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🫀 Science · Human Anatomy and Physiology · Lesson 12 of 12 · 6 min

Immune and lymphatic systems: innate, adaptive and vaccines

🛡️ Your body runs two defense teams: one that reacts to anything in minutes and one that learns a single enemy and remembers it for years. Vaccines work by training the second team.

💡 Key idea

Innate is fast and general; adaptive is specific with memory; active immunity is made by you, passive immunity is borrowed.

🧠 The idea

INNATE immunity is present from birth, fast and nonspecific: skin and mucous membranes, stomach acid, phagocytes such as neutrophils and macrophages, natural killer cells, inflammation and fever. ADAPTIVE immunity is slower the first time, specific to one antigen, and has memory. B LYMPHOCYTES mature in the bone marrow and, when activated, become plasma cells that secrete ANTIBODIES (humoral immunity). T lymphocytes mature in the thymus: helper T cells (CD4) coordinate the response, and cytotoxic T cells (CD8) kill infected cells (cell-mediated immunity). Memory cells make a second exposure faster and stronger. The lymphatic system returns leaked tissue fluid (lymph) to the blood and filters it through lymph nodes; the spleen filters blood, and tonsils guard the throat. Active immunity means your own body makes antibodies, after infection or a vaccine, and lasts long. Passive immunity means receiving ready-made antibodies, across the placenta, in breast milk or by injection; it works at once but fades in weeks to months.

✏️ Worked example

Classify a newborn's protection from antibodies that crossed the placenta. Step 1: did the baby's own B cells make them? No, the mother's did. Step 2: borrowed antibodies = passive. Step 3: it came naturally, not by injection, so natural passive immunity. Contrast a tetanus shot of toxoid: the person's own cells respond, so artificial active immunity.

📌 Takeaways

  • Innate: barriers, phagocytes, inflammation, fever. Adaptive: B cells (antibodies) and T cells.
  • B cells mature in bone marrow, T cells in the thymus; plasma cells secrete antibodies.
  • Vaccine = active (long-lasting); maternal antibodies or antibody injection = passive (short).

✅ Check yourself

Question 1 of 3

Which cell type secretes antibodies?

  1. Cytotoxic T cell
  2. Plasma cell
  3. Neutrophil
  4. Helper T cell
Show the answer and rationale

Answer: B

Activated B cells become plasma cells, which secrete antibodies. Cytotoxic T cells kill infected cells directly, helper T cells coordinate other cells, and neutrophils are innate phagocytes.

Question 2 of 3

A child receives a measles vaccine. What type of immunity results?

  1. Artificial active
  2. Natural active
  3. Artificial passive
  4. Natural passive
Show the answer and rationale

Answer: A

A vaccine makes the child's own immune system produce antibodies and memory cells, so it is active, and it is given on purpose, so it is artificial. Passive immunity would mean receiving ready-made antibodies, and natural active immunity comes from catching the disease.

Question 3 of 3

Which is an example of innate (nonspecific) immunity?

  1. Memory B cell response
  2. Cytotoxic T cell killing a virus-infected cell
  3. Phagocytosis by a macrophage
  4. Antibody made after a vaccine
Show the answer and rationale

Answer: C

Macrophages engulf many kinds of invaders without needing prior exposure, which makes phagocytosis innate. Antibodies, memory B cells and cytotoxic T cells all belong to the adaptive response, which is specific to one antigen.

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