Histology,[help 1] also known as microscopic anatomy or microanatomy,[1] is the branch of biology which studies the microscopic anatomy of biological tissues.[2][3][4][5] Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visible without a microscope.[5][6] Although one may divide microscopic anatomy into organology, the study of organs, histology, the study of tissues, and cytology, the study of cells, modern usage places these topics under the field of histology.[5] In medicine, histopathology is the branch of histology that includes the microscopic identification and study of diseased tissue.[5][6] In the field of paleontology, the term paleohistology refers to the histology of fossil organisms.[7][8]

Biological tissues

Animal tissue classification

There are four basic types of animal tissues: muscle tissue, nervous tissue, connective tissue, and epithelial tissue.[5][9] All animal tissues are considered to be subtypes of these four principal tissue types (for example, blood is classified as connective tissue, since the blood cells are suspended in an extracellular matrix, the plasma).[9]