This is of a particularly loose version of CT, loose meaning flexible and distendable. These properties are created by having small collagen fibres and numerous elastic strands. (As a trade-off, loose, irregular CT is not particularly strong, but strength is not its purpose.) This is typically found in the mesenteries, between muscle groups, and the axillary region. It is the white, cob-web like material that holds tissues and organs in place.


In this preparation, you should be able to identify:

• long, occasionally branching elastic fibres
• irregular, shorter, thicker collagen (Type I) fibres
• mast cells, with their cytoplasm filled with granules
• fibroblasts, aligned along the collagen bundles
• macrophages, or at least their euchromatic nuclei and
• occasional capillaries, and maybe a nerve trunk.

If you compare your slide material with Figs. 13-100 and 13-104 in the atlas, you'll appreciate that the epithelial layer is organized into finger-like projections called villi (#13 in Fig 13-104). Beneath the villi is a layer of denser CT called the submucosa (#12 in Fig 13-104). The connective tissues in the villi and the submucosa provide excellent contrasts in types of irregular CT.

Within villi, there are few fibres, many cells, and an abundance of lymph fluid percolating through. The cells tend to be quite separate, making their identification easier. You should be able to locate:

• mast cells (large, ovoid eosinophilic cells)
• macrophages (often with lipofuschin granules in their cytoplasm)
• lymphocytes
• plasma cells
• smooth muscle cells
• fibroblasts
• granulocytes (without Wrights stain, they are difficult to distinguish)
• endothelial cells lining blood and lymph capillaries

In contrast, the submucosa is composed mainly of collagen bundles, with attendant fibroblasts. The difference is quite striking, and reflects the functions of these two layers of the gut!

Slide 64 - dense, irregular CT

This specimen is a cross section through the foot of a guinea pig. Visible to the eye are the three metacarpal bones, a large pink central mass of skeletal muscle, and the thicker, denser epithelium of the plantar surface. Our objective is to locate the dermis or dense irregular CT just under the thick epithelium of the foot pad.

In contrast to the last slide, this region has quite dense, irregular CT.

Other forms of CT are also found on this slide. Use the diagram below to locate bone, tendon (dense, regular), and adipose CT.

An aspect of histology that is difficult to teach, but which shows on this slide, is that CTs come in all densities and degrees of regularity. Tendon is very dense, regular collagen bundles. The dermis beneath the footpad is dense, irregular CT. The periosteum surrounding bone is intermediate in both alignment of collagen fibres and density. The CT surrounding other structures, such as the fat cells, the glands, and the skeletal muscles, tends to be quite loose, to allow for movement.

Slide 18 is of dense, regular CT. (Loose, regular CT doesn't normally exist) Dense, regular CT is better known as tendon and ligament, and is composed of large bundles of aligned collagen. Grossly, they appear white...hence the term white fibrous CT. Examine the XS and LS portions, noting: paucity of vasculature large diameters of collagen bundles parallel arrays of collagen

Dancing Tendons! Notice how the connective tissue appears to 'dance' as you move up and down the focal plane.

Slide 19 is of yellow, fibrous CT, or elastic ligament. These are of importance in the equine suspensory apparatus and the nuchal ligament. In this tangential cut, the frayed ends of the elastic fibres take on a curved, splayed appearance. There are more fibroblasts, to maintain elastic filaments that become torn.

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On to adipose and reticular CT