Human Development Flashcards
Categories of Potentiality
Ability to differentiate other cells types
Totipotent - differentiate into all cell types (zygote, morula)
Pluripotent - many cell types (inner cell mass, epiblast)
Multipotent - restricted groups of cells (mesoderm, ectoderm, endoderm)
Unipotent - differentiation into a specific cell
Induced pluripotent stem cells
Differentiated cells that are pushed back to pluripotent status via iPS programming factors
Differential gene activity
- genes are reversibly turned on/off during different points in development for different gene expression
- cloning would not be possible if this was irreversible
- may be induced by programming factors (4 total)
Genomic equivalence
All cells have the same set of genes
Differential gene activity allows for differential gene expression between cells
First week progression of development following fertilization
Cleavage - blastomeres divide and shrink
Compaction - outer blastomeres form tight junctions, Inner blastomeres do not
Blastocyst formation - outer blastomeres form trophoblast layer, inner bastomeres form inner cell mass, fluid is pumped in to form blastocyst cavity
Hatching - growing blastocyst sheds zona pellucida to form floating blastocyst
Early implantation - cytotrophoblasts (inner layer of outer layer) and syncytiotrophoblasts (outer layer) form from Trophoblast, begin to implant into endometrium via metalloproteases, inner cell mass separates into hypoblast and epiblast, and produce protein and steroid hormones HCG (Human Chorionic Gonadotropin) which stops menstration
Hypoblast forms…
extra embryonic structures
Epiblast forms…
embryo proper
Chroriocarcinoma
Derived from syncytiotrophoblast, uses same mechanisms for implantation, most invasive cancer
Ectopic implantation
Implantation of blastocyte anywhere other than the uterus (uterine tubes, abdomen, etc.)
Normal implantation site of blastocyte
Fundus, or superior part of uterus between uterine tubes
Usually in posterior wall
Organogenic period
AKA embryonic period
Organ formation, most vulnerable to teratogens during this period
1-8 weeks
Fetal period
9-38 weeks
development of organs and organ systems
extensive growth
Lungs sufficiently developed at 24 weeks allowing premature births to survive with extensive clinical care
Post-natal development
Proliferation and Growth
Alveoli form in lungs
Closure of fetal shunts and vessels
Continued neuronal development
What factors play into pattern formation of cells
Cues from the environment
- cell-cell interactions, soluble factors (eg. growth factors), and extracellular matrix
Lineage : cell differentiation depends on cell of origin
Syndactyly
malformation due to unseparated digits
lack of apoptosis (morphogenetic error)
1st week of development
Ovulation (still in Meiosis II)
Fertilization (Finish of Oogenesis and Zygote formed)
Cleavage (Specialized cell division reducing cell size)
- Blastomeres form from cleavage (totipotent)
- Morula (day 4): loosely held mass of blastomeres
Compaction (day 5)(tight junctions, forms outer cell layer surrounding loosely held inner cell mass)
Blastocyst Formation (Fluid pumped in)
Hatching (Zona pellucida is shed & floating blastocyst)
Early Implantation
Syncytiotrophoblast
Releases matrix metalloproteases to break down extracellular matrix and aid in implantation
Also produce human chorionic gonadotropin to signal a stop to menstruation
2nd week of development
- Complete implantation
- Formation of primitive uteroplacental circulation
- no immunological rejection of fetus (Conceptus hides from mom’s immune system by reducing production of MHC Class I antigen) - Formation of bilaminar embryonic disk
- Formation of extraembryonic membranes/cavities
Prevalence of birth defects recognized by age 5
4-6%
Types of genetic screening regarding pregnancies
Carrier screening - determine carrier status in healthy people in high-risk population
Prenatal screening - identify if a fetus is at an increased risk of a defect
Newborn screening - detect genetic disorders that could be dangerous if left untreated
Contrast diagnostic testing and screening
Testing
- performed on at-risk population
- commonly expensive
- commonly has risk
- definitive
Screening
- performed on healthy patients
- inexpensive, quick, easy, reliable
- Defines at-risk population
- Not definitive
Amniocentesis
Invasive diagnostic test
Performed at 15 weeks and older
Samples amniotic fluid for genetic screening of cells
Chorionic villus sampling
Invasive diagnostic test
Performed in first trimester, 10-13 weeks
Samples placental tissue for genetic anomalies
First trimester screening
Performed between weeks 11-13
Ultrasound for measure of nuchal translucency (aneuploidy risk is continuous function of NT)
Blood work for serum markers (PAPP-A and hCG)
Assessing for:
Trisomy 21, 18 and 13
Second trimester screening
Performed between weeks 15-20
Testing for serum markers
Triple screen = msAFP, beta-hCG, uE3
Quad screen adds dimeric inhibin A
Abnormal maternal serum alpha-fetoprotein levels and associated risk
Low msAFP = higher risk for trisomy 21
High msAFP = higher risk for open neural tube defects
Note: twins can also cause elevated AFP, marker becomes less useful
Ultrasonography
Can be used diagnostically:
- confirm gestational age and number
- look for malformations
- confirm life
Or for screening:
- Structural abnormalities that associate with genetic abnormalies or aneuploidy
- AV canal defect and triploidy 21
- nuchal translucency
Cell free fetal DNA test
Isolate fetally derived DNA circulating in maternal plasma
-Shown to be accurate for high-risk groups, not as accurate for low-risk groups
Neuroectoderm
formed by chordin and noggin inhibition of BMP-4 signalling via Hensen’s node
notochord + somites
Bone morphogenetic protein-4
produced throughout embryonic plate
promotes ventral structure formation
blocked by chordin and noggin
Left-Right Body Axis formation
Hensen’s node cilia rotate counter-clockwise
concentration of nodal on left side of embryo
results in differential development