MSS: Cellular Stucture of Bone Flashcards
List some functions of bone.
- support and movement
- an attachment site for muscles (mechanical)
- protection for internal organs
- provides a home for bone marrow
- acts as a mineral reservoir (calcium)-metabolic
- collaborates with the endocrine system: is a source of some ‘non-classical hormones
What is the composition of bone?
It is 35% (ORGANIC)
- protein matrix
- bone cells (which contribute to the weight.)
65% (INORGANIC) minerals.
- calcium hydroxyapatite
- where 99% of calcium is found
- 85% of the Phosphorus
- 65% Sodium, Magnesium
Describe the organic (osteoid) protein matrix.
It is made up of mainly type 1 collagen.
It gives the bone both flexibility and tensile strength (the ability to resist stretching).
Describe the bone mineral.
It is mainly hydroxyapatite, which is hydrated calcium and phosphate (Ca10(PO4)6(OH)2).
It makes the bone rigid, brittle and gives it a high compressive strength (the ability to resist shortening).
(strength longitudinally)
What are the anatomical descriptions of the bones?
include functions
Anatomical bones
- Flat (protective function)
- long (limbs for large movements)
- short/cuboid (stability at joints, smaller and more precise movements)
- irregular (protect specific organs)
- sesamoid (pulley/reduce strain)
What are the macroscopic descriptions of the bone?
trabecular/cancellous/spongy bone (inner criss crosses)
cortical/compact bone (outer surface)
Cortical bone
- highly organised in repeating units called osteons, which are circular wrapped sheets of bone tissue (lamellae) organised around Haversian canals (which contain blood vessels, nerves etc)
- forms the outer surface of long and flat bones
- within the bone matrix (osteoid protein) there are lacunae cavities where osteocytes reside and are connected via minute canals called canaliculi
Trabecular Bone
- consists of the same structure as cortical bone, but with less organisation
- meshwork of bone tissue with spaces in between
- forms the inner surface of the bone
- within the bone matrix there are cavities called lacunae where osteocytes reside and are connected via minute canals called canaliculi
Compare the cortical and trabecular bone
CORTICAL long bones 80% of the skeleton appendicular skeleton 80-90% calcified mainly structural, mechanical, and protective
TRABECULAR vertebrae & pelvis 20% of the skeleton axial skeleton 15-25% calcified mainly metabolic large surface area
What are the microscopic descriptions of the bone?
- Woven bone (immature)
- Lamellar bone (mature)
Describe the structure of a long bone
What is the benefit of the growth plate?
compact bone (the outside)
spongy bone (the crisscrosses)
medullary cavity (space enclosed by cortical bone)
diaphysis (the main shaft in the middle)
epiphysis (shaft at the ends)
the growth plate/metaphysis (separates diaphysis and epiphysis)
Growth plate allows rapid linear growth
Define Endochondral ossification
Define Intramembranous ossification
Intramembranous ossification
- Direct differentiation of osteoblasts from connective tissue
- Flat bones
Endochondral ossification
- Bones form from a cartilage model
- Long bones
List the types of bone cells (and their origin).
The three main types of bone cells are:
- osteoblasts
- osteoclasts
- osteocytes
Mesenchymal (stromal) stem cells give rise to osteoblasts and osteocytes.
Haematopoietic stem cells give rise to all blood cells, and osteoclasts (which are the same lineage as macrophages).
Describe osteoblasts.
- bone-forming cells
- secrete osteoid to form new bone
- promote mineralisation of osteoid to become mature bone
- may terminally differentiate into osteocytes, found within the bone matrix (in lacunae)
- may remain inert along the bone surface and become lining cells
Describe osteoclasts.
- they are bone (digesting/) reabsorbing cells
- they are large and multinucleate which attach to the bone surface
- formed from the fusion of macrophages
- they secrete acid to dissolve bone minerals (releasing phosphate and calcium)
- they secrete enzymes (Cathepsin K- high affinity for type 1 collagen) to digest the organic matrix
- their life cycle is controlled by apoptosis