Following are definitions of terms which you will encounter frequently. There is only one type of mature erythrocyte red blood cell , but there are several types of immature erythrocytes.
One common type is called a reticulocyte. This is also referred to as humoral body fluid immunity. T cells provide cellular-level immunity by physically attacking foreign or diseased cells. A memory cell is a variety of both B and T cells that forms after exposure to a pathogen and mounts rapid responses upon subsequent exposures. Unlike other leukocytes, memory cells live for many years. B cells undergo a maturation process in the bone marrow, whereas T cells undergo maturation in the thymus.
This site of the maturation process gives rise to the name B and T cells. The functions of lymphocytes are complex and will be covered in detail in the chapter covering the lymphatic system and immunity. Smaller lymphocytes are either B or T cells, although they cannot be differentiated in a normal blood smear.
Abnormally high lymphocyte counts are characteristic of viral infections as well as some types of cancer. Abnormally low lymphocyte counts are characteristic of prolonged chronic illness or immunosuppression, including that caused by HIV infection and drug therapies that often involve steroids. Monocytes originate from myeloid stem cells. They normally represent 2—8 percent of the total leukocyte count. Macrophages are monocytes that have left the circulation and phagocytize debris, foreign pathogens, worn-out erythrocytes, and many other dead, worn out, or damaged cells.
Macrophages also release antimicrobial defensins and chemotactic chemicals that attract other leukocytes to the site of an infection. Some macrophages occupy fixed locations, whereas others wander through the tissue fluid. Abnormally high counts of monocytes are associated with viral or fungal infections, tuberculosis, and some forms of leukemia and other chronic diseases.
Abnormally low counts are typically caused by suppression of the bone marrow. Most leukocytes have a relatively short lifespan, typically measured in hours or days. Production of all leukocytes begins in the bone marrow under the influence of CSFs and interleukins. Secondary production and maturation of lymphocytes occurs in specific regions of lymphatic tissue known as germinal centers. Lymphocytes are fully capable of mitosis and may produce clones of cells with identical properties.
This capacity enables an individual to maintain immunity throughout life to many threats that have been encountered in the past. Leukopenia is a condition in which too few leukocytes are produced. If this condition is pronounced, the individual may be unable to ward off disease.
Excessive leukocyte proliferation is known as leukocytosis. Although leukocyte counts are high, the cells themselves are often nonfunctional, leaving the individual at increased risk for disease. Leukemia is a cancer involving an abundance of leukocytes. It may involve only one specific type of leukocyte from either the myeloid line myelocytic leukemia or the lymphoid line lymphocytic leukemia. In chronic leukemia, mature leukocytes accumulate and fail to die.
In acute leukemia, there is an overproduction of young, immature leukocytes. In both conditions the cells do not function properly. As in leukemia, the malignant leukocytes do not function properly, and the patient is vulnerable to infection.
Some forms of lymphoma tend to progress slowly and respond well to treatment. Others tend to progress quickly and require aggressive treatment, without which they are rapidly fatal. You may occasionally see platelets referred to as thrombocytes , but because this name suggests they are a type of cell, it is not accurate. A platelet is not a cell but rather a fragment of the cytoplasm of a cell called a megakaryocyte that is surrounded by a plasma membrane.
As noted earlier, thrombopoietin, a glycoprotein secreted by the kidneys and liver, stimulates the proliferation of megakaryoblasts, which mature into megakaryocytes. These remain within bone marrow tissue Figure 3 and ultimately form platelet-precursor extensions that extend through the walls of bone marrow capillaries to release into the circulation thousands of cytoplasmic fragments, each enclosed by a bit of plasma membrane.
These enclosed fragments are platelets. Granules are tiny sacs that contain various enzymes, compounds and other components that are used to defend against pathogens, reduce inflammation and destroy cells. What the granules are filled with or used for depends on the specific type of granular leukocyte.
Agranular leukocytes , also called agranular or agranulated white blood cells, usually lack these granules. While they may still contain a few, they're in a much fewer number and aren't relied on for their function as they are in granular leukocytes. Neutrophils are the most common type of leukocyte, granular or agranular. They make up 50 to 70 percent of human leukocyte counts.
They get their name "neutrophil" thanks to the neutral pH of the components that make up their granules. The main function of neutrophils is as phagocytes cells that engulf and destroy foreign bodies, usually bacteria and viruses.
Increased neutrophil counts usually indicate a bacterial infection. Low counts are correlated to increased risk of infection.
Eosinophils are mainly responsible for helping to break down blood clots and releasing chemicals that can kill parasites , especially parasitic worms. Their granules can also contain histamines, which are released in response to a pathogen entering the system.
B cells are two types: memory B cells and regulatory B cells. There are two types of T cells. One type of T cells produce cytokines that induce the immune response while the second type produces granules that are responsible for the death of the infected cells.
Lymphocytes, mainly T and B cells, produce memory cells which provide long-lasting immunity against specific pathogens. Granular leukocytes contain granules in their cytoplasms while agranular leukocytes lack granules in their cytoplasms. Thus, the presence and absence of granules in the cytoplasm is the key difference between granular and agranular leukocytes.
Moreover, there are three main types of granular leukocytes as neutrophils, eosinophils and basophils while there are two main types of agranular leukocytes as monocytes and lymphocytes. So, we can consider this too as a difference between granular and agranular leukocytes. Leukocytes are the main cells of the immune system of our body.
They protect us from the invading pathogens that could disrupt normal functioning. There are two main types of leukocytes: granulocytes and agranulocytes. Granular leukocytes contain granules in their cytoplasm while agranular leukocytes lack granules.
This is the key difference between granular and agranular leukocytes.
0コメント