Anatomy and Physiology / Unit 8: The Cardiovascular and Lymphatic Systems
8.7 Lymphatic System and Immunity
Notes
The lymphatic system returns leaked tissue fluid to the blood as lymph, absorbs fats from the intestine (lacteals) and houses immune cells.
- Structures: lymphatic capillaries, vessels with valves, lymph nodes (filter lymph; swell during infection), spleen (filters blood), thymus (T-cell maturation), tonsils and red bone marrow.
- Innate (nonspecific) defenses: skin and mucous membranes, phagocytes, natural killer cells, inflammation (redness, heat, swelling, pain), fever and interferons. They respond quickly with no memory.
- Adaptive (specific) immunity: B cells become plasma cells and produce antibodies (humoral immunity); T cells include cytotoxic T cells (kill infected cells) and helper T cells (coordinate); memory cells give faster response on a second exposure.
- Active immunity arises from infection or vaccination; passive immunity is received antibodies (placenta, breast milk). Vaccines use harmless forms of a pathogen to create memory cells.
- Allergies are overreactions; autoimmune diseases attack the body's own cells; HIV destroys helper T cells.
Practice
What is the main function of lymph nodes?
Nodes trap microbes and activate lymphocytes.
A person gets a vaccine against measles. Which result gives long-term protection?
Vaccines stimulate active immunity with memory cells.
A newborn is protected from infections in the first months by antibodies received from the mother's milk. This is:
The baby receives antibodies without producing them, and the protection is temporary.
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