Bio

• Mitochondria are the powerhouses of the cell, responsible for generating energy through cellular respiration.
• Bone density peaks at about 25-30 years of age
• Women lose bone mass more rapidly than men
• Bone is considered "old" after the age of 30
• Osseous tissue is connective tissue with the matrix hardened by calcium phosphate and other minerals
• Ossification is the formation of osseous tissue
• Osteon is the basic structural unit of compact bone
• Compact (dense or lamellar) bone is the outer shell of a long bone
• Spongy (cancellous or trabecular) bone is covered by more durable compact bone
• The skeleton is ¾ compact and ¼ spongy bone by weight
• Epiphyses and Diaphysis are features of bones
• Epiphysial line (Closed Growth Plate) is a feature of bones
• Medullary cavity (Marrow cavity) is a feature of bones
• Articular cartilage (Hyaline cartilage) is a feature of bones
• Periosteum is the external sheath that covers bone except where there is articular cartilage
• Endosteum is a thin layer of reticular connective tissue lining the medullary cavity and covering all honeycombed surfaces of spongy bone
• Four principle osseous cells:

  • Osteoprogenitor cells are stem cells found in endosteum, periosteum, and in central canals
  • Osteoblasts synthesize soft organic matter of matrix (osteoid) and deposit inorganic calcium into the skeleton
  • Osteocytes contribute to homeostatic mechanism of bone density and calcium and phosphate ions
  • Osteoclasts are bone-dissolving cells found on the bone surface
• The matrix of osseous tissue is about ⅓ organic and ⅔ inorganic matter

  • Organic matter includes collagen, carbohydrate-protein complexes, and sacrificial bonds
  • Inorganic matter includes hydroxyapatite, calcium carbonate, and other minerals
• Importance of ionic calcium in the body:

  • Cell-signaling and enzyme cofactors
  • Transmission of nerve impulses
  • Muscle contraction
  • Blood coagulation
  • Cell division
  • Exocytosis
• Importance of phosphate groups:

  • DNA
  • RNA
  • ATP
  • Phospholipids
• Compact bone has perforating (Volkmann) canals, central (Haversian) canals, concentric lamellae, circumferential lamellae, and interstitial lamellae
• Osteon arrangement:

  • Collagen fibers corkscrew down the matrix of a lamella in one directional helices
  • Enhances strength in tension and compression
• Spongy bone consists of slivers of bone called spicules, thin plates of bone called trabeculae, and spaces filled with red bone marrow

  • Few osteons and no central canals
  • Provides strength with minimal weight
• Bone marrow is soft tissue that occupies the marrow cavity of a long bone and small spaces amid the trabeculae of spongy bone

  • Red marrow (myeloid tissue) produces blood cells
  • Yellow marrow found in adults no longer produces blood
• Ossification in the human fetus and infant occurs through intramembranous ossification and endochondral ossification
• Bone growth and remodeling:

  • Bones grow in length (interstitial growth) and width (appositional growth)
  • Appositional growth involves deposition of new bone at the surface and formation of circumferential lamellae
  • Bone remodeling occurs throughout life with the growth and remodeling of bones
• Bone remodeling occurs throughout life at a rate of 10% per year
• Bone remodeling repairs and reshapes bones in response to use and disuse
• Wolff’s law of bone states that the architecture of bone is determined by mechanical stresses
• Remodeling is a collaborative and precise action of osteoblasts and osteoclasts
• Bony processes grow larger in response to mechanical stress
• Piezoelectricity of Collagen:
• Bone compression and subsequent decompression produce an electrical current
• Compression and Collagen produce a negative current
• Electrical signals direct bone growth and remodeling
• Tension (stretch) and apatite crystals produce a positive current
• Osseous Homeostasis:
• Calcium blood plasma setpoint is at ~10 mg/dL
• Adult body contains ~1,100 g of calcium (99% in skeleton)
• Thyroid gland + Calcitonin + Osteoblasts - Osteoclasts + Bone deposition