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Metabolism
The whole range of biochemical processes that occur within us (or any living organism). Metabolism consists both of anabolism and catabolism (the buildup and breakdown of substances, respectively). The term is commonly used to refer specifically to the breakdown of food and its transformation into energy.

Mucus
When you think of mucus, you might think of snot, which is that sticky stuff inside your nose. But that's only part of the story. You'll also find mucus in your mouth, lungs, stomach, and intestines. Wherever you find mucus, it protects and lubricates mucous membranes in your body.

Mucus colitis
A common gastrointestinal disorder involving an abnormal condition of gut contractions (motility) characterized by abdominal pain, bloating, mucous in stools, and irregular bowel habits with alternating diarrhea and constipation, symptoms that tend to be chronic and to wax and wane over the years. Although the disorder can cause chronic recurrent discomfort, it does not lead to any serious organ problems. Making the diagnosis usually involves excluding other illnesses. Alternative names include irritable bowel syndrome (IBS), nervous colon syndrome, and spastic colitis.

Mutation
A permanent change, a structural alteration, in the DNA or RNA. In humans and many other organisms, mutations occur in DNA. However, in retroviruses like HIV, mutations occur in RNA which is the genetic material of retroviruses. In most cases, such changes are neutral and have no effect or they are deleterious and cause harm, but occasionally a mutation can improve an organism's chance of surviving and of passing the beneficial change on to its descendants. Mutations are the necessary raw material of evolution.