Bone 1 Flashcards
Functions of bone
Hematopoiesis – the formation of blood cells from hematopoietic stem cells found in
the bone marrow.
•Lipid and mineral storage – bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals.
•Support – bone forms scaffolding for skeletal muscle and other soft tissues, it creates a framework that gives the general shape of the body.
•Protection – particularly the axial skeleton which surrounds the major organs of the body.
Components of bone-The Extracellular matrix
ECM) refers to the molecules that provide biochemical and structural support to the cells that populate bone.
Organic and inorganic portions
Organic portion of of ECM
90 % organic portion - • Mainly type I collagen (also type V, III, XI, XIII) .
Non-collagenous proteins (about 10%) constitute the ground substance and include proteoglycans, glycoproteins, bone specific proteins, growth factors and cytokines
Inorganic portion of ECM
represents about 50% of the dry weight of the matrix and is composed mainly of calcium phosphate in the form of hydroxyapatite crystals
Osteoprogenitor (osteogenic)
the stem cells of bone, they are derived from primitive
mesenchymal cells.
Form a population of stem cells that can differentiate into osteoblasts which secrete
the organic unmineralized matrix or osteoid
Osteoblasts
Synthesize uncalcified/unmineralized extracellular matrix called osteoid.
This will later become calcified/mineralized to form bone.
Osteocytes
As the osteoid mineralizes, the osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate/maintain bone mass.
Osteoclasts
Multinucleated giant cells derived from monocyte progenitor cells responsible for resorbing and remodeling bone by releasing H+ ions and lysosomal enzymes.
The balance of osteoblast to osteoclast activity is crucial in the maintenance of the tissue’s structural integrity. It also plays a role in conditions such as osteoporosis
Bone lining cells
Found on the inner and outer surface of bone; The endosteum and periosteum
Osteogenic cells
Are spindle shaped connective tissue cells (derived from embryonic mesenchyme stem cells) in the periosteum and endosteum that can differentiate into osteoblasts
inactive
osteoblasts
In mature bone in which there is no active new bone formation or remodeling, the osteoprogenitor cells become flattened spindle shaped cells closely applied to the bone surface
how do osteoblasts appear
Morphologically may appear as a cuboidal layer
(high secreting activity) or flattened (declining
secretions
what keeps osteoblasts in contact with other osteoblasts and osteocytes :;
Cytoplasmic processes
what are the precursors of glycosaminoglycans (of the osteoid matrix)
PAS positive granules in the cytoplasm of osteoblasts
osteoclast can secrete the osteoclast stimulating factor , what happens when it ceases the secretory function :
undergoes changes to its morphology
and becomes an osteocyte
mature bonne cells ,derived from osteoblasts
Osteocytes
osteocytes vs osteoblasts mounts of condensed nuclear chromatin, reduced amounts
of RER and a smaller Golgi apparatus ?
osteocytes have increased amounts
The fusion of hematopoietic monocyte progenitor cells
Osteoclasts
Howship’s lacunae
-are depressions on the bone surface that house osteoclasts
-These lacunae result from the osteolytic activities of
osteoclasts
Osteoclasts;Ruffled border
Finger-like evaginations along Howship’s lacunae depict sites of active
bone resorption
Osteoclasts;Clear zone
• Region of cytoplasm that surrounds the ruffled border • Microfilaments, anchor osteoclast to the boney surface and help isolate osteoclastic activity
Osteoclasts- Basal region
• Houses the organelles and
numerous nuclei of the cell
how does bone resorption happen :
-Lysosomal enzymes (from Golgi complex) and hydrogen ions released
into the confined space between bone matrix and the osteoclast’s
peripheral clear zone
-Decalcified bone matrix is then broken down by acid hydrolases, collagenous and proteolytic enzymes and the cell resorbs the organic and inorganic material
Bone lining cells
They are Osteoblast derived flat cells with little cytoplasm and scant
organelles
what is found on the outer (periosteal cells) and inner (endosteal
cells) surface of non-remodeling bone
Bone-lining cells
Function of the bone lining cells
Function in maintenance and nutritional support of
underlying cells
• Regulate movement of phosphate and calcium into and out
of bone
Periosteum
Attached to the outer circumferential lamellae by
Sharpey’s fibers (type 1collagen)
outer fibrous layer-Periosteum
consists mostly of a dense
irregular connective tissue with fibroblasts.
Contains blood vessels and nociceptors.
inner fibrous layer-Periosteum
contains
osteoprogenitor cells and their derivatives
(periosteal cells)
• Cells actively secreting matrix increase the width of
bone (appositional growth)
Endosteum
Lines any space or cavity in bone (marrow spaces, haversian canals, Volkmann's canal) • It contains mesenchymal stem cells which have the potential to differentiate into osteogenic progenitor cells and differentiated osteoblasts, fibroblasts, blood vessels, and sympathetic nerves • Contains osteoclasts (bone remodeling occurs from within)
Bone growth and remodeling-Elongation
a result of interstitial growth of cartilage at epiphyseal growth plate • Interstitial (internal) growth does not occur in bone
Bone growth and remodeling-increases in width
appositional growth
osteoprogenitor cells in the periosteum
Immature (primary or woven) bone
-First compact bone elaborated; contains numerous osteocytes and irregularly arranged collagen
• Low mineral content
• Remodeled and replaced by mature bone
Mature (secondary or
lamellar) bone
Replaces primary bone and made
up of Haversian systems, or
osteons
Immature bone -Gross
structure
Non-lamellar
No haversian
systems
Immature bone-Collagen fiber
arrangement
Random
disorganized
Immature bone-Osteocyte population density
High (many)
Immature bone-Constitution
Low mineral
density: high water content
Immature bone-Location
Embryo, newborn,
fracture callus,
growth plate
Mature-Gross structure
Lamellar,
haversian systems
Compact outside,
spongy inside
Mature Bone - Collagen fiber
arrangement
Parallel, stress
oriented
(organized)
Mature bone - Osteocyte population density
Relatively low
few
Mature Bone -Constitution
High mineral
density: low water
content
Mature Bone-Location
Develops from 1-
month post natal
Compact bone
Very dense and heavy
Spongy (cancellous) bone
Filled with spaces that are interconnected • in long bone space filled with red (containing hemopoietic cells) or yellow (containing primarily fat) bone marrow
Compact bone-Functional unit
Haversian
system or osteon
• Cylindrical and composed of 4 to
20 concentric lamellae
Compact bone- communication between lacunae and with
the Haversian canals
canaliculi permit communication between lacunae and with
the Haversian canals
what gives strength of the compact bone :
• Adjacent lamellae, have alternating directions of collagen fibers
interstitial lamellae
remnants of old remodeled
osteons between newly laid
down osteons
Volkmann’s canals
Connect adjacent Haversian canals to each other and to endosteum at the marrow cavity on the inside and periosteum on the outside • Allow for passage of neurovasculature through compact bone
outer circumferential lamellae lined by :
periosteum
innercircumferential lamellae lined by :
endosteum
