Updated August 23, 2020
Intra means inside. Intracellular processes are those that occur within the cell. Intracellular minerals are the minerals needed within the cell, and attempts to measure levels. Intracellular infections are those that occur within the cell, and therefore must be smaller than the cell itself. These include viruses, mycoplasma, certain smaller bacteria, and probably other unnamed or misunderstood critters. Intracellular toxins include those created inside by normal metabolism, and those that come from the outside. Cellular crowding by tau protein is a mechansim of Alzheimers. Of course, all processes involving the nucleus must be intracellular. This includes all DNA-related processes and materials, as well as nuclear hormones such as thyroid.