MS Systems: Bones and Bone Growth Flashcards
What are the functions of bones?
\+ Protection \+ Support \+ Movement \+ Storage of minerals (Ca, P, Mg) \+ Blood cell formation
What are the structural features of a long bone?
+Epiphysis (head)
+ Diaphysis (shaft)
+ Periosteum
What are features of the Epiphysis?
+ Articular surface
+ Covered by hyaline cartilage
What are features of the diaphysis?
+ Hollow cylinder
+ Contains bone marrow
+ Nutrient foramen
What are features of the periosteum?
Fibrous layer that covers external surfaces. Cells include:
- fibroblasts: synthesize collagen
- mesenchymal cells: can differentiate into osteoblasts and chondroblasts
- osteoclasts
What are the functions/features of osteoclasts?
+ Resorb bone matrix by demineralization in response to mechanical stresses and physiological demands
+ Multinucleated
+ Derived from haematopoietic cells
+ Regulated by osteoblasts and hormones
How to osteoclasts resorb bone?
+ Form a “sealing zone” on bone
+ Release H+ and hydrolytic enzymes to dissolve the mineral, liberate calcium and break down the extracellular matrix
+ Regulated by osteoblasts and hormones
What are the functions/features of osteoblasts?
+ Responsible for bone formation
+ Cuboidal cells, derived from osteoprogenitor cells that line the surface of the bone
+ Deposit the organic matrix, then cause mineralisation
+ Some become entombed during this process, mature into osteocytes
What are the features/functions of osteocytes?
+ Mature bone cells; embedded in lacunae, relatively inactive
+ Maintain bone matrix through cell-cell communication: via projections in canaliculi
+ Influence bone remodelling
+ Mechanosensing
What is the structure/function of compact bone?
+ Osteons or Haversian systems
+ Very strong, light cylinder that resists compressive (grav.) forces
+ Osteocytes buried alive in the bone matrix
What is the structure of cancellous/trabecular bone?
+ Spongy, porous, bone tissue that is filled with red bone marrow
+ Not as strong as cortical bone found in long bones, but very important for producing blood cells
+ Found in ends of long bones and the pelvis, ribs, vertebrae, and skull
What effect does calcitonin have on osteoclast activity and blood calcium levels?
It decreases the activity of osteoclasts, therefore decreasing blood Ca++ levels
Favours bone resorption/atrophy
What effect does parathyroid hormone (PTH) have on osteoclast activity and blood calcium levels?
It increases the activity of osteoclasts and releases Ca++
Favours bone formation/hypertrophy
What are the steps in the bone remodelling cycle?
+ Resorption
+ Reversal
+ Formation
+ Quiescence
How can bone mass and density increase?
Excessive mechanical stimulation
How 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 e.g orthodontic braces, head binding
How long do fractures of woven bone take to heal?
2-4 weeks
- dependent on the severity and position of the fracture and age of the patient
What are the steps of bone fracture healing?
+ Callus formation
- osteoblasts quickly form woven bone to bridge the gap
- woven bone is weak as the collagen fibres are irregular
+ Lamellar bone laid down
- collagen organised in regular sheets to give strength and resilience
Remodelling by osteoclasts to restore original bone shape
What is the foetus cartilage model is replaced by?
Bone (ossification)
- endochondrial (long bones)
- intremembranous (flat bones)
Bone growth begins in the shaft during foetal life
What is the foetus cartilage model is replaced by?
Bone (ossification)
- endochondrial (long bones)
- intremembranous (flat bones)
Bone growth begins in the shaft during foetal life
Where is does ossification begin/primary ossification?
Diaphysis
Where is does ossification begin/primary ossification?
Diaphysis
Where is the secondary centre of ossification?
Epiphysis (epiphyseal plate)
What are the zones of the epiphyseal plate?
\+ Ossification (osteogenic) zone \+ Calcification zone \+ Hypertrophic zone \+ Growth (proliferating) zone \+ Resting zone
When does fusion of the epiphyseal plate occur?
By the end of puberty
What is the chemical composition of bone matrix?
Calcium hydoxyapatite: (Ca5 (PO4)OH)
What are features of the medullary cavity?
+ Contains bone marrow supported by cancellous bone
- red bone marrow is one site of haematopoiesis
What are features of the resting zone?
On the epiphyseal side of the plate (reserve cells)
What occurs at the growth zone?
Cells undergo mitosis (proliferation)
What occurs at the maturation zone?
Cartilage cells are transforming and enlarging and the matrix calcifies
What occurs at the osteogenic zone?
+ Calcified cartilage removed by osteoclasts
+ Replaced by bone secreted by osteoblasts
