Basic Concepts and Congenital Anomalies

Question 1

Differentiation

Answer 1

– method by which you form distinct form and function
o Histogenesis – part of differentiation – formation of different tissue types
o Morphogenesis – part of differentiation – form of different organisms
 Morphological Processes – involve microtubules and microfilaments
• Localized growth
o Need a critical cell mass (~16 cells to proceed)
o Cells interact and influence one another to divide
o Primordium – proliferation of cells in a layer of cell
• Localized constriction and/or elongation – turning cuboidal cells into triangular in order to form tubes
o Ex: CNS
• Change cell shapes – affects microtubules of cells
o Mesothelium – squamous; flat cells that line structures
• Splitting of sheet – fusion of 2 layers and then separating them later
o Ex: body cavities
• Fusion of sheet – fusion of 2 layers of cells
o Ex: mesenteries in gut
• Folding of sheet
• Cell migration – cells migrate elsewhere
o Ex: nerve cells, blood cells, sex cells
• Cell aggregation – migrate and then aggregate to form a primordium elsewhere
o Ex: cartilage, lymph nodes

Question 2

Potency

Answer 2

o Egg – totipotent/pluripotent
o As fertilized egg develops more and more, cells become less and less potent – less things they are able to become
o Divide bilaminar disc (2 weeks) from cranial to caudal and 2 normal embryos will develop; must have all the cells on ½ of side
o Cloning – remove nucleus from cell (enucleate) and put into an egg cell  new individual forms

Question 3

Integration

Answer 3

– going to a prefunctional to a functional state
o Need:
 Nervous system – allows quick and direct responses
 Endocrine system – slow processing for long-term maintenance

Question 4

Induction

Answer 4

– interactions between cells that lead to a change in course of development of at least one of the interactants
 Time frame is very short; competent cell must receive induced signal within certain period of time
o Inducer – makes a chemical (diffusible or nondiffusible) that is secreted
o Evocator – chemical made; can be used in multiple species’ development
 Different organs have different evocators
o Competent cell
 Must express the appropriate receptor for the specific inducing signal molecule
 Must express components of the particular intracellular signal transduction pathway
 Must express the transcription factors that mediate the particular response

Question 5

Growth

Answer 5

o Growth rate – fastest growth rate occurs in very beginning
o Growth patterns
 Cranio-caudal growth axis
• Cranial region grows very fast in beginning of development (head is half of embryo); then slows down and caudal region increases growth rate
 Fast vs. slow growing tissues
• When a system is developing it inhibits the areas around it from growing
 Functional demands vs. growth
o Growth rate of various organs as a function of Total Body Weight

Question 6

Good vs. Bad Eggs

Answer 6

 58% of eggs lost before 2nd week
• 16% eggs fail when coming into contact with sperm
• 15% of eggs lost preimplantation
• 27% lost before formation of bilaminar disc at
 8% of eggs lost between 3rd and 6th week
 3% of eggs are late abortions
 31% of total eggs make it to term
• 2% malformations (x 3 = 6% of humans have congenital anomalies)
• 29% normal babies
 Spontaneous abortions are a beneficial development to species to limit anomalies
• Only mild anomalies actually make it to term; more severe anomalies are aborted prior to term

Question 7

Incidence of Birth Defects

Answer 7

 Genetic – 13-15%
 Environmental – 7-10%
 Multifactorial – 20-25%
 Unknown – 50-60%

Question 8

Teratogens

Answer 8

 Teratogens – can affect, DNA, RNA, enzymes, chemical differentiation, cellular and tissue differentiation, organ formation and functional differentiation
• 3 factors to consider the possible teratogenicity of an agent
o Critical period of development
 Week 1-2 - no anomalies develop because DNA is mostly getting replicated and embryo will spontaneously abort
• Highest rate of spontaneous abortions
 Week 3-12 – highest rate of anomalies – often multiple anomalies that affect multiple organ systems
• Highest rate is when differentiation is at its highest rate
 Week 12+ - anomalies occur at slower rate
o Dose of drug/chemical
o Genotype of embryo

Question 9

Congenital Anomaly CHaracteristics

Answer 9

o 30% of confirmed pregnancies are lost
o Most anomalies are lethal – never make it to term
 7% of all live birth have a congenital anomaly