NERVOUS
The "fight or flight" responsebegins here: When you're stressed, the brain's sympathetic nerves signal the adrenal glands to release a chemical variety pack, including epinephrine (aka adrenaline) and cortisol. Persistently high levels of these chemicals may impair memory and learning, and up your odds for depression. 
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ENDOCRINE
stress hormones trigger the liver to produce more blood sugar, to give you that kick of energy in the moment of perceived danger. But if the "danger" you're concerned with is a long-term dilemma and you're already at risk for type 2 diabetes, bad news: Elevated glucose levels may turn you into a card-carrying diabetic.
RESPIRATORY
At high-stress moments, you may find yourself breathing faster, feeling short of breath, or even hyperventilating. Over the long term, this strain on the system can make you more susceptible to upper-respiratory infections (so if you're considering a career in air-traffic control, you might want to stock up on Emergen-C).
CARDIOVASCULAR
Momentary, acute stress, like, say, when you're walking down the aisle to get married, will make your heart beat faster and blood pressure rise. Long-term stress, like unwelcome pressure from the folks to produce offspring, can cause narrowing of the arteries and elevate cholesterol levels, upping your chances of heart disease, heart attack, and stroke.
REPRODUCTIVE
stress can lengthen or shorten your menstrual cycle, stop it altogether, or make your periods more painful. High levels of stress make bacterial vaginosis (BV) more likely and, during pregnancy, may increase the chance of your baby's developing asthma or allergies later in life. Bring on the prenatal yoga.
IMMUNE
Short-term stress can actually boost the immune system, helping your body fight infection. Ongoing stress, however, turns things in the other direction, possibly slowing wound healing, leaving you more susceptible to infection, and worsening skin conditions such as eczema, hives, and yes — acne.
DIGESTIVE
Extreme stress isn't unlike the morning after a bender. It can cause dry mouth, indigestion, nausea, and gas, and it stimulates the muscles of the intestines, possibly causing diarrhea or constipation. Have these symptoms chronically, and you may increase your risk for irritable bowel syndrome, severe heartburn, and ulcers.
MUSCULOSKELETAL
Muscles tense to deal with what your body perceives as danger. No one who's pulled an all-nighter with only PowerPoint for company will be surprised that constantly tight muscles can cause headaches and neck, shoulder, and back pain. Chronic stress may also increase your likelihood of developing osteoporosis.