study of congenital malfunctions.
Teratology
What are the two general causes of congenital malformations?
Answer:
a. Genetics or heredity
b. Environmental or acquired
- (occurs when differentiating cells are destroyed by teratogens)
What are teratogens?
Agents that cause congenital malformations by damaging differentiating cells
Give examples of teratogens ( 4 example)
Answer: C,I,V,T
a. Chemicals and drugs
b. Ionizing radiation
c. Viruses
d. Toxins
What are the two main actions of teratogens?
Answer: (remember deletion and alteration)
- Deletions of essential primordial cells
- Alteration in genetic expression leading to loss of cell differentiation during early phases of fetal development
On what does susceptibility to teratogenesis depend?
On the genotype of the developing fetus and the interaction with adverse environmental factors.
What can teratogens cause in DNA?
Defects that result in malformations, which may be hereditary and passed to the next generations.
When is the fetus most sensitive to teratogens?
During cell differentiation and organogenesis.
How do teratogenic agents act on developing cells and tissues?
They act in specific ways, leading to sequences of abnormal developmental events
☆ (some cause cell death, some excessive growth or tissue, others cause expression of specific defective genes).
What determines the access of teratogens to developing tissues?
The nature of the teratogenic agent
♡ (e.g., oral teratogenic drugs may not cross the placental barrier easily, while ionizing radiation can readily penetrate the fetus).
What principle describes the relationship between teratogenesis and dosage?
Teratogenesis is dose-dependent and cumulative.
Enumerate the manifestations of deviant development.
Answer: (D, M, G, F)
Death
Malformation
Growth retardation
Functional deficit
Enumerate the four main classifications of teratogens.
Answer:
- Physical agents
- Chemical agents and drugs
- Toxins from plants
- Biological agents (viruses)
Give examples of physical agents as teratogens.
Trauma, ionizing radiation, heat, cold, pressure
Give examples of chemical teratogens (chemicals)
Answer:
- Organochlorine compounds (mga phenol - pentachloro, tetrachloro, trichloro )
–
pentachlorophenol, tetrachlorophenol, trichlorophenol (used as fungicides, herbicides, insecticides) - Chlorophenoxy derivatives of fatty acids – used as ▪︎herbicides
Give examples of chemical teratogens (drugs)
- Thalidomide – anti-nausea drug, most studied teratogenic drug, causes amelia (absence of limbs)
- Isotretinoin – anti-acne drug
Which hormones are examples of teratogens?
Synthetic preparations of progesterone and estrogen.
Which vaccines may act as teratogens?
Attenuated vaccines of Hog Cholera and Bluetongue.
Give examples of plant teratogens.
Answer:
- Poison hemlock (Conium maculatum) – contains coniine and gamma-coniceine
- Nicotiana tabacum – contains nicotine
- Veratrum californicum – a weed containing toxic alkaloid
(A. Malformations in Twinning (Double Monsters))
What are symmetrical conjoined twins?
Twins that present complete parts and are joined at some parts of the body.
What suffix is used for naming symmetrical conjoined twins?
The suffix “–pagus.”
What is the mechanism of formation of symmetrical conjoined twins?
Splitting of the zygote resulting in two blastoderms developing from one ovum.
Give examples of symmetrical conjoined twins.
Answer:
a) Encephalothoracopagus – joined at head and thorax
b) Thoracopagus – joined at thorax
c) Ileopagus – joined at ilium of pelvis
d) Ischiopagus – joined at ischium of pelvis
What are asymmetrical conjoined twins?
Twins formed due to abnormal placental circulation with,
☆ arteriovenous anastomoses at umbilical vessels.
