what is nicotine in
By Dr Ananya Mandal, MD. Nicotine is a chemical compound that is present in tobacco. When tobacco is smoked, nicotine is absorbed through the wall lining of the small air sacs in the lungs. When sniffed or chewed, it is absorbed through the mucous membranes of the nose or mouth. Nicotine can also be absorbed through the skin. Regardless of how nicotine is absorbed, it enters the bloodstream where it circulates throughout the body and travels to the brain where it crosses the blood-brain barrier. Once in the brain, it binds to and activates receptors called the cholinergic receptors.