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Micrograph shows a blood smear. The neutrophil and eosinophil are similar in structure, but the eosinophil is larger. Both are filled with granular structures, and have three purple-stained nuclei. These white blood cells are surrounded with donut-shaped red blood cells.
In this compound light micrograph purple-stained neutrophil (upper left) and eosinophil (lower right) are white blood cells that float among red blood cells in this blood smear. Neutrophils provide an early, rapid, and nonspecific defense against invading pathogens. Eosinophils play a variety of roles in the immune response. Red blood cells are about 7–8 µm in diameter, and a neutrophil is about 10–12µm. (credit: modification of work by Dr. David Csaba)

The environment consists of numerous pathogens , which are agents, usually microorganisms, that cause diseases in their hosts. A host    is the organism that is invaded and often harmed by a pathogen. Pathogens include bacteria, protists, fungi and other infectious organisms. We are constantly exposed to pathogens in food and water, on surfaces, and in the air. Mammalian immune systems evolved for protection from such pathogens; they are composed of an extremely diverse array of specialized cells and soluble molecules that coordinate a rapid and flexible defense system capable of providing protection from a majority of these disease agents.

Components of the immune system constantly search the body for signs of pathogens. When pathogens are found, immune factors are mobilized to the site of an infection. The immune factors identify the nature of the pathogen, strengthen the corresponding cells and molecules to combat it efficiently, and then halt the immune response after the infection is cleared to avoid unnecessary host cell damage. The immune system can remember pathogens to which it has been exposed to create a more efficient response upon re-exposure. This memory can last several decades. Features of the immune system, such as pathogen identification, specific response, amplification, retreat, and remembrance are essential for survival against pathogens. The immune response can be classified as either innate or active. The innate immune response is always present and attempts to defend against all pathogens rather than focusing on specific ones. Conversely, the adaptive immune response stores information about past infections and mounts pathogen-specific defenses.

Questions & Answers

The study of all life or living matterThe living organisms of a particular region.
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in which of the following stages of the cell cycle are chromosomes pulled apart to opposite poles of the cell
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Anaphase
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Digestive system is a system in mammals associated with the breaking down or assimilation of food substances into simple soluble and diffusable substances by mechanical and chemical means
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cells of the kidneys
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Describe cellular event during meiosis
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what is the difference between compound light microscope and electron microscope
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botany zoology microorganisms
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what is prokaryotit
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Deoxyribonucleic Acid
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Fonki
separate waste (urine) from the body
Simon
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dioxyribonucleic acid
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deoxyribonucleic acid
Simon
Practice Key Terms 2

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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