Heart rate is controlled by the two branches of the autonomic (involuntary) nervous system. The sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). The sympathetic nervous system (SNS) releases the hormones (catecholamines - epinephrine and norepinephrine) to accelerate the heart rate. The parasympathetic nervous system (PNS) releases the hormone acetylcholine to slow the heart rate. Such factors as stress, caffeine, and excitement may temporarily accelerate your heart rate, while meditating or taking slow, deep breaths may help to slow your heart rate.
Both photosystems contain many pigments that help collect light energy, as well as a special pair of chlorophyll molecules in the heart (reaction center) of the photosystem. The special pair of photosystem I is called P700, while that of photosystem II is called P680.
Dialysis performs the function of the kidneys if they've failed.
