I

Immune
Protected against infection.

Immune System
This body system, which includes white blood cells and lymph nodes, helps protect your body from disease. The immune system has different parts, all of which work together to fight off outside invaders like germs.

Immunity
The condition of being immune. Immunity can be innate (for example, humans are innately immune to canine distemper) or conferred by a previous infection or immunization.

Intolerance, food
Difficulty in digesting a food. Common offenders include milk products, wheat and other grains that contain gluten, and foods that tend to cause intestinal gas, such as cabbage or beans. Food intolerance is often mistaken for food allergy, but does not involve a histamine response against the food.

Irritable bowel syndrome (IBS)
Irritable bowel syndrome (IBS) is one of the most common ailments of the bowel (intestines). The term, irritable bowel, is not a particularly good one since it implies that the bowel is responding irritably to normal stimuli, and this may or may not be the case. The several names for IBS, including spastic colon, spastic colitis, and mucous colitis, attest to the difficulty of getting a descriptive handle on the ailment. IBS is best described as a functional disease. The concept of functional desease applies to the muscular organs of the gastrointestinal tract; the esophagus, stomach, small intestine, gallbladder, and colon. What is meant by the term, functional, is that either the muscles of the organs or the nerves that control the organs are not working normally, and, as a result, the organs do not function normally. The nerves that control the organs include not only the nerves that lie within the muscles of the organs but also the nerves of the spinal cord and brain.