Week 3 Embyonic Development Flashcards
When does conception occur in relation to LMP?
2 weeks LMP
What major event occurs during week 1 of embryonic development ?
Blastocyst formation
What major event occurs during week 2 of embryonic development ?
Implantation
What process leads to specialized structures and functions?
Differentiation
Critical period for neural tube defects ?
4-6 weeks LMP
What events happen during week 1 of preembryonic period ?
Fertilization and cleavage
What is the structure that results from fertilization called ?
Zygote
Where does fertilization usually occur ?
Ampulla of uterine tube
What are blastomeres ?
Cells that result from mitotic cleavage of zygote and are therefore smaller
What is the morula ?
Ball of 12-32 blastomeres
What is the function of the zone pellucida ?
Prevent polyspermy
What does the inner cell mass of blastocyst develop into ?
Embryo
What do the trophoblasts of the blastocyst develop into ?
Placenta
What 2 major events occur during week 2 of preembyonic period?
Implantation and bilaminar embryonic disc formation
What does the bilaminar embryonic disc form from ?
Inner cell mass
What 2 cavities does the bilaminar embryonic disc form between ?
Epiblasts
Hypoblasts
Function of the connecting stalk
Attach embryo to wall of chorionic cavity
What occurs in week 3 of embryonic development ?
Gastrulation
What happens during gastrulation ?
Bilaminar embryonic disc forms 3 germ layers
What begins gastrulation ?
Formation of primitive streak at caudal end of embryo
What are the 2 locations that the mesoderm does not migrate to ?
Prechordal plate (future mouth) Cloacal plate (future anus)
What is clinical significance of primitative node and pit that form at cranial end of primitive streak ?
Organizing Center for notochord mesoderm
What does the ectoderm become ?
Nervous system
Epidermis of skin
Eye, teeth, etc
What does the mesoderm become ?
Muscles Bones Cartilage Blood cells and vessels Dermis of skin Kidneys Ureters Genital system
What does the endoderm become ?
Lining of GI tract Liver Pancreas Lining of respiratory tract Bladder
When does neurulation, somite & coelom formation occur ?
Week 3 to late week 4
Briefly outline neural tube formation
Overlying ectoderm thickens —> neural plate
Neural plate invaginates in middle —> neural groove and folds
Neural folds fuse —> neural tube
Tube —> zips up in cranial and caudal directions
Briefly outline somite formation
Mesoderm beside notochord —> 2 longitudinal columns of paraxial mesoderm —> blocks (somites)
Appear near cranial end —> expand in cranial and caudal directions
What do somites form ?
Axial skeleton
Associated muscular and dermis
Briefly outline coelom formation
Small cracks form in lateral mesoderm —> coalesce into continuous horseshoe shaped cavity —> 3 body cavities (pericardial, pleural and peritoneal)
What future structure does the transversum give rise to ?
Diaphragm
What major event occurs during week 4 of embryonic development ?
Body folding
What two types of lateral mesoderm form during embryonic development ?
Somatic
Splanchnic
What does intermediate mesoderm form ?
Urogenital system
What does splanchnic mesoderm give rise to ?
Heart
Visceral layer of serous pericardium and blood vessels
What is most common cause of neural tube defect ?
Multifactorial
Structural effects of FASD
Facial features and other minor anomalies
Growth retardation (height, weight, head circumference)
Structural brain anomalies
Function effects of FASD
Impaired fine motor skills and coordination
Hearing loss
Behavioural/cognitive/learning deficits
Facial features associated with FASD
Small palpebral fissures Smooth philtrum Thin upper lip Micrognathia Minor ear anomalies Epicanthal folds Low nasal bridge Microcephaly
What effects are seen from alcohol consumption during first trimester of pregnancy ?
Major and minor structural anomalies
What effects does alcohol consumption have during 2nd and 3rd trimester ?
Neurodevelopmental effects
Growth effects
3 main determinants of embryonic / fetal health
Genome
Maternal health
Environment / exposures
How much folic acid should mother take pre-conception and throughout pregnancy ?
0.4-1 mg
5 mg in patient with increased risk
Describe gestational age
Time since first day of LMP (not pregnant for first 2 weeks)
Used to describe length of pregnancy (40 weeks)
Embryonic age
Time since ovulation
EA = GA - 2 weeks
What is best way to determine gestational age ?
Ultrasound at 7-14 weeks using CRL (crown rump length)
Explain each part of GTPAL
Gravita: # of pregnancies
Term: # of pregnancies delivered at term
Preterm: # of pregnancies delivered preterm (20-37 weeks)
Abortus: # of pregnancies delivered prior to 20 weeks
Living: # of living children
Schedule of visits for low risk pregnancy
Every 4 weeks until 28 weeks
Every 2 weeks from 28-36 weeks
Every week from 36 weeks on
When is gestational diabetes screen done?
24-28 weeks
Diagnostic tool for aneuploidy
Amniocentesis
What is NIPT
Non-invasive prenatal testing
- blood test on mom
- Trisomy 21 detection rate >99%
Goals of first trimester dating scan (3) ?
- establish viability
- date
- # of fetuses
Focus of 2nd trimester detailed scan ?
- fetal anatomy
- fetal growth
- amniotic fluid volume
- placenta location
What ultrasounds are routine during pregnancy in Canada ?
First trimester dating scan (7-14 weeks)
Second trimester detailed scan (18-22 weeks)
What can errors in chromosome segregation during mitosis result in ?
Whole chromosome loss or gain
What can errors in DNA replication during meiosis result in ?
Segmental duplications, deletions or rearrangements
Essential features of meiosis
Chromosomal pairing and exchange
What happens during meiosis I ?
DNA duplicated
Crossing over
Pairs line up at metaphase
Homologues separate
Errors in chromosome segregation at either MI or MII (non-disjunction) can result in what ?
Whole chromosome loss or gain
What can cause segmental duplications, deletions or rearrangements during meiosis
Errors in DNA replication or errors in meiotic recombination
Timeline for meiosis I in oogenesis
Begins in embryo
Resumes in puberty and continues through menopause
When does meiosis II resume in oogenesis
After ovulation and is triggered by fertilization
Whole chromosome gain or loss
Aneuploidy
Unbalanced structural variant
Concomitant gain or loss of chromatin
Reciprocal Translocation
Exchange of broken segments
Robertsonian translocation
Fusion of 2 Acrocentric chromosomes near centromere
Mendelian disease
Disease caused by inherited or de novo mutation of one or both members of a gene pair
4 patterns of Mendelian disease
Autosomal dominant
Autosomal recessive
X-linked recessive
Others
Differentiate between genetic, inherited and congenital
Genetic: caused by mutation of gene, gene pair or larger portion of genome
Inherited: transmitted from one or both parents
Congenital: present at birth
With autosomal recessive diseases about what % of children of unaffected carrier parents are affected ?
25%
What diseases are more likely if parents are consanguineous ?
Autosomal recessive
Differentiate familial from genetic and Mendelian
Familial: occurs more than once in a family (ex. COVID-19)
Mendelian: could be result of new mutation
Mitochondrial inheritance pattern
All children of affected women are affected
- all receive her mitochondria
What can genome/genomic testing show ?
Gain or loss of genomic material
Change in arrangement of genomic material
Change in nucleotide sequence
What resolution does cytogenetic testing have ?
Detect gain, loss, rearrangement of an entire chromosome or portion visible under light microscope (10 Mb)
What resolution does chromosomal microarray have ?
Gain or loss of 0.25 - 10 Mb
What resolution does sequence analysis have ?
Loss, gain or change down to a single base pair of DNA
What is the risk for relatives of someone with a multifactorial disease?
Increased risk to have the same or a similar disease themselves
Relation of multifactorial disorders and sex
These disorders are usually more common in one sex than the other
What is used to estimate recurrence risks of multifactorial diseases?
Empirical data
What are GWAS studies ?
Genome Wide Association Studies
Compare frequencies of genetic markers in patients with a multifactorial disease and controls.
How are polygenic risk scores determined ?
Use genome wide SNP genotypes of individuals to estimate risk for developing a multifactorial disease based on all SNPs “known” to be associated with an increased/reduced risk of the disease from GWAS studies
Pharmacodynamics vs pharmacokinetics
What drugs do to the body
What the body does to drugs
How do must drugs get into the blood?
Passive diffusion
What equation is used to predict relative drug absorption
Henderson-Hasselbach
.pH-pKa=log[A/HA]
What is bioavailability ?
The fraction of drug that reaches systemic circulation unchanged
F=amount of drug in systemic circulation / amount of drug administered
How does relative blood flow effect drug delivery ?
Drug is delivered to tissues based on perfusion
- Brain, heart,liver, kidneys
- Muscle, skin
- Fat
Will a weakly protein bound drug or a highly protein bound drug have a greater pharmacologic effect ?
Weakly
2 phases of liver enzyme-catalyzed metabolism of drugs
Phase I: oxidation/reduction/hydrolysis
Phase II: conjugation
What effect do inducers have on enzyme activity
Increase the rate of enzyme activity
What is the danger of enzyme inhibitors
Can lead to potential toxic effect of drug
What is first pass metabolism
Drugs delivered from GI tract are delivered to liver and metabolized before reaching systemic circulation
What are pro drugs ?
Drugs that are inactive when administered that rely on metabolism to produce pharmacologically active product
Why are lining and glandular epithelia at risk of malignant transformation ?
- proliferates often
- breast tissue: responds to hormonal changes, very dynamic, undifferentiated and develops along lifespan
