By Dr Ananya Mandal, MD
Nicotine is a chemical compound present in tobacco. It is readily absorbed into the bloodstream through mucosal surfaces lining the mouth, nose and airways. Nicotine may also be absorbed through the mouth when nicotine gum is chewed or through the skin when a nicotine patch is worn.
Pharmacology of nicotine
Within the body, nicotine is quickly distributed to all the organs and crosses into the brain via the blood-brain barrier.
Nicotine can reach the brain in as little as 7 seconds after being inhaled.
In the body, the half life or nicotine is around 2 hours. Half-life refers to the time taken for a drug to reduce to half its original concentration in the blood.
In the body, nicotine is metabolized in the liver by an enzyme system called the cytochrome P450 system, in particular which converts the nicotine to cotinine. Other metabolites of nicotine include N-oxide, nornicotine, nicotine isomethonium ion, 2-hydroxynicotine and nicotine glucuronide.
Once within the blood stream, nicotine travels to the brain where it binds to and activates receptors called cholinergic receptors. These receptors are abundant in the brain as well as in other areas of the body such as the muscles, heart, adrenal glands and other vital organs.
Normally, these receptors are activated by the neurotransmitter acetylcholine which is produced at nerve endings in the brain and in the nerves of the peripheral nervous system. Acetylcholine stimulation of the receptors is involved in maintaining healthy respiration, heart function and muscle movement as well as cognitive functions such as memory.
Since nicotine has a similar structure to acetylcholine, it can activate the cholinergic receptors. However unlike acetylcholine, nicotine disrupts normal brain function, causing chemical changes and addiction.
Reviewed by Sally Robertson, BSc