The lymphatic system is a body-wide network of vessels, nodes, and organs that helps keep tissues healthy. It collects extra fluid that leaks out of blood capillaries and returns it to the bloodstream. This prevents swelling and helps maintain normal blood volume and pressure.
It also supports immunity by moving immune cells and filtering harmful microbes from lymph.
Key Facts
- Lymph forms when excess tissue fluid enters small lymphatic capillaries.
- Lymph flow rate = volume of lymph moved / time.
- Net tissue fluid change = capillary filtration - capillary reabsorption - lymph drainage.
- Lymph nodes filter lymph and provide meeting places for white blood cells and antigens.
- The spleen filters blood, recycles old red blood cells, and helps detect blood-borne pathogens.
- The thymus is where many T cells mature before they help coordinate immune responses.
Vocabulary
- Lymph
- Lymph is a clear fluid made from tissue fluid that carries water, proteins, fats, waste, and immune cells through lymphatic vessels.
- Lymphatic vessel
- A lymphatic vessel is a thin tube that carries lymph toward larger ducts and eventually back into the bloodstream.
- Lymph node
- A lymph node is a small bean-shaped structure that filters lymph and activates immune responses.
- Spleen
- The spleen is an organ in the upper left abdomen that filters blood and helps fight infections.
- Thymus
- The thymus is an organ behind the breastbone where immature T lymphocytes develop into functional immune cells.
Common Mistakes to Avoid
- Thinking lymph vessels pump like the heart is wrong because lymph moves mainly by skeletal muscle contractions, breathing movements, and one-way valves.
- Confusing lymph nodes with glands is wrong because lymph nodes do not secrete hormones or fluids like endocrine or exocrine glands.
- Assuming lymph only carries germs is wrong because lymph also transports excess fluid, proteins, fats absorbed from the intestine, and immune cells.
- Forgetting the spleen filters blood rather than lymph is wrong because lymph nodes filter lymph, while the spleen monitors and cleans the bloodstream.
Practice Questions
- 1 A tissue bed filters 24 mL of fluid from blood capillaries each hour, reabsorbs 20 mL each hour, and drains 4 mL each hour through lymphatics. What is the net tissue fluid change per hour?
- 2 A lymphatic vessel moves 90 mL of lymph in 30 minutes. What is the lymph flow rate in mL/min?
- 3 Explain why a blocked lymphatic vessel in the leg can cause swelling and may also increase the risk of infection.