The figure illustrates several types of leucocytes, which are a crucial part of the body's immune system. These cells are designed to巡逻 the bloodstream and enter the tissues to search for and destroy病原微生物, damaged cells, and toxins. Each type of leucocyte has unique features and functionalities that enable them to carry out specific tasks within the body's defense mechanisms.
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Granular Leucocytes: These leucocytes are so named due to the presence of granular structures in their cytoplasm. They include neutrophils, eosinophils, and basophils. Neutrophils, the most common type, are rapidly mobilized in response to inflammation or infection, where they phagocytose (engulf) bacteria and help to break down their cell walls using enzymes like lysozyme. Eosinophils, known for their redness due to their granules, contain anti-histamine chemicals that reduce allergic reactions and play a role in combating parasitic worms. Basophils, with their large granules stained dark blue, release histamines during an allergic response and heparin, which prevents blood clotting. All of these granular leucocytes are born in the bone marrow and have a relatively short life span,一般在几小时内至几天内。
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Agranular Leucocytes: Also known as agranular leukocytes, these cells have fewer and less distinct granules. They are further divided into monocytes and lymphocytes. Monocytes are large, granular leucocytes that mature into macrophages in the tissues. These macrophages play a key role in phagocytosing infectious agents and clearing dead cells from the body. Lymphocytes, on the other hand, are smaller than monocytes and exist in a variety of tissues. They are critical for humoral immunity, producing antibodies that bind to foreign antigens, and they also engage in cell-mediated immunity by attacking infected cells directly. Both monocytes and lymphocytes mature in the bone marrow before traveling to the peripheral organs where they conduct their specific function.
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Platelets: While not technically leucocytes, platelets are derived from megakaryocytes, which are large cells in the bone marrow. These blood cells are critical for blood clotting. When damaged, platelets adhere to exposed endothelium (the inner lining of blood vessels) and form a fibrin gel, which traps neighboring platelets. This process is known as platelet aggregation and is essential for stopping blood loss and protecting the body from severe bleeding following injury. Platelets typically live for around 10 days, after which they are removed by macrophages in the liver and spleen., the figure illustrates the wide spectrum of immune defense mechanisms involving leucocytes of various types. Granular leukocytes are mobilized rapidly to respond to infection, while agranular leucocytes, such as monocytes and lymphocytes, work behind the scenes to produce antibodies and mediate cell-mediated immune responses. Additionally, platelets play a vital role in blood clotting and preventing excessive bleeding. Understanding the roles and functions of each type of leucocyte is key to comprehending the complex mechanisms of body defense.