Caffeine

Caffeine molecule (not to scale)

by

Chris Freundel

1998

''Caffeine: a bitter alkaloid C₈ H₁₀ N₄ O₂ found especially, in coffee, tea, and kola nuts and used medicinally as a stimulant and diuretic'' (Multipedia)

Caffeine is a substance found in coffee, tea, cola, and other plant products, like the Kola nut. It is also added to soft drinks to increase the sales of well-known beverages, (''extra kick'').

The following table shows some examples of the amount of caffeine in tea, coffee, soft drinks and chocolate. Note the different concentrations of caffeine in tea and coffee due to different preparations.

All the values are in mg of caffeine per 8 oz, and are average amounts.

Note that some milk chocolates can have as much caffeine in them as an 8 oz cup of Espresso.

Caffeine affects the functioning of numerous systems throughout the body. It acts on the central nervous system to increase alertness, enhance sensory perceptions, overcome fatigue, improves endurance and motor function for a short period of time, (depending on body weight, metabolic rate etc.). All thses symptoms are also produced during the ''fight or flight response'', bought about by adrenaline. The molecules of adrenaline attach themselves to proteins, (called beta-receptors) on the cell membranes of cells. One of these receptor sites is the Sino Atria Node (SAN) which stimulates the heart to generate faster heartbeats than 70 beats per min. Another symptom due to the increased heartbeat is increased renal blood flow. This decreases reabsorption of sodium and water in renal tubular and increases glomerular filtration rate leading to increased urination.

Caffeine and adenosine are both members of the purine family. It is thought that caffeine mimics cyclic AMP (cAMP) functions. Cyclic AMP is normally produced through exercise, excitement etc. Cyclic AMP production is the result of adrenaline release into the blood stream. Adrenaline attaches itself to beta-receptors in cells (e.g. in the SAN) and stimulates the cell to produce cAMP, which activates that cell. The enzyme phosphodiesterase starts to break down cAMP which results in the negation of the effects adrenaline has on the body, (e.g. Speed up heart rate; dilates bronchioles; mental activity increases, etc).

Negative feedback loop for adrenaline

The negative feedback loop for caffeine look the same, but the stimulus is not exercise or excitement etc., but caffeine.