Module 5: Cartilage and Bone
Learning Objectives:
By the end of this module, students will be able to:
- Classify the three types of cartilage based on the fibers that comprise them.
- Explain the two methods of cartilage growth.
- Describe the characteristics of the different types of bones.
- Compare and contrast the features of bone and cartilage.
- Summarize the two types of ossification.
- Describe the process of bone remodeling and repair.
- Explain how bone architecture can change with age.
Terms to Know
|
Bone
|
Bone (continued)
Cartilage
|
Two major forms of supportive connective tissue, cartilage, and bone, allow the body to maintain its posture and protect internal organs.
Cartilage
The distinctive appearance of cartilage is due to carbohydrates called chondroitin sulfates. Embedded within the cartilage matrix are chondrocytes or cartilage cells, and the spaces they occupy are called lacunae (singular = lacuna). A layer of dense irregular connective tissue, the perichondrium, encapsulates the cartilage. Cartilaginous tissue is avascular. Thus all nutrients need to diffuse through the matrix to reach the chondrocytes. This factor contributes to the prolonged healing (or lack of healing) of cartilaginous tissues.
The three main types of cartilage tissue are hyaline cartilage, fibrocartilage, and elastic cartilage. Hyaline cartilage, the most common type of cartilage in the body, consists of short and dispersed collagen fibers. Under the microscope, tissue samples appear clear. The surface of hyaline cartilage is smooth. Both strong and flexible, it is found in the rib cage and nose and covers bones where they meet to form moveable joints. It makes up a template of the embryonic skeleton before bone formation. A plate of hyaline cartilage at the ends of bone (growth plate) allows continued growth until adulthood. Fibrocartilage is tough because it has thick bundles of collagen fibers dispersed through its matrix. Menisci in the knee joint and the intervertebral discs are examples of fibrocartilage. Elastic cartilage contains elastic fibers as well as collagen. This tissue gives rigid support as well as elasticity. Tug gently at your ear lobes, and notice that the lobes return to their initial shape. The external ear contains elastic cartilage.
Bone
Bone is the hardest connective tissue. It protects internal organs and supports the body. Bone’s rigid extracellular matrix contains mostly collagen fibers embedded in a mineralized ground substance containing hydroxyapatite, a form of calcium phosphate. Both components of the matrix, organic and inorganic, contribute to the unusual properties of bone. Without collagen, bones would be brittle and shatter easily. Without mineral crystals, bones would flex and provide little support. Osteocytes, bone cells like chondrocytes, are located within lacunae. The histology of transverse tissue from long bone shows a typical arrangement of osteocytes in concentric circles around a central canal. Bone is