Final answer:
Rheumatoid arthritis (RA) is an autoimmune disease that causes inflammation in synovial joints, resulting in swelling, stiffness, and pain. It primarily affects the hands, feet, and cervical spine. The exact cause of RA is unknown, but it is believed to be a combination of genetic and environmental factors.
Step-by-step explanation:
Rheumatoid arthritis (RA) is an inflammatory disorder that primarily affects synovial joints of the hands, feet, and cervical spine. Affected joints become swollen, stiff, and painful. Although it is known that RA is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue, the exact cause of RA remains unknown. Immune cells from the blood enter joints and the joint capsule causing cartilage breakdown and swelling of the joint lining. Breakdown of cartilage causes bones to rub against each other causing pain. RA is more common people with declining estrogen levels, in particular post-menopausal people, and the age of onset is usually between 40 to 50 years. Researchers are still exploring possible causes and studies that suggest an X-linked genetic factor.