Cartilage is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bones at the joints, and is a structural component of the rib cage, the ear, the nose, the bronchial tubes, the intervertebral discs, and many other body components. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. 

Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body. Examples include the rings of the trachea, such as the cricoid cartilage and carina. 

Cartilage is composed of specialized cells called chondrocytes that produce a large amount of collagenous extracellular matrix, abundant ground substance that is rich in proteoglycan and elastin fibers. Cartilage is classified in three types, "elastic cartilage", "hyaline cartilage" and "fibrocartilage", which differ in relative amounts of collagen and proteoglycan. 

Cartilage does not contain blood vessels (it is avascular) or nerves (it is aneural). Nutrition is supplied to the chondrocytes by diffusion. The compression of the articular cartilage or flexion of the elastic cartilage generates fluid flow, which assists diffusion of nutrients to the chondrocytes. Compared to other connective tissues, cartilage has a very slow turnover of its extracellular matrix and does not repair. In embryogenesis, the skeletal system is derived from the mesoderm germ layer. Chondrification (also known as chondrogenesis) is the process by which cartilage is formed from condensed mesenchyme tissue, which differentiates into chondroblasts and begins secreting the molecules (aggrecan and collagen type II) that form the extracellular matrix.

1. What substance can cartilage be compared to?
2. Is it flexible or rigid?
3. Where is cartilage located in the body?
4. Anywhere else?
5. What is cartilage like compared to muscle?
6. What kinds of cells is cartilage made up of?
7. What are they called?
8. What do they produce?
9. How many types of cartilage are there?
10. How do they differ?
11. How do cartilage cells get nutrition?
12. How often does cartilage repair itself?
13. Does cartilage have blood vessels?

Numbered answers:
1. other connective tissues
2. flexibl
3. , the ear,
4. the rib cage
5. stiffer
6. specialized cells
7. chondrocytes
8. matrix
9. three
10. in relative amounts of collagen and proteoglycan
11. diffusion
12. never
13. no