BS2014: Bones, Joints & Movement

How many bones in the adult (human) skeleton

206

How many axial bones in the human skeleton

80

How many appendicular bones in the human skeleton

126

Role of axial skeleton

protection of internal organs

Role of appendicular skeleton

movement

What are the different types of bones found in the human skeleton

• flat bones

• irregular bones

• sesamoid bones

• short bones

• long bones

Flat bones

parallel layers of compact bone and spongy centre (e.g. skull, sternum)

Irregular bones

thin layers of compact bone surrounding a spongy centre (e.g. vertebrae, pelvis)

Sesamoid bones

bones embedded in tendon or muscle (e.g. patella)

Short bones

cube-shaped, thin layer of compact bone with spongy centre (e.g. wrist, ankle)

Long bones

long shaft, two articular surfaces, mostly compact bone (e.g. femur, tibia, fibula, humerus)

Proximal epiphysis

end of the long bone closer to the centre of the body

Distal epiphysis

end of the long bone further away from the centre of the body

Epiphysis

end of the bone

Metaphysis

connects the diaphysis to the epiphysis of the bone

• contains the growth plate in children

Diaphysis

the shaft of the long bone

Epiphysial line

the remnant of the epiphyseal growth plate that appears in long bone after growth has ceased

Endosteum

thin vascular membrane of connective tissue that lines the inner surface of bones, containing osteoprogenitor cells, osteoblasts, and osteoclasts

Periosteum

dense fibrous vascular membrane of connective tissue that lines the outer surface of bones, that supplies blood, nerves and stem cells for bone growth, healing and fracture repair

Medullary cavity

central hollow space in the diaphysis that stores yellow bone marrow

Osteogenic cell

bone cells in the inner periosteum, endosteum and bone canals which undergo cell division to differentiate into osteoblasts for bone growth, repair, and remodelling

Osteoblasts

cells responsible for synthesizing new bone to create, reshape and repair bones

Osteoblasts trapped in ECM

differentiate into osteocytes

Osteocytes

mature bone cells which make up 90-95% of bone cells in the adult skeleton and maintain metabolism by exchanging nutrients and waste with blood

Osteoclasts

specialised multinucleated cells which are responsible for resorption of bone tissue to facilitate bone remodelling, repair and calcium regulation

Osteoclast functions

dissolve and break down old bone to make space for osteoblasts to create new bone tissue for growth and repair

RANK ligand in regulation of osteoclast activity

• interacts with RANK (receptor) triggering the differentiation, activation and survival of osteoclasts

• trigger the fusion of precursor cells to form mature multi-nucleated osteoclasts

• in osteocytes, RANK ligand interaction with its receptor can trigger osteocyte activity increasing resorption of bone

What works to balance the effect of RANK, and how

osteoprotegerin (OPG), acts as a decoy in binding to RANK ligand preventing RANK ligan from interacting and activating its receptors on the surface of osteoclasts

Parathyroid modulation of RANK and OPG balance

stimulates the production of RANK ligand while simultaneously repressing OPG expression to increase osteoclast activity

Oestrogen modulation of RANK and OPG

increases OPG expression and inhibits RANK ligand signalling to reduce osteoclast activity

bone marrow

spongy tissue which produces blood cells and stores fats

red bone marrow

site of production of red blood cells, white blood cells, and platelets

yellow bone marrow

stores fat and acts as an energy reserve, replaces red bone marrow with age

haematopoiesis

the continuous highly regulated process of producing new blood cells from haematopoietic stem cells within the red bone marrow

Bone marrow over the human lifespan

• when born, bone marrow is essentially red

• rapid conversion of red bone marrow to yellow bone marrow form new-born stage to adult stage

• at 25 years old, 50-70% of bone marrow is yellow/BMAT

Patten for BMAT development

in a centripetal pattern from extremities to axial skeleton