Effects of Nicotine on Body Function

At a low concentration, the tobacco alkaloid nicotine acts as a ganglionic stimulant by causing a partial depolarization via activation of ganglionic cholinocep-tors (p. 108). A similar action is evident at diverse other neural sites, considered below in more detail. 

Autonomic ganglia. Ganglionic stimulation occurs in both the sympathetic and parasympathetic divisions of the autonomic nervous system. Parasympathetic activation results in increased production of gastric juice (smoking ban in peptic ulcer) and enhanced bowel motility ( laxative effect of the first morning cigarette defecation diarrhea in the novice). 

Although stimulation of parasympathetic cardioinhibitory neurons would tend to lower heart rate, this response is overridden by the simultaneous stimulation of sympathetic cardio-accelerant neurons and the adrenal medulla. Stimulation of sympathetic nerves resulting in release of norepinephrine gives rise to vasoconstriction peripheral resistance rises. 

Adrenal medulla. On the one hand, release of epinephrine elicits cardiovascular effects, such as increases in heart rate und peripheral vascular resistance. On the other, it evokes metabolic responses, such as glycogenolysis and li-polysis, that generate energy-rich substrates. The sensation of hunger is suppressed. The metabolic state corresponds to that associated with physical exercise - silent stress . 

Baroreceptors. Partial depolarization of baroreceptors enables activation of the reflex to occur at a relatively smaller rise in blood pressure, leading to decreased sympathetic vasoconstrictor activity. 

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