Three kinds of cartilage are classified according to the abundance of certain fibers and the characteristics of their matrix: It is in contrast to interstitial growth, in which new matrix is deposited within mature cartilage. Appositional growth involves cell division, differentiation, and secretion of new extracellular matrix, thereby contributing mass and new cells at the cartilage surface. The fibroblast-like cells of this layer have chondrogenic potentiality, and are responsible for the enlargement of cartilage plates by appositional growth. Lacunae are separated from one another as a result of the secretory activity of the chondrocytes.Ī highly fibrous, organized, dense connective tissue capsule known as the perichondrium surrounds cartilage. Individual lacunae may contain multiple cells deriving from a common progenitor. Chondrocytes are located within lacunae in the matrix that they have built around themselves. It is characterized by a prominent extracellular matrix consisting of various proportions of connective tissue fibers embedded in a gel-like matrix. CartilageĬartilage is a specialized form of connective tissue produced by differentiated fibroblast-like cells called chondrocytes. The electron transport chain of these mitochondria is disrupted by an uncoupling protein, which causes the dissipation of the mitochondrial hydrogen ion gradient without ATP production. They have numerous, smaller lipid droplets and a large number of mitochondria, whose cytochromes impart the brown color of the tissue. These cells are abundant in newborns and hibernating mammals, but are rare in adults. The function of white fat is to serve as an energy source and thermal insulator.īrown fat cells are highly specialized for temperature regulation. These cells can grow up to 100 microns and usually contain once centrally located vacuole of lipid - the cytoplasm forms a circular ring around this vacuole, and the nucleus is compressed and displaced to the side. When fat cells have accumulated in such abundance that they crowd out or replace cellular and fibrous elements, the accumulation is termed adipose tissue. They are especially common along smaller blood vessels.
White fat cells are specialized for the storage of triglyceride, and occur singly or in small groups scattered throughout the loose connective tissue. This degranulation process is protective when foreign organisms invade the body, but is also the cause of many allergic reactions. In particular, they release large amounts of histamine and enzymes in response to antigen recognition. These cells mediate immune responses to foreign particles. Mast cells are granulated cells typically found in connective tissue. Macrophages phagocytose foreign material in the connective tissue layer and also play an important role as antigen presenting cells, a function that you will learn more about in Immunobiology. Macrophages are indistinguishable from fibroblasts, but can be recognized when they internalize large amounts of visible tracer substances like dyes or carbon particles. You will encounter each of these later in the course for now, make sure you recognize that they all descend from monocytes, and that the macrophage is the connective tissue version. This system consists of a number of tissue-specific, mobile, phagocytic cells that descend from monocytes - these include the Kupffer cells of the liver, the alveolar macrophages of the lung, the microglia of the central nervous system, and the reticular cells of the spleen. The macrophage is the connective tissue representative of the reticuloendothelial, or mononuclear phagocyte, system. More details and chondrocytes can be found later in this laboratory osteocytes will be covered in the Laboratory on Bone. Some fibroblasts have a contractile function these are called myofibroblasts.Ĭhondrocytes and osteocytes form the extracellular matrix of cartilage and bone. These cells make a large amount of protein that they secrete to build the connective tissue layer.
The fibroblast synthesizes the collagen and ground substance of the extracellular matrix. Although the connective tissue has a lower density of cells than the other tissues you will study this year, the cells of these tissues are extremely important.įibroblasts are by far the most common native cell type of connective tissue.
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