biology inflammatory response

1. Red : Because the arteriole, which supplying blood to the injured area, dilates to provide more blood with more nutrients and oxygen for repairing the injury. As bloodflow increases, it looks red in colour.
Hot : Due to the increased bloodflow, it also brings more heat to the area.
Swollen : As more blood is flowing around the infected area, more tissue fluid is being squeezed out from the capillaries. Due to the accumulation of the tissue fluid, the area becomes swollen.
Pain : As there is accumulation of tissue fluid, it may trigger the pain receptor under skin. Therefore the sensation of pain is generated.

2. Lymphocytes are a kind of white blood cells. It produces antibodies to protect the body against pathogens by clumping the germs together and attracting phagocytes(another kind of white blood cell which engulf pathogens) to engulf the clumped germs.

3. Tissue fluid is a kind of fluid which mainly contains plasma. White blood cells may present, but red blood cells must be absent in tissue fluid. Tissue fluid is produced when blood flow through blood capillaries. As the water potential in the blood capillary is higher than the water potential outside, there is net water moving out of the capillary by osmosis and the fluid being "squeezes out" is called tissue fluid. It provide a medium for exchange of materials between the blood and the tissue cells. It also keeps the tissue cells moist and provide a constant fluid environment for the tissue cells.