Science · Regulation & defense
Immune and Lymphatic Systems
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- Innate defenses act quickly and broadly.
- Adaptive defenses target specific antigens and form memory.
- B cells make antibodies; cytotoxic T cells kill infected cells.
- The lymphatic system returns fluid and supports immune surveillance.
What you’ll be able to do
- Compare innate and adaptive defenses.
- Explain B cells, T cells, antibodies, and memory.
- Connect lymph flow, inflammation, and vaccination.
Start with barriers, then follow the response from rapid general defense to specific memory.
Optional review
If you’d like to review the basics, visit Anatomical Orientation, Organization, and Homeostasis. You can start this lesson without completing those first.
Innate defense responds first
Skin, mucus, cilia, tears, and stomach acid block entry. These are innate defenses: they act quickly and are not aimed at one exact germ. If tissue is damaged, inflammation increases local blood flow and vessel leakiness. Phagocytes can engulf microbes and debris. Fever can support defense, but neither inflammation nor fever identifies one specific antigen.
Innate cells recognize broad danger patterns. Neutrophils arrive quickly and engulf microbes. Macrophages engulf material and release signals. Natural killer cells can destroy abnormal cells without recognizing one unique antigen. Complement proteins can mark microbes, attract cells, and damage some microbial membranes.
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