Week 3 - Fetal Development

Question 1

Dermatome

Answer 1

That area of skin supplied by a single spinal nerve or spinal segment

Question 2

Myotome

Answer 2

That area of muscle supplied by a single spinal nerve or spinal segment

Question 3

Describe the major events that occur during embryonic development from zygote to tubular embryo

Answer 3

Zygote (fertilized egg) - mitotic cleavage - Morula (12-32 blastomeres) - Blastocyst (when cavity forms in morula)

Week 1 - Fertilization and Cleavage: blastocyst organization (cells clump at one end = embryo; flattened outer layer = trophoblasts aka pre placenta); blastocyst “hatches” out of zona pellicida - implants in uterine wall

Week 2 - Implantation and Bilaminar Disk formation:
Epiblasts (floor of amneotic cavity - embryo), hypoblasts (roof of yolk sac), trophoblasts (placenta)

Week 3 - Gastrulation: begins with primitive streak; Epiblast migrate and form endoderm, mesoderm, and ectoderm

Question 4

List various tests used to detect disease-causing genetic variants and explain why different tests are used in different clinical circumstances

Answer 4

Cytogenetics (Karyotyping): Looking for Structural abnormalities e.g. Gain, loss or rearrangement of an entire chromosome or
portion visible under light microscope (10 Mb)

Chromosomal Microarray: Can tell you gain or loss of chromosomal segments/chromosomes (NOT rearrangement); compare patient to reference

Sequence Analysis: Can tell you loss, gain, or change down to a single base pair of DNA

**When do you use each one clinically?** -- NOT SURE ON THIS PART 
In general testing done when suspect genetic disease to inform treatment e.g.: 
• Intellectual disability,
developmental delay
• Multiple malformations
• Stillbirth or neonatal death
• Recurrent miscarriages
• Infertility
• Prenatal diagnosis
• Suspected genetic disease

Question 5

Describe common congenital anomalies in humans and risk factors for these congenital anomalies

Answer 5

Down syndrome - risk factors: maternal age

Spina bifida - risk factors: SES status, environmental risk factors, teratogen exposure

Heart defects - 1% risk in population

Cleft palate/lip - family history?

Question 6

Define Cytogenetic resolution

Answer 6

Insertions or Deletions of genomic material e.g.

Question 7

Define Cytogenetic resolution

Answer 7

Insertions or Deletions of genomic material e.g.

Question 8

Define a translocation

Answer 8

Exchange of two chromosomal segments, usually between two non-homologous chromosomes

Question 9

What are two types of translocations and risks associated

Answer 9

Reciprocal – exchange of the broken segments (balanced - increased risk in offspring; unbalanced - miscarriage, congenital anomalies)

Robertsonian – fusion of two acrocentric chromosomes (chromosomes w/ centromeres closer to the end of chromosomes) near the centromere

Look at pictures for visual help

Question 10

What is the critical period during embryogenesis for teratogenesis?

Answer 10

3-9 weeks

Question 11

What is the critical period during embryogenesis for teratogenesis?

Answer 11

3-9 weeks

Question 12

Describe fetal alcohol spectrum disorder

Answer 12

FASD is a brain injury that can occur when an unborn baby is exposed to alcohol. It’s a lifelong disorder with effects that include physical, mental, behavioural and learning disabilities.

Features of FASD: Cognitive impairment, larger head, short palpebral fissures, flattened philtrum, thin upper lip

Question 13

Identify examples of some of the most significant teratogens in our population and their effects

Answer 13

Alcohol - FASD - developmental/neurological deficits, not necessarily dependency

Opioid - dependency issues

Smoking - jittery ?

Zika - microcephaly

Rubella - Damages the liver and how it processes Vitamin A leading to increased levels → Leads to cataracts, microphthalmia, seizures, hearing defects, encephalopathy, increased risk for type one diabetes.

Cat feces - toxoplasmosis

Raw fish - toxoplasmosis

Anti epileptics - neural tube defects

Question 14

Describe the coelom and indicate the cavities it becomes in the adult

Answer 14

The coelom forms the body cavities

will divide into 3 body cavities:
PERICARDIAL - space around heart
PLEURAL - space around lungs
PERITONEAL - space around GI

Question 15

Outline the process of neural tube formation

Answer 15

The notochord induces overlying ectoderm
to thicken and form a NEURAL PLATE.

The neural plate invaginates in the midline to produce a NEURAL GROOVE AND FOLDS.

The neural folds fuse to form a NEURAL TUBE below the surface ectoderm. The tube then ‘zips’ up in both cranial and caudal directions. **failure to close results in neural tube defects

At this stage, the embryo can
also be called a NEURULA.

Question 16

What may disrupt the process of neural tube formation

Answer 16

Lack of folic acid, others??

Question 17

Outline the process of gastrulation, including the formation of the three primary germ layers and indicate the major adult derivatives of these layers

Answer 17

Gastrulation begins with the formation of the PRIMITIVE STREAK (epiblasts form this) at the caudal end of the embryo

Concurrently, epiblasts delaminate (leave the epiblast layer) and displace cells in the hypoblast layer. These cells form ENDODERM.

Similarly, epiblasts delaminate and form a
middle layer or MESODERM.

Epiblasts remaining on top form ECTODERM

Question 18

Describe the rationale of ultrasounds in pregnancy

Answer 18

Screening for: amniotic fluid volume, neural tube defects, fetal anatomy (brain, spine, heart, kidneys, limbs, face), fetal growth (BPD, HC, AC, FL), placenta location, may include soft markers of aneuploidy,

Most accurate method for dating - Gestational Age (7-14 weeks - crown-rump length)

Question 19

What are the major adult derivatives of the three primary germ layers?

Answer 19

Endoderm - nervous system (CNS, PNS), epidermis of skin, eye, teeth, etc

Mesoderm - muscles, bones, cartilage, blood cells and vessels, dermis of skin, kidneys, ureters, genital system

Ectoderm - lining of GI tract, liver, pancreas (except islets), lining of respiratory tract, bladder

Question 20

What basic lab tests do you have done during pregnancy?

Answer 20

Blood type/screen, hemoglobin, infectious serology, TSH, pap smear, dating scan (7-14 weeks), detailed anatomic scan (18-20 weeks), gestational diabetes screen, group B strep swab

Question 21

What types of screening tools are available for examining abnormal fetal development?

Answer 21

Maternal age

Ultrasound

Serum biochemistry aka
SIPS (SIPS = serum integrated prenatal screen, Screens for: NTDs, T21 (80% detection rate for SIPS), T18, cannot screen for T13)

NIPT (non-invasive prenatal testing, cell free fetal DNA In serum - Trisomy 21; do this if you have a positive SIPS)

Question 22

What are the major adult derivatives of the three primary germ layers?

Answer 22

Endoderm - nervous system (CNS, PNS), epidermis of skin, eye, teeth, etc

Mesoderm - muscles, bones, cartilage, blood cells and vessels, dermis of skin, kidneys, ureters, genital system

Ectoderm - lining of GI tract, liver, pancreas (except islets), lining of respiratory tract, bladder

Question 23

What types of diagnostic tests are available for examining abnormal fetal development?

Answer 23

Amneocentisis (amniotic fluid to obtain fetal cells for testing), Chorinic villus sampling (placental villi), Fetal blood sample (from umbilical cord or heart, very rare)