Structure and Function of Arteries, Capillaries, and Veins. The walls of arteries and veins have three layers or tunics: 1  An outer layer (tunica adventitia) of connective tissue with collagen fibers. 2  A middle layer (tunica media) of circularly arranged smooth muscle and elastic fibers.
You might have heard that eating chocolate or greasy foods can cause acne, but these are both just myths. The truth is that food has little to do with breakouts. Acne occurs when the openings of hair follicles become blocked with oil secretions, dead skin cells and bacteria.
1 When you eat starchy carbs, grains, and sugar/fructose, it causes a surge of insulin and insulin-like growth factor called IGF-1 in your body. 2  This surge can lead to an excess of male hormones, which cause your pores to secrete sebum, a greasy substance that attracts acne-promoting bacteria.