Biology: Bone Structure and Function

Study Notes

Here are the study notes for the text:

Bone provides internal support, attachment for muscles and tendons, and encloses blood-forming elements of the bone marrow and vital organs of the cranial and thoracic cavities.
Bone is a connective tissue characterized by a mineralized extracellular matrix, producing a hard tissue capable of providing support and protection.
Bone matrix contains mainly type I collagen, along with other matrix proteins and traces of type IV, III, XI, and XIII collagens.
Four main groups of non-collagenous proteins found in the bone matrix:
- Proteoglycans (contribute to compressive strength, bind growth factors, and inhibit mineralization)
- Multiadhesive glycoproteins (e.g. osteonectin, osteopontin, sialoprotein I and II)
- Bone-specific, vitamin K-dependent proteins (e.g. osteocalcin, protein S, matrix Gla-protein)
- Growth factors and cytokines (e.g. insulin-like growth factors, tumor necrosis factor, transforming growth factor, platelet-derived growth factors, bone morphogenic proteins, interleukins)

Osteoprogenitor cells: derived from mesenchymal stem cells, give rise to osteoblasts, and are found on external and internal surfaces of bones.
Osteoblasts:
- Synthesize organic components of bone matrix
- Polarized cells, secreting matrix components at the bone surface
- Can become osteocytes or bone-lining cells
Osteocytes:
- Enclosed in lacunae, connected by canaliculi
- Involved in maintaining bone matrix
- Can become quiescent, formative, or resorptive osteocytes
Osteoclasts:
- Large, motile cells with multiple nuclei
- Resorb bone matrix, lying in enzymatically etched depressions (resorption bays)

Inorganic material (50% of dry weight):
- Hydroxyapatite
- Bicarbonate
- Citrate
- Magnesium
- Potassium
- Sodium
- Amorphous calcium phosphate
Organic matter:
- Type I collagen
- Ground substance (proteoglycan aggregates, multiadhesive glycoproteins)
- Calcium-binding glycoproteins (e.g. osteocalcin)
- Phosphatases

Periosteum:
- Dense fibrous outer layer
- Osteoprogenitor cells found in the innermost cellular layer
- Provides nutrition, repair, and growth of bone
Endosteum:
- Thin, single layer of connective tissue
- Covers small spicules or trabeculae of bone
- Lines internal marrow cavities

Compact bone:
- Dense, with no cavities
- Covers external surfaces of bone
Cancellous (spongy) bone:
- Areas with numerous interconnecting cavities
- Found in the ends of long bones, and in the interior of short bones

Intramembranous ossification:
- Osteoblasts differentiate directly from mesenchyme
- Primary bone tissue appears first
Endochondral ossification:
- Matrix of preexisting hyaline cartilage is eroded and replaced by osteoblasts
- Both processes produce primary bone tissue

Vitamin D deficiency:
- Rickets in children
- Osteomalacia in adults
- Impaired calcium absorption and bone calcification
Vitamin C deficiency:
- Impaired collagen production and maintenance
- Delayed healing of fractures
Vitamin A deficiency:
- Impaired skeletal growth and bone remodeling
- Increased bone resorption

Parathyroid hormone (PTH):
- Regulates bone resorption and calcium release
- Acts on the kidney to increase calcium reabsorption
- Balances calcium levels in the blood
Calcitonin:
- Inhibits bone resorption
- Lowers calcium levels in the blood
- Produced in response to hypercalcemia
Growth hormone:
- Essential for normal bone growth
- Excess or deficiency leads to abnormalities
Sex hormones (gonads):
- Affect skeletal maturation and closure of epiphyseal ossification centers
- Influence bone growth and development

Fracture repair:
- Hemorrhage and clotting
- Formation of granulation tissue (procallus)
- Transformation to cartilage (temporary callus)
- Remodeling of bone

Diarthroses:
- Joints that permit free bone movement
- Have a synovial cavity lined by a synovial membrane
- Contain synovial fluid
Synarthroses:
- Joints that have very limited or no movement
- Unite bones using bone, cartilage, or fibrous tissue
Components of a diarthrosis:
- A capsule continuous with a covering ligament
- A synovial or joint cavity lined by a synovial membrane
- Synovial fluid