Difference Between Bone and Cartilage

Main Difference – Bone vs Cartilage

Bone and cartilage are two types of connective tissues. They are made up of cells and extracellular matrix. Both bones and cartilages provide support and surfaces for the muscle attachment. They also protect the internal organs of the body. Bones and cartilages, along with the skeletal muscles, form the skeleton of vertebrates. Bones and cartilage differ by structure, cell types, types, and function. The main difference between bone and cartilage is that bone is a type of strong and nonflexible connective tissue whereas cartilage is a type of flexible connective tissue. There are two types of bones known as compact bone and spongy bone. The three types of cartilages are hyaline cartilage, fibro cartilage, and elastic cartilage. Cartilages act as shock absorbers. They can be found in the ear, nose, larynx, trachea, ribs, and joints.  

Key Areas Covered

1. What is Bone
      – Definition, Characteristics, Function
2. What is Cartilage
      – Definition, Characteristics, Function
3. What are the Similarities Between Bone and Cartilage
      – Outline of Common Features
4. What is the Difference Between Bone and Cartilage
      – Comparison of Key Differences

Key Terms: Bone, Cancellous Bone, Cartilage, Compact Bone, Connective Tissue, Elastic Cartilage, Fibro Cartilage, Hyaline Cartilage, Skeleton, Spongy Bone

What is a Bone

A bone is any rigid connective tissue that forms the skeleton of vertebrates. Bones are a type of living tissues, consisting of blood vessels and cells. At birth, humans have around 300 bones. In adolescence, the number of bone is reduced to 206. The main function of bones is to provide the structural support. Bones also protect the internal organs of the body. They serve as a storage of minerals as well. In addition, bones provide areas for marrow, which produce blood cells. A bone is composed of four components. They are the bone forming osteoblasts and osteocytes, bone resorbing osteoclasts, the nonmineral matrix or osteoid, and calcium deposited matrix. Two zones of bone can be identified based on the bone mineralization; these are hard outer layer and the spongy inner layer. The outer layer of the bone is called cortical or the compact bone. The inner layer is called trabecular or the cancellous bone. The outer layer of the bone is denser than the inner layer. A diagram of a compact bone is shown in figure 1.

Figure 1: Compact Bone

The osteoid is composed of 94% of type I collagen and other proteins. The calcified bone is composed of 25% organic matrix with the cells, 70% of the inorganic mineral, hydroxyapatite, and 5% of water. The hydroxyapatite is a crystalline form of calcium and phosphate. Two types of bones can be identified based on the pattern of collagen in the osteoid; woven bone and lamellar bone. The woven bones are mechanically less strong and contain a haphazard type of arrangement of collagen fibers. The lamellar bones are strong and contain a regular parallel arrangement of collagen fibers.

Figure 2: Bone remodeling

The growth of the bone occurs by a process called osteogenesis. The two types of osteogenesis are intramembranous ossification and endochondral ossification. The intramembranous ossification produces flat bones such as skull, mandible, and clavicle by replacing the connective tissue layer, which surrounds the bone. The endochondral ossification produces the long bones such as humerus, radius, femur, and tibia by replacing the hyaline cartilage. Bone modeling is the formation of new bones during childhood and adolescence. Bone remodeling is a combination of bone formation and bone resorption, which occurs during the replacement of new bones. Bone remodeling is shown in figure 2. 

What is Cartilage

Cartilage is a flexible, fibrous connective tissue, which is mainly found in the larynx, respiratory tract, external ear, and the articulating surface of the joints. Three types of cartilages can be identified in humans. They are hyaline cartilage, fibro cartilage, and elastic cartilage. The hyaline cartilage is smooth and shiny. The most common type of cartilage is the hyaline cartilage, and it is found in the nose, respiratory tract, and joints. The hyaline cartilage in joints is called the articular cartilage. The two major functions of the articular cartilage are to serve as a shock absorber and allow the smooth movement of the bones at joints. The articular cartilage stores the synovial fluid, which lubricates and nourishes the joints. The regenerative capacity of the articular cartilage is low. The fibro cartilage is found in the knee, and it is much tough and inflexible. The elastic cartilage is the most flexible cartilage, and it is found in ear, epiglottis, and larynx.

Figure 3: Types of Cartilages

Chondroblasts and chondrocytes are the cells found in cartilage and are involved in the formation and maintenance of the cartilage. The three types of cartilages are described in figure 3. 

Similarities Between Bone and Cartilage

• Bone and cartilage are two types of connective tissue, consisting of cells embedded in an extracellular matrix.
• Both bones and cartilages are involved in the formation of the skeleton of vertebrates.
• Both bones and cartilages are involved in providing support and the surfaces for the muscle attachment.

Difference Between Bone and Cartilage

Definition

Bone: Bone is any rigid form of connective tissue, which is composed of calcium salts and forms the skeleton of vertebrates.

Cartilage: Cartilage is a firm, flexible connective tissue, mainly found in the larynx, respiratory tract, external ear, and the articulating surface of the joints.

Type

Bone: Bone is a strong and nonflexible connective tissue.

Cartilage: Cartilage is a flexible connective tissue.

Composition

Bone: Bones are made up of proteins, calcium, and phosphorous.

Cartilage: Cartilages are made up of proteins and sugars.

Types of cells

Bone: Bones consist of osteocytes.

Cartilage: Cartilages consist of chondrocytes.

Bending

Bone: Bones can not be bent.

Cartilage: Cartilages can be bent.

Blood Vessels

Bone: Blood vessels are found in the bones.

Cartilage: Cartilages do not have blood vessels.

Lacunae

Bone: The lacunae of bones consist of canaliculi between osteocytes.

Cartilage: The lacunae of cartilages do not contain canaliculi between chondrocytes.

Role

Bone: Bones provide skeletal support and shape to the body.

Cartilage: Cartilages provide flexibility to the body. They smoothen the bone surfaces and joints.

Found in

Bone: Bones form the skeleton.

Cartilage: Cartilages are found in the ear, nose, larynx, trachea, ribs, and joints.

Categories

Bone: The two types of bones are compact bones and spongy bones.

Cartilage: The three types of cartilages are hyaline cartilage, fibro cartilage, and elastic cartilage.

Conclusion

Bone and cartilage are two types of connective tissue involved in providing support and surfaces for the muscle attachment. Since they are two types of connective tissues, both bones and cartilages consist of cells embedded in their extracellular matrix. Bone is a hard connective tissue, which is rich with hydroxyapatite. It is involved in providing structural support to the body. Cartilage is a flexible connective tissue, which is rich in fibrous proteins. It is involved in providing smooth surfaces for the movement of bones at joints. The main difference between bone and cartilage is their structure and function.

Reference:

1. “Introduction to Bone Biology: All About our Bones.” International Osteoporosis Foundation, Available here. Accessed 20 Aug. 2017.
2. “Structure, Type, and Location of Cartilage – Boundless Open Textbook.” Boundless, 2 Jan. 2017, Available here. Accessed 20 Aug. 2017.

Image Courtesy:

1. “624 Diagram of Compact Bone-new” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “Bonemetabolism” By Shandristhe azylean – I (Shandristhe azylean) created this work entirely by myself.(Original File:Bonemetabolism.png created by JE.at.UWOU|T. Uploaded 05:04, 17 November 2006 (UTC).) (CC BY-SA 3.0) via Commons Wikimedia
3. “412 Types of Cartilage-new” By OpenStax College – Anatomy & Physiology, Connexions Web site. Available here, Jun 19, 2013. (CC BY 3.0) Available here.