reproduction and development - part b Flashcards
embryonic period of development
- first 8 weeks
- tissues and organs form
- structures that support and nourish the embryo also form
fetal period of development
- 9th week –> birth
- organs begin to function and coordinate to form organ systems
fertilization
- when the sperm and ovum unite
- in the fallopian tube
- sperm + ovum = zygote
cleavage
- cell division without the enlargement of cells
2 then 4 then 8 cells
morula
- 16 cells
- not part of the cleavage stage
blastocyst
- has a trophoblast
- has an inner cell mass
trophoblast
- develops into chorion
- develops into placenta
- part of the blastocyst
- secretes the hormone hCG
inner cell mass
develops into the embryo
- part of the blastocyst
implantation
- the embedding of the blastocyst into the endometrium
- enzymes secreted by the trophoblast digest some of the tissues and blood vessels of the endometrium
hCG
- human chorionic gonadotropin
- maintains the corpus luteum
- levels of hCG begin to decline after first two months
granulation and tissue formation
-during the second week of development
amniotic cavity
space between the inner cell mass and trophoblast
embryonic disc
- comes from the inner cell mass
- has two layers:
ectoderm and endoderm
gastrulation
- the process of forming the primary germ layers (meso, endo, ecto)
gastrula
a developing embryo
progression of embryonic development
zygote –> morula –> blastocyst –> gastrula
morphogenesis
- the start is marked by gastrulation
- series of events that form distinct structures of the developing organism
- is dependant on embryonic cells being able ot become different
ectoderm layer
- nervous system
- epidermis
mesoderm layer
- muscles
- skeleton
- reproductive organs
endoderm layer
- endocrine glands
- lining of digestive + respiratory systems
skeleton formation
- mesoderm cells come together to form a rod like structure called the notochord
notochord
- develops into the skeleton/ backbone
- a rod of mesoderm cells
neurulation
- ectoderm above the notochord begin to thicken
- folds develop amd fuse to make the neural tube
- will develop into the brain and spinal chord
amnion
- transparent sac
- filled with fluid
- protects embryo from trauma and temp fluctuations
yolk sac
- contributes to the digestive tract formation
- produces the 1st blood cells and future egg/sperm
- only attatched to the baby not the mom
allantois
- forms foundation of the umbilical cord
chorion
- outermost membrane
- encloses everything else
- will form the fetal portion of the placenta
chorionic villi
- establish the beginnings of the placenta
placenta
disk shaped organ that is rich in blood vessels
- fully developed by week 10
- blood systems DO NOT mix
- nutrients and oxygen diffuse from the mother’s circulatory system to the baby
- wastes from baby go to mother
- comes from the trophoblast layer
two parts:
- embryonic/fetal portion
- maternal portion
embryonic/fetal portion of placenta
chorion tissue comes from embryo
maternal portion of the placenta
blood pools form the mother’s circulatory system
umbilical cord
- forms near 8th week
- has 2 arteries and 1 vein going to placenta/mom
embryonic period
- time of morphogenesis
fetal period
time of growth and refinement
gestation
period of time between fertilization and birth
human gestational period
- 40 weeks
- fetus considered “full term”
teratogens
any agents that cause a structural abnormality in the baby
- ex. smoking or alcohol
first trimester
- weeks 1-12
- most sensitive to drugs/alcohol
- formation
fetal period of development begins
- formation
- part of 1st trimester
- weeks 9-12
- body growth accelerates
- end of week 12: ecternal genetalia is distinguishable
second trimester
- weeks 13-24
- framing/walls
- nervous system starts to function
- mother begins to feel movement
third trimester
- weeks 25-38
- finishing touches
- body mass increases
- digestive and respiratory tracts form LAST
