Flashcards in Topic 17: Development II Deck (29):
What happens after cleavage?
normal cell cycle resumes
cell division slows
animal body starts to take shape during next 2 stages of development:
What is gastrulation?
morphological process by which hollow blastula becomes layered embryo (gastrula) with:
- a digestive tube
- embryonic germ layers
What are the steps to gastrulation in sea urchins?
1. mesenchyme cells at vegetal pole migrate into blastocoel
2. invagination at vegetal pole
3. archenteron forms
4. archenteron extends across blastocoel
5. mouth formation
What is invagination?
when the cells of the vegetal plate flatten and buckle and fold inward
What are filopodia?
mesenchyme cells produce this at tip; they are thin extensions
What are the steps to gastrulation in birds?
1. formation of epiblast and hypoblast
2. formation of primitive streak
3. formation of 3 germ layers
What is a trophoblast?
outer single layer of cells
What is the inner cell mass?
the cluster of cells that become an embryo
What are the steps to gastrulation in humans?
2. formation of epiblast and hypoblast
3. formation of 4 extraembryonic membranes
4. formation of 3 germ layers
What is organogenesis?
process of organ formation
What is neurulation?
formation of the brain and spine
What forms the notochord?
What forms the nerve cord?
What is induction?
the process by which cells stimulate or influence differentiation of neighboring cells
What are the steps in neurulation?
1. formation of the notochord
2. formation of neural plate
3. formation of neural tube
How does the neural plate form?
the notochord induces the ectoderm above it to thickem
How does the neural tube form?
the neural plate rolls up
What does the neural tube develop into?
anterior portion -> brain
remainder -> spinal cord
What happens to the notochord?
most of it disappears, some form vertebral discs
Why does spina bifida happen?
it occurs when the neural tube doesn't form properly
What is the neural crest?
it's between the neural tube and ectoderm
cells migrate -> nerves, teeth, skull, bones
What are somites? What do they do?
blocks of mesoderm cells next to notochord
migrate -> segmented/repeated structures - ribs, vertebrae, muscless
What happens during the first trimester?
the biggest changes for the mother and embryo
the implanted embryo secretes hCG and acts like LH on corpus luteum - maintains progesterone, estrogen secretion
How does the placenta form?
when first implanted, the nutrients come directly from the endometrium
weeks 2-4 the triploblast mixes with endometrium to form the placenta
What is the placenta?
an organ of exchange between mother and embryo - exchanges nutrients, gases, immunity, waste
What connects the embryo to placenta?
the umbilical cord
Identical vs fraternal twins
identical twins come from the same egg and sperm
fraternal twins come from 2 different eggs and sperms
What happens during birth?
it begins with labor, then
uterine contractions to push the fetus and placenta out
it is regulated by prostaglandins, hormone like estradiol and oxytocin