Your opponent stands ready as you prepare to hit the serve, but you are confident that you will smash the ball past your opponent. This, in turn, leads in many instances to interstitial, arteriolocapillary, or septal fibrosis. Among the cells that may be found in connective tissue are fibroblasts (flattened cells that produce and maintain the fibers and ground substance), macrophages (phagocytic cells), mast cells (which contain heparin and histamine), and fat cells. Connective tissue consists of cells, fibers, and ground substance. Lymph contains a liquid matrix and white blood cells.

They act as the great storehouse for the body of salts and minerals, as well as of fat. Polysaccharides and proteins secreted by fibroblasts combine with extra-cellular fluids to produce a viscous ground substance that, with embedded fibrous proteins, forms the extra-cellular matrix. (b) Dense irregular connective tissue consists of collagenous fibers interwoven into a mesh-like network. Under the microscope, tissue samples appear clear. Connective tissue is classified as connective tissue proper, osseous tissue, and cartilaginous tissue, depending on the composition of the cells and the type, properties, and orientation of intercellular structures. The external ear contains elastic cartilage. The detailed mechanisms underlying this are dealt with in Chapter 12, but briefly, although there are diverse specific pathogenic mechanisms driving age-related tissue events, there are a number of generic processes that explain the changes seen in most tissues. Platelets are cell fragments involved in blood clotting. LM × 800. Loose connective tissue, which fills the spaces between organs, vessels, nerves, muscles, and other body structures, forms the internal medium through which nutrients are delivered to cells and the products of metabolism are removed. Irregularly arranged connective tissue with fibers that are irregularly interwoven may be loose (areolar) or dense. Young athletes, dancers, and computer operators; anyone who performs the same movements constantly is at risk for tendinitis. Another type of connective tissue is rich in pigment cells (for example, in the choroid of the eye). Without mineral crystals, bones would flex and provide little support. The distinctive appearance of cartilage is due to polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans. The mast cell, found in connective tissue proper, has many cytoplasmic granules. Figure 1. Connective tissue provides structure and support and is a “space filler” for areas not occupied by other tissue. The fibrillar components are reticular fibers, collagenous fibers, and elastic fibers. It is also found between organs and as such contributes to the body's shape, plasticity, and partitioning. In recently formed wounds the collagen can be very immature and edematous with a variety of inflammatory cells, perhaps neutrophils. Adipocytes are cells that store lipids as droplets that fill most of the cytoplasm. A prime example is the macrophage, a cell type derived from circulating monocytes in the blood. Conversely, the elastic component allows an elastic stretch, or temporary elongation, with the tissue returning to its previous length when the stress is removed. In other tissues, stretching in several directions is achieved by alternating layers where fibers run in the same orientation in each layer, and it is the layers themselves that are stacked at an angle. Elastic connective tissue—predominance of elastic fibers or bands (ligamentum nuchae) or lamellae (aorta). Genetic defects of the fibrillin 1 (FBN1) gene present on chromosome 15 cause a multisystem connective tissue disorder known as Marfan’s syndrome. Bone is a highly vascularized tissue. They are found throughout the body, but are most abundant in the reticular tissue of soft organs, such as liver and spleen, where they anchor and provide structural support to the parenchyma (the functional cells, blood vessels, and nerves of the organ). The extracellular matrix (ECM) is found in the spaces between cells, forming a large proportion of tissue volume. Bruce M. Carlson MD, PhD, in The Human Body, 2019. These fibers are composed of protein macromolecules of tropocollagen that have a coiled helix of three polypeptide chains. This arrangement gives the tissue greater strength in all directions and less strength in one particular direction. Macrophages represent a major line of immune defense (see Chapter 8), and they also play an important role in the removal of damaged tissue. the ground substance & fibers make up the extracellular matrix. Collagenases are a group of enzymes that belong to the family of Zn2+-dependent proteolytic enzymes known as matrix metalloproteinases. 8. A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. The antibacterial activity of penicillin and other β-lactams is due to their inhibition of a transpeptidase that is required for cross-linkage of peptidoglycans.

Note the small blood vessels that permeate the tissue. These cells can differentiate into any type of connective tissue cells needed for repair and healing of damaged tissue. Radiation-induced changes in connective tissue involve, among other things, excessive deposition of collagen in tissues. Fibers of the extracellular matrix confer elastic properties on tissues such as large blood vessels, lungs and skin, which contain elastin and fibrillin. In contrast, white fat adipocytes store lipids as a single large drop and are metabolically less active. A thorough discussion of the composition of connective tissue is presented in Chapter 2. The condition causes pain and tenderness in the area around a joint. The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibers. Embedded within the cartilage matrix are chondrocytes, or cartilage cells, and the space they occupy are called lacunae (singular = lacuna). These veins open into the internal jugular vein and thus avoid first-pass metabolism. Lysozyme found in body fluids is microbicidal for certain gram-positive bacteria and the yeast Candida albicans. It consists of two groups of substances: (1) those probably derived from secretory activity of connective tissue cells including mucoproteins, protein-polysaccharide complexes, tropocollagen, and antibodies; and (2) those probably derived from the blood plasma, including albumin, globulins, inorganic and organic anions and cations, and water. The physiological functions of connective tissues are determined by the nature and organization of their extracellular components. Proper connective tissues have two sub-types. A few distinct cell types and densely packed fibers in a matrix characterize these tissues. The dominant fiber type is collagen. Most of the cells of the connective tissue are developmentally related even in the adult; for example, fibroblasts may be developed from histiocytes or from undifferentiated mesenchymal cells. Integrins link the intracellular cytoskeleton with the ECM through this RGD motif.

Loose connective tissue is found between many organs where it acts both to absorb shock and bind tissues together.
Many cells of the immune system leave the blood and reside in the connective tissues. Clusters of mesenchymal cells are scattered throughout adult tissue and supply the cells needed for replacement and repair after a connective tissue injury. The knee and jaw joints and the the intervertebral discs are examples of fibrocartilage. Connective tissues can have various levels of vascularity. Its extensive distribution and role in cell nutrition and protective processes make this tissue a participant in almost all of an animal’s physiological and pathological reactions, including inflammation, physiological and reparative regeneration, healing of wounds, and sclerotic processes. She issues a stern warning about the risk of aggravating the condition and the possibility of surgery. In case of severe pain, X-rays can be examined to rule out the possibility of a bone injury. Severe cases of tendinitis can even tear loose a tendon. It consists of cells, fibers & ground substances. In both of these roles, they are major facilitators of tissue regenerative responses after injury. In contrast, fixed macrophages are permanent residents of their tissues. Elastic fiber contains the protein elastin along with lesser amounts of other proteins and glycoproteins. The fibers found in connective tissue include flexible collagen fibers with high tensile strength, delicate reticular fibers, and elastic fibers, which can undergo extensive stretching. They occur in spaces between the fibers, the areolae. Connective Tissue Proper. Furthermore, it provides protection against infection, gives passage to nerve and blood vessels through other tissues and fixes organs together. They are largely responsible for the cohesion of the body as an organism, of organs as functioning units, and of tissues as structural systems. Connective tissue pervades the entire organism, ensuring its matricial interconnections and its structural stability.

Blood is a fluid connective tissue containing erythrocytes and various types of leukocytes that circulate in a liquid extracellular matrix. Bone’s rigid extracellular matrix contains mostly collagen fibers embedded in a mineralized ground substance containing hydroxyapatite, a form of calcium phosphate. Elastases belong to the family of serine proteases similar to trypsin and are found in exocrine pancreatic tissue and leukocytes. Reticular fiber is also formed from the same protein subunits as collagen fibers; however, these fibers remain narrow and are arrayed in a branching network. It provides protection to internal organs and supports the body. For the passionate athlete, it may be time to take some lessons to improve technique.

Examples are adipose tissue, blood, bone, cartilage, hematopoietic tissues, and lymphatic tissues. Osteocytes, bone cells like chondrocytes, are located within lacunae.
A structural characteristic of connective tissue is the presence of well-developed intercellular structures (fibers and ground substance).

In many sources, this type is listed as connective tissue proper; however, it is …