Based on morphology and function, the tissues of the body are classified into four basic kinds: epithelial, nervous, connective, and muscle tissue:1
Epithelial tissue is found throughout the body in two forms: membranous and glandular.
- Membranous epithelium forms such structures as the outer layer of the skin, the inner lining of the body cavities and lumina, and the covering of visceral organs.
- Glandular epithelium is a specialized tissue that forms the secretory portion of glands.
Nervous tissue (see Chapter 9) helps coordinate body movements via a complex control system of prestructured motor programs and a distributed network of reflex pathways mediated throughout the CNS.2
The primary types of CT cells are macrophages, which function to cleanup debris (phagocytes); mast cells, which release chemicals associated with inflammation; and the fibroblasts, which are the principal cells of CT.3
Connective tissue (CT) is found throughout the body. CT serves to provide structural and metabolic support for tissues and organs of the body. Connective tissue includes bone, cartilage, tendons, ligaments, and blood tissue.
The CT types are differentiated according to the extracellular matrix (ECM) that binds the cells:1
- Embryonic CT
- Connective tissue proper
- Loose CT
- Dense regular CT
- Dense irregular CT
- Elastic CT
- Reticular CT
- Adipose CT
- Cartilage and bone tissue
- Hyaline cartilage
- Elastic cartilage
- Blood (vascular) tissue
Connective tissue proper (CTP) has a loose, flexible matrix called ground substance. The most common cell within CTP is the fibroblast. Fibroblasts produce collagen, elastin, and reticulin fibers. Collagen and elastin are vital constituents of the musculoskeletal system.
The collagens are a family of ECM proteins that play a dominant role in maintaining the structural integrity of various tissues and in providing tensile strength to tissues. The major forms of collagen are outlined in Table 5-1.4
Table 5-1. Major Types of Collagen |Favorite Table|Download (.pdf)
Table 5-1. Major Types of Collagen
Bone, skin, ligament, and tendon
Cartilage, nucleus pulposus
Blood vessels, gastrointestinal tract
CT disorders include systemic lupus erythematosus (see Chapter 8), rheumatoid arthritis (see later), spondyloarthropathies (eg, ankylosing spondylitis—see Chapter 8, Reactive arthritis—see later), polymyalgia rheumatica, polymyositis, and dermatomyositis (see Chapter 13), scleroderma (see Chapter 13), Sjögren's syndrome (see later), crystal-induced arthropathies (eg, gout—see Chapter 8), and juvenile rheumatoid arthritis (see later).
Elastic fibers are composed of ...