Begin with slides 8 (trachea), 45 (nose) and 91 (lung) of canine hyaline cartilage. All three examples are of mature cartilage. Note the basophilic staining areas in the matrix of the cartilage in Slides 8 and 91. What component(s) of the extracellular matrix would stain basophilic?
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Slide 90 is of canine epiglottis, a part of the body containing elastic cartilage.
The epiglottis is unique in that it is the only place in the body where cartilage forms a marrow cavity. In this preparation the elastic fibres permeating the matrix are clearly visible although they are poorly stained. Q: How would you classify the epithelium surrounding the epiglottis? |
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Slide 74 is of a guinea pig joint.
We'll examine it again later for the structure of bone and the joint cavity; for now, let's look at articular cartilage and fibrocartilage. Study the slide at low power to orient on the two ends of bones, the joint capsule of DWFCT that holds the bones together, and the articular cartilage. Q: What is unique about articular cartilage? Fibrocartilage can be found where tendons, ligaments and joint capsules attach to bones. When you think you have found some, please call one of us to confirm your diagnosis. |
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Bone tissue can be presented in a variety of manners. Slides 14 and 50, for example, are of mature, dried, ground bone. This was prepared by taking a bone fragment, drying it, and holding it against a grind stone until it was about 15 µm thick.
CAUTION: THESE SLIDES ARE THICK. DO NOT USE HIGH POWER OBJECTIVES.
Bone dust and debris fill the spaces where vessels and living cells once existed. Compare this longitudinal section of dried bone to pictures in your textbook to learn to recognize canaliculi, lacunae, osteonal (Haversian) canals, connecting (Volkmann's) canals, cementing lines and interstitial bone. Then repeat the exercise with slide 50, which is a similar preparation in cross section instead of longitudinal section.
Slide 74 also demonstrates bone remodelling and the cells of bone can now be seen. The slide shows active osteoblasts on the outer circumference of the diaphyseal bone, and osteoclasts on the inside, indicating a growing bone. Along the edges of the marrow cavities you will be able to locate and compare osteoclasts and megakaryocytes.
| Lower jaw bone forms almost exclusively from membrane bone. To study membrane bone growth, turn to our old friends slides 6 and 17. Look around the developing teeth for mesenchymal "membranes" which will later become periosteum, and for spicules of bone, osteoblasts, osteocytes and osteoclasts. Osteoclasts are easier to find on slide 17 because it is a thicker section. Compare with Figure 5-1 in the atlas. |  |
Slide 74 shows endochondral ossification. Both bones in this section have growth plates, remnants of cartilage that will continue to grow and provide cartilage upon which bone will form. Look in these regions for zones of rest, hyperplasia, hypertrophy, degradation, calcification and replacement. The atlas will be of assistance in this exercise, particularly Figure 5-6, page 24.
Secondary bone growth is also occurring in this tissue...from the "bottom" of articular cartilage, bone is forming to expand the epiphyseal region so that its size will remain in proportion to the rest of the growing bone.
Slides 74 contains good examples of the synovial membranes , internal ligaments, and joint capsule CT. These elements comprise the joint cavity, secrete its synovial fluid, provide strength for joint integrity and phagocytic capability to maintain aseptic conditions. All of the components are of mesodermal origin, including the synovial epithelia. Synovial epithelium is composed of two kinds of cells, both of which can be seen in these slides. F-cells are low cuboidal or squamous in shape. They get their name from being fibroblast-like. They secrete synovial fluid. M-cells are macrophage-like. They are larger and more cuboidal in shape, frequently found at the periphery of the synovial space. In addition to lining the capsule, they are phagocytic.
The loose-to-variably dense connective tissue around joints is well vascularized to provide fluid and nutrients to the joint space and articular cartilage. There is considerable opportunity for an acute inflammatory response in such a vascularized tissue, explaining the stiffness and tenderness of joints that frequently accompanies systemic infections such as flus.
| Slide 76 is of vertebrae from a guinea pig. It has excellent examples of bone, bone marrow, endochondral bone formation, young periosteum, skeletal muscle attaching to bone, and the disks in between the vertebrae. Disks are composed of an inner nucleus pulposis, a remnant of the notochord consisting of much ground substance rich in hyaluronic acid and a few mesenchymal cells, and an outer anulus fibrosis which is composed of dense CT and fibrocartilage blending into the nearby bones. The combination of dense, strong outer capsule and mushy core creates an ideal shock absorber. Look for these features on slide 76. |  |
In addition, slide 76 also may include part of the aorta and the spinal cord. Look for them if you wish as an optional exercise. The class set of slide 76 is half of H&E and half of Masson's trichrome stain. After examining your own slide, swap with someone who has the other stain.
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