Cartilage and Pigmentation Disorders

Pigmentation Disorders

Pigmentation disorders affect the color of skin due to variations in melanin production and distribution.

• Vitiligo: Most common pigmentation disorder; characterized by patchy loss of melanin, resulting in white areas on the skin. The immune system attacks melanocytes.

• Albinism: Genetic condition where individuals cannot produce tyrosinase, an enzyme required for melanin synthesis. Results in a complete lack of pigment.

• Freckles: Localized areas of increased melanin production.

• Birthmarks: Excessive amount of dermal blood vessels, sometimes called "strawberry spots."

Melanin is the pigment responsible for skin, hair, and eye color. Its production is regulated by genetic and environmental factors.

Types of Cartilage

Major Cartilage Types

Cartilage is a flexible connective tissue found in various parts of the body. It provides support, flexibility, and cushioning.

• Hyaline Cartilage: Most abundant type; found in nose, ribs, joints, and at the articulating ends of bones.

• Elastic Cartilage: Contains elastic fibers; found in the ear (pinna) and epiglottis.

• Fibrocartilage: Contains dense collagen fibers; found in the spinal column (intervertebral discs) and meniscus of the knee.

Bone and Skeletal System

Skeletal Tissues

The skeletal system consists of bones and cartilage, which provide structure, protection, and facilitate movement.

• Bone: Hard connective tissue that forms the skeleton.

• Cartilage: Softer, flexible tissue found in joints and other areas.

• Perichondrium: Dense connective tissue membrane surrounding cartilage.

Growth of Cartilage

Cartilage grows by two mechanisms:

• Appositional Growth: New cartilage is added to the surface.

• Interstitial Growth: Cartilage expands from within.

Skeletal Divisions

The skeleton is divided into two main parts:

• Axial Skeleton: Includes the skull, vertebral column, and rib cage. Provides support and protection for the central nervous system and vital organs.

• Appendicular Skeleton: Includes bones of the upper and lower limbs, and girdles (shoulder and pelvic). Facilitates movement.

Bone Classifications

Types of Bones

Bones are classified based on their shape and structure:

• Long Bones: Longer than they are wide; found in limbs (except carpals and patella). Have a shaft (diaphysis) and ends (epiphyses).

• Short Bones: Cube-shaped; found in wrists (carpals) and ankles (tarsals).

• Sesamoid Bones: Form within tendons; example is the patella.

• Flat Bones: Thin and often curved; examples include sternum, ribs, and skull bones.

• Irregular Bones: Complex shapes; examples include vertebrae and some facial bones.

Structure of Long Bones

Long bones have distinct regions:

• Diaphysis: Shaft; contains the medullary cavity filled with yellow marrow (fat storage).

• Epiphyses: Ends of the bone; contain spongy bone and are covered with articular cartilage.

Bone Membranes

Periosteum and Endosteum

Bones are covered and lined by specialized membranes:

• Periosteum: Dense irregular connective tissue covering the outer surface of bone. Has two layers:

  • Outer Fibrous Layer: Provides protection.

  • Inner Osteogenic Layer: Contains osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells).

• Endosteum: Thin membrane lining the medullary cavity and spaces within spongy bone.

Bone Tissue Types

Compact and Spongy Bone

Bones are composed of two main types of tissue:

• Compact Bone: Dense and strong; contains the Haversian system (osteons) with central canals for blood vessels.

• Spongy Bone: Porous and lightweight; contains trabeculae (plates) with spaces for red marrow (site of blood cell production).

Functions of Bone

Main Functions

Bones perform several vital functions:

• Support: Framework for the body.

• Protection: Shields vital organs (e.g., skull protects brain).

• Movement: Muscles attach to bones to produce movement.

• Mineral Storage: Stores calcium and phosphate, released as needed.

• Hematopoiesis: Production of blood cells in red marrow.

Compact Bone Anatomy

Microscopic Structure

Compact bone is organized into osteons (Haversian systems):

• Central Canal: Contains blood vessels and nerves.

• Lamellae: Concentric rings of bone matrix around the central canal.

• Volkmann's Canals: Perforating canals that connect osteons.

• Lacunae: Small spaces housing osteocytes (bone cells).

• Canaliculi: Tiny channels connecting lacunae, allowing communication and nutrient exchange.

Summary Table: Types of Cartilage

Summary Table: Bone Classifications

Key Terms and Definitions

• Osteoblast: Bone-forming cell.

• Osteoclast: Bone-resorbing cell.

• Osteocyte: Mature bone cell residing in lacunae.

• Diaphysis: Shaft of a long bone.

• Epiphysis: End of a long bone.

• Periosteum: Membrane covering the outer surface of bone.

• Endosteum: Membrane lining the inner surface of bone.

• Medullary Cavity: Central cavity in long bones, contains marrow.

• Trabeculae: Plates in spongy bone.

• Haversian System (Osteon): Structural unit of compact bone.

Relevant Equations

• Bone Growth Rate: Additional info: The rate of bone growth is proportional to the activity of osteoblasts, which are influenced by hormones and nutrients.

• Calcium Homeostasis: Additional info: Calcium levels in blood and bone are regulated by hormones such as parathyroid hormone and calcitonin.

Examples and Applications

• Example: The patella is a sesamoid bone that improves the leverage of the quadriceps muscle during knee extension.

• Application: Understanding bone structure is essential for diagnosing fractures and bone diseases such as osteoporosis.