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Originally Posted by Aedes  Speaking as a well-entrenched insider in the medical profession, I think you've got it half right. There are both intrinsic and extrinsic things that can affect a given disease.
Take pneumonia. Pneumonia is an infection of the lungs (typically a bacterial infection). The bacteria that most often produce pneumonia have toxins that cause tissue injury, that provoke inflammation, and that ultimately produce symptoms. So here it seems that the bacteria is a foreign object or substance, right? And you're correct that much of the damage caused by pneumonia is caused by the body's inflammatory response.
But now consider that there are intrinsic host factors that affect susceptibility to pneumonia and risk of complications with it. The elderly are FAR more susceptible to pneumonia than people who are young andhealthy. People with cystic fibrosis (which is a genetic disease) have pulmonary infections all the time. These are unmodifiable risk factors. There are many other extrinsic things that will alter a host's intrinsic susceptibility -- for instance smoking (extrinsic) will lead to a host who is intrinsically more susceptible to infection by pneumonia pathogens. If someone develops cancer (sometimes intrinsic, sometimes extrinsic), the chemotherapy (extrinsic) will lead to a host with an intrinsically weak immune system that is more susceptible.
So diseases can't cleanly be thought of as intrinsic or extrinsic. But to be sure, very often there are external factors that either cause injury or that provoke an injurious response by the body, and there are tons of examples. |
Aedes;
From your outline the one thing that jumps out at me is this genetic disease, this is truely intrinsic, it is something amiss from the outset effecting the constitution, or in effect being the constitution of that individual. I would think that would warrent a catagory of its own. I do not think the fact the an individual is weakened by say a bacterial infection and left more susceptible negates the premise that most diseases are reactionary in nature. Once the constitution is compromised it is further compromised by foreign organisms and their by products, the seige is on so to speak.
No a change in the degree of susceptibility due to previous infection does not negate the premise. The example of smoking increasing susceptibility is due to the bodies reaction to this foreign substance. It may well be naive of me but, with the acception of genetic disorder, it still sounds like the major cause of disease is of a reactionary in nature. Risk factors or susceptibility do not change the nature of the premise or negate it. I am missing something I take it? Perhaps if with each assault upon the constitution, it is considers its new state, still the individuals constitution, and still vulnerable to attack by the same said agents--- sorry doc, I've got a hard head.