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Connective Tissue

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Slide 1: Section shows, on the right side, active fibroblasts with oval nuclei and abundant densely staining cytoplasm surrounding a paraffin pellet, which has been extracted during slide preparation. On the left side (nearest the oval-shaped blood vessel), less active fibroblasts with elongate nuclei and thin strands of cytoplasm can be seen. Other cells are also present. Not all cells are identifiable.  

Slide 2: Fibroblasts (elongated dark nuclei and scant cytoplasm) are often oriented along collagen bundles in this irregular C.T. Also here are nuclei of migrant cells (not unambiguously identifiable) and endothelial cells lining blood vessels. The apparently empty spaces between cells and fiber bundles in life are occupied by ground substances which are extracted during the preparation of routine paraffin-embedded sections.  

Slide 3: EM of a fibroblast sectioned through its nucleus and the processes of another fibroblast surrounded by bundles of collagen fibers in various orientations. At the lower part of the image is a free surface covered by a thin mesothelial cell (cytoplasm only in this section).  

Slide 4: This high magnification, plastic embedded section shows fibroblasts, collagen bundles and mast cells. (Yup, you noticed, slide 4 does not exist...)  

Slide 5: Mast cells in mesentery are seen along blood vessels, whole mount, Giemsa stain. See text with Slide 3-32.  

Slide 6: TEM of loose connective tissue containing a mast cell and fibroblasts.  

Slide 7: A higher magnification of the mast cell in slide #7 to show granule details. Note the 'scrolled' appearance of many of the granule contents.  

Slide 8: Reticular cells are a special type of fibroblast. They have large nuclei and long cytoplasmic processes and are especially visible in the clear part of this field. Macrophages with ingested material are also visible. Most of the small cells, with densely staining nuclei and hardly any visible cytoplasm, are lymphocytes.  

Slide 9: Adipocytes (white or unilocular fat cells) and small blood vessels. Note that only one adipocyte (at the top) is sectioned through its nucleus. plastic-embedded section.  

Slide 10: TEM image of part of an adipocyte, with lipid extracted. Note the lack of a membrane separating the lipid from the rest of the cytoplasm, the sparse organelles and the external lamina.  

Slide 11: Macrophages in spleen. Ti02 injected animal. Note the brown particulate material in the cytoplasm of phagocytic cells. The vast majority of cells in this image are lymphocytes and other immune system cells in this organ which is a filter of blood. In the light microscope macrophages can rarely be identified unambiguously unless they contain phagocytosed material (lysosomal enzymes cannot digest titantinum dioxide).  

Slide 12: Macrophages (Kupffer cells) in liver. Ti02 injected animal.  

Slide 13: TEM, Macrophage (in human bronchus-note the cilia of the epithelial lining). Note the residual bodies (how are these formed? ; remember Cell Biology!), the many heterolysosomes and irregular nuclear profile. Lung macrophages migrate through the epithelium in the gas exchange regions and are cleared up the airways. That is why this macrophage is on an epithelial free surface and not in a connective tissue.  

Slide 14: TEM of a macrophage in lung of a smoker. Note the numerous membrane infoldings and the large number of lysosomes. The more electron dense granules are probably residual bodies of lysosomes. When smokers inhale the particulates of cigarette smoke where do you think that they go?  

Slide 15: Giant cells are multinucleate cells resulting from the fusion of many macrophages as they attempt to engulf material too large for their size. In this case the foreign substance is the fibrils of thread sewn through the skin of an animal (forming a structure called a thread granuloma). Note the cross and oblique sections of the thread fibrils (colorless) with giant cells wrapped part way or all the way around them.  

Slide 16: Lymphocytes are small cells with densely staining, fairly round nuclei and very sparce cytoplasm. Plasma cells are larger and have eccentric nuclei and often a light staining, Golgi containing region adjacent to the nucleus. These are antibody secreting cells that develop from one type of lymphocyte. Polymorphs or neutrophils can be identified by their multilobulated nuclei. In this connective tissue you should be able to identify good examples of each of these cell types as well as resident fibroblasts.  

Slide 17: Higher magnification image than slide 17. Note the nuclear lobulation of the polymorphs. There are also some lymphocytes present. The very large cell may be a macrophage.  

Slide 18: This high magnification image has a large number of plasma cells. Note the light juxtanuclear region often visible and occasionally the "cartwheel" appearance of some nuclei.  

Slide 19: Lymphocytes and plasma cells are often found in the connective tissue underneath the lining of the large intestine. Note also that there are occasional intraepithelial lymphocytes. What type is the epithelium? (Ans. Simple columnar epithelium with goblet cells.)  

Slide 20: T.E.M. of a plasma cell in loose connective tissue. Note the dilated RER; Golgi region is not in this section.  

Slide 21: What is the epithelium type? (Ans. stratified squamous, non-keratinized epithelium). Find some of the invading lymphocytes and polymorphs.  

Slide 22: Collagen bundles (type I) are extensively found in the capsule (to the left of the image) and reticular fibers (type III) are also found in the capsule and are the fibers of the stroma of the lymph node. In an H&E stained section, such as this, the two different types of fibers cannot be distinguished morphologically. The light area under capsule is the subcapsular sinus (which is a diagnostic feature for lymph nodes). Compare this image with Slide 24 which is stained for reticular fibers.  

Slide 23: The area in this image is analogous to the one in the previous transparency. Silver impregnation stains the reticular fibers dark brown to black.  

Slide 24: Reticular fibers are the CT fibers of the stroma of the liver lobules (remember Cell biology?). Reticular stain.  

Slide 25: Stroma of the cornea. On the surface is a simple squamous epithelium. The collagen bundles are ordered and the fibroblasts (only their blue nuclei are clear) are flattened between the bundles.  

Slide 26: TEM of a bundle of collagen fibers in longitudinal section. Note the periodicity.  

Slide 27: TEM of several elastic fibers in cross section among bundles of collagen fibers (also in cross section) and parts of a fibroblast. Note the elastin (amorphous central region) and microfibrillar (on surface) portions composing each elastic fiber.  

Slide 28: The elastic fibers in this image are stained darkly blue with Verhoff stain. (dermis of skin)  

Slide 29: TEM, Fibroblast and adjacent matrix containing banded interstitial collagen fibers and microfibrils (not banded but they appear hollow - note a bundle right next to the fibroblast).  

Slide 30: Mesenchyme beneath embryonic skin. Note the thin-walled developing blood vessels (spaces lined by simple squamous epithelium). Find the mesenchymal cell in anaphase of mitosis.  

Slide 31: Most of this image is mesenchyme. Note the stellate cells with intensely stained perinuclear cytoplasm and occasionally visible cytoplasmic processes. The mesenchymal matrix is composed mostly of ground substance with few fibrous elements. To the corner of the field the mesenchyme is "condensing" into an area of developing bone (see Unit 4 part II Slide 3). Compare with 3-29.  

Slide 32: This "mucous" connective tissue does not contain any mucus! It has fewer cells and more ground substance than mesenchyme and its ground substance is rich in hyaluronic acid. It is found in only a few regions of an embryo (umbillcal cord).  

Slide 33: Loose connective tissue at low power as seen in a mesentery whole mount. Note the blood vessels. This is from microscope slide 100 in the slide boxes of those of you lucky enough to have it. No micrograph can do justice to this thick slide; this is one instance where examining the actual microscope slide will teach you much more!  

Slide 34: Loose connective tissue. (Endometrium). Note the extensive cellularity and relative paucity of fibers. The columnar epithelium is part of an endometrial gland.  

Slide 35: Dense irregular connective tissue. The overwhelming bulk of this tissue is collagen. Also, a few blood vessels and other unidentifiable (for now!) structures.  

Slide 36: In this low power slide, find and compare the loose connective tissue regions immediately surrounding the mammary gland secretory elements with the dense, more fibrous regions (dense irregular connective tissue) separating the lobules.  

Slide 37: Dense irregular connective tissue and adipose connective tissue (breast) The field also shows some ducts and glandular elements.  

Slide 38: Dense regular connective tissue of a developing tendon. Note active fibroblasts (tendon cells) with abundant cytoplasm and juxtanuclear Golgi areas. Toluidine blue and acid fuchsin stain (faded); plastic embedded section.  

Slide 39: Dense regular connective tissue. Mature tendon. The cornea also has dense regular CT- see Slide 3-25a. Compare tendon cells with those in slide #33 and #37.  

Slide 40: Reticular connective tissue forms the stroma of a lymph node. Reticular CT contains both reticular cells (a special type of fibroblast) and reticular fibers (cf slides #9, 24). Do you always have reticular connective tissue when you find reticular fibers? (Ans. No, reticular fibers are also found in other adult CT types and are made by other types of fibroblasts).  

Slide 41: Adipose connective tissue. Note that this adipose tissue contains brown (mutlilocular) and white fat cells (typical of embryos and newborns, not most adult adipose tissue which is of the unilocular (white) type.


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