Cartilage and Connective
YOUR JOB DURING THIS LAB: After completing this assignment you should be able to (a) recognize the different types of cartilage under the light microscope and indicate the cell types present; (b) describe the areas where you might expect to find the different forms of cartilage and why; (c) identify areas containing the major forms of collagen, particularly types I, II, III, and IV and (d) identify the major types of connective tissue fibers and understand their molecular composition. You should also be able to identify dense regular CT, dense irregular CT, loose CT and mucous CT at the level of the light microscope.
CARTILAGE IN ITS VARIOUS FORMS
Images to introduce hyaline cartilage
Glass slides to view hyaline cartilage.
Slide #93 - trachea: Very similar to image D4, this shows hyaline cartilage to very good advantage. You should identify the perichondrium (which may in some places be pulled away), the cells and lacunae, and the extracellular matrix material. Do you think this cartilage was actively growing when the sample was prepared? On what basis did you decide?
Slide #90 - nasal cavity: This is a good slide on which to conduct a mini-review for yourself. The hyaline cartilage should be obvious as masses of blue, translucent material. Also, locate the epithelium and classify it. Look at the surrounding connective tissue and classify it. Find the glandular ducts; what could they be doing? What do you think the dark pink masses represent?
Hyaline cartilage on this slide is predominantly young, as evidenced by usually only one chondrocyte per lacuna and the presence of a chondrogenic layer (visible sometimes in oblique section with large euchromatic nuclei).
- developing bone/extremities: USE LOW MAGNIFICATION FOR THIS SLIDE in
order to orient yourself. Find the hyaline cartilage "model"
upon which bone development is occurring (endochondral ossification). On
some slides, both the outer fibrous layer of the perichondrium with
flattened fibroblasts and the inner chondrogenic layer with chondroblasts
having ovoid, euchromatic nuclei will be visible.
Images to introduce elastic cartilage.
Glass slides on which to find elastic cartilage.
Slide #56 - external ear: Locate at low power the blue stained regions of elastic cartilage. Note the occasional vertical deeply stained regions. What do you think they are; are they "real"? (NO, they are simply folds that occurred when the tissue was placed on the slide - practice will allow you to distinguish biological information/structure from preparation artifacts.) Observe the change in shape and size of the chondrocytes as they become progressively enclosed by matrix. How does this cartilage compare with the hyaline cartilage examined previously? Why are the elastin fibers hard to visualize here?
Slide #17 - elastic cartilage: This slide of the epiglottis has been selectively stained in order to visualize the elastin fibers. Orient yourself at low magnification and look at the elastic cartilage in the center of the tissue. This is also a good slide to look at other structures - find the elastin fibers in the surrounding connective tissue, for example.
- vocal folds/epiglottis: Use the orientation diagrams included here to
find the epiglottis. Compare the areas of hyaline cartilage with those of
elastic cartilage. Examine the cartilage of the epiglottis at high power
and try to locate the poorly stained elastin fibers.
Image of fibrocartilage.
Glass slide for fibrocartilage.
Slide #18/18A - pubic symphysis: Fibrocartilage is found at transition areas between hyaline cartilage and dense regular CT. Most of the cartilage here is hyaline cartilage, with only small regions of fibrocartilage located on each side, as the hyaline cartilage merges into the surrounding CT. Note the eosinophilic staining of the matrix caused by the large number of collagen fibers and the absence of any perichondrium. If you have slide #18A, compare the appearance and organization of the fibrochondrocytes there with those shown in your text Plate 15 (Ross & Romrell).
TYPES OF CONNECTIVE TISSUE AND FIBRILLAR PROTEINS
Dense Regular Connective Tissue
This form of CT is characterized by relatively few cells, embedded in extensive amounts of extracellular material, most of which will be regularly arranged collagen fibers. Dense CT is found wherever unidirectional tension must be supported; for example, in tendons connecting muscle and bone, in aponeuroses where specialized tendons connect muscle and bone, and in ligaments.
Images to introduce regular dense connective tissue.
Slide #11 - aponeuroses: here the collagen bundles and fibroblasts are arranged in multiple layers or sheets. Within each layer the fibers follow a parallel wavy course, with the exact direction of the fibers slightly different in different layers. Collagen fibers often go from one layer into an adjacent layer. THE DENSE REGULAR CT IS ORGANIZED IN A REASONABLY WELL DEFINED BAND - THE REST OF THE UNDERLYING CT ON THIS SLIDE IS DENSE IRREGULAR CT.
Slide #13 - skeletal muscle and tendon: Here the muscle is stained much darker than the tendon; today look at the tendon region of the slide.
This tissue is characterized by relatively few cells embedded in collagen fibers, with the fibers not arranged as uniformly as noted in the previous slides. Dense irregular connective tissue is very common, much more so than is dense regular CT.
Image for dense irregular CT.
Slide #59 - thin skin: A thick band of loose fibrous CT is located beneath the stratified squamous keratinized epithelium. Note the paucity of nuclei in relation to collagen fiber bundles. Much dense irregular CT is also seen on this slide.
Remember that there are three types of fibers seen histologically; collagen fibers, elastin fibers and reticular fibers. Reticular fibers are similar in biochemical composition to collagen fibers, but will stain differently when placed in alkaline silver salts.
Images for CT fibers
Glass slides for CT fiber observation.
Slide #9 - mesentery: This is not a section, but rather a whole mount of the mesentery, a thin membranous area of loose connective tissue. The elastin fibers, here unstained by the routine H & E preparation, can be seen as faint glassy fibers forming a network throughout the tissue.
Slide #80 - aorta: Here, in contrast, the elastin fibers can be seen even with the naked eye (although not resolved) as a thick purple/black band.
Slide #11 and Slide #59: You have viewed these already, but they are good examples of the appearance of collagen fibers. Almost any slide that you examine in your collection will exhibit some collagen fibers - try one or two at random and look.
Slide #14 - reticular tissue: This shows the reticular fibers in lymphoid tissue, stained selectively. Compare this slide with:
- lymph node: Here in an H & E preparation the reticular fibers are
not very noticeable.
Mucous Connective Tissue
This type of CT has fibroblasts embedded in a viscous ground substance. The appearance of this type of tissue alters as the tissue ages.
Image for mucous CT.
Glass slides for mucoid CT.
Slide #12 - umbilical cord: This slide shows a large blood vessel, look at low magnification for the tell-tale red blood cells in the lumen, surrounded by mucoid CT. For now, concentrate on the structure of the latter tissue type.
Slide #195 - placenta: Here the CT is mesenchymal, having more mesenchymal cells per unit area than fibroblasts present in the true mucoid CT. The ground substance here is also less viscous than seen in mucoid CT; therefore, it stains poorly.
Loose CT is characterized by a much more cellular aspect; there are usually more cell nuclei in relation to the amount of extracellular fibers, those fibers present are not organized regularly, and the cellular composition is usually more diverse than seen in dense or mucoid CT.
Images to introduce loose CT.
Glass slide for loose CT.
Slide #9 - mesentery: This is, again, a whole mount, not a section.