<Tr> <Td> Absent </Td> <Td> Absent </Td> </Tr> <Tr> <Td> Grade + </Td> <Td> Mild: Both feet / ankles </Td> </Tr> <Tr> <Td> Grade + + </Td> <Td> Moderate: Both feet, plus lower legs, hands or lower arms </Td> </Tr> <Tr> <Td> Grade + + + </Td> <Td> Severe: Generalised bilateral pitting edema, including both feet, legs, arms and face </Td> </Tr>

What are the 2 basic reasons why oedema would result