L11 - Bones

Flashcards on bone biology, covering bone structure, remodeling, bone cells, bone development, and osteoporosis .

Cortical Bone

Compact and dense. 80% of total bone mass. 10% porous. Provides strength to structure.

Cancellous Bone

Also known as trabecular or spongy bone, it makes up 20% of total bone mass, is highly porous 50-90%. Network of thin porous trabeculae in directions of stress - shock absorption. Provides a large bone surface for mineral exchange.

Bone ECM

Bone Extra Cellular Matrix, made primarily of collagen fibrils (Type 1) and hydroxyapatite crystals. Collagen provides elasticity and hydroxyapatite crystals provide rigidity to the matrix.

Bone remodeling

The process of replacing old bone tissue with new bone tissue, which occurs constantly throughout life to repair damage and maintain mineral homeostasis.

Osteoblasts

Bone cells derived from the mesenchymal lineage that form new bone matrix in a two-step process: laying down collagen fibres to form the osteoid and then mineralizing that matrix. Can terminally differentiate into an osteocyte, or return to resting bone lining cell.

Osteoclasts

Bone-resorbing cells derived from hematopoietic precursor cell lines that resorb or degrade bone matrix by secreting proteases that break down the collagen fibers in the bone matrix.

Osteocytes

Cells that used to be osteoblasts that embedded themselves in the bone matrix, acting as mechanosensing cells that respond to load in the skeleton by communicating with each other, the bone surface, and controlling the activity of other cells.

Ossification

Mineralization, becoming bone.

Intramembranous ossification

One of the two types of ossification during development, in which flat bones form through the stimulation of osteoblasts differentiating and laying down bone in the middle of mesenchymal tissue condensation.

Endochondral ossification

The process by which long bones form from a cartilage template.

Proliferation →Hypertrophy and calcification → Degradation and invasion → Bone Formation.

Epiphysis

The end of a long bone, located at the joint space.

Diaphysis

The shaft of the bone located between the epiphysis.

Growth plate

The epiphysial line or physis that sits at the ends of long bones and is responsible for longitudinal growth.

Osteoporosis

The most common bone metabolic disease, characterized by an imbalance in bone remodeling where too many osteoclasts are resorbing bone and not enough osteoblasts are making new bone, leading to a net loss in bone mass.

Estrogen

Acts on osteoclasts and osteoblasts to decrease bone resorption and increase bone formation. A decrease in estrogen (eg. during menopause) is associated with rapid bone loss, due to an increase in bone resorption and a decrease in bone formation.

Testosterone

Increases bone formation. This converts into estrogen, so by losing testosterone, there is a reduction in estrogen. Reductions in bone mass.