Early Development Lecture Sep 27 Flashcards
WHere does implantation usually occur?
the superior posterior wall of the uterine cavity, but implantation can occur at other abnormal sites
WHat are the two possible causes of twinning during development?
- 2 eggs released in ovulation and fertilized (non-identical)
- Separation of pluripotent inner cell mass resulting in the production of two genetically identical fetuses
What two major developmental events occur when the embryo is in the morula stage?
- Formation of inner and outer cells
- Compation - tight junctions and gap junctions form between adjacent blastomers and cells flatten together to form a tight ball.
What adhesion molecules have a big role in compaction?
cadherins
what does a blastocyst have that a morula doesn’t?
a blastocoel - a fluid-filled space
What happens when the embryo implants in the uterine epithelial lining?
What has to happen to the embryo before that can occur.
THe embryo first has to hatch out of the zona pellucida.
Then part of the outer trophoblast cells fuse together to form the syncytriotrophoblast, which invades the epithelial tissue.
What are two things improper implantation can cause?
ectopic pregnancy
placenta previa
What hormone does the syncriotrophoblast does to signal for continued secretion of estrogen and progesteron by the corpus luteum?
What effect does this happen?
Human chorionic gonadotropin (HCG)
It represses sloughing of the endometrium and maintains the pregnancy
What happens in the decidual reactions?
The invasion of synctriotropobloast into the endometrium treiggers a reaction by the uterine stromal cells to swell and accumulate glycogen and lipid.
The transformed cells are called decidual cells and they’ll form a distinct layer that surrounds the torphoblast called the decidue.
This may serve as a protection of the fetus from mother immune attack
What does delamination result in?
The inner cell mass cells pull away from the adjacent trophectoderm to form a fluid space called the amniotic cavity
The inner cell mass cells flatten and form two layers of cells. WHat are the layers?
- epiblast (the cells closest to the amniotic cavity - they’re tall and columnar)
- Hypoblast (cuboidal)
THe hypoglast cells proliferate and extend below the embryonic disc to enclose a space known as what?
the yolk sac
What calles form the connecting stalk which will eventually become the umbilical cord?
cells that break off the wall of the primary yolk sac to fill the space between the yolk sac and trophoglast (they are called extraembryonic mesoderm cells)
What is the first sign of gastrulation?
The development of the primitive streak and node.
This is from cells that proliferate and migrate to the midline of the epiblast
How are the mesoderm and endoderm formed?
THe primitive streak of the epiblast invaginates and as cells from the epiblast moves toward the streak, they will be laid down between the hyphoblast and the epiblast - first the endoderm and then th emesoderm
Cells that remain in the epiblast after gastrulation are called what?
ectoderm
How does the notochord develop?
Many cells which migrate through the primitive node will descend into the mesoderm and then migrate rostrally and form a thick cord ot cells called the notochord.
The notochord is important for mechanical support and as an inducer ot nervous system development.
How does neurulation occur?
Ectoderm cells directly over the notochord are induced to proliferate and form a thickening called the neural plate
the neural plate begins to buckle and form the neural folds
the neural folds curve around and fuse with the opposite side to form a tube, called the neural tube.
the neural tube is then completely surrounded by ectoderm.
What do neural crest cells eventually develop into?
They are sometimes called thd 4th germ layer because they develop into spinal and autonomic ganglia, schwann cells, the meninges, adrenal medulla and malanoctyes
What are the two major subdivision of mesoderm?
Whichin one of the mesoderms, what are the sub categories?
- extraembryonic mesoderm
- Embryonic mesoderm (arises from the epiblast)
THe embryonic mesoderm is further divided by the third and fourth week ino:
paraxial mesoderm
intermediate
lateral mesoderm
What gives rise to somites? what are somites?
What do the somites give rise to?
THe paraxial mesoderm has two thickenings near the notochord/neural tube
they form in pairs (we usually get about 42-44)
They give rise to most of the axial skeleton and associated musculatur and adjacent dermis of the skin
What will the intermediate mesoderm participate in the formation of?
the urogenital system
What happens to the lateral mesoderm?
the lateral mesoderm will begin to display fluid spaces which will coalesce to split the lateral mesoderm into dorsal and vental wings
the dorsal wing is called somatic mesoderm (this will help form lateral and bentral bodywall.
THe ventral wings, or splanchnic mesoderm, will surrounde the gut and form mesentery.
the fluid-filled space that separates the two leaves of lateral mesoderm are called what?
coelom
