The circulatory system transports essential materials in the body and helps regulate certain functions. Its primary components include the heart, blood vessels, and blood itself. Both the blood vessels and the heart contain three tissue layers, with the heart’s layers creating the endocardium, the myocardium, and the epicardium. Blood vessels consist of the following tissuess: smooth muscle, connective, and epithelial. If the lymphatic system is considered part of the circulatory system, then lymphatic tissues also fall into the tissues in the circulatory system category.
All tissues, including those in the circulatory system, consist of cell groups that collectively perform specific functions. Main tissue varieties include connective tissue, muscle tissue, and epithelial tissue. The latter type generally makes up the linings or organs. In turn, connective tissue, consisting of collagen and other substances, strengthens, supports, and helps keep organs together. Muscle tissues, on the other hand, contain proteins that help organs constrict and move.
Two types of blood vessels, veins and arteries, carry blood to and from the heart, respectively. These tubes are of varying lengths and widths, but each is built from the same three layers of tissues in the circulatory system. A layer of smooth muscle tissue helps the vessels contract and move blood. This layer is surrounded by more elastic connective tissue that allows the vessels to expand and handle higher blood pressure. The innermost layer, endothelial tissue, is a form of eipithelial tissue that provides a barrier between the blood and other vessel layers, helps in processes like blood clotting, and facilitates the rate of blood flow.
Endothelial cells create the innermost tissues in the circulatory system's main fixture — the heart — as well. This endocardium layer serves as both a heart-blood barrier and as a guide for underlying myocardial tissue. The myocardium is arguably the heart of the heart, so to speak, as it actually dictates the muscular contractions that cause the heart to pump. It is composed of parallel and durable muscle fibers known as cardiac muscle cells. The outermost tissue layer of the epicardium provides protection for the heart, and it consists of connective tissue.
Another circulatory system that works with the blood circulatory system is the lymphatic system. This network of lymph and lymph vessels helps collect and remove fluids from the body and helps produce disease-fighting agents. Lymphatic tissues in the circulatory system have cells known as lymphocytes that perform these functions. The tissue may be loose, dense, or nodular in structure. The latter type makes up lymph nodes.
