Vitamin A is not a single compound but a series of derivatives of retinol, including retinol, retinal, retinoic acid, retinol acetate, and retinol palmitate. Vitamin A is found only in animals and helps maintain the ability of the human eye to adapt to low light conditions and improve night blindness. Additionally, vitamin A can preserve the integrity of the skin's mucous membranes and participate in the proliferation of bone cells and osteoclasts.