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Loose connective tissues are the most abundant in the body. In this general type of connective tissue (often divided into adipose, areolar, and reticular), the fibers are loosely woven and there are many cells. It is located around nerves and blood vessels, among others, and is composed of thin and relatively few fibers (collagenous, elastic, and/or reticular) and cell types, all embedded in a semifluid ground substance (Figure 3.1a). There are large numbers of cells and cellular processes, including fibroblasts, often adipocytes, immune cells, blood vessel and lymph vasculature cells, and neuronal processes (nerves) (Figure 3.1b). Functionally, this tissue provides cushioning, support, elasticity, and immune functions.

Table 3.1 General Features of Connective Tissues

Characteristic	Description
General types	Loose (adipose, areolar, reticular); dense (e.g., tendon, cartilage, and bone); fascia (e.g., epimysium)
Cells	Main cell types: Fibroblasts, adipocytes, resident macrophages, plasma cells
Extracellular matrix (ECM)	Main composition: Polysaccharides, water, glycosaminoglycans (GAGs), proteoglycans, glycoproteinsAdditional components: Collagen I/III, elastin, depending on subtype
Function	Envelops, separates tissues and cells, cushions, supports, immune function, and more

Figure 3.1 Loose and adipose connective tissues. (a) Loose connective tissue stained with hematoxylin and eosin (H&E). Elastic fibers (EF) and fibroblasts (F) are indicated. (b) Arteries and nerve in loose connective tissue (CT); H&E stained. (c) Adipose tissue near muscle fibers surrounded by dense fibrotic tissue induced by repetitive strain injury; Masson’s Trichrome stained. (d) Adipocytes around skeletal muscle fibers; H&E stained.