thyroid, adrenal and pituitary glands. Their secretions diffuse directly into the blood vessels. Exocrine glands remain connected to their ducts, and secrete their products through the ducts to the epithelial surface. Exocrine glands can be both internal and external, and are found in the pancreas and liver, as well as sweat and oil glands.
Connective tissue Connective tissue connects body parts. As such, it is the most common and widely distributed of all body tissues. Connective tissues perform multiple functions, but are primarily concerned with protecting, supporting and binding together body tissues. Characteristics of connective tissue Connective tissues have the following characteristics: They have variations in blood supply. Although most connective tissues have good blood supply, meaning they are well vascularised, there are exceptions. Tendons and ligaments have poor blood supply, while cartilage is avascular. Connective tissues are made of many different types of cells, as well as non-living substances found outside of cells, called the extracellular matrix. The extracellular matrix is what makes connective tissue different from other tissues. The matrix is produced by the connective tissue cells and secreted to the exterior of the cell. Depending on the connective tissue type, the matrix may be liquid, semisolid or very hard. The extracellular matrix is what allows connective tissue to be able to bear weight and withstand stretching. The matrix also consists of various types and amounts of fibers. These include collagen fibers known as white fibers, elastic fibers known as yellow fibers, and reticular, or fine collagen, fibers. The fibers are made and secreted by the connective tissue cells. Connective tissue types are largely determined by the amount and type of fibers in the matrix. Bone Bone, or osseous tissue, is composed of bone cells sitting in cavities called lacunae. These cells are surrounded by a very hard matrix that contains calcium salts and large amounts of collagen fibers. Figure 5 describes what the bony tissue looks like when cells are removed: 15
