Cartilage (table 5.6) is a supportive connective tissue with a flexible rubbery matrix. It gives shape to the external ear, the tip of the nose, and the larynx (voicebox)— the most easily palpated cartilages in the body. Cells called chondroblasts16 (CON-dro-blasts) secrete the matrix and surround themselves with it until they become trapped in little cavities called lacunae17 (la-CUE-nee). Once enclosed in lacunae, the cells are called chondro-cytes (CON-dro-sites). Cartilage is free of blood vessels except when transforming into bone; thus nutrition and waste removal depend on solute diffusion through the stiff matrix. Because this is a slow process, chondrocytes have low rates of metabolism and cell division, and injured cartilage heals slowly. The matrix is rich in chon-droitin sulfate and contains collagen fibers that range in thickness from invisibly fine to conspicuously coarse. Differences in the fibers provide a basis for classifying cartilage into three types: hyaline cartilage, elastic cartilage, and fibrocartilage.
Hyaline18 (HY-uh-lin) cartilage is named for its clear, glassy microscopic appearance, which stems from the usually invisible fineness of its collagen fibers. Elastic cartilage is named for its conspicuous elastic fibers, and fibrocartilage for its coarse, readily visible bundles of collagen. Elastic cartilage and most hyaline cartilage are sur rounded by a sheath of dense irregular connective tissue called the perichondrium.19 A reserve population of chondroblasts between the perichondrium and cartilage contributes to cartilage growth throughout life. There is no perichondrium around fibrocartilage.
You can feel the texture of hyaline cartilage by palpating the tip of your nose, your "Adam's apple" at the front of the larynx (voicebox), and periodic rings of cartilage around the trachea (windpipe) just below the larynx. Hyaline cartilage is easily seen in many grocery items—it is the "gristle" at the ends of pork ribs, on chicken leg and breast bones, and at the joints of pigs' feet, for example. Elastic cartilage gives shape to the external ear. You can get some idea of its springy resilience by folding your ear down and releasing it.
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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.