All the organs and systems of a human being are laid down in the first ten weeks after conception and then grow and consolidate through the rest of the pregnancy
Any 'poisons' in the mother's system (such as alcohol, nicotine and other drugs) can affect the formation and growth of the baby's organs.
Also a shortage of something can affect the formation and growth of a system. An example of this is a shortage of folic acid in the diet which can lead to a condition of the spine called spina bifida. Fro this rason folic acid is added to bread. (In the USA)