Bone Remodeling _______________ units – adjacent osteoblasts and osteoclasts deposit and resorb bone at periosteal and endosteal surfaces

Bone Deposition Occurs where bone is ____________ or added strength is needed Requires a diet rich in ____________, vitamins ___, ___, and ___, calcium, phosphorus, magnesium, and manganese ____________ ____________ is essential for mineralization of bone

Sites of new matrix deposition are revealed by the: Bone Deposition Sites of new matrix deposition are revealed by the: ___________ ___________ – unmineralized band of bone matrix ____________ __________ – abrupt transition zone between the osteoid seam and the older mineralized bone

Accomplished by ______________ Bone Resorption Accomplished by ______________ Resorption bays – grooves formed by osteoclasts as they break down bone matrix Resorption involves osteoclast secretion of: ____________enzymes that digest organic matrix Acids that convert __________ __________ into soluble forms

Bone Resorption Dissolved matrix is transcytosed across the osteoclast’s cell where it is secreted into the interstitial fluid and then into the blood

Importance of Ionic Calcium in the Body Calcium is necessary for: Transmission of __________ _____________ Muscle _____________ Blood ______________ Secretion by _________ and _________ ________ Cell ___________

Two control _______ regulate bone remodeling Control of Remodeling Two control _______ regulate bone remodeling Hormonal mechanism maintains calcium homeostasis in the ___________ Mechanical and _______________ forces acting on the skeleton

Hormonal Mechanism Rising blood Ca2+ levels trigger the thyroid to release _____________ ___________ stimulates calcium salt deposit in bone Falling blood Ca2+ levels signal the ___________ glands to release PTH PTH signals osteoclasts to degrade bone matrix and release ______ into the _________

Hormonal Control of Blood Ca PTH; calcitonin secreted Calcitonin stimulates calcium salt deposit in bone Thyroid gland Rising blood Ca2+ levels Imbalance Calcium homeostasis of blood: 9–11 mg/100 ml Falling blood Ca2+ levels Imbalance Thyroid gland Osteoclasts degrade bone matrix and release Ca2+ into blood Parathyroid glands Parathyroid glands release parathyroid hormone (PTH) PTH Figure 6.11

Response to Mechanical Stress _________ law – a bone grows or remodels in response to the forces or demands placed upon it Observations supporting ________ law include Long bones are thickest _________________ (where bending stress is greatest) Curved bones are thickest where they are most likely to ____________

Response to Mechanical Stress Trabeculae form along lines of stress Large, bony projections occur where heavy, active muscles attach

Response to Mechanical Stress Figure 6.12

Bone Fractures (Breaks) Bone fractures are classified by: The position of the ________ ________ after fracture The ______________ of the break The ______________ of the break to the long axis Whether or not the bones ends penetrate the _____

Types of Bone Fractures _____________ – bone ends retain their normal position _____________ – bone ends are out of normal alignment

Types of Bone Fractures ___________ – bone is broken all the way through ___________ – bone is not broken all the way through ___________ – the fracture is parallel to the long axis of the bone

Types of Bone Fractures _____________ – the fracture is perpendicular to the long axis of the bone __________ (open) – bone ends penetrate the skin __________ (closed) – bone ends do not penetrate the skin

Common Types of Fractures ______________ – bone fragments into three or more pieces; common in the elderly _____________ – ragged break when bone is excessively twisted; common sports injury _____________ – broken bone portion pressed inward; typical skull fracture

Common Types of Fractures _______________ – bone is crushed; common in porous bones _______________ – epiphysis separates from diaphysis along epiphyseal line; occurs where cartilage cells are dying _______________ – incomplete fracture where one side of the bone breaks and the other side bends; common in children

Stages in the Healing of a Bone Fracture ___________ formation Torn blood vessels hemorrhage A mass of clotted blood (hematoma) forms at the fracture site Site becomes swollen, painful, and inflamed Figure 6.13.1

Stages in the Healing of a Bone Fracture Fibrocartilaginous ________ forms _____________ tissue (soft callus) forms a few days after the fracture _____________ grow into the tissue and __________ cells begin cleaning __________ Figure 6.13.2

Stages in the Healing of a Bone Fracture The fibrocartilaginous callus forms when: Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone Fibroblasts secrete collagen fibers that connect broken bone ends Osteoblasts begin forming spongy bone Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies

Stages in the Healing of a Bone Fracture _________ callus formation New bone trabeculae appear in the fibrocartilaginous callus Fibrocartilaginous callus converts into a bony (hard) callus Bone callus begins 3-4 weeks after injury, and continues until firm union is formed ______ months later Figure 6.13.3

Stages in the Healing of a Bone Fracture Excess material on the bone shaft exterior and in the medullary canal is removed Compact bone is laid down to reconstruct shaft walls Figure 6.13.4