- The autonomic nervous system (ANS) is divided into three main divisions: the sympathetic, parasympathetic, and enteric nervous systems.
- Among these, the sympathetic division is primarily responsible for controlling the body's 'fight or flight' reaction.

- When an individual encounters a stressful or threatening situation, the sympathetic nervous system is activated.
- This leads to several physiological changes, including increased heart rate, dilation of the bronchi in the lungs, dilation of pupils, and redistribution of blood flow towards the muscles.
- These adaptations prepare the body to either confront the threat or escape from it.

- In contrast, the parasympathetic nervous system supports the 'rest and digest' functions, promoting relaxation and conservation of energy.
- The enteric nervous system primarily governs the gastrointestinal tract, and the somatic nervous system controls voluntary movements of skeletal muscles.

Therefore, the correct answer is : Sympathetic.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 68.