Iodine it is an element that is required for the thyroid gland to produce thyroid hormones.
The body does not produce iodine on its own so it needs to come from dietary sources like eggs, prunes bananas, shrimp, cod, etc or you can take supplements of iodine.
When you consume iodine it quickly absorbed and enters into your bloodstream and thenyour thyroid that has tiny cells that capture the circulating iodine and takes in and oxidizes it so it can begin to be used to create (T3) and (T4 which are thyroid hormones.
Answer:
they have thin membranes to allow diffusion of substance for short distance
they are numerous to increase the surface area of absorption
hope this helps