Bones Flashcards
What is the long bone made up of?
epiphysis
diaphysis
periosteum
metaphysis
What is the epiphysis?
The articular head of the long bone
What is the diaphysis?
The shaft. A hollow cylinder containing bone marrow in the marrow cavity where red blood cells are produced. Made up of compact bone
What is the periosteum?
Fibrous connective tissue which envelopes external surfaces
What cells are found in the periosteum?
Fibroblasts, mesenchymal cells and osteoclasts
What is the metaphysis?
Found between epiphysis and diaphysis, region of growth in childhood
What are the 2 types of bone?
Trabecular/cancellous and compact/cortical bone
Structures found in cortical/compact bone
Haversian canals which carry blood along the long axis, Volkman’s canals carry blood perpendicularly, cells structured in concentric circles, each layer contains collagen fibres which have a high degree of orientation, calcium hydroxyapitite present for strength and solidity
Properties of trabecullar/cancellous bone
Fewer lamellular layers so weaker bones but more flexible. Site of haemopoeisis in bone marrow
Explain the process of trabecullar bone remodelling
- Quiescence (dormancy)
- Resorption by osteoclasts (when triggered to do so)
- Reversal: surface exposed to osteoprogenitor cells- osteoblasts differentiate
- Formation: osteoblasts lay down new bone
Explain the process of compact bone remodelling
Osteoclasts resorb bone (acts as a cutting cone) and then osteoblasts lay down new matrix become enclosed and mature into osteocytes (acts as a closing cone)
What is Wolff’s law?
Bones grow and remodel in response to the load with which it is placed with
Explain the process of bone growth from fetus to adult
The cartilage model is formed by chondroblasts and reshaped by chondrocytes. Cartilage is replaced by bone by ossification. Bone growth begins in the diaphysis during fetal life
Explain the process of after-birth endochondral ossification
The secondary centre of ossification is located in the epiphysis. Ends of the bond separate from the diaphysis by plates of hyaline cartilage which forms the epiphyseal plate. In this, columns of cartilage cells undergo cell division, are removed by osteoclasts and the space is invaded by osteoblasts which lay down the bone. Growth begins at the epiphyseal side and moves towards the diaphysis, growth ceases when the structures connect.
What causes the growth of bones to stop?
Production of sex steriods causes the epiphyseal plates to close by process of synostosis
Describe the different zones in after-birth endochondral ossification
resting zone: chondroblasts put down cartilage model at epiphyseal plate
proliferating zone: chondroblasts undergo cell division increasing in number
hypertrophic/maturation zone: chondroblasts become buried and mature into chondrocytes swelling and increasing the cytoplasm which causes the matrix to calcify
ossification zone: disorganised bone from calcification zone becomes remodelled
Healing time for fracture?
Dependent on cells in local periosteum, between 2-4 weeks depending on the location of the fracture, the severity and the age of the individual
What happens when a fracture occurs in the body?
Inflammation and additional blood flow causes the osteoblasts to form woven bone rapidly to bridge the gap. It is weak as the collagen fibres are irregular. Lamellar bone is laid down, presence of collagen in organised layers give strength
What is a fibroblast?
A cell which forms collagen and other fibres
What are osteoprogenitor cells?
Stem cells which give rise to osteoblasts
What hormones control the equilibrium between osteoclasts and osteoblasts?
Calcitonin: decreases activity of osteoclasts parathyroid hormone (PTH): increases activity of osteoclasts
What is Rickets caused by?
Vitamin D deficiency due to failure of calcium ions
What is Scurvy caused by?
Vitamin C deficiency due to lack of collagen
Explain how the equilibrium between osteoblasts and osteoclasts is controlled?
Controlled by signalling between different cells in the bone and actions of hormones:
calcitonin decreases osteoclast activity and decreases calcium ion levels
parathyroid hormone increases osteoclast activity and releases calcium ions
