Blood is mostly made up of water, as are our organs and muscles. To read specifically about edema, swelling caused by fluid retention where excess fluid is trapped in the body's tissues, see our article Edema: Causes, Symptoms and Treatments.
If you use the Amsoil Ea15K01 and the ASM oil (For 3rd gen Prius), then you can safely go 15,000 miles between oil changes. I drive 25,000 miles per year in my Prius. Amsoil backs up their products by a written warranty.
Depends from car to car. Mainly due to the location of the oil filter. But, an oil change should not ever be an oil change. With better oils on the market some cars do not need oil changes that frequently anymore. The average interval is around 8-10k or six months. Toyota for example recommends a service interval of 8k or six months.