Bones are dynamic, living tissues that form the framework of the human body. They provide essential structure, enable movement, and safeguard delicate internal organs. This intricate system continually remodels itself, adapting to demands throughout life.
Defining Cortical Bone
Cortical bone, also known as compact bone, is the dense, solid outer layer of nearly all bones in the body. It presents a smooth, white appearance, contributing significantly to the skeletal system’s rigidity and strength. This type of bone accounts for approximately 80% of the total bone mass in an adult human skeleton. Cortical bone forms the primary component of the shafts of long bones, such as those in the arms and legs, and also creates the protective outer shell of other bone types. Its substantial density allows it to withstand considerable weight and stress.
The Microscopic Architecture
The internal structure of cortical bone is organized into repeating cylindrical units called osteons, or Haversian systems, each a microscopic structure typically extending several millimeters in length. At the center of each osteon lies a Haversian canal, which contains blood vessels and nerves for nourishing the bone tissue. Concentric layers of bone matrix, known as lamellae, surround this central canal. Tiny spaces called lacunae are embedded within these lamellae, each housing a bone cell called an osteocyte. These osteocytes communicate with each other and the Haversian canal through microscopic channels called canaliculi, facilitating nutrient and waste exchange.
Primary Functions of Cortical Bone
Cortical bone provides the main structural support for the entire body, allowing it to maintain shape and posture. It offers protection to internal organs, such as the skull shielding the brain and the ribcage encasing the heart and lungs. Cortical bone also acts as a system of levers that muscles pull against, enabling a wide range of movements like walking, running, and jumping. This bone type functions as a reservoir for essential minerals, predominantly calcium and phosphate, which are released into the bloodstream as needed for various bodily processes.
Cortical Bone vs. Cancellous Bone
Bones are composed of two primary tissue types: cortical bone and cancellous bone, also known as spongy or trabecular bone. Cancellous bone is porous and less dense, featuring an open network of thin bone struts called trabeculae. Found primarily at the ends of long bones and inside other bones, cancellous bone offers flexibility and acts as a shock absorber. Cancellous bone also houses bone marrow, where blood cell production occurs. The metabolic turnover rate of cancellous bone is significantly higher than that of cortical bone.