Caffeine increases a person���s heart rate because it is a central nervous system stimulant, says MedlinePlus. It is absorbed and passed quickly into the brain and stimulates the brain and nervous system.Continue Reading
Caffeine blocks the action of the chemical phosphodiesterase at the cellular level, explains biologist Neal Smatresk in an article for Scientific American. This chemical breaks down the second chemical messenger cyclic adenosine monophosphate. Many neurotransmitters and hormones exert their actions indirectly through second messengers, as they cannot cross the cell membrane.
Smatresk states that the effects of caffeine are prolonged when it stops the breakdown of cyclic adenosine monophosphate, and the body���s response is significantly amplified. This response prompts the norepinephrine and epinephrine in the heart to raise the heart rate and force of contractions. These chemical messages cause a ���fight or flight��� behavior, especially in stressful or urgent situations. Aside from increasing the rate and force of the heart, they also increase blood pressure and deliver more oxygen to the brain and other tissues.
The effects of caffeine start around 15 minutes after consumption and last up to six hours, according to the University Health Service from the University of Michigan. Caffeine generally helps people become less sleepy and more alert when taken in moderate amounts.Learn more about Nutritional Amounts & Limits