilization occurs in the
lateral, widest portion of oviduct
fertilization occurs when
sperm traveling from vagina encounter an egg
If more than one egg is fertilized ____
fraternal twins may be conceived
- Cleavage
series of rapid mitotic divisions
characterize early embryonic development
cleavage divisions lead to increase in ___
cell number w/o corresponding growth in protoplasm
total volume of cytoplasm constant
cleavage results in
progressively smaller cells
progressively smaller cells resulting from cleavage cause increase in
nuclear: cytoplasm ratio
surface: volume ratio of each cell
cleavage increase of surface to volume ratio improves
gas and nutrient exchange
indeterminate cleavage
cells maintain ability to develop into complete organism
if cells from first division separate, each cell can develop into own organism
identical twins are result of
indeterminate cleavage
determinate cleavage
cells whose future differentiation pathways determined early in dev
cells must be together for survival - cannot develop into own organism
differentiation
specialization of cells that occurs during dev
first complete cleavage of zygote occurs
~32 hours after fertilization
second cleavage occurs after
60 hours
third cleavage @
72 hours
significance of third cleavage
8-celled embryo reaches uterus
morula
solid ball of embryonic cells
(as cell dev continues)
blastulation
transition of morula –> blastula
blastulation begins when
morula develops fluid-filled cavity - blastocoel
blastocoel
fluid filled cavity formed in morula during blastulation
blastocyst
mammalian form of blastula
blastula
time
structure
formed on the 4th day of blastulation
perimeter: blastoderm
interior: blastocoel
gastrulation begins when
blastula implanted in uterus
gastrulation
cell migrations transform single cell layer of blastoderms in blastula into three-layered structure: gastrula
gastrula
structure and function
three primary germ layers
differential development of:
tissues
organs
systems of body
three primary germ layers of gastrula
ectoderm
endoderm
mesoderm
ectoderm
(1 of 3 primary germ layers of gastrula)
integument
lens of eye
retina
nervous system
integument
epidermis
hair
nails
epithelium of nose, mouth, anal canal
endoderm
epithelial linings of digestive and respiratory tracts
parts of liver, pancreas, thyroid, bladder lining
mesoderm
musculoskeletal
circulatory
excretory
gonads
connective tissue
portions of digestive and respiratory
Development
3 types
external
non-placental internal
placental internal
external development
early dev of may occur outside mother’s body
e.g. land, water
external development
fish and amphibians
lay eggs
fertilized externally in water
embryo develops within egg, feeding on nutrients stored in yolk
external development
reptiles, birds, some mammals (duck-billed platypus)
develops externally on land
fertilization internal, then egg layed
eggs protect embryo
eggs
embryonic membranes
chorion
allantois
amnion
yolk sac
chorion
lines inside of shell
moist membrane
permits gas exchange
allantois
sac-like structure
respiration, excretion
blood vessels transport:
O2, CO2, H2O, salt, nitrogenous waste
amnion
encloses amniotic fluid
amniotic fluid (amnion)
aqueous env.
protects developing embryo from shock
yolk sac
encloses yolk
blood vessels transfer food to dev. embryo
non placental internal development
early dev within body protects young
marsupials, some tropical fish
exchange of food and oxygen bw young & mother limited
may be born very young
placental internal development
two main components
placenta
umbilical cord
placental internal develompent
specialized circulatory system
mother —> fetus
supplies oxygen
removes CO2, metabolic waste
placenta and umbilical cord develop within
first few weeks following fertilization
placenta and umbilical cord outgrowths of 4 extraembryonic membranes
amnion
chorion
allantois
yolk ac
amnion
(pid)
thin, tough membrane
contain watery fluid - amniotic fluid
amniotic fluid (pid)
shock absorber of external and localized pressure from uterine contractions during labor
chrion (pid)
membrane
surrounds amnion
leads to placenta formation
allantois (pid)
third membrane
develops as outpocketing of gut
blood vessels of allantoic wall enlarge —> umbilical cord
umbilical vessels (pid)
connect fetus to placenta
yolk sac (pid)
early dev of blood vessels —> umbilical vessels
Birth and Maturation
labor
childbirth
differentiation of cells until adulthood
labor
series of strong uterine contractions
3 distinct stages
1 stage labor
cervix thins out, dilates
amniotic sac ruptures, releasing fluids
mild contractions
2 stage labor
rapid contractions
birth of baby
cutting umbilical cord
3 stage labor
uterus contracts
expells placenta, umbilical cord
maturation
embryo –> adult
cell division
growth
differentiation
maturation forms
suspended in temporary state
e.g. arthropods - pupal stage
uninterrupted
e.g. mammals
differentiation of cells complete when
all organs reach adult form
