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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
Parkinson's disease is both chronic and progressive. This means that it persists over a long period of time and that its symptoms grow worse over time.
Patients who have been on total parenteral nutrition for more than a few days may need to have foods gradually reintroduced to give the digestive tract time to start working again.
Chronic necrotizing aspergillosis has a slowly progressive process that, unlike invasive aspergillosis, does not spread to other organ systems or the blood vessels. It most often affects middle-aged and elderly individuals, spreading to surrounding tissue in the lungs. The disease often does not respond to conventionally successful treatments, and requires individualized therapies in order to keep it from becoming life-threatening.
The lipid bilayer is made of phospholipids. They are arranged in a double layer because one of their ends is attracted to water while the other is repelled by water.