Obviously today we do not view coffee and caffeinated substances to be this marvellous medical elixir.
So what are the effects of caffeine on the different systems in our bodies?
I'll be starting with the nervous and cardiovascular systems
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| Nervous and cardiovascular systems |
Caffeine and the nervous system
Caffeine is a central nervous system stimulant-It increases brain and spinal cord activity, speeding up physical and mental processes.
Caffeine also affects the autonomic nervous system -A branch of the peripheral nervous system which controls smooth muscle, internal organs and glands (click for more information on the nervous system).
There has been reports that caffeine increases skin conductance (sweat gland activity). A 500 mg anhydrous (dry weight) caffeine dose can produce behaviour similar to General Anxiety Disorder also referred to as 'caffeinism' (Bruce et al., 1986). Caffeinism is a condition resulting from ingestion of a large dose of caffeine shown by diarrhoea, elevated blood pressure, restlessness and insomnia.
Putting things into perspective: a 500 mg dose all at once is a large amount considering an average cup of instant (heaped tea spoon) coffee contains 60 mg (Center for science in the public interest., 2012). A large dosage of caffeine can produce extreme symptoms due to the rapid rate at which caffeine is absorbed. So do not fear drinking your morning cup of coffee as 500 mg is a high dose and was used for experimental purposes.
Note how some of the effects caffeine has on the nervous system appear anxiety reducing (i.e increasing concentration and reducing tiredness) and some effects similar to anxiety (insomnia and restlessness).
Cardiovascular system
Caffeine has an interesting effect on blood flow. In moderate amounts caffeine can increase blood pressure-the effect is more significant in those who do not regularly consume caffeine (Bruce., 1986: James 1997). But surprisingly has little effect on heart rate (France and Ditto 1992).
How does this change in blood flow come about?
Caffeine molecules compete with adenosine for adensosine receptors on cardiovascular cells (See previous post on receptors). In the cardiovascular system adenosine causes dilatation of coronary and cerebral blood vessels. Caffeine inhibits this process, meaning the blood vessels remain constricted. The narrower diameter of the blood vessels result in higher blood pressure (James 1997).
Time for a little analogy......
Imagine you have gone shopping for a new garden hose. Your standing in the aisle looking at the different diameters of garden hoses you can buy. Whilst you do this you imagine watering your garden with your new hose. The pressure of the stream of water coming out of the end of the hose depends on the diameter of the hose. Logically the narrower the diameter of hose the higher the pressure.
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| Hoses varying in diameter |
When adenosine is present in the blood, this causes the smooth muscle in the blood vessels to relax- the vessel wall gets thinner and the space where blood flows in the vessel gets wider: this is vasodilatation. When caffeine is present and binds to adenosine receptors instead of adenosine; it has the opposite effect. The smooth muscle in the vessel wall contracts and gets thicker so the space where blood flows gets narrower resulting in a higher pressure in that vessel: this is vasoconstriction.
Upcoming posts....
I'll be looking at the physiological effects of caffeine on the gastrointestinal and respiratory systems and also the effect on renal function (think peeing!). I also hope to do a bit about caffeine and health.
References
Braun S., 1996., Buzz:
The Science and Lore of Alcohol and Caffeine., Cary., NC., USA., Oxford
University Press
Bruce M, Scott N, Lader M, Marks V., 1986., The psychopharmacoloical and
electrophysiological effects of a single dose of caffeine in healthy human
subjects., British Journal of Clinical Pharmacology., 22, 81-87.,
[Online]., Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1401080/?page=1 .,
[Accessed: 02/10/2013].
Center for science in the public interest., 2012., Caffeine
content of food & drugs (online).,
(Updated 2012)., Available at: http://www.cspinet.org/new/cafchart.htm.,
[Accessed: 03/10/2013].
France C and Ditto., 1992., cardiovascular
reponses to the combination of caffeine and mental arithmetic, cold pressor and
static exercise stressors., Phychophysiology., 29., 272-282.
