What Is the Biology of Alzheimer's Disease?

Aging is characteristic of all living animals. Biology is the study of such characteristics in living organisms. Though Alzheimer's is not a normal part of aging, the risk of the disease increases with time, according to the Mayo Clinic. The medical website defines Alzheimer's disease as the degeneration of healthy brain tissue causing a steady decline in memory and mental ability. Currently, the fatal disease affects over five million Americans, and a cure has yet to be discovered.

Identification

• Biological features of Alzheimer's's disease manifest in the patient's brain and behavior. While certain changes in daily behaviors are symptomatic of the disease's onset and also present throughout its progression, the brain may display no signs in the early stages of the disease. "There's no specific diagnostic test ... An MRI (magnetic resonance imaging) can't really tell you much," says Dr. Alan R. Jacobs in Ladies Home Journal. However, a positron emission tomography, or PET scan, which allows doctors to view the brain in action, may reveal certain disruptions in cell activity patterns that are consistent with the disease such as reading, hearing, thinking and saying words.

Brain Pattern Disfunction

• Alzheimer's disease affects the body's most important organ--the brain. The biology of Alzheimer's shows that it "disrupts both the way electrical charges travel within cells and the activity of neurotransmitters" within the brain, according to the Alzheimer's Association. "At the cellular level, our brains code our thoughts, memories, skills and sense of who we are," says the Association. These patterns, which change over time in healthy individuals due to new experiences and skills, are also changed as a result of the disease.

Physical Affect on the Brain

• The biology of Alzheimer's disease changes the physical appearance, or structure of the brain, as well as its function. It leads to "nerve cell death and tissue loss throughout the brain" and causes it to shrink dramatically over time, according to the Alzheimer's Association. In advanced Alzheimer's, the brain's cortex, or wrinkled outer layer, shrivels and shrinks, while the ventricles, fluid-filled spaces within, get larger. Plaques, abnormal clusters of protein fragments, and tangles, twisted strands of protein, are also found in the brain tissue of Alzheimer's patients.

Progression/Time Frame

• The progression of the disease is a biological factor that can vary greatly among patients. Plaques and tangles throughout the brain's cortex occur in a predictable pattern. Their rate of spread differs between patients in the earliest stages and those in the most severe, advanced stage. "People with Alzheimer's live an average of eight years, but some people may survive up to 20 years," says the Alzheimer's Association. Changes in the brain related to the disease may occur as early as 20 years before it is actually diagnosed. The disease's course depends partially on how early the patient is diagnosed and their overall health. A person may live with moderate to mild Alzheimer's for two to ten years, whereas severe Alzheimer's lasts only one to five years.

Stage Features

• Changes in certain behavior indicate the stage of Alzheimer's the patient is in. Problems learning, thinking, planning and remembering things may be symptomatic of the earliest stages, before any scans or tests can reveal it. Mild to moderate Alzheimer's displays these symptoms to the point where they affect the individuals everyday life. It may go beyond forgetfulness and affect speaking and the understanding of speech, as well as one's ability to determine time and space. Mood swings and other personality changes may occur in this stage, the time many patients are first diagnosed, according to the Alzheimer's Association. In the most severe stage, "individuals lose their ability to communicate, to recognize family and loved ones and to care for themselves," according to the website.