5. Bone growth and healing

5 reasons for why we need bone

• mechanical support

• transmission of forces generated by muscle

• protection of vital organs

• calcium homeostasis

• haematopoiesis

how often are bones completely replaced

once every 10 years

2 different microscopic types of bone

woven bone

lamellar bone

what bones feature lamellar bone

most matures ones

how does collagen run in lamellar bone & why’s that good

opposite directions in alternating layers so the bone resists torsion forces

How are (type 1) collagen fibres ordered in woven bone

criss crossed over eachother to make a woven sorta vibe

when’s woven bone needed

when it’s made quickly or when bone’s needed asap

examples for both needs of woven bone

embryo development when made quickly. Fracture healing when it’s needed asap

what happens to woven bone over time

osteoblasts turn the woven bone into lamellar bone after some time, surrounding the bone and making osteoids

what are osteoids

minerals required for making lamellar bone

what are osteoids made of

type 1 collagen and glycosaminoglycans

what gives woven bone the rigidity to turn into lamellar bone

calcium salts

Two ways of bone growth in the embryo

• intramembranous ossification

• endochondral ossification

what’s intramembranous ossification

when bone forms in a sheet of immature connective tissue

what bones form w intramembranous ossification

flat bones, face bones, clavicle

what bits of bone aren’t calcified yet & why

shoulders and head, so the baby can be easily pushes out of the uterus

What happens in endochondral ossification

bones form from pre-existing cartilage models, that act as templates

what bones form w endochondral ossification

base of the skull, long bones

what form of ossification’s slower

endochondral. much slower.

how are osteons & spongy bone connected

perpendicular canals called spongy bone

How does lacunae form

osteoblasts become trapped in the osteoid they form, turning int osteocytes

Step 1 of bone remodelling

Pre-osteoclasts arrive at the bone surface

Pre-osteoclasts arrive at the bone surface

the pres differentiate into osteoclasts

the pres differentiate into osteoclasts

they secrete acid & proteins onto the bone surface, creating an excavation pit

they secrete acid & proteins onto the bone surface, creating an excavation pit

the osteoclast undergoes apoptosis, ending the resorption phase

the osteoclast undergoes apoptosis, ending the resorption phase

Mesenchymal stem cells are activated into osteoblasts to replace the excavated bone

Mesenchymal stem cells are activated into osteoblasts to replace the excavated bone

the make osteiods, which are mineralised to form mature bone

what do used osteocytes become after use here

osteocytes or bone lining cells

what is the bone remodelling process modulated by

cell-to-cell interactions and cytokines

How are pre-osteoclasts activated

osteoblasts (or stromal cells) give a protein called RANK ligand to the RANK receptor on the pre. And also give an M-CSF to the M-CSF receptor.

How do osteoblasts stop activation of osteoclasts

they produce osteoprotegerin (OPG) to bind to the RANK ligand, preventing it from binding to the receptor on the pre.

why would activation wanna be stopped

to avoid constant resorption, which can cause osteonecrosis

how to control the rate or resprtion

the ratio of RANK to OPG is altered by Hormones, Vit D, inflammatory cytokines, and growth factors

what can rapidly increase resorption

steroids

How does bone strength change over time

increases till it peaks at 20-25. then decreases over time

why’s bone strength decrease anyway

osteoblasts can’t keep up w osteoclasts. also genes.

what can help maintain bone strength

exercising, not too much alcohol, sleeping

what’s a pathological fracture

a fracture due to less dense bones, due to less calcium.

4 steps to normal fracture healing, and how long they take

Haematoma (day 0-1)

Soft callus (day 1- week 2)

Bony callus (week 2- week 3)

Remodelling (week 3- months)

What’s a haematoma

blood clot around a fracture

how’s a haematoma formed

rupture of blood cells w the fracture, filling in the fracture gap

what does the haematoma form

a fibrin mesh, sealing the fractured site, providing a scaffold for the action of inflammatory cells, fibroblasts, and support for new capillary growth.

What do platelets and inflammatory cells do in the haematoma

releast PDGF, TGF-β, FGF and other growth factors

what do these growth factors do

promote osteoprogenitor cells in the periosteum, medullary cavity and surround soft tissues.

what do osteoprogenitor cells activate into

osteoclasts and blasts

what’s a soft callus here

connection between the two bones while all this activation’s happening.

what do the clasts and blasts do next

make woven bone on the connection between the two bits of bone

what’s sometimes formed w woven bone

hyaline and fibrocartilage

what’s the cartilage do

forms along the fracture line, then undergoes endochondral ossification to form a bony callus

what happens to the woven bone

turned into lamellar by clasts and blasts

what happens to the bone as it matures

bits that don’t udnergo stress are resorbed

when’s remodelling done

when there’s spongy bone and compact bone there now. fracture’s bridged. it’s all made of lamellar bone.

what can caused impaired healing

• inadequate immobilisation

• avascular necrosis

• bone loss

• space/tissue between fragments

• extensive trauma

• infection

• intra-articular fractures for joints

• age

• drugs like steroids

what bones or parts of bone heal slower

tibia heals slow.

diaphysis fractures heal slower than metaphysis

What’s osteonecrosis/avascular necrosis

ischaemic necrosis of bone & bone marrow due to lack of blood supply to the bone

what can osteonecrosis be caused by other than fractures

steroids, alcohol, sickle cell anaemia, blood clotting. (non-traumatic osteonecrosis)

what’s idiopathic osteonecrosis

osteonecrosis w no risk factors impacting the person

What’s osteomyelitis

infection of the bone/bone marrow

how’s osteomyelitis happen

• pressure ulcers and trauma,

• ischemia,

• lack of blood supply,

• foreign bodies previous explosed to infection

2 type of osteomyelitis

haematogenous or multimicrobial

haematogenous meaning

coming from 1 organism

Multimicrobial meaning

coming from multiple different bacteria

what’s staphylococcus aureus

bone pain + systematic signs of infection

what;s used to diagnose osteomyelitis

blood or bone culture

what’s used to treat osteomyelitis

antibiotics

why’s treatment for osteomyelitis have to be good

if the acute case is only partially fixed, it becomes chronic

what sort of response is caused by a bacterial infection

a neutrophilic inflammatory response