An arrector pili musclea. is associated with each sweat gland,b. can cause a hair to stand up straight,c. enables each hair to be stretched when wet,d. provides new cells for continued growth of its associated hair.

Manufacturers of shampoos and conditioners often claim their products contain vitamins that are necessary to keep hair shafts healthy. Do hair shafts need vitamins? (Hint: Vitamins are required for cells to carry out certain reactions.) Why or why not? How valid are these claims?

The hair and nails are sometimes called accessory organs. Are these structures technically organs? Why or why not?