Histology of the bone Flashcards
What are the general features of bone tissue?
Bone tissue is a specialized type of connective tissue composed of an extracellular matrix and bone cells (osteoblasts, osteocytes, and osteoclasts). The mineralized matrix provides hardness to bones, allowing them to support the body structurally, store minerals, and protect soft tissues.
Describe the structure and function of the periosteum.
The periosteum is a fibrous membrane covering the outer surface of bones, except at joint surfaces. It has two layers: a fibrous outer layer and an osteogenic inner layer. It plays a key role in bone growth, repair, and attachment of tendons and ligaments.
What are the organic and inorganic components of bone tissue?
Organic components (1/3): Cells (osteoblasts, osteocytes, osteoclasts), Type I collagen fibers (providing tensile strength), and ground substances like proteoglycans and glycoproteins.
Inorganic components (2/3): Mainly calcium phosphate, calcium carbonate, and hydroxyapatite crystals.
How are bones classified based on their structure?
Gross classification: Compact bone (dense, forms outer layer) and spongy bone (porous, found inside bones).
Histological classification: Woven/immature bone (found in embryonic skeleton and fracture healing) and lamellar/mature bone (structured, found in both compact and spongy bone).
Differentiate between osteoblasts, osteocytes, and osteoclasts
Osteoblasts: Responsible for forming new bone matrix; they are cuboidal cells that secrete osteoid.
Osteocytes: Mature bone cells derived from osteoblasts; they maintain the bone matrix and act as mechanosensors.
Osteoclasts: Large, multinucleated cells responsible for bone resorption; they contain lysosomes and have a ruffled border for matrix resorption.
What are the two types of bone ossification, and which bones form through each process?
Intramembranous ossification: Bone forms directly from mesenchymal tissue, primarily forming flat bones like cranial bones, mandible, and clavicle.
Endochondral ossification: Bone forms by replacing a cartilage model, responsible for the formation of long bones like the femur and humerus.
What are the zones of the epiphyseal plate, and what occurs in each zone?
Zone of Reserve Cartilage: Small resting cells.
Zone of Proliferation: Larger cells undergoing mitosis.
Zone of Hypertrophy: Enlarged chondrocytes in columns.
Zone of Calcified Cartilage: Matrix calcification and chondrocyte apoptosis.
Zone of Ossification: Removal of calcified cartilage and deposition of new bone.
What is bone remodeling, and why is it important?
Bone remodeling is the continuous process of bone deposition by osteoblasts and resorption by osteoclasts. It is essential for maintaining bone strength, adapting bone structure to physical stress, and regulating calcium and phosphate levels in the body.
What are the differences between compact bone and spongy bone?
Compact bone: Dense, forms the outer layer of bones, consists of closely packed osteons or Haversian systems, provides strength for weight-bearing.
Spongy bone (Cancellous): Found in the interior of bones, has a porous, lattice-like structure made of trabeculae, houses red or yellow bone marrow, provides support and flexibility.
Describe the structure of an osteon in compact bone.
An osteon, or Haversian system, is the fundamental unit of compact bone. It consists of a central Haversian canal surrounded by concentric lamellae of bone tissue. The canal contains blood vessels and nerves. Osteocytes are located in lacunae between lamellae, and they communicate through canaliculi.
What are Sharpey’s fibers and what is their function?
Sharpey’s fibers are collagen fibers that anchor the periosteum to the underlying bone. They penetrate the bone matrix and are especially abundant at sites of ligament and tendon attachment, providing stability to the bone-periosteum interface.
Differentiate between red bone marrow and yellow bone marrow.
Red bone marrow: Hematopoietic tissue found in flat bones like the sternum and pelvis, and in the epiphyses of long bones in adults. It produces blood cells.
Yellow bone marrow: Primarily fat tissue, found in the medullary cavity of long bones in adults. It can revert to red marrow under certain conditions, such as severe blood loss.
Outline the steps of intramembranous ossification.
Mesenchymal cells cluster and differentiate into osteoblasts, forming ossification centers.
Osteoblasts secrete osteoid, which mineralizes, trapping some osteoblasts that become osteocytes.
The trabecular matrix forms and expands, creating spongy bone.
The outer layer forms compact bone, and the periosteum develops around the bone.
What are the key steps involved in endochondral ossification
A cartilage model of the bone forms in the embryo.
The perichondrium develops into the periosteum, and a bone collar forms around the diaphysis.
Chondrocytes in the center of the model enlarge, and the matrix calcifies, leading to chondrocyte death.
Blood vessels invade the calcified cartilage, bringing osteoprogenitor cells that differentiate into osteoblasts, forming the primary ossification center.
The process continues with the formation of secondary ossification centers in the epiphyses after birth.
How do hormones regulate bone growth?
Growth hormone: Stimulates overall growth, indirectly through somatomedin, which promotes cartilage growth at the epiphyseal plate.
Thyroid hormone: Stimulates bone growth and maintains normal activity at the epiphyseal plates.
Calcitonin: Inhibits osteoclast activity, lowering blood calcium levels.
Parathyroid hormone: Increases blood calcium levels by stimulating osteoclast activity.
Sex hormones (Estrogen and Testosterone): Increase bone formation rates and are responsible for the growth spurts and closure of epiphyseal plates during puberty.
