bone Flashcards
what are the 4 functions of bone
weight bearing/support for the mechanical function of joints and muscles
protection e.g. skull and vertebral column
mineral store - Ca
blood formation in the red bone marrow - it is the supporting tissue for haemopoiesis
gross anatomy of bones
compact bone (cortical) spongy bone (trabecular) blood vessels medullary cavity (found in the shaft of long bones and filled with bone marrow) bone marrow membranes surrounding the surface
what are the 2 membranes surrounding the bone surfaces
periosteum (on the outside)
endosteum (covers the internal surface of the bone)
osteons/Haversian system
found in compact bone
organisation of bone in circular structures
central Haversian canal with blood vessel running through and horizona perforating/ Volkmann’s canals (connect the Haversian canals and also filled with blood vessels)
osteocytes and concentric rings of bone matrix - lamellae - around Haversian canals
spongy bone
also called cancellous or trabecular bone or diploe
less dense than compact bone, more porous
network of lamellated trabeculae filled with bone marrow
NO HAVERSIAN SYSTEMS
orientation of trabeculae reflect main directions of mechanical forces
What are the 6 types of bones
flat bone (frontal - skull) short bone (carpal) sesamoid bone (patella) sutural bone irregular bone (vertebrae) long bone (femur)
what are the 2 types of bone formation
endochondral
intramembranous
endochondral bone growth
most common - long bones endochondral ossification: 1. bone forms as cartilage model first 2. blood vessels invade cartilage 3. cartilage replaced with bone 4. cartilage remains in epiphyseal growth plate to allow further growth (eventually ossifies when growth is complete)
intramembranous bone growth
flat bones of skull, mandible, maxilla and clavicles
more straightforward than endochondral ossification
NO CARTILAGINOUS PHASE
1. mesenchymal cells develop into osteoprogenitor cells
2. these mature into osteoblasts that start depositing bone
3. residual mesenchyme cells develop blood vessels and bone marrow
4. this also occurs in adult cortical bone and doesnt stop when you stop growing
what makes up bone
cells - osteoblasts, osteocytes, osteoclasts
extracellular matrix
what makes up the ECM in bone
~45% hydroxyapatite crystals - make bone stiff and supportive, high strength under compression
~35% type I collagen - provides some flexibility and reduces risk of fraction, high strength under tension
~20% water
bone is a composite material and a very dynamic tissue
bone turnover
constant process, even in adults
healthy bone has a balance between bone removal and formation
main cells involved are osteoclasts and osteoblasts
osteoblasts
immature bone cells created from osteoprogenitor cells in periosteum and endosteum
derived from mesenchymal lineage
produce bone matrix and initiate calcification
become osteocytes once surrounded by the matrix that they have created
osteocytes
mature bone cells found inside lacunae
numerous processes lying in canaliculi
canaliculu connect lacunae to each other - allows communication between cells
function - may maintain bone matrix and sense mechanical forces
osteoclasts
fairly large cells with ruffled border, mutlinucleated cell derived from haematopoietic stem cells
found on bone surface
function: resorb bone matrix
Howship’s lacunae: resorption pits
how do osteoclasts resorb bone
release acids from the ruffled border onto the mineral which dissolves the minreals in the bone in order to break it down, forms resorption pit
osteoporosis
resorption>formation
fairly common, weaker spongy bone structure
bone structure is weaker and struts are thinner
seen in elderly patients
much more likely to fracture a bone
paget’s disease
increased resorption/formation much less common than osteoporosis both processes are in XS bones aren't formed properly tissue is weaker and it is painful
osteopetrosis
reduced resorption
bone becomes stone like
too dense and brittle
NOT THE SAME AS OSTEOGENESIS IMPERFECTA
differentiation between osteoblasts and osteoclasts is regulated by…
specific regulatory molecules
osteo
bone
chondro
cartilag
arthro
joints
how many bones are there in the human skeleton
270 at birth
206 in adults
axial skeleton
trunk of the body
skull, vertebral column, ribcage
maintains upright posture
transmits weight from trunk to lower limbs
appendicular skeleton
appendages - upper and lower limb bones
locomoter and protective functions
