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Bone and Bone growth
| Question | Answer |
|---|---|
| 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. |
| What is bone made out of? | Osteoblasts, osteocytes and osteoclasts. |
| What is the structure of collagen? | Fibre framework in a mucopolysaccharide rich semisolid gel "ground substance. |
| What is the function of collagen? | Gives bone its tensile strength. |
| How is bone different to cartilage? | Bone is hardened by precipitation of calcium phosphate (hydroxyapatite) crystals within matrix. |
| What is the function of the hydroxyapatite? | Gives bone it compressional strength. |
| What are the four sections of a long bone? | Epiphysis, Metaphysis, Diaphysis and Periosteum. |
| What is the epiphysis? | Head- articular surface, covered by hyaline cartilage. |
| What is the metaphysis? | Between epiphysis and diaphysis- region of growth in childhood. |
| What is the diaphysis? | Shaft- hollow cylinder, contains bone marrow in marrow cavity (Red blood cell formation). |
| What is the periosteum? | Fibrous connective tissue sheath covering external surfaces. |
| What cells are included in the periosteum? | Fibroblasts (synthesize collagen), Mesenchymal cells (can differentiate into osteoblasts and chondroblasts) and osteoclasts. |
| What are the descending layers of bone? | Periosteum, Shaft of compact bone and Medullary cavity. |
| What are the two major kinds of long bone? | Trabecular (Cancellous) and Cortical. |
| Describe the structure of trabecular bone. | Spongy and porous. |
| 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). |
| What is the structure of cortical bone? | Solid. |
| What are the functions of cortical bone? | Bone on the outside forms the shaft of the long bone. Provides stiffness and strength. |
| 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. |
| How are the cells arranged in cortical bone? | Concentric circles (like an onion). Inside each layer are collagen fibres. |
| 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. |
| What is the composition of the bone matrix? | Organic matrix, crystallised mineral salts and water. |
| What constitutes the organic matrix? | Mostly protein fibres-collagen. Collagen is highly organised in parallel arrangement (in cortical and trabecular bone). |
| What constitutes the crystallised mineral salts? | Hydroxyapatite- Ca10(PO4)6(OH)2 |
| What causes rickets? | Vitamin D deficiency- failure of Ca2+ absorption. |
| What causes scurvy? | Vitamin C deficiency- lack of collagen. |
| 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. |
| 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. |
| 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. |
| What are osteoprogenitor cells? | Stem cell population, gives rise to osteoblasts (as well as other cells). |
| 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. |
| 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. |
| 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. |
| Which hormones control the osteoblast-osteoclast equilibrium? | Calcitonin and Parathyroid hormone (PTH). |
| What is the function of Calcitonin? | Decreases activity of osteoclasts, i.e. decreases blood Ca2+ levels. |
| What is the function of Parathyroid hormone? | Increases the activity of osteoclasts, releases Ca2+. |
| What is the process of trabecular bone remodelling cycle? | Resorption by osteoclasts. Surface exposed to osteoprogenitors. Osteoblasts differentiate. Osteoblasts lay down new bone. Quiescence. |
| Is bone dynamic and remodelled throughout life? | Yes indeed. |
| What is the affect of excessive mechanical stimulation on bones? | Bone mass and density can increase. |
| Why can bone mass and density decrease? | Non-weight bearing (immobilisation). Sex-hormone deficiency (e.g. menopause). Endocrine/nutritional disorders. |
| What is Wolff's law? | Bone adapts to the load under which it is placed. |
| What are common examples of Wolff's law? | Weight-bearing exercise, orthodontic braces, (Amerindian) head binding. |
| Describe bone growth from fetus to adult. | Cartilage model->Replaced by bone (ossification). Bone growth begins in the shaft during fetal life. |
| What is the Cartilage model? | Formed by chondroblasts then reshaped chondrocytes. |
| What is ossification? | The replacement of cartilage by bone. Endochondral (long bones). Intramembranous (flat bones). |
| Where does ossification begin? | In the diaphysis. |
| Is the Primary ossification centre active before birth? | Yes indeed. |
| What is the secondary centre of ossification called? | Epiphysis. After birth bone begins to develop in the ends of bone. |
| 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. |
| What is a chondroblast? | Site where chondrocytes are formed in the growing matrix. |
| When does the fusion of epiphyseal plates occur? | At the end of puberty. |
| How long does a fracture usually take to heal? | 2-4 weeks dependent on severity and position and age. |
| How does a fracture heal? | Inflammation and additional blood flow lead to callus formation and lamellar bone is laid down. |
| 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. |
| What happens when lamellar bone is laid down? | Collagen is organised in regular sheets to give strength and resilience. |
Created by:
robertspedding
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