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Allergies, autoimmunity and the lymphoid organs sheet
5-mark answer frame

Describe the lymphoid organs of the human body. Explain allergy and autoimmunity.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Define lymphoid organs. Organs where lymphocytes originate, mature and multiply.
  2. 2 · Primary lymphoid organs. Bone marrow (makes all blood cells) and thymus (near the heart; large at birth, small by puberty); immature lymphocytes become antigen-sensitive; T-lymphocytes develop and mature.
  3. 3 · Secondary lymphoid organs. Spleen (filters blood, reservoir of RBCs), lymph nodes (trap antigens), tonsils, Peyer's patches, appendix; MALT about 50% of lymphoid tissue.
  4. 4 · Allergy. Exaggerated response to allergens (pollen, mites, dander); IgE; histamine and serotonin from mast cells; sneezing, watery eyes; treated with anti-histamines, adrenalin, steroids.
  5. 5 · Autoimmunity. The body attacks self-cells for genetic and unknown reasons, e.g. rheumatoid arthritis.
  6. 6 · Close in one line. So the same system that protects us can, when misdirected, harm us.

Scoring tip: Do not call the thymus a secondary organ. Name all five secondary organs to secure the mark.