Histology of Blood
- Introduction to blood.
- Cellular components of blood
- How to look at blood smears.
- White blood cells in connective tissue
- White blood cells and inflammation
Blood is a highly specialized, fluid tissue.
Blood is traditionally classified as a specialized form of connective tissue. To appreciate the basic unity of blood and other varieties of connective tissue, consider the following.
- All of the several blood cell types originate in the connective tissue of bone marrow.
- Certain white blood cells, notably lymphocytes and monocytes, move freely back and forth between blood and other connective tissues.
- The chemical composition of plasma is very similar to that of interstitial fluid in ordinary connective tissue.
All connective tissue consists of cells embedded in a matrix that consists of ground substance and fibers. Blood may thus be described as connective tissue whose matrix consists of free-flowing ground substance (plasma) with no fibers.
One highly specialized cell type, the red blood cell (RBC, erythrocyte), normally occurs only in blood. Other blood cells, the so-called white blood cells (WBCs, leukocytes), are found in other connective tissues as well.
For historical reasons, a couple of the white blood cell types have two different names, depending on whether they are found in blood or in other connective tissues (monocyte in blood = macrophage in ordinary connective tissue; basophil in blood = mast cell in ordinary connective tissue).
Because blood is so easily sampled, and because many readily observable features of blood are altered in specific ways by disease processes, examination of blood cells can be extremely informative. Modern laboratories provide automated analysis in the form of a CBC, or complete blood count.
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Last updated: 7 June 2022 / dgk