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  • 0:01 What is Cancellous Bone?
  • 0:30 Types of Bone Tissue
  • 1:45 Structure of Cancellous Bone
  • 2:35 Cancellous Bone in Children
  • 3:45 Osteoporosis
  • 5:35 Lesson Summary
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Cancellous Bone: Definition, Structure & Function

Lesson Transcript
Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

In your body, you have only two types of bone tissue: cortical and cancellous bone. In this lesson, we will learn about the structure and function of cancellous bone, which plays a crucial role in producing blood cells and stem cells and is the primary tissue affected by osteoporosis.

What Is Cancellous Bone?

Cancellous bone, also known as spongy or trabecular bone, is one of the two types of bone tissue found in the human body. Cancellous bone is found at the ends of long bones, as well as in the pelvic bones, ribs, skull, and the vertebrae in the spinal column. It is very porous and contains red bone marrow, where blood cells are made. It is weaker and easier to fracture than cortical bone, which makes up the shafts of long bones.

Types of Bone Tissue

The bones of the arms and legs in humans are the largest in the body and are known as long bones. Long bones are made up of two types of tissue. The central part of a long bone is composed of cortical bone. Cortical bone is very dense and strong and, therefore, difficult to fracture. Its primary purpose is providing structural support to the body and its organs and tissues. In the center of long bones is a central canal where blood vessels, nerves, and bone marrow are found. At the ends of the long bones, cortical bone gives way to cancellous bone. Cancellous bone is also found in the pelvic bones, and in the ribs and vertebrae.

In total, cancellous bone makes up about 20% of the typical adult human skeleton. Cancellous bone is much more porous and, therefore, weaker than cortical bone. Although it is still strong, it is more easily fractured than cortical bone. In addition to providing structural stability, cancellous bone contains most of the body's red bone marrow, which produces blood cells. The bone marrow found in cancellous bones also contains many stem cells that are used to repair damaged or broken bone.

Structure of Cancellous Bone

Cancellous bone is also known as spongy bone because it resembles a sponge or honeycomb, with many open spaces connected by flat planes of bone known as trabeculae. Inside the trabeculae are three types of bone cells: osteoblasts, osteocytes and osteoclasts. Osteoblasts are the cells that make new bone. They produce layers of hard tissue made primarily of calcium and phosphate until they are completely surrounded, at which point they become osteocytes. Finally, osteoclasts are larger cells that break down and destroy old or damaged bone so that it can be repaired and replaced by osteoblasts. This repair and rebuilding cycle is constantly ongoing to keep bones strong and healthy.

Cancellous Bone in Children

In babies, most of the skeleton is composed of cancellous bone, and all the bone marrow is red bone marrow. As children grow up, the bones get longer and cancellous bone is slowly converted into stronger cortical bone in the long bones. The red bone marrow is also slowly converted to yellow bone marrow, which is composed primarily of fat cells. During the teenage years, the growth plates close and cancellous bone is only left at the ends of the long bones. It remains into adulthood in the vertebrae, ribs, pelvis, and skull, and the bone marrow in these areas continues to produce blood cells. Yellow bone marrow in cortical bone can be converted back into red bone marrow even in adulthood following severe illness or blood loss.

Bone starts as cartilage in the fetus and, as it develops during infancy and childhood, the cartilage is converted first into cancellous (spongy) bone, and then finally into cortical (compact) bone in the center of the long bones in the arms and legs. Children have a much higher percentage of cancellous bone in their skeleton than adults.

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