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In the Beginning 

In the Beginning
Chapter:
In the Beginning
Author(s):

Lionel H. Opie

DOI:
10.1093/med/9780198525677.003.0001
Page of

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date: 23 May 2019

Chapter 1 outlines the defence systems that the body has developed over centuries to protect itself from the environmental threats to early humankind. It discusses the stress reaction triggered by the ‘fight or flight’ impulse, and how it is managed by the adrenergic or sympathetic nervous system, which increases heart rate and blood pressure, helping people to escape from dangerous situations. Conversely, the balancing system comes into play during sleep or relaxation. This is the system that protects the heart and reduces blood pressure. Paradoxically, exercise also increases the activity of the parasympathetic system, decreasing resting heart rate and blood pressure. It also addresses how modern lifestyles promote over-activity of the sympathetic nervous system, and hamper the balancing parasympathetic system.

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