Term 1 review: support, hormones, reproduction and immunity

Immunity has three lines. The first line keeps pathogens out: skin, tears, mucus with cilia, saliva and stomach acid, and in plants cutin, cork and the cell wall. The second line is inflammation, started by histamine. The third line is acquired immunity. A macrophage shows an antigen to a helper T cell; the helper T cell activates B cells, which become plasma cells that make antibodies and memory cells, and it also activates cytotoxic T cells that destroy infected cells. Antibodies work by neutralization, agglutination, precipitation, lysis and antitoxins. Suppressor T cells switch the response off. The first meeting with a pathogen gives the slow primary response; the next meeting gives a fast secondary response because of memory cells. The lymphoid organs are the bone marrow and thymus (primary) and the spleen, tonsils, Peyer’s patches, appendix and lymph nodes (secondary). The chapters link up. The bone marrow sits inside the bones of Chapter 1. The thymus makes thymosin, a hormone, so it belongs to the immune system and to the glands of Chapter 2. Pituitary hormones from Chapter 2 run the cycle, the birth and the milk of Chapter 3. Cutin and cork, met in Chapter 1 as support, come back in Chapter 4 as defences. For any real health question, a doctor decides.