Cartilage and Bone Anatomy

Cartilage

• Cartilage is a dense connective tissue.
• It's a semi-rigid form of connective tissue.
• It forms parts of the skeleton where flexibility is needed.
• Costal cartilage attaches ribs to the sternum, for example.
• Articular cartilage covers bone surfaces participating in synovial joints, providing smooth, low-friction gliding for movement.
• Cartilage is avascular, meaning it obtains nutrition through diffusion.
• It forms the temporary skeleton of a developing fetus.
• Gradually replaced by bone.
• Newborn bones are soft and flexible, mainly composed of cartilage.
• The proportion of cartilage and bone in the skeleton changes as the body grows.
• Cartilage remains in certain sites of the body, including articular surfaces of most bones.
• Cartilage is also found in the air passage (nasal, laryngeal, tracheal, and bronchial cartilages).
• It is present in the external ear and Eustachian tube.

Bone

• Bone is a vascularized dense connective tissue.
• It's composed of cells and a matrix (organic [collagen fibers] and inorganic [Ca, Phosph]).
• Bone is hard due to its extracellular matrix.
• Bone is elastic due to the presence of organic fibers.
• Bone exists in two forms: compact bone (hard bone) and spongy bone (cancellous bone).
• Compact bone forms the surface layer of all bones and the tubular shafts of long bones.
• It provides strength for weight-bearing.
• Long bones have increased amounts of compact bone in the shaft.
• Compact bone consists of Haversian systems, cylindrical units.
• Spongy bone looks like a sponge and is filled with red bone marrow.
• It's formed of trabeculae; the lamellae branch and anastomose.
• Spongy bone is found inside compact bone and in the ends of long bones and the bodies of other bone types.

Periosteum

• It's a fibrous connective tissue covering the surrounding bone, excluding articular cartilage.
• It's highly sensitive and richly supplied with nerves

Blood Supply of Bone

• Periosteal arteries: Main blood supply source for all bone types. They come from nearby main vessels or attached structures. They supply the outer compact bone. The bone dies if deprived of periosteum.
• Articular arteries: Supply joints and bone ends. They branch into epiphyseal and metaphyseal branches.
• Nutrient arteries: Enter the bone through the nutrient canal. Branch into proximal and distal branches within the medullary cavity. Supply the bone marrow, spongy bone, and deep compact bone.

Bone Marrow

• It's fatty vascular tissue filling the medullary cavity of long bones and the meshes of cancellous bone.
• Involved in blood cell production.
• At birth, bone marrow is mostly red.
• During childhood, yellow marrow replaces red marrow in some areas.
• In adults, red marrow is mainly in the spongy bone of certain bones (skull, vertebrae, sternum, ribs, hip, upper end of femur and humerus). Yellow marrow fills the medullary cavity of most long bones.

Functions of the Skeleton

• Skeleton supports the body.
• It provides shape to the body.
• It protects soft organs.
• It enables movement through attached skeletal muscles.
• It acts as a lever.
• It stores minerals (like calcium) and fats.
• It's a site of blood cell formation.

Growth of the Bone

• Growth in length happens through continuous bone deposition on either side of the growth plate until it ossifies and fuses with the diaphysis.
• Growth in thickness occurs by sub-periosteal bone deposition by osteoblasts.
• Osteoclasts are involved in the formation of the marrow cavity.

Types of Bones

• Bones are classified into five types based on shape: long, short, flat, irregular, sesamoid, and pneumatic.
• Long bones: Have a long tubular shaft with a central medullary cavity and expanded ends (e.g., humerus, femur).
• Short bones: Cuboidal, thin cortex of compact bone with cancellous bone inside (e.g., carpal, tarsal).
• Flat bones: Internal bone layer enclosed between inner and outer layers of compact bone (e.g., skull vault, ribs, sternum, scapula).
• Irregular bones: Have various shapes (e.g., vertebrae, hip bones).
• Sesamoid bones: Small bones embedded in tendons to reduce friction (e.g., patella).
• Pneumatic bones: Contain air spaces (e.g., maxilla, frontal bones).

This quiz explores the structure and functions of cartilage and bone, two types of connective tissue. It covers key characteristics, such as the role of cartilage in joints and how bone develops over time. Test your knowledge of these essential components of the skeletal system!