What other body system is directly connected to the sympathetic nervous system?

The other system of the body that is directly connected to sympathetic nervous system is respiratory system. it is the part of autonomous nervous system and it is involved in controlling unconscious processes of the body such as breathing, heartbeat and movement of substances along digestive system. in respiratory system when oxygen levels lowers and those of carbon dioxide increases in the blood  the sympathetic nerves relay information to the respiratory center in the brain which in turn increases the rate of breathing. 

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