L18. Early Development 2 Flashcards
What does the syncytiotrophoblast do?
- produce hCG ( stop menstruration by keeping estrogen and progesterone high)
- produce proteolytic enzymes that digests and invade the endometrium and surround the blastocyst
- forms trophoblastic lacuna (gaps that allow maternal blood to flow through)
What are the 2 layers that grow around the amnionic cavity?
- epiblasts
2. amnioblast
What forms the Heuser membrane?
hypoblast cells that start to migrate
What surrounds the primary yolk sac/
- Heuser membrane
2. Hypoblast
What is the extraembryonic mesoderm?
- extraembryonic reticulum is invaded by the epiblasts cells
- extraembryonic mesoderm lines along the Heuser’s membrane and the cytotrophoblast
- separates the cytitrophoblasts from the amnioblast
What is the chronic cavity?
Forms between the 2 layers of mesoderm as fluid fills in the gaps
What happens on day 13 of implantation?
- Heuser’s membrane and connected extraembryonic mesoderm elongates and buckles
- definitive yolk sac forms as remnants of the primary yolk sac
What are the characteristics at the start of gastrulation?
- syncitiotrophoblasts have started to establish the placenta
- amniotic cavity forms
- definitive yolk sac forms
- embyo proper is formed
- has 2 layers; hypoblast and epiblast
How does the placenta form?
The extraembryonic mesoderm digs deeper into the synciyotrophoblast and thus it pushes down the cytotrophoblast
What are the 2 contributing components to the placenta?
- maternal component: decidua basalis
2. fetal component: chorionic villi
What is the function of the placenta?
allows gas, nutrients and waste exchange.
blood comes close to one another but do not contact.
What are the 4 barriers between the mother’s and fetuses blood?
- synctiotrophoblast
- cytotrophoblast
- connective tissue surrounding the blood vessel
- epithelial of the blood vessel
What is the function of the amnion?
protects the embryo, eliminates waste
What is the function of the yolk sac?
produces blood until the liver forms
germ cells form here
migrate to gonads
What is gastrulation?
rearrangement of cells into the primary germ layers (mesoderm, endoderm and ectoderm)
Identify all the components on page 3 part 2
page 3 part 2
What forms the embryo?
epiblast
What is the first evidence of gastrulation?
the appearance of the primitive streak
Identify the primitive peak, primitive node and primitive groove
They form the primitive streak ( page 3 part 3)
How does the endoderm form?
- cells in the middel of the epiblast ingress
2. ingressing cells displace the hypoblast, the endoderm forms
What does the endoderm form
- lines the gut wall
2. generates visceral tissues
What happens after the formation of the endoderm
- second set of cells ingress from the epiblast to fomr the mesoderm
- mesoderm forms the muscle,bones and blood vessels
After the formation of the endoderm and mesoderm what happens?
The epiblast forms the ectoderm
What is the epithelial mesenchymal transformation?
- loss of adhesion between cells at the primitive streak
- transformation of cells at the primitive peak to mesoderm
- Slug a DNA-binding transcription factor regulates this gene expression of the primitive streak
- expression of Slug causes adhesion lost between cells
What happens to the esoderm on day 16
- mesoderm migrates beyond the primitive streak
- mesoderm fills the gap between all the ectoderm and endoderm
- migration of mesoderm between ectoderm and endoderm
What is the fate of the ectoderm?
skin,hair,lenses of eyes, internal and external ear,nose, sinuses,mouth,anus,tooth enamel, all pats of the nervous system,mammary glands
What is the fate of the mesoderm?
Middle cell layer of the embryonic disc and precursor to the muscles, bones, lymphatic tissue, spleen, blood cells,heart and lungs, reproductive and excretory system
What is the fate of the endoderm?
it forms the inner cell layer of the embryonic disc which forms the lining of the lungs, the tongue,tonsils, urethra and associated glan, bladder and digestive system
What are the 3 mesodermal regions?
1.paraxial
2. intermediate
3.lateral
planes
What does the lateral plane of the mesoderm form
somatopleure (dorsal)
splanchnopleure (ventral)
When does the mesoderm start to differentiate
as the neural late buckles inwards
What does the paraxial mesoderm differentiate into
Somites
What are somites
Somites are brick like blocks that form the neural tube
What is neurulation
formation of the nervous system
What is induction
process whereby one cell or group of cells influences the developmental fate of another
What induces the formation of the nervous system
specialized mesodermal structure (notochord)
Describe neurulation
- formation of the neural tube
1. neural plate (specialized epidermal tissue) buckles inward ,forming the neural tube
2. neural groove forms and the neural folds fuse dorsally and seal off the neural tube
3. neural tissue is initially ectodermal- gows cranially from the primitive node
4. primtive node does not really move backwards , the embryo grows forward
Describe somitogenesis
- growth anterior of the primitive nodes
- neural tubes and somites form in area aterior of primitive node
- neural tube will form the spinal cord
What do somites form
muscles, limbs,vertebrae
What does the neural tube form
Forms the spinal cord
Describe the process of patterning in the neural tube?
- Bone morphogenic proteins that are prominent at the dorsal end of the neural tube form a downward gradien
- sonic hedgehog proteins at the notochord are produced ventrally and form an upward gradient ( towards the forsal end)
- the relative amount of BMP and Shh in neural tube determines which transcription factor gets expressed in that cell.
- grid of different expressed transcription factors in the neural tube
- each transcription factor domain has progenitor cells that will eventually become neurons
