Joints and Cartilage Anatomy Quiz

Bone Tissue Overview

• Bone is the primary constituent of the skeletal system.
• It supports soft tissues and protects vital organs.
• It acts as a lever system for muscles, enabling body movement.
• Bone is a reservoir for minerals and contributes to homeostasis.
• It houses bone marrow, a hematopoietic organ.

Bone Tissue Composition and Properties

• Bone is a specialized connective tissue, composed of cells and matrix.
• The bone matrix is mineralized and rigid.
• Despite its hardness, bone tissue is dynamic and changes shape in response to forces.
• Bone is a continuous tissue that adapts to forces and pressures within the body

Bone Structure

• Bones have a central cavity that houses bone marrow.
• The outer surface of a bone is covered by periosteum, a dense connective tissue layer.
• An inner cellular layer of periosteum contains osteogenic cells and osteoblasts.
• The endosteum, a specialized thin connective tissue, lines the medullary cavity.
• It contains osteogenic cells and osteoblasts as well.

Bone Matrix

• Bone matrix contains both organic and inorganic components.
• These components are responsible for bone consistency and hardness.

Inorganic Components of Bone Matrix

• Inorganic components make up approximately 65% of bone's dry weight.
• Primarily composed of minerals; calcium and phosphorus form hydroxyapatite crystals.
• These crystals are arranged in an orderly manner along collagen fibers, within an amorphous ground substance.
• The combination of collagen and hydroxyapatite provides bone hardness.
• Decalcification (removal of minerals), exposes and maintains the shape but makes the bone flexible and rubbery.

Organic Components of Bone Matrix

• Approximately 35% of bone's dry weight is comprised of organic components.
• Consists primarily of type I collagen, forming large beams.
• Includes ground substance, proteoglycans, and adhesion glycoproteins.
• Removal of organic components leaves the bone with minerals but brittle.

Bone Cells

• Osteogenic cells are mesenchymal stem cells, found in periosteum and endosteum.
• They divide by mitosis and differentiate into osteoblasts.
• Osteoblasts are bone-forming cells.
• They produce and secrete osteoid, the organic component of the bone matrix.
• When completely surrounded by matrix, osteoblasts become osteocytes.

Osteocytes

• Mature bone cells, derived from osteoblasts.
• They reside in lacunae, interconnected by canaliculi.
• Canaliculi are thin channels that form a network for nutrients and waste exchange between osteocytes and blood vessels.
• Osteocytes secrete substances that maintain bone matrix.

Osteoclasts

• Large, multinucleated cells derived from bone marrow.
• Responsible for bone resorption (breakdown).

Bone Resorption

• Process where osteoclasts break down bone tissue and release minerals into the bloodstream.
• Osteoclasts secrete protons into the space adjacent to bone, acidifying the environment.
• This acidic environment dissolves the inorganic components of the bone matrix.
• Enzymes secreted by osteoclasts further degrade the organic components.

Ossification

• Process of bone formation during embryonic development and throughout life.
• Two main types:
  • Intramembranous ossification (flat bones).
    • Mesenchymal cells differentiate into osteoblasts and secrete bone matrix.
    • These form trabeculae, forming a network of spongy bone.
    • Connective tissue in between trabeculae transforms into bone marrow.
  • Endochondral ossification (long bones).
    • Begins with a model of hyaline cartilage.
    • Chondrocytes within the center of the cartilage model enlarge and die.
    • Osteoblasts replacing the cartilage form spongy bone.
    • Compact bone forms around the spongy bone.

Bone Growth

• Chondrocytes in the epiphyseal plate proliferate and hypertrophy.
• Ossification replaces the cartilage, causing bone lengthening.
• The epiphyseal plate closes, stopping longitudinal bone growth.
• Bone continues thickening through appositional growth from the periosteum.

Bone Remodeling

• Continuous process in adult bones where resorption and formation of bone are balanced.
• Adapts bone structure to respond to forces (weight, posture).
• Maintains calcium homeostasis.

Calcium Homeostasis

• Bone is a major reservoir for calcium.
• Blood calcium regulation maintains proper function of muscles, nerves, and blood clotting.
• Parathyroid hormone (PTH) regulates blood calcium levels when it is low.
• Calcitonin regulates blood calcium levels when it is high.

Bone Classification

• Bones are classified into categories according to their shape:
  • Long bones
  • Short bones
  • Flat bones
  • Irregular bones
  • Sesamoid bones. bone

Bone Structures and Components

• Compact bone is dense, forms the external layer of most bones and the diaphysis.
• Spongy bone is porous, fills the epiphyses and interior of some bones.
• Diaphysis is the long shaft of a long bone.
• Epiphysis are the enlarged ends of a long bone.
• Epiphyseal plate is the location of longitudinal bone growth.
• Periosteum is the fibrous membrane covering the outer surface of bone (except at articular surfaces).
• Endosteum is the thin membrane lining the medullary cavity.

Bone Repair

• Series of steps that the body follows to rebuild bone structure in response to bone fracture.

Articulations

• How bones connect to each other
  • Synarthrosis (immovable or have minimal movement)
    • Synostosis
    • Synchondrosis
    • Syndesmosis
  • Diarthrosis (freely movable)

Diarthroses

• Most limb articulations, have various types of movement.
• Bones are covered with hyaline cartilage that helps with smooth movement.
• Synovial fluid, nourishes and lubricates the articulation.