The etiology of autonomic dysfunction may be primary, such as pure autonomic failure (PAF), secondary, such as that due to cervical spinal cord injury (SCI) or due to drugs and chemical. An understanding of the components of the autonomic nervous system (ANS), their function and their supraspinal, spinal and peripheral organization is essential to appreciate autonomic dysfunction. Animal studies have indicated that after lesions of rostral ventrolateral medulla (RVLM), arterial pressure is maintained by the renin-angiotensin system and by arginine vasopressin (AVP). Gastrointestinal (GI) tract function is to retain nutrients and eliminate waste. These functions are accomplished by the motility, secretion, and absorption processes of the GI tract, which are regulated via exocrine, endocrine, and neural mechanisms. Neurons in the anterior hypothalamus preoptic area (POA) have intrinsic temperature sensitivity and drive many thermoregulatory effector mechanisms. Impairment of temperature regulation is a recognized hazard for persons with SCI.