Bones form the foundational framework of the human body, providing structure and support for movement. Joints, where two or more bones meet, are crucial connections that enable a wide range of motion. Understanding the components within these joints helps clarify how the body achieves fluid and effective motion. This article explores articular cartilage, a specific component found within these joints, contributing significantly to their function.
Anatomy of a Long Bone
Long bones are longer than they are wide, forming the primary skeletal elements in the limbs. Examples include the femur, tibia, and humerus. Each long bone consists of two main parts: the shaft, known as the diaphysis, and the wider ends, called the epiphyses. The diaphysis forms the central, tubular portion of the bone, composed mainly of dense compact bone that surrounds a hollow medullary cavity.
The epiphyses, located at both the proximal and distal ends, are wider sections filled with spongy bone. The outer surface of the bone is covered by a fibrous membrane called the periosteum, except where bones connect to form joints.
Location on Long Bones
Articular cartilage, a specialized connective tissue, is found at the ends of long bones where they form joints. This smooth, glistening tissue covers the surfaces of the epiphyses within synovial joints. It is primarily composed of hyaline cartilage, which forms a thin, protective layer, allowing bones to articulate without direct contact.
Articular cartilage is observed in major long bones that participate in extensive movement, such as the femur and tibia in the knee joint, or the humerus in the shoulder and elbow joints. It is not found within the diaphysis, medullary cavity, or the spongy bone within the epiphyses.
The Role of Articular Cartilage
The primary functions of articular cartilage stem from its unique location and composition. It acts as a smooth, low-friction surface, enabling bones to glide past each other with minimal resistance during joint movement. This smooth interface allows for pain-free motion and prevents wear and tear on the underlying bone. Without this lubrication, direct bone-on-bone contact would lead to significant friction and damage.
Articular cartilage also functions as a shock absorber. It distributes mechanical forces across the joint, cushioning the impact experienced during activities like walking, running, or jumping. The tissue’s ability to compress under pressure and then return to its original shape helps dissipate energy from impacts. This dual role of reducing friction and absorbing shock protects the bone and maintains joint integrity over time.