Lecture 2 Flashcards
What properties do sea urchin eggs have
- Transparent eggs
- Holoblastic cleavage
- Rapid cell division
What is the status of cells at the late blastula stage
Blastoele is surrounded by monolayer of cuboidal cells
Where does grastulation begin
At the vegetal pole
What occurs at the vegetal pole
Apical membrane constricts. Form vegetal plate. Bottle cells lose adherance, ingress in to blasoele. Form PMC
What re the precursors for mesoderm cells
Pre mesenchyme cells
What allows the cuboidal cells to change
Lack of cadherins, the constriction of the membrane by actin/myosin
What is convergent extension
The invagination of the vegetal pole from the blastopore
What is the process of convergent extension
Cells elongate perpendicular to membrane.
Lamellipodia at each end act on each other elongating the archtenon. This narrows the cells
This is mediolateral intercarlation
How does the arrchtenon attach to the animal pole
SMC are on the tip of invagination.
SMC have filopodia which search for ventral pole of basal membrane of animal pole.
This is most likely aided by proteins in blastoele
SMC attach, pull archtenon
What is the anus and mouth
Anus: site of invagination at vegetal pole
Mouth: site of anchorrage at animal pole
What occurs at the 16-32 cell range in mamallian embryos
Increased adherance leading to compaction
Trophoblasst and internal mesenchme cells are formed
What does the trophoblast secrete
Na+ into the middle of the embryo causing water to enter and a cavity, blastoele is formed
What does the Inner cell mass form
ICM forms the tissues, organs, yolk sac epitheliem, amniotic membrane, vasculature placenta layer, umbilocal cord
What does the trophoblast form
Chorionic layer of the placenta
Where are embryonic stem cells taken from
The inner cell mas pre grastrulation
What layers are formed from the Inner Cell Mass
Hypoblast, adjacent to the blastoele
Epiblast
What does the hypoblast do
Hypoblast spreads around the blatoele. Forms the Heuser’s membrane
What does Heuser’s membranw form
The yolk sac, extraembryonic endodem, that helps trasnport nutrients from the yolk to the embryo
What happens if the Egg is in not lost
Sac is usually lost in 2% of people. If not lost: Meckel’s diverticulum, malfunction in small intestine
What will the epiblast form
The extraembryonic ectoderm. This will form the amniotic membrane
What animals have an amniotic membrane
mammals, reptiles, birds
What form is the rest of the epiblast layer
Simpple cuboidal layer
What part of the embryo allows the embryo to the implant
Trophoblast attatches to the endometrium
What processes occur at the endometrium
Trophoblast proliferates rapidly. Sycytiotrohblasts invades the wall. Whole blastoele is contained within the wall
Wha surrounds the blastoel
Cytotrophoblast
How is the maternal placental circulation established
Syncytiotrophoblast creates cavities called lunae that will be filled with maternal blood
What is formed by at the rostral and caudal enda
Apposing epiblast and hypoblast cells form buccopharygeal (mouth) membrane at the rostral end
The chodal membrane is formed at the caudal end, the anus
What day does gastrulation begin
Day 14
What occurs on day 14
A ridge along the rostral-caudal midline at the posterior end is formed. This is the primitive streak
What appears at one of the streak
The primitive node at the rostral end
How is the endoderm
Epiblasts ingress through the streak invading the hypoblast to the periphery
What is formed by the endoderm
Epithelium of gut, lungs, liver, gall bladder, pancreas
What is formed by the mesoderm
Tissues, organs, muscle, bone
What is the the role of the notchors in lower invertebrates
Notochord spans midline. Large diameter with lipid vacuoles.
Anchorrage point fot skeletal muscles. Provides rigid/flexibilty for flight, swimming
What underlies the forebrain
Pre chordal plate (rostral end) made from ecto and mesoderm layers
What is the role of the notochord in higher verterbrates
Smaller diameter.
Patterns adjecent nervous systems
Is replaced by vertebrae column but nucleus pulposus remains
How are somites formed
Made from paraxial mesoderm cells (adjacent to notochord)
What is formed from somites
Sclerotome: Axial skeleton, spine and ribs
Myotome: Skeletal muscle
Dermatome: Connective tissue of dermal layer
How many and how frequently are somites formed
Every 5hrs in humans, 90 mins in chicks, 30 mins in zebrafish.
40-44 in humans, will become 36
What is formed from the intermediate mesoderm
blood cells, kidneys, bladdr, reproductive organs,
What is formed by the lateral mesoderm
connective tissue, membranes of body’s cavities, skeleton, connective tissue of limbs, vessels, heart
What layer of the trilaminar disk forms the nervous system
Formed from the neural plate, thickened part of the ectoderm
What proteins are transcribed prior
Soz2 Sox3
What happens to the neural plate
Plate will become columnar
How is the neural tube formed
Microtubules drive the elongation along basal apical axis
Plate cells at the mid line constricat their apical surface. driven by actin/myosin
What happens if the neural tube fails to close
Anencephaly, non-closure at rostral end. Death
Spinal bifida: caudal end, possible life, paralysis if alive
What is the phylotypic stage
The stage where the vertebrae body plan is visible
It is where different verterbrae are most similar
