bone Flashcards
2 types of bone
cortical and cancellous
cortical bone
○ 80% of skeleton mass
○ Hard exterior of bone
○ Packed osteons or haversian systems
- Cancellous
(trabecular/spongy)
○ Boney struts organised into a loose network
○ Forms internal bone tissue, porous - contains marrow
- Woven bone
○ When bone is initially formed (primary bone) has random collagen weave, mechanically weak (fetal bone development, repaired fractures)
- Lamellar bone
○ Is secondary bone created by remodelling of woven bone
○ Has a regular parallel alignment of collagen into sheets (lamellae) and is mechanically strong
- Senescence
○ Resorption exceeds formation
○ Skeletal mass decreases
- Osteoprogenitor cells
○ Stem cells
osteoprogenitor cells located in
§ Located in inner cellular layer of periosteum, endosteum and lining of osteonic canals
- Osteoblasts
○ Form bone
○ Derived from osteoprogenitor cells
○ Synthesize organic components of bone matrix
○ Located on surface of bone tissue
- Bone formation
○ Active osteoblasts produce and secrete collagen
○ Collagen fibrils form osteoid (organic matrix)
○ This then becomes mineralized - ossification
- Osteocytes
○ Mature bone cells
osteocytes differentiate from
§ Differentiate from osteoblasts.
osteocytes reside in
§ Reside within lacunae, canaliculi contain ECF carrying nutrients to nourish the osteocytes
- Osteoclasts
○ Degrade/resorb bone
○ Large, motile, multinucleated, bone resorbing cells
○ Haematopoietic origin
resorption
□ osteoclasts Adhere tightyl to established bone matrix
□ Seceret bone degrading chemicals (HCl) and enzymes - collagenase
collagenase
bone degrading enzyme
bone recycling
□ Degraded mineral and organic components and endocytosed by the osteoclast
□ Delivered to nearly capillaries to the enter the circulation
- Intramembranous ossification
○ Bone development from fibrous membranes
- Endochondral ossification
○ Bone development from hyaline cartilage
- Intramembranous ossification examples
- Formation of flat bones of the skull, the mandible, and the clavicles
- Intramembranous ossification process
- Condensation of mesenchymal cells to form a bone template membrane
2. Differentiation into osteoblasts at the ossification centre
3. Osteoblasts secrete the extracellular matrix and deposit calcium - oseoid
4. Vascularization of the mesenchyme
5. The spongy bone is remodelled into a thin layer of compact bone on the surface of the spongy bone
endochondral ossification
- All of the bones of the body, except for the flat bones
endochondral ossification process
○ In long bones, chondrocytes form a template of hyaline cartilage
○ Blood vessels invade the cavities
○ Osteocytes calcify the osteoclasts modify the calcified matrix into spongy bone
○ Osteoclasts create a marrow/medullary cavity
○ Secondary ossification centres form int ehh epiphyses
○ Hyaline cartilage persists until adolescence at the epiphyseal plate that is responsible for the length growth of long bones
3 phases of remodelling
- Activation
- Osteoclasts recruited
2. Resorption of bone
- Osteoclast degrade bone, until reversal
3. Formation of bone
i. OB activation and mineralisation
- Serum Ca levels
○ Tightly regulated
○ Hypercalcaemia
§ Confusion, depression, weakness, kidney stones and abnormal heart rhythm including cardiac arrest
§ Depresses neuromuscular activity
○ Hypocalcaemia
§ Impaired clotting, muscle spasms, seizures, confusion, or cardiac arrest
§ Potentiates neuromuscular activity
Factors regulating plasma Ca
- Regulated by calcium sensing cells that release calciotropic hormones
three calico hormones
PTH
Calcitriol
calcitonin
- PTH
- From parathyroid gland
- Calcitriol
i. From kidney
- Calcitonin
- From thyroid
- Too much calcium in bood
○ Release calcitonin hormone
- Not enough calcium in blood
○ Release parathyroid hormone
