Peptides and Glycoproteins (iv)

These hormones encounter several problems in carrying out their function.

1. Problem 1. Transport in the bloodstream
   Hormones are secreted into the blood, which is a watery fluid. To be transported effectively they must either be water-soluble or bound to something in plasma (often a protein) which makes them water soluble.
2. Problem 2. The target cell membrane.
   In order to modify the function of their target cells, hormones must exert their effects inside the cell. If the cell membrane is impenetrable to some hormones how do they exert their effects inside the cell?
3. Problem 3. The intracellular fluid.
   Assuming a hormone is able to enter the target cell a further problem is the aqueous intracellular fluid. This poses particular problems for lipid-soluble hormones.