They're dissolved in fluid that diffuses through the very thin walls of capillaries. The lymphatic vessels are larger than capillaries but smaller than the smallest veins. These lymph ducts then empty the lymph back into the blood by way of the veins.
Doctors evaluate lymph nodes when a cancer is diagnosed to determine if it has spread.
Lymph nodes also produce essential components of the immune system, including white blood cells that make antibodies to destroy foreign organisms. Bacteria trapped by lymph nodes may cause them to swell and become tender, producing a condition called lymphadenitis. Occasionally, the bacteria cause the lymphatic vessels to become inflamed, producing a condition called lymphangitis. The person has tender, red streaks along the skin and usually a fever and chills. Staphylococci and streptococci are the bacteria that most frequently cause lymphangitis.