Biomedical Engineering Reference
In-Depth Information
Development
time*
Stage
Remarks**
18 days
Neurula
Rudiments of central nervous system forming.
22 days
Embryo is size of a sesame seed; heart begins
beating; from about this stage onward, dif-
ferentiated tissues contain
multipotent
stem
cells, i.e.,
adult stem cells
able to produce dif-
ferent cell types found in the tissue in which
they reside.
24 days
Pharangyla
Appearance of this stage is similar in all ver-
tebrates; rudimentary tail and gill slits are
present; earliest cells of the future brain and
spinal cord are forming.
31-32 days
Embryo about the size of a lentil; first nerve
cells of the future cerebral cortex appear; arm
and leg buds appear.
35 days
Embryo about the size of a blueberry; olfac-
tory nerve forms connections in the brain;
this is the first sensory nerve to form synapse
with brain cells.
40 - 44 days
“Quickening”
Embryo about the size of a kidney bean; first
muscular movements; eyelids, fingers, and
nose appear.
45 days
First brain waves, but not the type marking
consciousness.
56 days
Embryo
becomes a
fetus
Fetus about the size of a kumquat; organ sys-
tems are formed by eight weeks, but they are
not functionally mature.
60 days
Gender is recognizable from the genitalia.
66 days
Fetus about the size of a fig; human-like facial
features are present.
Continued on the next page
Search WWH ::
Custom Search