Embryogenesis week 1

Question 1

Embryonic period vs fetal period

Answer 1

Zygote (1 cell)–> Embryo (body plan, 3 layers, 3 axes)
3 layers-> 4 tissues-> organs
Segmentation head limb and trunk formation and embryo folding

Fetal period: growth and maturation, continued development of some systems

Perinatal- 22 weeks- 1month after birth
Neonate- 2 mo old and later

Question 2

Gestational age vs Prenatal age

Answer 2

Gestational age- from last menstrual period (2 weeks more)

Prenatal age- from fertilization

Question 3

Embryonic development week one

Answer 3

Major events: fertilization, cleavage, blastocyst formation, bilaminar disc

one cell- ball of cells (morula)- then fluid filled cyst with disk

After zygote formation the next step is called cleavage

Question 4

cleavage

Answer 4

cell division: rapid every 12-24 hours, no G1 or G2, controlled, divisions asynchronous, no cell growth (ratio of cyto to nucleus foes from 600:1 to 3:1)

Activation of embryonic Genome: maternal program controls the 1st cell division, the embryo genome is activated at 2-4 cell stage, new proteins are needed for cleavage and for blastocyst formation

Constancy of genome: all cleavage stage blastomeres and eventually all nucleated cells of the individual have the same complete genome.

Blastocyst formation: 2 cell lineages at the 8-16 cell stage

Question 5

Development of the blastocyst

Answer 5

The trophoblast becomes the first tissue of the embryo, its an epithelium cells joined by junction, forms layers, cells are polarized

The inner cell mass is the embryoblast

Begining of cell differentiation mediated by cell position, number of cell divisions, cytoplasmic determinants, cell-cell interactions

Question 6

The trophoblast

Answer 6

the trophblast forms extraembryonic tissue. Trophoblast formation requires expression of certain parental derived alleles, trophoblast formation is an example of genomic imprinting

Question 7

The inner cell mass

Answer 7

most of these cells become part of the embryo, ICM remodels into bilaminar disc (epiblast and hypoblast)

The epiblast will be the ectoderm and the hypoblast will be the endoderm

Question 8

Regulation

Answer 8

the ability of an embryo/organ primordia to produce normal when parts have been removed or added, the ability to regulate declines with age, early on can make chimeric embryos

Question 9

Potency

Answer 9

Potency is the developmental potential of a cell
totipotent (has all developmental pathway options), pluripotent- all options except trophoblast
multipotent- has several pathway
bi and uni

Developmental field: finite area of embryo that develops into many related structures

Question 10

Differentiation

Answer 10

once cells final decisions are made they remain firm, cell division result in daughter cells with the same phenotyp

Stemm cells are an example though when differentiation does not = post mitotic the still have some pluripotent capabilites

Question 11

developmental decisions are patterned

Answer 11

gene expression during embryonic developmet is patterned (follows a specific plan is choreographed)

Patterning in the embryo

Question 12

twins

Answer 12

usually occurs at a divsion of bllastocyst stage
sometimes occurs by division at 2 cell stage
if divsion happens after embryonic disc formation–> conjoined twins

Question 13

Hatching from zona pellucida

Answer 13

ZP keeps the blastomeres together, provides an immunological barrier, prevents premature implantation