BIOL125 Lecture Notes - Lecture 4: Epiphyseal Plate, Metaphysis, Clavicle
Bone Anatomy and Histology
Bones
- Bones are the major component of the Skeletal system; have many functions other
than as support for other tissues
- A living, active organ with a very good blood and nerve supply
- Responsible for: storing calcium, phosphate and other minerals; vital for calcium ion
regulation in body fluids
- Calcium ions needed for: bone and teeth strength and hardness; muscle contraction
regulation; nervous impulse transmission; and blood clotting, both the platelet plug
and haemostatic plug formation (in extrisnci, intrinsic and common pathways) eg:
Ca2+ released by arriving platelets helps attract more platelets to the sit of blood
vessel damage
Bone Matrix
- Bones: connective tissue with hard background matrix; matrix weight (or mass)
mainly due to calcium phosphate [Ca3(PO4)2]
- Bone mass: 98% matrix and 2% cells
- Bone matrix mineral composition: primarily Hydroxyapatite crystals ie. Lots of
calcium phosphate combined with some calcium hydroxide, plus smaller amounts of
other calcium salts, and sodium, magnesium and potassium ions
- Hydroxyapatite crystals laid down onto collagen fibres in cartilage model to form
bone
Properties of Bone Components
- Inorganic: very hard, withstands compression forces; however also brittle and fairly
inflexible, so cannot withstand bending or twisting forces, nor sudden impacts
- Collagen fibres/organic: great tensile strength (stronger than steel), so can be
twisted, bent and pulled without breaking; cannot withstand compression forces
however, and will simply bend out of the way
- The combination of both inorganic and organic components therefore gives bone
great strength, some flexibility, the ability to withstand compression, and to be
highly resistant to shattering
Bone cells 1
- Osteocytes: most abundant bone cell type; maintain both organic (protein) and
mineral components of bone matrix; each osteocyte sits in a singly lacuna; lacunae
connected by canaliculi
- Osteoprogenitor cells: stem cells; present in small numbers; produce osteoblast cells
- Osteoblasts: make and release organic components of matrix; elevate local
concentrations of calcium phosphate decomposition of minerals onto collagen;
form extra bone along stress lines. Why does exercise create stronger bones (as well
as stronger muscles)?
- Osteoclasts: large cells with 50+ nuclei; secrete acids and proteolytic enzymes to
remove and recycle minerals in bone matrix ie. Dissolve matrix to release minerals;
play a major role in regulation of calcium and phosphate ion concentrations in blood
Compact versus Spongy Bone 1
- Matrix composition same in both compact and spongy bone, but arrangement of
bone differs
- Compact bone: parallel osteons; along shaft strength; bears major weight of force
applied to bone
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Document Summary
Bones are the major component of the skeletal system; have many functions other than as support for other tissues. A living, active organ with a very good blood and nerve supply. Responsible for: storing calcium, phosphate and other minerals; vital for calcium ion regulation in body fluids. Calcium ions needed for: bone and teeth strength and hardness; muscle contraction regulation; nervous impulse transmission; and blood clotting, both the platelet plug and haemostatic plug formation (in extrisnci, intrinsic and common pathways) eg: Ca2+ released by arriving platelets helps attract more platelets to the sit of blood vessel damage. Bones: connective tissue with hard background matrix; matrix weight (or mass) mainly due to calcium phosphate [ca3(po4)2] Bone matrix mineral composition: primarily hydroxyapatite crystals ie. lots of calcium phosphate combined with some calcium hydroxide, plus smaller amounts of other calcium salts, and sodium, magnesium and potassium ions. Hydroxyapatite crystals laid down onto collagen fibres in cartilage model to form bone.
