The lymphatic system returns water and proteins from various tissues back to the bloodstream and produces lymphocytes, which make antibodies to defend the body against invasion by agents such as viruses, bacteria, or fungi. It also collects some venoms and toxins that it will return over time to the circulation system.
Lymph nodes are usually found in groups in different places throughout the body, including the neck, armpit, chest, abdomen, pelvis and groin. They often swell when the lymphatic system is protecting the body.
The lymphatic system mainly relies on body movement and contraction of nearby muscles to move its contents (including some venoms and toxins) along, as it does not have a pump like the circulatory system. Lymph vessels, like veins, have one-way valves so that lymph can flow in only one direction.