BONE Flashcards
- an example of specialized connective tissue
- its ECM is different because its matrix hardens
a connective tissue characterized by a
mineralized extracellular matrix (abundance of
calcium and phosphate)
BONE
Bone matrix contains mainly
type 1 collagen
FOUR MAIN GROUP S OF
NONCOLLAGENOUS PROTEINS FOUND IN
THE BONE MATRIX
Proteoglycans
Multiadhesive glycoproteins
Bone specific, vitamin K dependent
proteins
Growth factors and cytokines, which are
small regulatory proteins
contribute to the compressive strength of
bone
responsible for binding growth factors and
may inhibit mineralization
Proteoglycans
what are the Multiadhesive glycoproteins
Osteonectin
Osteopontin
Sialoprotein I and II
-
serves as a glue between the collagen
and hydroxyapatite crystals
Osteonectin
mediates attachment of cells to bone
matrix
Osteopontin
mediate cell attachment and initiate
calcium phosphate formation
Sialoprotein I and II
what are the Bone specific, vitamin K dependent proteins
Osteocalcin
Protein S
Matrix Gla-protein (MGP)
what are the Growth factors and cytokines, which are small regulatory proteins
Insulin like growth factors (IGFs)
Tumor Necrosis Factor (TNF-)
Transforming Growth Factor (TGF-)
Platelet Derived Growth Factors (PDGFs)
Interleukins (IL 1, IL 6)
Bone Morphogenic Proteins (BMPs)
is now used clinically to induce bone growth after bone surgery involving large bone defects, spinal fusions, or implantation of graft materials
Recombinant human BMP 7
(osteogenic protein 1)
BONE STRUCTURE consists of
Bone matrix
Periosteum
BONE CELLS consists of
Osteoprogenitor Cells
Osteoblasts
Osteocytes
Osteoclasts
Bone lining cells
–
contains spaces called lacunae connected
by a network of canaliculi
–
each lacunae contains a osteocyte which
osteocyte numerous processes extend into
small tunnels called canaliculi
Bone matrix
–
consists of dense connective tissue, with a
primarily fibrous layer covering a more
cellular layer
–
bone is vascularized by small vessels that
penetrate the matrix from the periosteum
Periosteum
cells derived from mesenchymal stem cells
give rise to osteoblasts
presursor cells of osteoblast
Osteoprogenitor Cells
Osteoprogenitor Cells are found on the
external and internal surfaces
of bones and may also reside in the
microvasculature supplying bone.
Osteoprogenitor Cells appear as
flattened or squamous cells
lightly staining
elongate, or ovoid nuclei
inconspicuous acidophilic or slightly
basophilic cytoplasm in growing bones
requires a population of renewable
osteoprogenitor cells (osteoblast precursor
cells) that are responsive to molecular
stimuli that transform them into bone
forming cells
synthesis of osteoprogenitor cells (ig?)
Osteogenesis
*
key factor that triggers
differentiation of osteoprogenitor cells
*
prompts the expression of genes that are
characteristic of the phenotype of the
osteoblast.
Core Binding Factor Alpha 1 (CBFA1)
Osteoblasts located exclusively at the ____________, usually side by side in a layer
somewhat resembling a simple epithelium
surfaces of bone matrix
synthesizes the ORGANIC components of
bone matrix
Osteoblasts
Osteoblasts are polarized cells matrix components are secreted at the cell surface in contact with older bone matrix, producing a layer of new (but not yet calcified) material called _________ between the osteoblast layer and the bone formed earlier
osteoid
During active matrix synthesis: osteoblasts
have a ________________ shape and
basophilic cytoplasm
cuboidal to columnar
During decline of synthesizing activity:
osteoblast ____________ and cytoplasmic
basophilia is reduced
flatten
found in cavities (lacunae) between layers
(lamellae) of bone matrix
mature form of osteoblast
less basophilic; less synthetic ability
Osteocytes
individual osteoblasts are gradually
surrounded by their own secretion and
become osteocytes enclosed singly within
spaces called
lacunae
cells are involved in maintaining the bony matrix and their death is followed by resorption of this matrix
Osteocytes
histologic properties of osteocytes
- are flat, almond-shaped cells
▪ exhibit a significantly reduced RER and Golgi apparatus and more condensed nuclear chromatin
transition from osteoblasts to osteocytes
the cells extend many long __________ which also become surrounded
by calcifying matrix
cytoplasmic processes
osteocyte and its processes occupy each
lacuna and the canaliculi radiating from it
Processes of adjacent cells make contact
via __________ and molecules are
passed via these structures from cell to cell
can provide nourishment for a chain of
about ten cells
gap junctions
TYPES OF OSTEOCYTES
Quiescent osteocytes
Formative osteocytes
Resorptive osteocytes
*
exhibit a paucity of rER and a markedly
diminished Golgi apparatus
*
an osmiophilic lamina representing mature
calcified matrix is seen in close apposition
to the cell membrane
Quiescent osteocytes
show evidence of matrix deposition and
exhibit c ertain characteristics similar to
those of osteoblasts.
*
rER and Golgi apparatus are more
abundant, and there is evidence of osteoid
in the pericellular space within the lacuna
Formative osteocytes
*
like formative osteocytes, contain
numerous profiles of endoplasmic
reticulum and a well developed Golgi
apparatus. More over, lysosomes are
conspicuous.
Resorptive osteocytes
multi nucleated giant cells involved in the
resorption and remodeling of bone tissue
*
come from series of hemopoiesis
Osteoclasts
Osteoclasts lie within enzymatically etched depressions or crypts in the matrix known as ________________ in bone undergoing resorption
resorption bays (formerly called Howship lacunae)
In active osteoclasts the surface against
the bone matrix i s folded into
irregular projections, which form a
ruffled border
without this structure there’s impaired resorption of bone
ruffled border
surrounding the ruffled border is a
_________________
between the osteoclast and the matrix in
which bone resorption occurs
subcellular pocket microenvironment
in to this subcellular pocket the osteoclast
secretes _____________ and other enzymes
and pumps protons, forming an acidic
environment locally for dissolving
___________ and promoting the
localized digestion of collagen
collagenase; hydroxyapatite
Osteoclasts have receptors for
_________ a thyroid hormone, but not for
parathyroid hormone.
calcitonin
Osteoblasts activated by PTH
produce a
cytokine called
osteoclast stimulating factor
–
characterized by dense, heavy bones
(“marble bones”)
–
osteoclasts lack ruffled borders, and
bone resorption is defective
Osteopetrosis
*
cells that remain on the bone surface when
there is no active growth
*
derived from those osteoblasts that
remain after bone deposition ceases
Bone lining cells
All cells except ________ originate from
the mesenchymal stem cells
osteoclasts
mesenchymal stem cells differentiate into
osteoprogenitor cells, osteoblasts, and finally osteocytes and bone-lining cells.
types of bone lining cells
Periosteal cells
Endosteal cells
Osteoprogenitor cells and bone lining cells
Osteoclasts
Bone lining cells on external bone surfaces
–
form the innermost layer of the periosteum
Periosteal cells
Bone lining cells on internal bone surfaces
Endosteal cells
–
line the marrow cavities, the osteonal
( canals, and the perforating
(Volkmann Volkmann’s) canals.
Osteoprogenitor cells and bone lining cells
bone lining cells that have a similar microscopic appearance
and are often difficult to distinguish from
each other.
Osteoprogenitor cells and bone lining cells
originate from hemopoietic progenitor
cells, which differentiate into bone
resorbing cells that also line bones
Osteoclasts
COMPONENTS OF BONE MATRIX
Inorganic material
Hydration shell
Organic matter
Calcium binding glycoproteins
represents about 50% of the dry weight of
bone matrix
Inorganic material
most abundant inorganic material found in the bone matrix
combination of calcium and phosphate
Hydroxyapatite
aside from hyrdoxyapatite, what are the other inorganic materials found in the bone matrix?
Bicarbonate
Citrate
magnesium
Potassium
sodium
amorphous (noncrystalline)CaPO4
a layer of water and ions forms around the
hydrated surface ions of hydroxyapatite
–
facilitates the exchange of ions
between the crystal and the body
fluids
Hydration shell
contains proteoglycan
aggregates and several specific
multiadhesive glycoproteins,
including osteonectin
Organic matter
Organic matter embedded in the calcified matrix is
–
Type I collagen
–
ground substance
Calcium binding glycoproteins example
osteocalcin, and the phosphatases
released in matrix vesicles by osteoblasts
PERIOSTEUM ENDOSTEUM Principle Function
Provide nutrition of osseus
Provision of a continuous supply of new osteoblasts for repair or growth of bone
consists of a dense fibrous outer layer of
collagen bundles and fibroblasts
attaches to bone tissue through perforating
fibers
Periosteum
bundles of periosteal collagen fibers that
penetrate the bone matrix, binding the
periosteum to bone
Perforating or Sharpey’s fibers
mesenchymal stem cells found in the
innermost cellular layer of the periosteum
–
has potential to divide by mitosis and
differentiate into osteoblasts
–
play a prominent role in bone growth
and repair
Osteoprogenitor cells
provides covering to inner layer of bones
a single very thin layer of connective tissue,
containing flattened osteoprogenitor cells
and osteoblasts
Endosteum
–
covers the small spicules or
trabeculae of bone that project into
these cavities
–
considerably thinner than the
periosteum.
–
lines the large internal marrow
cavities of bone
Endosteum
TYPES OF BONE
Compact Bone
Cancellous (spongy) Bone
Long Bone
Short Bones
Flat Bones
areas with numerous interconnecting cavities
all surfaces of ________ are covered with endosteum
cancellous bone
bulbous end of long bones composed of spongy bone covered with a thin layer of compact bone
Epiphyses
Long Bone
* Has two components:
Epiphyses
Diaphysis
cylindrical part is almost totally composed of compact bone, with a thin component of spongy bone on its inner surface around the bone marrow cavity
Diaphysis
usually have a core of spongy bone surrounded completely by compact bone
Short Bones
calvaria (skullcap) have two layers of compact bone called
plates (tables)
the plates of the calvaria are separated by a thicker layer of spongy bone called the
diploë
- first bone tissue to appear in embryonic development and in fracture repair
- immature bone
PRIMARY BONE TISSUE
PRIMARY BONE TISSUE characterized by irregular array of collagen fibers called
woven bone
PRIMARY BONE TISSUE are usually temporary, except in:
o near the sutures of the calvaria
o in tooth sockets
o in the insertion of some tendons
SECONDARY BONE TISSUE
* shows multiple layers of organized calcified matrix referred to as
lamellar bone
each complex of concentric bony lamellae surrounding a small canal containing blood vessels, nerves, and loose connective tissue
Osteon (Haversian system)
- outer boundary of each osteon is a more collagen-rich layer which we call as?
Cement line
CATEGORIES OF VASCULAR CHANNELS
Haversian canals
Volkmann’s Canals
- longitudinal channels in the centers of the haversian systems/ osteons containing one or two blood vessels
- parallel
- connected with one another and communicate with the free surface and marrow cavity through transverse and oblique channels called Volkmann’s Canals
Haversian canals
- are not surrounded by concentrically arranged lamellae but traverse the bone in a direction perpendicular or oblique to the lamellae
- larger than the haversian canals
- traversing the bone
Volkmann’s Canals
- Bone formation
- Has two process : in both processes, the bone tissue that appears first is primary or woven
OSTEOGENESIS
two process of OSTEOGENESIS
Intramembranous ossification
Endochondral ossification
in which osteoblasts differentiate directly from mesenchyme and begin secreting osteoid
Intramembranous ossification
in which the matrix of preexisting hyaline cartilage is eroded and replaced by osteoblasts producing osteoid
Endochondral ossification
Vitamin D Deficiency diseases
Rickets
Osteomalacia (adults)
- results from faulty absorption of calcium form foods and a diminished phosphate concentration in plasma
- epiphyseal discs become thicker and irregular, and the cartilage matrix and osteoid tissue fail to calcify
Rickets
- causes a diminution in calcium content of the bone
Osteomalacia (adults)
inability of tissues that originate from mesenchyme to produce and maintain fibers, and ground substance diminished
* causes destruction of osteocollagenous fibers and a production of organic matrix in bones
* deficiency may lead to growth retardation and delayed healing of fractures
Vitamin C Deficiency
diminution in the rate of skeletal growth and interference with the process of remodeling together with the balance between bone deposition and erosion
Vitamin A Deficiency
HORMONES INFLUENCING GROWTH AND MAINTENANCE OF BONES
Parathyroid hormone
Calcitonin
Growth Hormone
Sex Hormones
- regulates bone resorption controlling the release of calcium to the blood
- regulates hypocalcemia
- acts upon the kidney to increase the rate of resorption calcium from the glomerular filtrate
- its renal effect prevents a continual loss of calcium in the urine that would ultimately deplete the calcium stores in the bones
Parathyroid hormone
- inhibits resorption activity
- oppose the function of PTH
Calcitonin
Calcitonin * a thyroid hormone, excreted by the
parafollicular C cells of the thyroid gland
Calcitonin exerts its calcium lowering effect by inhibiting the actions of both
PTH and vitamin D
Calcitonin secreted in response to a
hypercalcemic stimulus
Growth Hormone Produced by the
anterior pituitary
GH deficiency and excessive production leads to?
lack (dwarfism),
excessive production (gigantism)
decline in this hormone secretion disturbs the balance between bone deposition and bone resorption resulting in fragile bones (aging)
Sex Hormones
this hormone affects the appearance and closure of the secondary or epiphyseal ossification centers
* skeletal maturation is accelerated and growth stunted (precocious puberty)
Sex Hormones
BONE REPAIR process
1) Fracture →
2) hemorrhage (from torn vessels) and clotting →
3) fibroblasts and capillaries invades the clot forming granulation tissue (procallus) →
4) transforms to dense fibrous tissue and later into cartilage (temporary callus) →
5) Bone is remodelled
JOINTS Classification
Diarthroses
Synarthroses
- permit free bone movement
- joints that generally unite long bones and have great mobility, such as elbow and knee joints
Diarthroses
- very limited or no movement occurs
- example : skull
Synarthroses
Components of Diarthroses:
Capsule
Synovial or joint cavity
Articular cartilage
continuous with a covering ligament which inserts into the periosteum of both bones
Capsule
lined by synovial membrane and containing synovial fluid as a lubricant
Synovial or joint cavity
covers the ends of epiphyses
Articular cartilage
colorless, transparent, viscous fluid
o derived from blood plasma, but with a high concentration of hyaluronic acid produced by cells of the synovial membrane
Synovial Fluid
- specialized connective tissue that lines the joint cavity
o
which extends folds and villi into
the cavity and secretes the
lubricant synovial fluid.
Synovial Membrane
Three Types Of Synarthroses
(Based On The Type Of Tissue Uniting The
Bone Surfaces):
Synostoses
Synchondroses
Syndesmoses
o
bones are united by bone tissue
and no movement takes place
o
in older adults, __________ unite
the skull bones
synostoses
o
bones are joined by hyaline
cartilage
o
epiphyseal plates of growing
bones
o
in adults a _____ unites
the first rib to the sternum with
little movement
synchondroses
o
bones are joined by an
interosseous ligament of dense
connective tissue or fibrocartilage
o
pubic symphysis
Syndesmoses
