Kaplan Nursing Entrance Practice Exam

The correct choice is that breathing rate is the factor least affected by the parasympathetic nervous system. The parasympathetic nervous system is primarily associated with the body's rest and digest functions. Its activities generally decrease heart rate, enhance digestive processes, and can influence blood pressure indirectly by affecting heart rate and vascular smooth muscle.

The heart rate is significantly slowed down by the parasympathetic nervous system through the release of acetylcholine, which acts on the heart's pacemaker cells. Digestive rate is directly stimulated by parasympathetic activity, increasing the secretion of digestive enzymes and enhancing peristalsis. Blood pressure can be influenced as well, since a lower heart rate can lead to lower blood pressure over time as part of the relaxation response.

Breathing, on the other hand, is primarily regulated by the autonomic nervous system but is significantly influenced by the sympathetic nervous system during physical activity or stress, while also being under voluntary control. The parasympathetic influence on breathing is less prominent compared to its impact on the heart or digestive system, making the breathing rate the least affected by parasympathetic activation.