Bone 1

Front 1

What are 5 functions of the skeleton?

Back 1

Support
Protection
Allows movement
Mineral storage
Haematopoesis

Front 2

What are the organic and inorganic components of bone?

Back 2

Organic - type I collagen, ground substance
Inorganic - hydroxyapatite crystals (calcium & phosphate)

Front 3

Describe woven bone

Back 3

Immature, random orientation of collagen, produced when osteoid is produced rapidly, e.g. fracture repair, foetal development

Front 4

Describe lamellar bone

Back 4

Regular parallel bands of collagen forming sheets
Forms compact or cancellous bone

Front 5

Describe the orientation of lamellae in a) cancellous bone and b) compact bone?

Back 5

a) Parallel
b) Arranged in concentric circles around Haversian system

Front 6

What are the 4 main cell types of bone?

Back 6

Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts

Front 7

Describe osteoprogenitor cells

Back 7

Mesenchymal cells of origin, give rise to osteoblasts --> osteocytes
Found in periosteum, endosteum, Haversian channels, Volkmann's canals

Front 8

Describe osteoblasts

Back 8

Bone-producing cells, they produce osteoid (organic) part of matrix, act as partial barrier for osteoclasts and extracellular fluid for mineral concentrations
Basophilic, extensive E.R. and Golgi, cuboidal

Front 9

Describe osteocytes

Back 9

Maintenance of bone matrix, transport of hormones and metabolites, embedded in their own secretions in small lacuna
More stellate, less E.R. and Golgi, possess numerous filopodia

Front 10

Describe osteoclasts

Back 10

Cells of myeloid origin, situated in Howship's lacunae
Bone resorption, they secrete proteolytic enzymes
Acidophilic cells, multinucleated, ruffled membrane, abundant mitochondria and lysosomes

Front 11

Describe the action of pyrophosphate (PP)

Back 11

Pyrophosphate inhibits mineralisation of soft tissues

Front 12

What does alkaline phosphatase (ALKP) do?

Back 12

Breaks down PP, allowing mineralisation to occur

Front 13

What does calcitonin do?

Back 13

Produced by the thyroid gland, it inhibits osteoclast function and thus reduces bone resorption and release of calcium into plasma

Front 14

What does parathyroid hormone (PTH) do?

Back 14

Interacts with osteoblasts and increases RANK ligand and decreases osteoprotegerin release, thus indirectly increasing osteoclast function, increasing bone resorption

Front 15

Describe intramembranous ossification

Back 15

Mesenchymal cells differentiate into osteoblasts
Osteoid produced and mineralisation occurs
Osteoblasts trapped and mature into osteocytes
Forms islands of developing bone spicules which fuse and form woven bone with CT trapped in between.
Blood vessels and mesenchymal cells penetrate CT

Front 16

Describe endochondral ossification

Back 16

Hyaline cartilage is formed, osteogenic cells differentiate into osteoblasts which produce matrix under perichondrium = bone collar. Perichondrium now called periosteum. Bone collar reduces diffusion to interior cartilage, degeneration of chondrocytes. Blood vessels invade the empty spaces, carrying mesenchymal cells which differentiate into osteoblasts. Woven bone produced. Epiphyses at each end form 2 secondary ossification centres. Articular cartilage remains at each end. Woven bone becomes lamellar bone.