Embryology Flashcards
What is Anencephaly?
- Cranial neuropore doesn’t close so parts of the brain, cranium and skin don’t form.
- Brain is exposed to the amniotic fluid which causes further damage.
-Rarest because most are miscarried
What is spina bifida?
The spinal neuropore doesn’t close so the spinal cord remains open. Leads to paralysis below the lesion, Bladder problems.
Meninigcole or myelomeningcole
What is commitment?
- Irreversible decision to differentiate into a particular fate/direction
- Consists of specification (commitment to a particular fate but can change with the environment), determination, differentiation
How do cells communicate?
- Cells can communicate with each other to restrict their potency.
- Embryonic induction is a cell’s fate is changed by signals from an adjacent group of cells
What is the difference between the localised determinant theory and the regulative development theory?
-localised determinant theory: maternal determinants unevenly segregated during cleavage; cell fate predetermined
- regulative development theory: cell not committed to any cell fate at early stages; cell fate not predetermined
- it is influenced by its surroundings or position within the embryo. The cell initially has the potential to become any type of cell.
How do identical twins form?
-From regulative development
- 30% of identical twins form from cleavage divisions
- 70% of identical twins form from ICM
What are mesoderm inducing factors?
- Mesoderm inducing factors are TGFs and FGFs. Include activin, nodal, GDP, nodal. NODAL IS NECESSARY
- Different concentrations induce different mesoderm fates
What does hypoblast form?
Heusser’s membrane (lines yolk sac)
What do the 3 germ layers form?
- Ectoderm (epidermis, nervous system, bone & cartilage)
- Mesoderm (bone & connective tissue & tendon, organs)
- Endoderm (lining of digestive tracts, organs, respiratory tracts)
Specific details about mesoderm:
- Paraxial mesoderm: bone, cartilage, skeletal muscle, connective tissue, skin
- Intermediate mesoderm: kidney, gonad, reproductive tract
- Lateral plate: bone, cartilage, connective tissue, blood, heart, smooth muscle, tendons, vasculature
What happens in gastrulation?
- Primitive streak (invagination of epiblast cells) forms on dorsal ectoderm, primitive node forms
- Cells from the epiblast move towards primitive streak and move down to replace the hypoblast layer and form the endoderm
- The next set of cells fill the sub-germinal layer and form a mesoderm.
- The remaining cells form the ectoderm.
- During this process, adherents’ junctions, tight junctions are lost to allow cells to migrate.
- At the caudal end and the rostral ends, the epiblast and hypoblast are tightly held together – form the buccopharyngeal membrane and cloacal membrane.
What transcription factor do mesodermal cells express?
Tbx2
What is the axial mesoderm?
Forms cells of prechordal mesoderm – gives rise to connective tissue of head
What is paraxial mesoderm?
- Mesodermal cells on either side of axial mesoderm (adjacent to axial mesoderm)
- Form a compact mass of mesenchyme and at the rostral ends, they bud off to form somites. Subsequentially, somites are added to the caudal ends.
What are the cells at the most caudal end?
Cells at the most caudal region are called extraembryonic mesoderm and migrate into trophoblasts to give rise to the vasculature of the chorion and placenta.
What is neurulation?
- The folding process in vertebrae and the production of the central nervous system.
- Transformation of the neural plate into the neural tube from the dorsal ectoderm.
- Cell movements and cell shape changes place the developing nervous system inside the embryo, where it forms the neurons and glia of both the central and peripheral nervous systems.
- As the primitive streak recedes caudally, the midline surface ectoderm thickens to form the neural plate.
- The neural plate folds along the midline (invaginates) causing the lateral sides to rise, to form the neural groove.
- Folds form where cells constrict their apical surfaces, becoming wedge-shaped, and are known as hinge points.
- The lateral edges of the neural plate move towards each other and fuse to form the neural tube.
- The epidermis also fuses, placing the neural tube within the embryo.
- Cells of the neural plate elongate to form a pseudostratified columnar epithelium, while cells of the epidermis remain cuboidal.
-the caudal neuropore closing last of all.
