Cytology, more commonly known as cell biology, studies cell structure, cell composition, and the interaction of cells with other cells and the larger environment in which they exist. The term "cytology" can also refer to cytopathology, which analyzes cell structure to diagnose disease. Microscopic and molecular studies of cells can focus on either multi-celled or single-celled organisms.
That fact that we as humans are made up of millions of tiny cells, and that other lifeforms around us are similarly constituted, now barely needs explanation. The concept of the cell is relatively new, however. The scientific community did not accept the idea of the existence of cells until the late 18th century.
Recognizing the similarities and differences of cells is of the utmost importance in cytology. Microscopic examination can help identify different types of cells. Looking at the molecules which form a cell, sometimes called molecular biology, helps in further description and identification. All fields of biology depend on the understanding of cellular structure. The field of genetics exists because we understand cell structure and components.
Another important aspect in the discipline of cytology is examining cell interaction. By studying how cells relate to other cells or to the environment, cytologists can predict problems or examine environmental dangers to cells, such as toxic or cancer-causing substances. In humans and other multi-cellular structures, cytology can examine the presence of too many of one kind of cell, or the lack of enough of a certain kind of cell. In a simple test like a complete blood count, a laboratory can look at white blood cells and identify the presence of an infection, or it may examine a low level of certain types of red blood cells and diagnose anemia.
Certain autoimmune disorders can be diagnosed by abnormal cell reactions. Hashimoto's thyroiditis, for example, is an autoimmune condition caused by abnormal cell reaction. Instead of white blood cells recognizing the presence of normal thyroid cells, these antibodies attack them, causing low thyroid. If untreated, this condition can result in retardation, extreme fatigue, obesity, and ultimately death. Through cytology, the abnormal reactions of these antibodies can be recognized, and treatment can be undertaken long before this condition creates irreversible problems.
Cytopathology has similar aims, but tends to look for cells that should not be present in an organism. Urinalysis and blood tests, for example, can scan for the presence of parasites or bacteria which can cause illness and death. Hence, in cytology, understanding single-celled organisms like many forms of bacteria is as important as understanding multi-cellular structures.
This is also one of the main diagnostic tools for detecting cancer. A woman's yearly gynecological exam almost always involves a pap smear, a collection of tissues that are analyzed at the cellular structure to detect early formations of cancer cells. Early detection can lead to greater survival rates. Similarly, needle biopsies of lumps in the breast or elsewhere can detect cancer cells and provide an excellent means for diagnosis.