Ch6

• Chondrocytes


  Cells encased in small cavities (lacunae) within jelly-like extracellular matrix
• Bones perform several important functions
• Functions of bones

  • Support
  • Protection
  • Movement/anchorage
  • Mineral storage
  • Blood cell formation
  • Triglyceride (fat) storage
  • Hormone production
• Types of cartilage

  • Hyaline cartilage - Provides support, flexibility, and resilience, most abundant type, contains collagen fibers only
  • Elastic cartilage - Similar to hyaline cartilage, but contains elastic fibers, found in external ear and epiglottis
  • Fibrocartilage - Thick collagen fibers, has great tensile strength, found in menisci of knee, vertebral discs, pubic symphysis
• Cartilage

  • Composed of highly resilient (springy), molded cartilage tissue that consists primarily of water
  • Contains no blood vessels or nerves
• Formation of the human skeleton

  Initially consists of just cartilage, which is replaced by bone, except in areas requiring flexibility
• Perichondrium


  • Layer of dense connective tissue surrounding cartilage like a girdle
  • Helps cartilage resist outward expansion
  • Contains blood vessels for nutrient delivery to cartilage
• Hematopoiesis


  Occurs in red marrow cavities of certain bones
• Osteocalcin secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism
• The gross structure of all bones consists of compact bone sandwiching spongy bone
• Groups of bones based on location

  • Axial skeleton - Skull, vertebral column, rib cage
  • Appendicular skeleton - Bones of upper and lower limbs, girdles that attach limbs to axial skeleton, shoulder and hip bones
• Classification of bones by shape

  • Long bones - Longer than they are wide, shaft + 2 ends, all limb bones (except patella, wrist bones, ankle bones, and finger bones) are long bones
  • Short bones - Cube-shaped bones, e.g., wrist and ankle bones, sesamoid bones form within tendons, e.g., patella
  • Flat bones - Thin, flat, slightly curved, e.g., Sternum, scapulae, ribs, most cranial bones of the skull
  • Irregular bones - Complicated shapes that do not fit preceding groups, e.g., Vertebrae and hip bones
• Bones are classified by their location and shape
• Types of bones based on shape

  • Thin, flat, slightly curved bones: e.g., Sternum, scapulae, ribs, most cranial bones of the skull
  • Irregular bones: Complicated shapes that do not fit preceding groups, e.g., Vertebrae and hip bones
• Spongy bone

  • Made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae
  • Open spaces between trabeculae are filled with red or yellow bone marrow
• Bones have 3 levels of structure: Gross, Microscopic, Chemical
• Bones are organs because they contain different types of tissues
• Compact bone

  • Dense outer layer on every bone that appears smooth and solid
• Tissues found in bones

  • Bone (osseous) tissue
  • Nervous tissue
  • Cartilage
  • Fibrous connective tissue
  • Muscle cells
  • Epithelial cells in its blood vessels
• Structure of typical long bone

  1. All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes

  2. Diaphysis: Tubular shaft that forms long axis of bone, consists of compact bone surrounding central medullary cavity filled with yellow marrow in adults

  3. Epiphyses: Ends of long bones that consist of compact bone externally and spongy bone internally, articular cartilage covers articular (joint) surfaces

  4. Between diaphysis and epiphysis is epiphyseal line, remnant of childhood epiphyseal plate where bone growth occurs
• Membranes – periosteum & endosteum


  1. Periosteum: White, double-layered membrane that covers external surfaces except joints, contains fibrous layer (outer layer consisting of dense irregular connective tissue) and osteogenic layer (inner layer abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cells), contains nerve fibers and blood vessels, anchoring points for tendons and ligaments, contains perforating (Sharpey’s) fibers that secure periosteum to bone matrix

  2. Endosteum: Delicate connective tissue membrane covering internal bone surface, covers trabeculae of spongy bone, lines canals that pass through compact bone, contains osteogenic cells that can differentiate into other bone cells
• Structure of short, irregular, and flat bones

  1. Consist of thin plates of spongy bone (diploë) covered by compact bone

  2. Compact bone sandwiched between connective tissue membranes

  3. Periosteum covers outside of compact bone, and endosteum covers inside portion of compact bone

  4. Bone marrow is scattered throughout spongy bone, no defined marrow cavity

  5. Hyaline cartilage covers area of bone that is part of a movable joint
• Blood Vessels & Nerves

  Bones are well vascularized, nutrient artery and vein are main vessels serving the diaphysis, run through hole in wall of diaphysis called nutrient foramen, nerves accompany blood vessels
• Hematopoietic tissue in bones, also called red marrow, found within trabecular cavities of spongy bone and diploë of flat bones, such as the skull and sternum
• In newborns, medullary cavities and all spongy bone contain red marrow. In adults, red marrow is located in heads of femur and humerus, but most active areas of hematopoiesis are flat bone diploë and some irregular bones
• In adults, red marrow is located in heads of femur and humerus, but most active areas of hematopoiesis are flat bone diploë and some irregular bones
• Bone markings


  • Sites of muscle, ligament, and tendon attachment on external surfaces
  • Areas involved in joint formation or conduits for blood vessels and nerves
• In newborns, medullary cavities and all spongy bone contain red marrow
• Yellow marrow can convert to red if a person becomes anemic
• Bone is a dynamic tissue since cells continuously resorb and deposit bone in a process called remodeling
• Microscopic Anatomy of Bone
• Cells of Bone Tissue

  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Bone-lining cells
  • Osteoclasts
• 3 types of bone markings

  • Projection
  • Surfaces
  • Depression/openings
• Osteoprogenitor cells


  Mitotically active stem cells found in periosteum and endosteum
• Osteoblasts

  Bone-forming cells that secrete unmineralized bone matrix called osteoid
• Bone-lining cells

  Flat cells on bone surfaces believed to help maintain matrix where bone remodeling is not occurring
• Osteoclasts


  Giant, multinucleate cells function in bone resorption
• Osteocytes


  Spider-shaped mature bone cells in lacunae that maintain bone matrix and act as stress or strain sensors
• Microscopic Anatomy of Compact Bone

  • Osteon (Haversian system)
  • Canals and canaliculi
  • Interstitial and circumferential lamellae
• Canals and canaliculi


  Central (Haversian) canal contains blood