The ionic form of iron (Fe2+ and Fe3+) can damage the molecules present in the cell and in the blood. Protective protein escorts namely transferring and ferritin bind to the ionic form of iron during its transport and storage.
In small intestine during absorption, the ionic form of iron is actively transported into the mucosa of intestinal lining. Once inside the mucosal cells, it binds to the ferritin protein. These iron-ferritin complexes of mucosal cells are the stored form of iron.
Following its active absorption, the binding of iron to ferritin in mucosal cells of intestinal lining is referred to as the mucosal iron barrier. When needed, a few of the stored iron is passed into the portal blood while the major proportion of the stored iron is released from the barrier only when the epithelial cells are sloughed off.
In evolutionary theory, the relationship between the rough-skinned newt and the common garter snake is considered an example of co-evolution. The mutations in the snake's genes that conferred resistance to the toxin have resulted in a selective pressure that favors newts which produce more potent levels of toxin.
Answer: Calcium and vitamin D are the two most important nutrients for bones. Most cells in your body use calcium to signal various processes. It's also responsible for the strength and hardness of the bones.
