Cartilage (karati-lij) is a rigid connective tissue. It provides support, frameworks, attachments, protects underlying tissues, and forms structural models for many developing bones.
Cartilage matrix is abundant and is largely composed of collagenous fibers embedded in a gel-like ground substance. This ground substance is rich in a protein-polysaccharide complex (chondromucoprotein) and contains a large amount of water. Cartilage cells, or chondrocytes (konodro-sitz), occupy small chambers called lacunae and thus are completely within the matrix.
A cartilaginous structure is enclosed in a covering of connective tissue called perichondrium. Although cartilage tissue lacks a direct blood supply, blood vessels are in the surrounding perichondrium. Cartilage cells near the perichondrium obtain nutrients from these vessels by diffusion, which is aided by the water in the matrix. This lack of a direct blood supply is why torn cartilage heals slowly, and why chondrocytes do not divide frequently.
The three types of cartilage are distinguished by their different types of intercellular material. Hyaline cartilage has very fine collagenous fibers in its matrix, elastic cartilage contains a dense network of elastic fibers, and fi-brocartilage has many large collagenous fibers.
Hyaline cartilage (fig. 5.23), the most common type, looks somewhat like white glass. It is found on the ends of bones in many joints, in the soft part of the nose, and in the supporting rings of the respiratory passages. Parts of an embryo's skeleton begin as hyaline cartilage "models" that bone gradually replaces. Hyaline cartilage is also important in the growth of most bones and in repair of bone fractures (see chapter 7, page 206).
Elastic cartilage (fig. 5.24) is more flexible than hyaline cartilage because its matrix contains many elastic fibers. It provides the framework for the external ears and parts of the larynx.
Fibrocartilage (fig. 5.25), a very tough tissue, contains many collagenous fibers. It is a shock absorber for structures that are subjected to pressure. For example, fi-brocartilage forms pads (intervertebral disks) between the
Hyaline cartilage cells (chondrocytes) are located in lacunae, which are in turn surrounded by intercellular material containing very fine collagenous fibers (160x micrograph enlarged to 640x).
Fibrocartilage contains many large collagenous fibers in its intercellular material (450x micrograph enlarged to 1,800x).
individual bones (vertebrae) of the spinal column. It also cushions bones in the knees and in the pelvic girdle.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.