Bone Flashcards
3 types of cartilage
- Hyaline cartilage: spacious in b/w cells
- Elastic cartilage: like hyaline but w/ dense elastic fibres (dark staining)
- Fibrocartilage: collagen fibres in rows (//) >shock absorber *No perichondrium
List the components in CT
- Cells: produce & secrete extracellular matrix (ECM)
- Fibres (F): support
- Ground substance (GS): “fills” space b/w cells & fibres
- ECM = GS + F + fluid (water)
2 types of chondrogenic growth
- Appositional: new cartilage forms @ surface of existing cartilage
- Interstitial: new cartilage forms w/in existing cartilage
Describe Appositional growth
- new cells derived from inner perichondrium
- resemble fibroblast
- produce type I collagen
- differentiate into chondroblast & secrete matrix
- matrix increase cartilage mass
- new fibroblasts produced to maintain cell population of perichondrium
Describe interstitial growth
- new cells arise from division of cells w/in lacunae
- chondrocytes retain ability to divide & surrounding matrix is distensible (stretched) => further secretory activity
- lots of daughter cells in lacunae but later matrix separates them
Ca2+ required for:
- enzyme activity
- muscle contraction
- mediate cell adhesion & movement
- exocytosis
- membrane permeability
What do bones store?
- Ca2+: stored as hydroxyapatite crystals
- (& phosphate)
What 2 hormones control Ca2+ levels in blood?
- Parathyroid hormone (PTH): Lo -> Hi by stimulating osteocytes & osteoclasts; Increase absorption in SI; reduce loss in kidneys
- Calcitonin: Hi -> Lo. Inhibit PTH on esteoclast (= Inhibit bone resorption)
4 types of Bone cell
- Osteogenic (stem) cell
- Osteoblast
- Osteocyte
- Osteoclast: (lots of nuclei)
Why is decalcification necessary before sectioning tissue?
remove calcium bc blades blunt quickly or poor sections produced.
- Done by Ca2+ chelators (EDTA): slow & gentle
- or acids (nitric, formic): fast but harsh on tissue
5 zones of epiphyseal plate & add brief description of each
- Zone of reserved cartilage: give cells
- … proliferation: cells proliferates = tiss. become longer
- … hypertrophy: tiss. rapidly grow in size
- … calcified cartilage: Ca2+ fixed in by osteoblasts
- … ossification: hard bone, vascular & neural supply develop
Explain how cartilage becomes bone (in long bones)
- Proliferation: of chondrocyte
- Condensation: contain prehypertonic chondrocyte
- Hypertrophy: contain hypertrophic chondrocyte, BV, progenitor
- Bone marrow: osteoclast make bones smoother, & precursor cells -> osteoblast + …clast
Describe the steps to thickening bone
- Initial core is broken down/resorb by osteoclast
2. Osteoblast deposits in the middle = middle gets larger
Cells in bone include
osteocytes, progenitor cells, osteoblasts, bone-lining celss, osteoclasts
Mineralised (bone) matrix consist of… & provides…
a) mineral (hydroxyapetite crystals); collagen (Type I); ground substance
b) support & protection
Summarise bone repair process
- hematoma forms (when bone + BV broken) => inflammation
- Soft callus takes away clot & replaces w/ fibrous tiss.
- Hard callus forms
- Bone remodelled (bone strength back to normal)
3 types of ground substances (GS) and function of each (5)
- Proteoglycan macromolecules > compressive strenght & bind to growth factors
- Multi-adhesive glycoproteins > attach bone cells & collagen fibres to mineralised GS
- Factors:
- Osteocalcin > captures Caa2+ from blood, attract & stimulate osteoclast
- Sclerostin > inhibits further bone formation by osteocytes
- Bone morphogenic proteins (BMPs) > mesynchymal cells -> osteoblasts
Functions of osteoblast
> secrete bone matrix
secrete osteoid (unmineralised bone): Type I collagen, bone matrix proteins (BMPS), ALP
calcification if bone matrix (add Ca2+)
What is the clinical marker that indicate if osteoblasts are active?
Osteocalcin & alkaline phosphatase (ALP)
What is the osteoprogenitor cells?
- Osteoblast precursor cells derived from mesenchymal cells (in bone marrow)
- found in internal & external bone surfaces & microvasculature
- make (diff. into) periosteal & endosteal cells
Role of osteoprogenitor cells?
required for osteogenesis (new bone formation)
What are osteocytes ?
- mature osteoblast- surrounded by osteoid/bone matrix. In lacunae
- smaller than osteoblast bc reduced perinuclear cytoplasm
- has cytoplasmic processes through canaliculi = contact other cells
Role of osteoblast
> maintain bone matrix
> can synthesise new matrix & carry out matrix degeneration
What are bone lining cells?
- periosteal & endoosteal derived from esteoblast
- flat cells: reduced cytoplasm
Role of bone lining cells
> cover bone not remodelling (by osteoclast)
maintain and support nutrition of osteocytes
regulate movement of Ca & PO4 in & out of bone
Role of osteoclast
> bone resorption (break down): by releasing protons (H+) & lysosomal hydrolases
Clinical marker of osteoclast activity
tartrate-resistant acid phosphatase (TRAP)
Formation of osteoclast (according to cell stages)
- Hematopoietic stem cell
- Monocyte/macrophage
- preosteoclast
- osteoclast
Formation of osteocyte (according to cells stages)
- mesenchymal stem cell
- Pre-osteoblast
- osteoblast
- osteocyte
when decalcifying w/ chelators (EDTA)
- EDTA in pH 7-7.5 is used as the agent
- Process is very slow: 6-8 weeks
- Preserves the enzymes
factors that influence decalcification process
- temp (25ºC)
test used to check if Ca2+ present in tissue (after decalcification)
Ca oxalate test using ammonium oxalate (after neutralised w/ NH4OH
Intramembranous vs endochondral ossification
- Intramembranous: ossification w/in CT membranes in flat bones. spongey appearance
- Endochondral: ossification w/in hyaline cartilage template in long bones. Has 1º & 2º ossification
State the location of type I & II collagen
I: fibrocartilage
II: Hyaline, elastic
Types of decalcifying agents
- Strong mineral acids
- Weak inorganic acids
- chelating agents
What is bone fixed w/ & the duration?
Neutral buffered formalin for 12-24hrs
