Thalidomide - why birth defects?

Thalidomide - why birth defects?

A human being is formed 

A four-week-old fetus is dominated in the front by a big head and in the rear the body is elongated in a tail. Now is the time for the beginning of arms, legs, brain, spine, eyes, ears, nervous system, and interior organs to form. The fetus needs oxygen and nutrients to be able to grow. 


In the fifth week of a pregnancy, one can vaguely see five fingers in the top of the arm bud. Along this top there is a growth zone where a continues interaction between individual cells in the growth zone. Underlying cells in the limb bud tissue rules the evolution of the whole arm. The mechanism is analogue in other extremities and organs. 


Thalidomide injuries occur during "active periods”

A fetus grows in active periods or stages. If a person takes thalidomide during pregnancy, the chemical molecule thalidomide can reach the embryo through the placenta. To cause a thalidomide embryopathy the mother must take thalidomide during the fetus active periods, because the effect of thalidomide disappears very rapidly in the human body. 30 minutes after taking a tablet, the effects are gone. That is why many mothers who took thalidomide could give birth to babies that were unaffected by thalidomide.


Thalidomide exhibits anti-angiogenesis characteristics, preventing vascularization in the limb bud tissue of developing embryos. The process of limb or organ growth involves the induction of cytokines (tissue hormones that facilitates communication between cells) which stimulate new blood vessel growth (angiogenesis) into developing limb buds or organs. Thalidomide inhibits these cytokines and blocks angiogenesis, causing insufficient nutrient and oxygen delivery to the developing organs or limbs. 



Blood vessels acts as a "roadmap”

Angiogenesis in new blood vessel growth acts as a "roadmap” for the continuous development of limbs or organs. When the chemical signal to the cells in the growth-zone is inhibited, they cannot function normally and the interaction with underlying tissues is disturbed. The development of the fetus is continued according to a genetic clock. The embryo can't reverse the development and redo a prior step that went wrong. The result is a malformation. The more frequent exposition to the drug and the higher the dose; the higher the probability for more severe disturbances of the development. Taking only one 100 mg. tablet early in pregnancy, when limb buds and organs are forming, could be enough to give birth defects.


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