20.2
Bone Structure
Within the skeletal system, the structure of a bone, or osseous tissue, can be exemplified in a long bone, like the femur, where there are two types o…
Within the skeletal system the structure of a bone, or osseous tissue, can be exemplified in a long bone like the femur where there are two types of osseous tissue, cortical and cancellous.
Covering the cortical, or compact bone, is a membrane called the periosteum, which contains connective tissue, capillaries, and nerves. The neighboring outer solid layer found along the diaphysis, the shaft, forms a dense protective shell around the medullary canal, the cavity that stores yellow bone marrow, composed primarily of fat cells. This space is also covered in a thin lining, the endosteum, in which bone growth, remodeling, and repair occur.
Within the compact layer are osteons, structural units arranged in concentric rings called lamellae that contain osteoblasts, cells critical for bone formation and growth. These cells eventually mature into osteocytes in the hollow space, the lacuna.
Through the center of each osteon runs the Haversian canal, which contains more blood and lymphatic vessels as well as nerve fibers. Towards the rounded ends of the long bone, the epiphyses, is the second type of osseous tissue known as cancellous or spongy bone.
This inner layer is composed of a honeycomb-like network of trabeculae, grouped arrangements that form along the lines of stress points to maximize strength with minimal mass. Between each trabecular pore is red bone marrow, which contains hematopoietic stem cells that form into red and white blood cells and platelets that ultimately enter into the circulatory and lymphatic systems.
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Q1: What are the two main types of bone tissue in a long bone?
Long bones like the femur contain cortical bone and cancellous bone. Cortical, or compact bone, forms a dense protective outer shell along the shaft, while cancellous, or spongy bone, occupies the rounded ends. Each type has distinct structural features and functions within the skeletal system.
Q2: What is the periosteum and what does it contain?
The periosteum is a membrane covering cortical bone that contains connective tissue, capillaries, and nerves. It provides structural support and supplies nutrients and oxygen to the bone tissue. The periosteum also plays a role in bone growth and repair processes.
Q3: How are osteons organized within compact bone?
Osteons are structural units arranged in concentric rings called lamellae. Each osteon contains osteoblasts, cells critical for bone formation and growth, which mature into osteocytes in hollow spaces called lacunae. A Haversian canal runs through the center, carrying blood vessels, lymphatic vessels, and nerve fibers.
Q4: What is the medullary canal and what does it store?
The medullary canal is a cavity within the shaft of long bones that stores yellow bone marrow, composed primarily of fat cells. This space is lined by the endosteum, a thin membrane where bone growth, remodeling, and repair occur. The medullary canal provides structural support while minimizing bone weight.
Q5: What is the structure and function of trabeculae in cancellous bone?
Trabeculae are grouped arrangements forming a honeycomb-like network in cancellous bone. They align along stress points to maximize strength with minimal mass. Between trabecular pores lies red bone marrow containing hematopoietic stem cells that produce red and white blood cells and platelets for circulation.
Q6: How does red bone marrow differ from yellow bone marrow in location and function?
Red bone marrow occupies the spaces between trabeculae in cancellous bone at the bone ends and contains hematopoietic stem cells that produce blood cells and platelets. Yellow bone marrow fills the medullary canal in the shaft and consists primarily of fat cells. Both types serve distinct metabolic and storage functions.
Q7: What role do osteoblasts and osteocytes play in bone structure?
Osteoblasts are cells critical for bone formation and growth, located within osteons in compact bone. As bone matures, osteoblasts differentiate into osteocytes, which reside in lacunae and maintain bone tissue. Together, these cells sustain bone integrity and support ongoing remodeling processes.