Mesenteric lymph nodes are small, bean-shaped structures located in the abdomen, specifically within the mesentery, which is the tissue that attaches the intestines to the abdominal wall. These nodes play a crucial role in the immune system by filtering lymph fluid and trapping harmful substances, such as bacteria and viruses, that may enter the body through the digestive tract. These lymph nodes are part of the lymphatic system, which helps maintain fluid balance and supports immune function. When the body detects an infection or inflammation, the mesenteric lymph nodes can become swollen as they produce more immune cells to fight off the threat.