Final answer:
Pus is an accumulation of dead pathogens, neutrophils, tissue fluid, and cellular debris resulting from the immune response to an infection. It is indicative of the body's battle against an infection and can help diagnose specific types of bacteria due to distinctive characteristics like color in certain strains.
Step-by-step explanation:
Pus is a substance that is commonly associated with the process of infection and the body's immune response to it. It is an accumulation of dead pathogens, neutrophils (which represent 50-60 percent of all leukocytes and are the first responders at the site of infection), tissue fluid, and other cells that may be caught in the crossfire. When pathogens invade the body and cause an infection, like pyelonephritis (an infection of the kidneys), the immune system responds by sending neutrophils and macrophages to the site to phagocytose the pathogens. As these immune cells do their job, they eventually die and leave behind cellular debris, which is visible as pus. Moreover, the presence of pus, which can be suppurative (pus-producing), can signal specific types of bacterial infections when viewed under a microscope, as certain strains like Pseudomonas aeruginosa might produce distinctive pigments such as pyocyanin or pyoverdin. Pyuria, the presence of pus or white blood cells in the urine, is another indicator of an infection that can be analyzed. Various skin conditions are also associated with pus, including acne, pyoderma, and more severe infections such as necrotizing fasciitis.