Reproduction and development Part 7 Flashcards
After cleavage
the rate of cell division slows
The remaining stages of embryonic development are responsible for
morphogenesis
What is morphogenesis
the cellular and tissue-based processes by which the animal body takes shape
During gastrulation
a set of cells at or near the surface of the blastula moves to an interior location, cell layers are established, and a primitive digestive tube forms
two- or three layered embryo
gastrula
cell layers produced by gastrulation is called
germ layers
ectoderm
outer layer
endoderm
inner layer
mesoderm
between ecto and endoderm
mouth develops from the first opening
blastopore
mouth forms in the embryo
protostomes
mouth develops in the second opening
deuterostomes
Examples of deuterostomes
sea urchins, humans, and other vertebrates
Organogenesis
regions of the embryonic germ layers develop into rudiments of body organs
Human gestation can be divided into
3 trimesters of about 3 months each
First semester
the embryo secretes hormones that signal its presence and regulate the mother’s reproductive system
Human chorionic gonadotropin (hCG)
acts to maintain the secretion of progesterone and estrogens by the corpus luteum through the first months of pregnancy
occasionally when an embryo splits during the first month of development, it results in
identical or monozygotic twins
Fraternal, or dizygotic twins
arise when two eggs are fertilized and implant as two genetically distinct embryos
Why can’t some embryos complete development
This is due to chromosomal or other abnormalities. These spontaneously abort and occur in about 1/3 of all pregnancies.
