Re: What are the medical effects of stress on the body?

Dear Megan,
      Thank you for your question about the medical, or shall I say 
physiological, effects of stress on the body. The causes and 
consequences have been studied by scientists around the world ever 
since Hans Seyle, in 1936, gave us our first definition of the concept 
of stress: "the nonspecific response of the body to any demand."
     You know that many functions of the body, for example heartbeat 
and digestion, are not under voluntary control, which is made evident 
by the fact that they continue during sleep. These functions are 
controlled by the autonomic nervous system, which keeps the body in 
a state of homeostasis (equilibrium) through the opposition of its two 
subsystems the sympathetic and the parasympathetic nervous 
systems. To learn about these systems in detail, have a look at 
Carlsson’s textbook "Physiology of Behavior" (1991) or look up the 
following webpage:  http://www.britannica.com/bcom/eb/article/4/0,5716,119944+1+1107
04,00.html
	    In short, the sympathetic nervous system reacts when the 
organism is threatened. This system is therefore responsible for all 
the physiological reactions of your body to a stressor. For example, it 
increases heartbeat and breathing rate, digestion stops and the 
pupils dilate. The parasympathetic nerve fibers connect to the same 
organs as the sympathetic nerve fibers, but they cause just the 
opposite effects. After the stress is over, the parasympathetic division 
says, in effect, "Okay, the heat's off, back to normal." The heart then 
goes back to its normal rate, the stomach relaxes, digestion starts 
again, breathing slows down, and the pupils of the eyes contract. 
Thus, the parasympathetic division rests the body after stress and 
accumulates energy for the next emergency. 
     The sympathetic reaction to stress is believed to have evolved to 
help animals in situations of danger, in which they are face with the 
choice of "fight or flight". Humans have evolved beyond the necessity 
to defend our lives on a daily basis, but exams, dentist appointments, 
first dates and other stressors of the modern world all call upon our 
sympathetic nervous system!
     If humans experience less acute stress (the type a hungry bear 
could elicit), we are experiencing more chronic stress (the type cause 
by a demanding job or a difficult relationship) than ever. This chronic 
stress places the body in a constant state of desiquilibrium which 
imposes great strains on our various systems. Chronic stress is 
known to cause problems of the heart, liver; lungs and kidneys and to 
be linked to a variety of diseases, most notably cancer. Chronic 
stress also affects reproduction, causes depression and leads to 
self-destructing behaviors such as smoking, alcoolism, drug abuse 
and suicide.
     If you are looking for something really "in depth", as you say, have 
a look at the book "Neurobiological and Clinical Consequences of 
Stress", by Friedman, Charney and Deutch (1995).
     I hope this was helpful. Cheers !
     Benoit

References:

Carlsson (1991) Physiology of Behavior (4th Ed.) Boston: Allyn and 
     Bacon.
Friedman et al (1995) Neurobiological and Clinical consequences of 
     Stress. New York: Raven Press.