Describe the general characteristics of connective tissues that set them apart from other animal tissues.
Connective tissues are characterized by several features that distinguish them from epithelial, muscular, and nervous tissues:
1. Abundant Extracellular Matrix: They have a relatively sparse population of cells scattered within a large amount of non-living extracellular material (matrix), which can be fluid, gel-like, or solid.
2. Diverse Cell Types: They contain various cell types (e.g., fibroblasts, adipocytes, chondrocytes, osteocytes, blood cells) specific to the type of connective tissue.
3. Origin: They all originate from the mesoderm germ layer.
4. Vascularity: Most are well-vascularized (have a good blood supply), though some, like cartilage, are avascular.
5. Functions: They primarily support, bind, protect, insulate, and transport substances.