Real or perceived dangers can increase blood pressure by triggering the body's "flight-or-fight" response. Immediately after the sense of danger abates, the sympathetic nervous system, or SNS, reduces the blood and oxygen surge needed for defense or escape from danger, according to the website Severe Hypertension. This regulating process, in which the SNS works to lower blood pressure, is called the relaxation response.
Function
The sympathetic nervous system controls nerve impulses throughout the body. Nerve tissue connected to the spinal cord sends messages from the brain to the organs, muscles and tissues of the body. The SNS controls life-sustaining functions under physical and emotional stress. Danger, real or imagined, activates signals in the brain that send messages to this system. Oxygen surges through the increased volume and force of blood entering the muscles, and increases blood sugar needed for greater energy. Impulses from the sympathetic nervous system reduce functions such as digestion, hunger and elimination. Once the crisis is over the sympathetic nervous system returns blood volume and pressure to its previous levels and returns the body to a resting state, reports Severe Hypertension.
Significance
The sympathetic nervous system releases chemicals that dilate and contract blood vessels. It also activates heart muscle to regulate the heart beat. Normal fluctuations in blood pressure from daily activity, strenuous exercise and diet are instantly corrected by the sympathetic nervous system. This system sends messages through the spinal cord controlling the force of blood vessel dilation and constriction in a healthy heart, maintaining and lowering the force of the beating heart, according to the text "Gray's Anatomy."
Considerations
Blood vessels with plaque and triglyceride build-up cannot adequately respond to the sympathetic nervous systems attempt to lower blood pressure. Medical attention, cardiovascular exercise or lower sodium intake may reduce narrowing and stiffening of blood vessels that increase pressure. Medications that interact with the sympathetic nervous system may be necessary to lower blood pressure when the body is unable to regulate itself. Obesity and weight gain directly affect muscle-sympathetic nerve activity, notes the American Heart Association.
Expert Insight
Baroreceptors are triggers within the dermatomes, receptors in the skin that respond to external forces. When the body sweats, these receptors notify the hypothalamus to regulate body temperature. Baroreceptors react to muscle tension, sweating and anxiety associated with danger. The SNS and these baroreceptors work together in lowering and raising blood pressure, according to a 1992 study in "AJP, Endocrinology and Metabolism." The study notes that bradycardia, the slowing of the heart rate below 60 beats per minute, is a dangerous condition that could result from the sympathetic nervous system's attempts to lower blood pressure. These two tools of regulation must work together to regulate blood pressure.
Evidence
The role of long-term regulation of blood pressure by the SNS was the focus of a study that measured muscle-sympathetic nervous system action in healthy young men. Published in 2010 in the "Journal of Hypertension," it determined that the sympathetic nervous system's affect on blood pressure fluctuated drastically in young men with the similar blood pressures. As males age, however, the results change. The study indicates that the SNS is not equipped to lower blood pressure long-term when obesity and weight gain continue to increase blood pressure.
References
- Severe Hypertension: The Role of the Nervous System in Blood Pressure
- American Heart Association: Hypertension
- "Experimental Physiology": A Sympathetic View of the Sympathetic Nervous System and Human Blood Pressure Regulation
- "AJP Endocrinology and Metabolism": Interactions between ANG II, sympathetic nervous system, and baroreceptor reflexes in regulation of blood pressure I. A. Reid
- Bartleby.com: "Gray's Anatomy"
