A scanning electron microscope image of a single white blood cell (yellow/right), engulfing anthrax bacteria (orange/left) – scale bar is 5 µm (false color) The<unk>  is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the<unk> . The innate<unk>  provides a preconfigured response to broad groups of situations and stimuli. The adaptive<unk>  provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions. Nearly all organisms have some kind of<unk> . Bacteria have a rudimentary<unk>  in the form of enzymes that protect against virus infections. Other basic<unk>  mechanisms evolved in ancient plants and animals and remain in their modern descendants. These mechanisms include phagocytosis, antimicrobial peptides called defensins, and the complement<unk> . Jawed vertebrates, including humans, have even more sophisticated defense mechanisms, including the ability to adapt to recognize pathogens more efficiently. Adaptive (or acquired)<unk> ty creates an<unk> logical memory leading to an enhanced response to subsequent encounters with that same pathogen. This process of acquired<unk> ty is the basis of vaccination. Dysfunction of the<unk>  can cause autoimmune diseases, inflammatory diseases and cancer.<unk> deficiency occurs when the<unk>  is less active than normal, resulting in recurring and life-threatening infections. In humans,<unk> deficiency can be the result of a genetic disease such as severe combined<unk> deficiency, acquired conditions such as HIV/AIDS, or the use of<unk> suppressive medication. Autoimmunity results from a hyperactive<unk>  attacking normal tissues as if they were foreign organisms. Common autoimmune diseases include Hashimoto's thyroiditis, rheumatoid arthritis, diabetes mellitus type 1, and<unk> ic lupus erythematosus.<unk> logy covers the study of all aspects of the<unk> .
Immune system
Integumentary system
Endocrine system
Coagulation
Reproductive system
Adaptive immune system
Bone conduction
Muscular defense