1. Arthritis: It is an inflammation of joints. It is a painful disorder of bones, ligaments, tendons, etc. In this disorder, joints become swollen, stiff and painful. It can lead to disability. 

2. Arthritis is of three types: 

1. Osteoarthritis: In this disorder, the joint cartilage is degenerated. It is caused by various factors like aging, obesity, muscle weakness, etc. This is the most common type of arthritis that affects hands, knees and spine. 

2. Gouty arthritis (Gout): In this disorder, joint pain occurs due to the deposition of uric acid in joints. If uric acid is produced in excess or is not excreted, it accumulates in joints as sodium urate. The accumulated sodium urate degenerates the cartilage causing inflammation and pain. It generally affects the joints of feet. 

3. Rheumotoid arthritis: It is an autoimmune disorder where body’s immune system attacks its own tissues. In rheumatoid arthritis, synovial membrane swells up and starts secreting extra synovial fluid. This fluid exerts pressure on joint and makes it painful. Membrane may develop abnormal granulation tissue called pannus. Pannus may erode cartilage. Fibrous tissue gets ossified and may lead to stiffness in joints. 

3. Osteoporosis: 

1. In this disorder, bones become porous and hence brittle. It is primarily age related disease and is more common in women than men. 

2. As age advances, bone resorption outpaces bone formation. Hence, the bones lose mass and become brittle. More calcium is lost in urine, sweat, etc., than it is gained through diet. Thus, prevention of disease is better than treatment by consuming adequate amount of calcium and exercise at young age. 

3. Osteoporosis may be caused due to decreasing estrogen secretion after menopause, deficiency of vitamin D, low calcium diet, decreased secretion of sex hormones and thyrocalcitonin.