19.10: Disorders of the Autonomic Nervous System
The autonomic nervous system (ANS) is an intricate network of nerves that controls functions such as the regulation of heart rate, digestion, and blood pressure regulation. When this system malfunctions, it can lead to various disorders that affect multiple bodily functions. One common feature of many autonomic disorders is the involvement of smooth blood vessels, which play a crucial role in regulating blood flow throughout the body.
Raynaud's disease, also known as Raynaud's phenomenon, is a disorder characterized by episodes of reduced blood flow to the fingers and toes in response to cold temperatures or emotional stress. This condition is believed to arise from an overreaction of the ANS, specifically the sympathetic nervous system, which controls the constriction and dilation of blood vessels. In individuals with Raynaud's disease, the small arteries that supply blood to the extremities constrict excessively, leading to a decrease in blood flow. As a result, affected areas may turn white or blue and become cold or numb.
Autonomic dysreflexia is a potentially life-threatening condition that primarily affects individuals with spinal cord injuries above the T6 level. Typically, autonomic dysreflexia is triggered by a noxious stimulus, such as a full bladder or bowel impaction. In this disorder, the ANS responds inappropriately, leading to a sudden increase in blood pressure. This response is due to an imbalance between sympathetic and parasympathetic nervous system activity. While the sympathetic system causes vasoconstriction, the parasympathetic system counters this effect by promoting vasodilation. In autonomic dysreflexia, the exaggerated sympathetic response overrides the parasympathetic activity, resulting in uncontrolled vasoconstriction of the smooth blood vessels. This, in turn, leads to a severe increase in blood pressure that can have serious consequences if left untreated.
Hypertension, commonly known as high blood pressure, is a prevalent disorder that affects millions of people worldwide. While it can have various causes, dysregulation of the autonomic nervous system is often implicated in its development. The ANS plays a critical role in maintaining blood pressure within a normal range. The sympathetic nervous system, for instance, stimulates the constriction of blood vessels, leading to an increase in blood pressure, while the parasympathetic system promotes vasodilation, resulting in lowered blood pressure. In individuals with hypertension, there is often an elevated sympathetic response, leading to chronic vasoconstriction of the smooth blood vessels. The sustained elevation in blood pressure can have detrimental effects on the cardiovascular system, increasing the risk of heart disease, stroke, and other complications.
