The Human Body- Barriers against Pathogens:
1.
Skin: Prevents bacteria from entering the body. If skin is broken, bacteria will have access to the cells
below. The bacteria continue to grow and multiply and cause disease.
2.
Mucus: Lines the respiratory and digestive tracts and acts as a barrier to bacteria. Mucus traps pathogens
present in air and food. When the mucus is swallowed, gastric juice in the stomach destroys the bacteria.
3.
Tear Glands: Produce the enzyme, lysozyme. This enzyme destroys bacteria by breaking down their cell
walls.
4.
Immune System: Collection of cells and tissues that defend your body against pathogens.
Cells
Tissues
Leucocytes
(White blood cells)
Phagocytes
Thymus Spleen Bone Marrow Lymphatic System
Lymphocytes
B-cells
Plasma
Memory
T-cells
Helper
Killer
The Mechanism of Leucocytes:
1.
Phagocytes:
-group of immune cells specialized in finding and “eating” bacteria, viruses, and dead or injured body cells
-enzymes dissolve bacteria
-leaves pus (destroyed pathogens, dead leucocytes, blood serum)
2.
Lymphocytes:
-surface of these immune cells have receptors which can match to only one specific antigen (markers to
recognize self and foreign substances)
B cells: presence of antigens (pathogens) signal B-cells to produce antibodies
-B cell incorporates some of its antibodies into its cell membrane in such a manner that the
antibody faces the faces the outside of the cell (like a receptor)
-each antibody (specific protein) is specific for a single antigen (markers to recognize self and
foreign substances)
-when the Y shaped antibody on a B cell finds a matching antigen, the B-cell begins to divide
rapidly to produce plasma and memory cells, that are clones of the original B-cell
-the plasma cells produce antibodies that are carried throughout blood plasma and tissue fluid
-antibodies can then neutralize antigen molecules
-the memory cells “remember” specific intruders
-the second time a pathogen tries to invade the body, memory cells secrete large amounts of the
antibody
-very quickly, all the invading pathogens are destroyed
-memory cells can give immunity to diseases
T-cells: form clones after they attach to antigen. Like B-cells, they too form memory cells.
-they respond to whole cells
-come in two different types, helper cells and killer cells
-Helper cells activate B cells and Killer T cells
-Killer T cells attack cells of the body infected by pathogens, can also attack cancer cells