BONE Flashcards
Specialized CT composed of calcified ECM
bone
calcified ECM is called
Bone matrix
3 major cell types
Osteocytes
Oscteoblast
Osteoclast
purpose of bone
Solid support for our body, protects organs and harbors cavities containing bone marrow where blood cells are formed.
formation of blood cells
hematopoesis
happens inside the bone
formation of blood cells happens where
medulary cavity of bone/ bone marrow
serves as reservoir of calcium, phosphate and other ions that can be released in a controlled fashion to maintain constant concentration of body fluid.
Bone matrix
normal calcium level
8.6-10.3
Aids in movement by forming system of levers that multiply forces generated during muscle contraction.
Bone
matrix that covers the bone
periosteum
periosteum layer
outer fibrous layer
inner cellular layer
perforating fiber
sharpey’s fiber
attachment to the external circumferential lamellae of bone
perforating fiber
single unit of a functioning bone
osteon
osteon is also known as
Haversian system
diff parts of osteon
central canal
nerve, vein and arteries
middle of osteon
central canal
bone is highly
vascularized
housing where osteocytes resides in
lacuna
lacuna parts
osteocyte and canaliculi
so that osteocyte can communicate with other osteocytes that is housed in other lacunae
canaliculi
maintain the bone
osteocyte
has many spaces in between
spongey bone
where can u see osteon?
compact bone
stemlike structures that weaves and interconnect are called
trabeculae
trabeculae contains
Endosteum Osteoclast Lamilae Osteocytes in a lacuna Canaliculi
osteons also communicate with one another through
perforating canals/ Volkmanns canal
spongey bone also known as
cancellous bone
central canal also known as
haversian canal
osteaoblast
synthesize and secretes organic components of bone matrix ex. type 1 collagen, proteoglycans, glycoproteins
mature osteoblasts location
surfaces of the bone matrix, usually side by side in a layer somewhat resembling epithelium
when actively engaged in matrix synthesis, osteoblast have
cuboidal to clumnar shape and basic cytoplasm
when their synthesizing activity decline
they flatten and basophilia is reduced; inactive osteoblast represent most of flattened bone lining cells in both endosteum and periosteum
lining of trabeculae of spongey bone
endosteum
osteoblast secretes
osteoid
layer of new but not yet calcified material between the osteoblast layer and the pre existing bone surface
osteoid
crystal grow and further mineralize with formation of
calcium hydroxyapatite
enclosed within the lacuna that are regularly spaced throughout the mineralized layer
osteocytes
these cells maintaine boney matrix
osteocytes
osteocytes death followed by
rapid matrix resorption
dendritic processes of osteocytes
canaliculi
absorbed again to be reused
resorption
bone marrow derived, large motile cells and have multiple nuclei involved in resoption and remoddeling of bone tissue./tagasira and remodel
osteoclasts
they are actually monocytes that becomes macrophage and then the macrophage, nagdikit dikit
osteoclasts
in areas of bone undergoing resorption osteoclasts lie bet. enzymatically atched depression of cavity in the matrix known as resorption cavities also known as
howship lacunae
External and internal surfaces of bone are covered by tissue layers with bone-forming cells, called
periosteum and endosteum
is organized much like the perichondrium
periosteum
The outer layer is dense connective tissue,
with small blood vessels, collagen bundles, and fibroblasts
periosteum
Bundles of periosteal collagen fibers, called ____, penetrate the bone matrix, binding the periosteum to bone
perforating (or Sharpey) fibers
The principal functions of periosteum are to
nourish the osseous tissue and provide a continuous supply of new osteoblasts for appositional bone growth or repair
___ covers small trabeculae
of bony matrix that project into the marrow cavities
endosteum
thinner than the
periosteum
endosteum
endosteum also contains
osteoprogenitor cells, osteoblasts, and bone lining cells.
osteoprogenitor cells can only be
osteoblast and osteocytes, not osteoclasts
osteoclast came from
bone marrow
frequently found in immobilized patients and
in postmenopausal women, is an imbalance in skeletal
turnover so that bone resorption exceeds bone formation.
Osteoporosis
Osteoporosis leads to
to calcium loss from bones and reduced bone mineral density (BMD)
represents 80% of the total bone mass,
compact/ cortical bone
constituting about 20% of total bone mass.
cancellous (trabecular or spongy) bone
In long bones, the bulbous ends—called
epiphyses
are composed of spongy bone
covered by a thin layer of compact bone.
epiphyses
The cylindrical part—the
diaphysis
is almost totally composed of compact bone, with a thin region of spongy bone on the inner surface around the central marrow cavity
diaphysis
The flat bones that form the calvaria
(skullcap) have two layers of compact bone called
plates, separated by a thicker layer of spongy bone called the diploë.
Microscopic examination of bone tissue shows two types of organization:
lamellar bone and woven bone
usually more immature than lamellar bone.
woven bone
Most bone in adults, compact or cancellous, is organized as
lamellar bone
characterized by multiple layers or lamellae of calcified matrix
lamellar bone
lamellar bones are organized
either parallel to each other or concentrically around a central canal
refers to the complex of concentric lamellae surrounding a small central canal that contains blood vessels, nerves, loose connective tissue, and endosteum
osteon (or Haversian system)
The outer boundary of each osteon is a more collagen- rich layer called the
cement line
The central canals communicate with the marrow cavity and the periosteum and with one another through
transverse perforating canals (or Volkmann canals)
spaces between osteon is occupied by
interstitial lamellae
remnants of osteon that where partially resorb during bone remodeling
interstitial lamellae
a fluorescent molecule that binds newly deposited osteoid matrix during mineralization with high affinity and specifically labels new bone under the UV microscope
tetracycline
important parameter in the diagnosis of certain bone
disorders
tetracycline
continuous throughout life and involves process of resobption and bone formation
bone remodeling
in compact bone remodeling
resorbs part of old osteon and produces new one
is nonlamellar and characterized by random disposition of type I collagen fibers and is the first bone tissue to appear in embryonic development and in fracture repair.
Woven bone
usually temporary and is replaced in adults by lamellar
bone, except in a very few places in the body, for example, near the sutures of the calvaria and in the insertions of some tendons.
Woven bone
has a lower mineral content (it is more easily penetrated by x-rays) and often a higher proportion of osteocytes than mature lamellar bone
Woven bone
forms more quickly but has less strength than lamellar bone.
Woven bone
Bone development or
osteogenesis
___, in which osteoblasts
differentiate directly from mesenchyme and begin secreting osteoid.
Intramembranous ossification
___, in which a preexisting matrix of hyaline cartilage is eroded and invaded by osteoblasts, which then begin osteoid production.
Endochondral ossification
The names refer to the mechanisms by which the bone forms initially; in Intramembranous ossification Endochondral ossification and , the bone tissue that appears first is temporary
woven bone, which is soon replaced by stronger lamellar bone.
Osteogenesis imperfecta, or
“brittle bone disease,”
Osteogenesis imperfecta refers to a group of related congenital disorders in which
the osteoblasts produce deficient amounts of type I collagen or defective type I collagen due to genetic mutations.
Such defects lead to a
spectrum of disorders, all characterized by significant fragility of the bones.
The ___ is responsible for the growth in length of the bone and disappears at adulthood, causing bone growth to cease.
epiphyseal cartilage
An epiphyseal growth plate shows distinct regions of
cellular activity and is often discussed in terms of five zones:
- resting zone
- Proliferative zone
- Hypertrophic cartilage zone
- calcified cartilage zone
- ossification zone
In summary, growth in length of a long bone occurs by
proliferation of chondrocytes in the epiphyseal plate.At the same time, chondrocytes in the diaphyseal side of the plate hypertrophy, their matrix becomes calcified, and the cells die. Osteoblasts lay down a layer of new bone on the calcified cartilage matrix.
Main features of bone fracture repair.
(a) A fracture hematoma forms.
(b)A fibrocartilaginous (soft)
callus forms
(c) A hard (bony) callus forms.
(d) The bone is remodeled.
The skeleton serves as
the calcium reservoir, containing 99% of the body’s total calcium in crystals of hydroxyapatite.
1% is in
the blood
-free calcium/ionize calcium
The principal mechanism for raising blood calcium levels is the
mobilization of ions from hydroxyapatite crystals to interstitial fluid, which occurs primarily in cancellous bone.
PTH from the
parathyroid glands
acts in bone to raise low blood calcium levels by stimulating osteoclasts and osteocytes to resorb matrix and release Ca2+.
PTH from the
As discussed earlier the PTH effect on osteoclasts is
indirect; PTH receptors occur on osteoblasts, which respond by secreting paracrine factors that stimulate osteoclast activity
Calcitonin, synthesized within
the thyroid gland,
reduces elevated blood calcium levels by opposing the effects of PTH in bone.
Calcitonin
2 polypeptide hormones that target bone during calcium homeostasis
PTH and Calcitonin
adjacent bones are capped and held
together firmly by connective tissues
joints
The type of joint determines
the
degree of movement between the bones
Synostoses
in which bones are united only by bone tissue and no movement takes place. ex. skull bones
Syndesmoses
join bones by dense connective tissue only. Examples include the interosseous ligament of the inferior tibiofibular joint and the posterior region of the sacroiliac joints.
Symphyses
are immobile joints with a pad of fibrocartilage between the articular cartilage covering the ends of the bones. All symphyses, such as the pubic symphysis, occur in the midline of the body.
diarthroses
permit free bone movement
In a diarthrosis, ligaments and a capsule of dense connective tissue maintain
proper alignment of the bones.
The capsule encloses a sealed joint cavity that contains
synovial fluid, a clear, viscous liquid.
Synovial fluid is derived from
blood plasma, but with a high concentration of hyaluronan produced by cells of the synovial membrane.
bone-bone
ligament
muscle-bone
tendon
rheumatoid arthritis
chronic inflammation of the synovial membrane causes thickening of this connective tissue and stimulates the macrophages to release collagenases and other hydrolytic enzymes. Such enzymes eventually
cause destruction of the articular cartilage, allowing direct contact of the bones projecting into the joint
autoimmne disease, antibodies attacking synovial membrane, nawawala si synovial fluid and cartilage= direct contact of bone to bone.
rheumatoid arthritis
macrophage-like synovial cells (type A) derived from
blood monocytes. These cells bind, engulf, and remove tissue debris from synovial fluid.
These modified macrophages, which represent approximately 25% of the cells lining the synovium
macrophage-like synovial cells (type A) derived from
Fibroblastic synovial cells, or type B cells, produce
abundant hyaluronan and other extracellular components. = synovial fluid
important in regulating inflammatory events within diarthrotic joints.
macrophage-like synovial cells (type A) derived from
Each intervertebral disc consists mainly of a thick outer layer of fibrocartilage forming a tough____, and a shockabsorbing inner, gel-like core, the ___
annulus fibrosus
nucleus pulposus
Within an intervertebral disc, collagen loss or other degenerative changes in the annulus fi brosus are often accompanied by displacement of the nucleus pulposus, a condition variously called a
slipped or herniated disc
This occurs most frequently on the posterior region of
the intervertebral disc where there are fewer collagen
bundles. The affected disc frequently dislocates or shifts
slightly from its normal position. if it moves toward nerve
plexuses, it can compress the nerves and result in severe
pain and other neurologic disturbances. The pain accompanying
a slipped disc may be perceived in areas innervated
by the compressed nerve fi bers—usually the lower
lumbar region.
slipped or herniated disc
