Bone and Bone growth
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| What are the functions of bone? | Enables movement- attach of muscles.
Protection of vital organs.
Structural support.
Storage of minerals (Ca2+, Mg, PO43-)
Haematopoiesis- blood cell formation.
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| What is bone made out of? | Osteoblasts, osteocytes and osteoclasts.
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| What is the structure of collagen? | Fibre framework in a mucopolysaccharide rich semisolid gel "ground substance.
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| What is the function of collagen? | Gives bone its tensile strength.
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| How is bone different to cartilage? | Bone is hardened by precipitation of calcium phosphate (hydroxyapatite) crystals within matrix.
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| What is the function of the hydroxyapatite? | Gives bone it compressional strength.
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| What are the four sections of a long bone? | Epiphysis, Metaphysis, Diaphysis and Periosteum.
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| What is the epiphysis? | Head- articular surface, covered by hyaline cartilage.
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| What is the metaphysis? | Between epiphysis and diaphysis- region of growth in childhood.
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| What is the diaphysis? | Shaft- hollow cylinder, contains bone marrow in marrow cavity (Red blood cell formation).
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| What is the periosteum? | Fibrous connective tissue sheath covering external surfaces.
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| What cells are included in the periosteum? | Fibroblasts (synthesize collagen), Mesenchymal cells (can differentiate into osteoblasts and chondroblasts) and osteoclasts.
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| What are the descending layers of bone? | Periosteum, Shaft of compact bone and Medullary cavity.
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| What are the two major kinds of long bone? | Trabecular (Cancellous) and Cortical.
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| Describe the structure of trabecular bone. | Spongy and porous.
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| What is the function of trabecular bone? | Gives supporting strength to the ends of weight bearing bone.
Allows distribution of stresses.
Have high SA for metabolism (e.g. regulation of calcium ions).
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| What is the structure of cortical bone? | Solid.
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| What are the functions of cortical bone? | Bone on the outside forms the shaft of the long bone.
Provides stiffness and strength.
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| Describe the blood supply to a bone. | Haversian canals carry blood along the long axis of the bone.
Volksman's canals carry blood perpendicularly.
Majority of cells in very close contact to blood vessels.
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| How are the cells arranged in cortical bone? | Concentric circles (like an onion).
Inside each layer are collagen fibres.
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| How is spongy (cancellous/trabecular) bone different to compact bone? | Fewer lamellar layers in the "spongy" trabecular region.
Less coordinated (weaker and more flexible) than compact bone.
More open, less dense, site of haemopoiesis in bone marrow.
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| What is the composition of the bone matrix? | Organic matrix, crystallised mineral salts and water.
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| What constitutes the organic matrix? | Mostly protein fibres-collagen. Collagen is highly organised in parallel arrangement (in cortical and trabecular bone).
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| What constitutes the crystallised mineral salts? | Hydroxyapatite- Ca10(PO4)6(OH)2
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| What causes rickets? | Vitamin D deficiency- failure of Ca2+ absorption.
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| What causes scurvy? | Vitamin C deficiency- lack of collagen.
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| What is the definition of an osteoblast? | Bone forming cell. They cover the surface of bone forming an osseous matrix in which it becomes enclosed as an osteocyte.
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| What is an osteoclast? | Osteophage- a large, multinucleated cell derived from haematopoietic cells. In response to mechanical stresses and physiological demands they resorb bone matrix by demineralization.
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| What is an osteocyte? | Bone cell-trapped, "retired" osteoblasts. Mature bone cells- embedded in lacunae, relatively inactive. Maintain bone matrix through cell to cell communication (via projections in canaliculi) and influence bone remodelling.
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| What are osteoprogenitor cells? | Stem cell population, gives rise to osteoblasts (as well as other cells).
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| What is the function of osteoblasts? | When stimulated to form bone, they will deposit organic matrix (collagen) then hydroxyapatite. Some become entombed in this process and mature into osteocytes.
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| What is the function of an osteoclasts? | Form a "sealing zone" on bone- release H+ and hydrolytic enzymes that dissolve the mineral, liberate calcium and break down the extracellular matrix. Regulated by hormones and osteoblasts.
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| What controls the actions of osteoblasts and osteoclasts? | Equilibrium between osteoblast and osteoclast activity is controlled by signalling between the different cells in bone and via the actions of hormones.
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| Which hormones control the osteoblast-osteoclast equilibrium? | Calcitonin and Parathyroid hormone (PTH).
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| What is the function of Calcitonin? | Decreases activity of osteoclasts, i.e. decreases blood Ca2+ levels.
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| What is the function of Parathyroid hormone? | Increases the activity of osteoclasts, releases Ca2+.
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| What is the process of trabecular bone remodelling cycle? | Resorption by osteoclasts.
Surface exposed to osteoprogenitors.
Osteoblasts differentiate.
Osteoblasts lay down new bone.
Quiescence.
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| Is bone dynamic and remodelled throughout life? | Yes indeed.
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| What is the affect of excessive mechanical stimulation on bones? | Bone mass and density can increase.
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| Why can bone mass and density decrease? | Non-weight bearing (immobilisation).
Sex-hormone deficiency (e.g. menopause).
Endocrine/nutritional disorders.
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| What is Wolff's law? | Bone adapts to the load under which it is placed.
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| What are common examples of Wolff's law? | Weight-bearing exercise, orthodontic braces, (Amerindian) head binding.
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| Describe bone growth from fetus to adult. | Cartilage model->Replaced by bone (ossification). Bone growth begins in the shaft during fetal life.
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| What is the Cartilage model? | Formed by chondroblasts then reshaped chondrocytes.
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| What is ossification? | The replacement of cartilage by bone.
Endochondral (long bones).
Intramembranous (flat bones).
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| Where does ossification begin? | In the diaphysis.
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| Is the Primary ossification centre active before birth? | Yes indeed.
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| What is the secondary centre of ossification called? | Epiphysis. After birth bone begins to develop in the ends of bone.
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| Describe the process of bone growing in the epiphyseal plate. | Bone is laid down in the shaft of the hand.
The bony parts are separated by a plate of cartilage.
As long as the plate of cartilage is present and active the bone will increase in length.
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| What is a chondroblast? | Site where chondrocytes are formed in the growing matrix.
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| When does the fusion of epiphyseal plates occur? | At the end of puberty.
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| How long does a fracture usually take to heal? | 2-4 weeks dependent on severity and position and age.
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| How does a fracture heal? | Inflammation and additional blood flow lead to callus formation and lamellar bone is laid down.
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| What is involved in callus formation? | Osteoblasts quickly form woven bone, to bridge the gap.
Woven bone is weak as the collagen fibres are irregular.
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| What happens when lamellar bone is laid down? | Collagen is organised in regular sheets to give strength and resilience.
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robertspedding
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