Epithelium is lining tissue. Keratin hardens squamous epithelium. Connective tissues consist of cells within a matrix. Fibroblasts secrete collagen and elastin. Loose connective tissue has loose collagen strands, whereas dense connective tissue has tightly packed collagen fibrils.
Adipose tissue consists of adipocytes hugely swelled with lipid.
The matrix of blood is plasma, which carries red blood cells, white blood cells, and platelets. Cartilage consists of chondrocytes in lacunae, in a collagen matrix. In bone, osteocytes communicate through canaliculi. Osteoclasts and osteoblasts tear down and rebuild bone tissue. Osteoprogenitor cells can become osteoblasts.