Developmental Biology Flashcards
Fertilization
in mammals, an egg can be fertilized within 24 hrs after ovulation
Cleavage
- a series of rapid mitotic division
- results in progressively smaller cells w/ an increasing ratio of nuclei to cytoplasm
- increases the surface-area-to-volume ratio - improving gas to nutrient exchange
- first complete cleavage of a zygote occurs approx 32 hours after fertilization
- the second cleavage occurs 60 hrs and the third cleavage approx 72 hrs = 8 celled embryo reaches th uterus
Morula
a solid ball of embryonic cells
Blastulation
- begins when the morula develops a fluid-filled cavity called the blastocell - after the 4th day becomes the blostula
- the blastula is the stage of the embryo that implants in the uterus
Gastrulation
- after week 2, the embryo is fully implanted in the uterus
- blastula becomes a 3-layered structure called gastula
Ectoderm
integumentary system, lens of the eye, the retina, and the nervous system
Endoderm
epithelial linings of the digestive and respiratory tracts
Mesoderm
musculoskeletal system, circulatory system, excretory system, gonads, connective tissue, and the portions of digestive and respiratory organs
Neurulation
- at the end of gastrulation, regions of the germ layers begin to develop into a rudimentary nervous system - starts before week 3
- the notochord develops into a closed tube, which gives rise to the brain and spinal cord (CNS)
- the cells at the tip of each neural fold give rise to many components of the PNS - sensory ganglia, autonomic ganglia, adrenal medulla, and schwann cells
Organogenesis
body organs begin to form
Growth
organs increase in size
Gametogenesis
Eggs develop in women and sperm develop in men
Placental Development
- the placenta and umbilical cord supply oxygen and nutrients to the fetus and removes carbon dioxide to metabolic wastes
- the umbilical cord are outgrowth of the amnion, chorion, allontois, and yolk sac
- the amnion contains the amniotic fluid that acts as a shock absorber of external pressure
- placenta formation begins with the chorion, a membrane that surrounds the amnion that assists with the transfer of nutrients from the mother to the fetus
- the allontois become the umbilical vessels which will connect the fetus to the developing placenta
Gestation
approx 9 months and subdivided into 3 trimesters
First Trimester
major organs begin to develop and heart beats ~ 22 days