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.
The dermis of the skin is an example of dense irregular connective tissue rich in collagen fibers. Dense irregular elastic tissues give arterial walls the strength and the ability to regain original shape after stretching Figure 4. The distinctive appearance of cartilage is due to the presence of polysaccharides called chondroitin sulfates, which bind with ground substance proteins to form proteoglycans. A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage.
Cartilaginous tissue is avascular, thus all nutrients need to diffuse through the matrix to reach the chondrocytes. This is a factor contributing to the very slow healing of cartilaginous tissues.
The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage Figure 4.
Hyaline cartilage , the most common type of cartilage in the body, consists of short and dispersed collagen fibers and contains large amounts of proteoglycans. Under the microscope, tissue samples appear clear. The surface of hyaline cartilage is smooth.
Both strong and flexible, it is found in the rib cage and nose and covers bones where they meet to form moveable joints. It makes up a template of the embryonic skeleton before bone formation. A plate of hyaline cartilage at the ends of bone allows continued growth until adulthood. Fibrocartilage is tough because it has thick bundles of collagen fibers dispersed through its matrix.
The knee and jaw joints and the the intervertebral discs are examples of fibrocartilage. Elastic cartilage contains elastic fibers as well as collagen and proteoglycans.
This tissue gives rigid support as well as elasticity. Tug gently at your ear lobes, and notice that the lobes return to their initial shape. The external ear contains elastic cartilage. Bone is the hardest connective tissue.
It provides protection to internal organs and supports the body. Both components of the matrix, organic and inorganic, contribute to the unusual properties of bone. Without collagen, bones would be brittle and shatter easily. Without mineral crystals, bones would flex and provide little support.
Osteocytes , bone cells, are located within lacunae. The histology of transverse tissue from long bone shows a typical arrangement of osteocytes in concentric circles around a central canal Figure 4.
Bone is a highly vascularized tissue. Unlike cartilage, bone tissue can recover from injuries in a relatively short time. Cancellous bone looks like a sponge under the microscope and contains empty spaces between trabeculae, or arches of bone proper. It is lighter than compact bone and found in the interior of some bones and at the end of long bones.
Compact bone is solid and has greater structural strength. Blood is a fluid connective tissues. Blood has two components: cells and fluid matrix Figure 4. Erythrocytes, red blood cells, transport oxygen and some carbon dioxide. Leukocytes, white blood cells, are responsible for defending against potentially harmful microorganisms or molecules. This type of tissue contains many cells, a loose arrangement of fibres, and moderately viscous fluid matrix. This is an example of dense irregular connective tissue.
It is the layer of skin underneath the epidermis, called the dermis. It contains collagen fibres and fibroblasts. Also at the top of the picture not labelled you can see a small capillary - can you find it? This type of tissue contains a dense woven network of collagenous and some elastic fibres in a viscous matrix.
It is found in joint capsules, in the connective tissue that envelops muscles muscle fascia , and it forms dermis of skin. It is impact resistant. Look at this image and make sure you can recognise loose and dense connective tissue. This is an example of dense regular connective tissue.
Distinguish the connective tissues from all epithelial tissues on the basis of location, cell density and the presence of discrete fibers. Distinguish between loose irregular areolar , dense irregular, or dense regular connective tissues on the basis of fiber packing and orientation.
Identify, at the light and electron microscopic levels, collagen, reticular, and elastic fibers. Identify and list the cell types found in the various kinds of general connective tissues, and describe their origins and functions.
The common fiber types include collagen, elastic, and reticular. Slide 43 Thick Skin, Sole of the Foot. They tend to have a wavy appearance and may be sectioned obliquely, transversely or longitudinally. Nuclei of fibroblasts fibrocytes are numerous among the collagen fibers. Slide 92 Thick Skin, Monkey Finger. Again note the wavy collagen fibers of the dermis in this slide of thick skin.
Slide 47 Submaxillary Gland, Verhoeff's Hematoxylin. Elastic fibers stain black with Verhoeff's Hematoxylin and are seen as branching black lines. In this slide, the elastic fibers are clearly visible around ducts and vessels collagen fibers are green. Both elastic and collagen fibers and various connective tissue cells are visible in this preparation. Verhoeff's Hematoxylin stains elastic fibers black and Van Gieson stains collagen acidophilic. In your slide the acidophilic collagen fibers may not be obvious.
Mast cells are easily identified due to the metachromasia of granules with toluidine blue. Slide 79 Spleen, Reticular stain.
However, these fibers stain black with silver stain and are often called argyrophilic fibers. The spleen demonstrates the supportive network of reticular fibers present in many organs. This slide demonstrates both collagen red and reticular black fibers. The common cell types in connective tissue include: fibroblasts, mast cells, plasma cells, macrophages, adipocytes, and leukocytes.
Slide 72 Tendon. Fibroblasts are the most common cell type of connective tissue.
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