Blood Cell Types
The erythrocytes, or red blood cells ("corpuscles"), contain hemoglobin (substance that is able to bind with oxygen). Oxygen from the lungs is carried by the erythrocytes to all the tissues of the body. A person who has anemia, a condition caused by too few erythrocytes in the blood, may experience weakness, fatigue, and shortness of breath.
There are five different types of leukocytes, or white blood cells, within the body, including the following:
These cells fight viral, bacterial, and other infections and participate in the hypersensitivity responses seen in allergic reactions.
Neutrophils, basophils, and eosinophils are granulocytes (white blood cells that destroy bacteria). Granulocytes are distinguished by the small particles, or granules, that reside within each cell and contain substances to fight infections. Granulocytes undergo many stages of development before becoming mature neutrophils, basophils, or eosinophils. The more immature, myeloid series of granulocytes include cells known as myeloblasts, promyelocytes, myelocytes, metamyelocytes, band forms ("stab cells"), and polymorphonuclear leukocytes (PMNs).
If there is a "block" in the development of the myelogenous (granulocytic) cell line, either chronic myelogenous leukemia (CML) or acute myelogenous leukemia (AML) may result.
Monocytes are medium-to-large mobile cells that can travel along the walls of the blood vessels and adhere to tissue surfaces. They contain cellular systems that consume foreign substances by surrounding and digesting of microorganisms and foreign particles or enveloping foreign substances within the plasma membrane.
Monocytes originate in the bone marrow as immature monoblasts and promonocytes. Once these early cell forms develop into monocytes, they circulate in the bloodstream for about 24 hours. If the monocytes detect an area of inflammation, they move into tissues to become macrophages (larger phagocytic cells that help lymphocytes to detect foreign microorganisms and launch immune system responses).
Lymphatic tissue contains both fixed and circulating elements. Many different types of lymphatic cells interact to combat infections and recognize abnormal cells within the body. Fixed lymphoid tissue is found in the lymph nodes, spleen, thymus, tonsils and adenoids, bone marrow, and various sites within the gastrointestinal tract, respiratory system, and liver.
Circulating lymphatic cells, such as the lymphocytes (nongranular leukocytes with a single nucleus) and monocyte/macrophage cells, originate from stem cells in the blood-forming tissues. The stem cells give rise to daughter cells that ultimately develop into B-cells or T-cells. Daughter T-cells migrate to the thymus, where they mature into T-cells. It is believed that daughter B-cells complete their development within the bone marrow.
B-cells combat infections by changing into plasma cells, which secrete antibodies. Plasma cell antibodies become attached to the invading germ, which is then recognized and destroyed by the blood granulocytes. T-cells are able to detect virus-infected cells within the body. They interact with macrophages to rid the body of the virus.
If there is a "block" in the development of lymphocytes, either chronic lymphocytic leukemia (CLL) or acute lymphocytic leukemia (ALL) may result.
Although platelets are classified as a type of blood cell, they are actually just pieces of megakaryocytes (bone marrow giant cells that contain a many-lobed nucleus [cell center]). Platelets are the major blood-clotting elements of the body. They group together to seal off blood vessel damage caused by cuts or other traumatic injuries.
A person with a low level of platelets in the circulating blood (called thrombocytopenia) may experience excessive bleeding.