This condition causes abnormal production of blood cells. This includes white blood cells in the bone marrow. Cancer of the blood. Cancers including leukemia and lymphoma can cause uncontrolled growth of an abnormal type of blood cell in the bone marrow. This results in a greatly increased risk for infection or serious bleeding. Myeloproliferative disorder. This disorder refers to various conditions that trigger the excessive production of immature blood cells. This can result in an unhealthy balance of all types of blood cells in the bone marrow and too many or too few white blood cells in the blood.
Some medicines can raise or lower the body's white blood cell count. Conditions such as extreme physical stress caused by an injury or emotional stress can also trigger high white blood cell levels.
So can inflammation, labor or the end of pregnancy, smoking, or even extreme exercise. Search Encyclopedia. What Are White Blood Cells? Types of white blood cells Among your white blood cells are: Monocytes. 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 [link] 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. Each megakarocyte releases — platelets during its lifespan. Following platelet release, megakaryocyte remnants, which are little more than a cell nucleus, are consumed by macrophages.
After entering the circulation, approximately one-third migrate to the spleen for storage for later release in response to any rupture in a blood vessel. They then become activated to perform their primary function, which is to limit blood loss. Platelets remain only about 10 days, then are phagocytized by macrophages.
Platelets are critical to hemostasis, the stoppage of blood flow following damage to a vessel. They also secrete a variety of growth factors essential for growth and repair of tissue, particularly connective tissue. Infusions of concentrated platelets are now being used in some therapies to stimulate healing. Thrombocytosis is a condition in which there are too many platelets.
This may trigger formation of unwanted blood clots thrombosis , a potentially fatal disorder. If there is an insufficient number of platelets, called thrombocytopenia , blood may not clot properly, and excessive bleeding may result.
The Webscope feature allows you to move the slides as you would with a mechanical stage. You can increase and decrease the magnification. There is a chance to review each of the leukocytes individually after you have attempted to identify them from the first two blood smears. In addition, there are a few multiple choice questions. Are you able to recognize and identify the various formed elements?
You will need to do this is a systematic manner, scanning along the image. The standard method is to use a grid, but this is not possible with this resource. Try constructing a simple table with each leukocyte type and then making a mark for each cell type you identify. Attempt to classify at least 50 and perhaps as many as different cells. Based on the percentage of cells that you count, do the numbers represent a normal blood smear or does something appear to be abnormal?
When scientists first began to observe stained blood slides, it quickly became evident that leukocytes could be divided into two groups, according to whether their cytoplasm contained highly visible granules:.
We will consider the granular leukocytes in order from most common to least common. All of these are produced in the red bone marrow and have a short lifespan of hours to days.
They typically have a lobed nucleus and are classified according to which type of stain best highlights their granules Figure 2. Figure 2. A neutrophil has small granules that stain light lilac and a nucleus with two to five lobes. A basophil has large granules that stain dark blue to purple and a two-lobed nucleus. The most common of all the leukocytes, neutrophils will normally comprise 50—70 percent of total leukocyte count.
They are called neutrophils because their granules show up most clearly with stains that are chemically neutral neither acidic nor basic. The granules are numerous but quite fine and normally appear light lilac. The nucleus has a distinct lobed appearance and may have two to five lobes, the number increasing with the age of the cell.
Neutrophils are rapid responders to the site of infection and are efficient phagocytes with a preference for bacteria. Their granules include lysozyme , an enzyme capable of lysing, or breaking down, bacterial cell walls; oxidants such as hydrogen peroxide; and defensins , proteins that bind to and puncture bacterial and fungal plasma membranes, so that the cell contents leak out. A burn injury increases the proliferation of neutrophils in order to fight off infection that can result from the destruction of the barrier of the skin.
Eosinophils typically represent 2—4 percent of total leukocyte count. The granules of eosinophils stain best with an acidic stain known as eosin. The nucleus of the eosinophil will typically have two to three lobes and, if stained properly, the granules will have a distinct red to orange color.
The granules of eosinophils include antihistamine molecules, which counteract the activities of histamines, inflammatory chemicals produced by basophils and mast cells. Some eosinophil granules contain molecules toxic to parasitic worms, which can enter the body through the integument, or when an individual consumes raw or undercooked fish or meat.
Eosinophils are also capable of phagocytosis and are particularly effective when antibodies bind to the target and form an antigen-antibody complex. High counts of eosinophils are typical of patients experiencing allergies, parasitic worm infestations, and some autoimmune diseases. Low counts may be due to drug toxicity and stress. Basophils are the least common leukocytes, typically comprising less than one percent of the total leukocyte count.
The granules of basophils stain best with basic alkaline stains. Basophils contain large granules that pick up a dark blue stain and are so common they may make it difficult to see the two-lobed nucleus. In general, basophils intensify the inflammatory response. They share this trait with mast cells. In the past, mast cells were considered to be basophils that left the circulation.
However, this appears not to be the case, as the two cell types develop from different lineages. The granules of basophils release histamines, which contribute to inflammation, and heparin, which opposes blood clotting. High counts of basophils are associated with allergies, parasitic infections, and hypothyroidism.
Low counts are associated with pregnancy, stress, and hyperthyroidism. Agranular leukocytes contain smaller, less-visible granules in their cytoplasm than do granular leukocytes. The nucleus is simple in shape, sometimes with an indentation but without distinct lobes. There are two major types of agranulocytes: lymphocytes and monocytes see Figure 1 in Production of the Formed Elements.
Lymphocytes are the only formed element of blood that arises from lymphoid stem cells. Although they form initially in the bone marrow, much of their subsequent development and reproduction occurs in the lymphatic tissues. Lymphocytes are the second most common type of leukocyte, accounting for about 20—30 percent of all leukocytes, and are essential for the immune response.
The size range of lymphocytes is quite extensive, with some authorities recognizing two size classes and others three. This finding has led to the three size range classification. The three major groups of lymphocytes include natural killer cells, B cells, and T cells. Thus, they provide generalized, nonspecific immunity. The larger lymphocytes are typically NK cells.
B cells and T cells, also called B lymphocytes and T lymphocytes , play prominent roles in defending the body against specific pathogens disease-causing microorganisms and are involved in specific immunity. One form of B cells plasma cells produces the antibodies or immunoglobulins that bind to specific foreign or abnormal components of plasma membranes.
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.
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