The sympathetic system does not directly affect:

The sympathetic nervous system, which is part of the autonomic nervous system, is primarily responsible for the body's "fight or flight" response. It prepares the body for action by increasing heart rate, enhancing blood flow to muscles, and elevating respiratory rate to supply more oxygen to the body.

In terms of its direct effects, the sympathetic nervous system does increase heart rate to facilitate greater blood circulation during stressful situations. It also influences blood flow by redirecting it away from non-essential functions to areas that would benefit from increased perfusion, such as the muscles. Additionally, it stimulates respiratory rate to enhance oxygen uptake and delivery.

However, the sympathetic system does not have a direct role in the enzymatic breakdown of food molecules. This process, primarily managed by the digestive system through enzymes released by the pancreas and the action of the gastrointestinal tract, largely operates through the parasympathetic nervous system, which promotes digestion and metabolic functions at rest.

Understanding these mechanisms illustrates the specific roles of the sympathetic and parasympathetic divisions, clarifying why the enzymatic breakdown of food molecules is not directly impacted by sympathetic activation.