The Timing of Exposure
Some pretty spectacular changes occur over nine months of pregnancy. A newly fertilized, single cell morphs into a complex, specialized, self-conscious organism. Cells don't just have to multiply in number; they also change their appearance and how they work in order to form all of the different tissues and organs that make up the human body. The whole process is highly regulated; changes must occur at the right time and in the right place. In some areas of the developing brain, exposure to nicotine messes up this orderly progression.
How can nicotine from a few cigarettes (or even from a nicotinin how similar nicotine's action is to that of the native neurotransmitter, acetylce replacement patch) have such a profound effect? The answer lies holine. During the development of the brain, each neurotransmitter acting through its own receptor can tell a neuron to start or stop dividing, to differentiate, to form connections with other cells and even to die. How the neuron interprets stimulation by the neurotransmitter depends on the context in which it occurs. A signal at the wrong time can miswire whole regions of the brain. Because nicotine binds to cholinergic receptors, it can stimulate them just like acetylcholine. But unlike acetylcholine, nicotine is not regulated internally; the neurons see it whenever mom smokes another cigarette. Depending on when during brain development exposure occurs, nicotine can reduce the number of neurons in a brain region or change the way the neurons signal. Neither of these options is particularly appetizing when you think about it.
The Way Pregnancy Works
A developing child is also wholly dependent on its mother's body to:
- supply nutrients
- provide oxygen
- remove waste products like carbon dioxide (CO2)
Because of this relationship, changes in how the mother's body works have consequences for the fetus. If you've read How Nicotine Works, you know that just the nicotine in cigarettes alters a smoker's blood pressure, heart rate, and even their metabolism. The other constituents of cigarette smoke, such as carbon monoxide (CO), can also change or interrupt basic physiological processes. CO is an odorless, colorless gas produced by burning carbon containing compounds. Combusting fuel in a car engine, for example, produces a lot of carbon monoxide. CO displaces oxygen from the molecule that normally carries it through your bloodstream to your organs and tissues. High levels of CO can be deadly; you simply can't provide enough oxygen to maintain cellular processes throughout the body, which is why you shouldn't sit idling in a closed-up car for too long! When a pregnant woman smokes, the trace amounts of CO that she inhales mean less oxygen will be delivered to her tissues and to her fetus.