Bone Flashcards
What are the cells which are found in bone
Osteoprogenitor cells
Osteoblasts
Osteoclasts
Osteocytes
What is contained in the extracellular matrix
Collagen
Calcium hydroxyapatite
What makes up bone
Cells
Extracellular matrix
What are osteoblasts and osteoclasts derived from
Embryonic mesenchyme - osteoprogenitor cells - form a stem cell population within bones
What do osteoblasts secrete
Osteoid
Unmineralized bone
Define osteocytes
Osteoblasts which have become trapped within mineralised (within there own matrix) bone
Function unknown - suspected to do with calcium
Connect to surrounding cells via canaliculi - oxygen
Describe osteoclasts
Derived from monocytes
Multinucleated cells
Absorb bone - as they do become dropped which they sit in Howship’s lacunae
Activity is linked to that of osteoblasts - coordinated such as RANK-L
What is bone
A dynamic living tissue
What are the ways in which bone can be typed
Origin
Mode of formation
Gross appearance
What are the types of origin
Primary (woven)
Secondary (lamellar)
What are the types of mode of formations
Membranous
Endochondrial
What are the divisions by gross appearance
Spongy/cancellous
Compact
Osteons
Appositional
What is osteoid
Osteoblasts extracellular matrix created
Describe secondary bone
Also called lamellar bone
Stronger than primary (woven) bone
Forms osteons
Central haversian canal containing blood vessels
Surrounding concentric rings of lamellar bone with osteocytes
What are the two ways in which bone can form
Intramembranous
Endochondrial
What bones are formed from intramembranous formation
Flat bones of the skull
Some cortical bone shafts
What bones are formed from endochondrial formation
All other bones
(expect those formed by intramembranous)
Describe intramembranous ossification
Formation of bone from a membrane precursor
Bone is deposited directly in a primitive embryonic mesoderm without a cartilaginous proforma
Starts in 2nd trimester of embryonic life
Small clusters of progenitor cells within a primitive mesenchyme transform into osteoblasts and deposit isolated islands of bone
The islands enlarge creating a meshwork of bone
Osteoblasts will continue to deposit until all holes are filled in - create primary plate of bone
Overtime woven bone will be remodelled to lamellar bone
Describe endochondrial ossification
Hyaline cartilaginous template into bone
Cartilaginous proformas form during 2nd trimester of intrauterine life
Shaft/diaphysis becomes calcified and blood vessels grow into the developing bone
osteoprogenitor cells differentiate into osteoblasts, lay down bone to form primary centre of ossification
Profomer cartilage is eroded away as new bone forms
Later secondary centres of ossification form in the heads/epiphysis of bones
By birth most bones have primary centre of ossification and some have secondary
As ossification centre expand cartilage becomes restricted to epiphyseal growth plates that separate epiphysis from diaphysis
Cartilage remains on articular surface
Describe synovium
Lines the inside of the joint capsule
1-4 layers of synovial cells
Type A - phagocytes
Type B - rich in rER
Variable shapes - squamous to cuboidal
Richly vascular, highly innervated
Describe the hyaline cartilage of the proformers
Synthesised by chondroblasts that differentiate from progenitor cells within the embryonic connective tissue (mesenchynme)
Produce a glassy amorphous looking matrix within which the cells become trapped causing them to transform into less synthetically active chondrocytes
Cartilage is encapsulated by a fibrous perichondrium that contains both progenitor cells and differentiated chondroblasts
What are the features of osteoclasts
Occur frequently in developing bone even from the outset
Multi-nucleate cells digest bone
Play a significant part in the remodelling of bone during growth phase
What is the first type of bone to be produced
Primary bone
How can secondary bone occur as
Open framework (woven bone)
Compact lamellae
Osteons
How does long bone increase in length
By adding new bone at the epiphyseal plates
Heads are re-sculpted and additional bone is added to the outside of the shaft
