Bones Flashcards
Function of bones
storage, hematopoiesis,
protection, movement
Types of tissue in bones
Connective tissue with calcified matrix. this matrix surrounds osteocytes and osteoblasts
Structurally, there are 4 types of bones
Long bones
Short bones
Flat bones
Irregular bones
Bones vary in their proportions of ___ and ____;
compact
cancellous
(spongy) bone
Appearance of compact and caancellous bone
compact bone is dense and solid in appearance
• whereas cancellous bone is characterized by open space
partially filled with needle-like structures
What is diaphysis
Main shaft of long bone • Hollow, cylindrical shape and thick, compact bone • Function is to provide strong support without cumbersome weight
What is epiphyses
Both ends of a long bone, made of cancellous bone filled with marrow • Bulbous shape • Function is to provide attachments for muscles and give stability to joints
What is articular cartilage
Layer of hyaline cartilage that
covers the articular surface of
epiphyses
Hyaline cartilage function
Elastic cartilage
Function is to cushion jolts and blows
What is periosteum (appearance, where does it attach, what does it have, function)
Dense, white, fibrous membrane that covers bone • Attaches tendons firmly to bones • Contains cells that form and destroy bone • Contains blood vessels important in growth and repair • Contains blood vessels that send branches into bone • Essential for bone cell survival and bone formation
In adult medullary or marrow cavity is filled with
Yellow marrow
What is endosteum
thin epithelial
membrane that lines
medullary cavity
Parts of the long bone
endosteum medullary cavity Periosteum Articular cartilage Epiphyses Diaphysis
What is the inner portion of short, flat and irregular bones
Cancellous bone, covered on the outside with compact bone
What can be found inside cancellous bone of a few irregular and flat bones
Red marrow
Name bones with high red marrow
ribs, pelvis and skull.
Composition of bone matrix can be divided into
___
inorganic salts and organic matrix
The hardness of bone results from the deposition of:
Hydroxyapatite—highly specialized chemical crystals of
calcium and phosphate
Hydrozyapatite is found between ___
collagen
apart from hydroxyapatite, what other salt is a part of the bone
10% calcium carbonate
Magnesium and sodium are also found in bone
How calcium carbonate crystals are oriented in the bone
Slender, needle-like crystals are oriented to most effectively
resist stress and mechanical deformation
Organic matrix of the bone is secreted by ____
bone cells (osteoblasts, derived from mesenchymal stem cells).
Role of mesenchymal cells
derives osteoblasts
What is a ground substance
Made of collagenous fibers and a mixture of protein
and polysaccharides which forms a gelatanous
material
Role of ground substance
important in bone growth,
repair and remodeling as it acts as a medium for the
diffusion of nutrients, oxygen and metabolic waste
Four types of structures make up each osteon:
Lamella
Lacunae
Canaliculi
Havesian canal
What are lamella
concentric rings that are , islands of calcified matrix. Altered by growth.
Think of Tree rings
What are lacunae
small spaces containing tissue fluid in which bone cells (osteocytes)
are located between hard layers of the lamella
What are canaliculi
ultrasmall canals radiating from the osteocytes and connecting them to
each other and to the Haversian canal (part of network that allows excretion and
absorption of nutrients)
What are haversian canal
extends lengthwise through the center of each osteon and
contains blood vessels and lymphatic vessels
Structure of the Cancellous Bone
There are no osteons in cancellous bone; instead, it has
trabeculae-needle like bony spicules
– Nutrients are delivered and waste products removed by
diffusion through tiny canaliculi (canals radiating from
bone cells)
– Bony spicules are arranged along lines of stress,
enhancing the bone’s strength
Difference between osteoblast and osteoclast and osteocyte
Osteoblasts deposit calcium as they create new bone matrix • Osteoclasts break down bone matrix during bone resorption
-Osteocyte—is a transformed osteoblast
that is trapped in the surrounding bone
matrix.
• Final differentiation state for an osteoblast
All bone surfaces are covered with layer of cells mostly made of
___, and less ____
osteoblasts (bone building)
less osteoclasts (bone reabsorbing
cells)
Osteoclasts- cell specificity
Giant multinucleate
Formed by the fusion of several
precursor cells-multinucleated
Osteoclasts develop from ___. Attach to ____
Stem cells in bone marrow
Attach to bone surface by integrins
When does the formation of bone tissue stop
The formation of bone tissues continues throughout life, long after growth stops.
RANK protein is expressed by ___, as well as ___
Osteoblasts
OPG (osteoprotegerin)
RANK and OPG relationship
OPG is RANK inhibitor
Function of RANK
essential for osteoclast formation, function and survival. Continually binds to osteoclast
Estrogen role in bone remodelling
Limits the RANK ligand receptors on osteoblasts
OPG function
Reduce RANK and osteoblast activity
What happens in postmenopausal women
Decreased estrogen->increased RANK receptors->increased activity of osteoclasts
Stimulator of osteoblast induction of osteoclast differentiation
Parathyroid hormone-> trigger release of calcium
opposing effects of parathyroid hormones have ___
Calcitonin
What can affect Calcium Balance?
Age
Disease
Diet
Medications
When people have positive, negative and equal balance
Children usually have a positive balance that allows
bone to grow
• In adults input and output should be the same
• Post-menopausal women tend to have a negative
calcium balance
PTH is released when
When plasma Ca is low
PTH action
ØMobilizes calcium from
bone
ØEnhances renal
reabsorption of calcium
ØStimulates release of
Calcitriol
• Calcitriol increases intestinal
calcium absorption
Calcitonin is released as a response to
Ca2+ is high)
ØDecreases bone resorption
ØIncreases renal calcium
excretion
PTH and Vitamin D relationship
PTH will stimulate kidney to convert 25(OH)D3 to calcitriol ( the first activation of vitamin D was in the liver).
PTH together with Vitamin D will increase plasma calcium
Actions of Vitamin D on calcium regulation:
Increased reabsorption in the proximal and distal
convoluted tubules of the kidney
– Vitamin D stimulates osteoblast activity to increase
bone mass and calcification
– In the intestine increases the synthesis of calcium
binding proteins on intestinal cells
Disorders of vitamin D can cause ___
weak bones
(rickets in children or osteomalacia in adults
Development of Bone is ___
osteogenesis
When the skeleton forms in a fetus it is made of ___
cartilage
Changing of cartilage to bone tissue requires
constant activity by the osteoblasts
and osteoclasts
• Calcification by laying down of calcium salts (calcium and
phosphorous)
In the adults sculpting of the bone allows bones to ___
respond to stress
or injury by changing size shape and density
Exercise and bone health
Exercise stimulates osteoblasts to secrete more collagen which
makes bones stronger
There are two mechanisms for bone formations
- Intramebranous -some flat bones, no cartilage
2. Endochondral cartilage, vascular, long and flat bones
Intramembranous bones: examples and how do they begin
bones)-less common
• Flat bones, like the bones of the skull or jaw bone,
– does not begin with a cartilage model.
– Instead, dense areas of mesenchymal cells (multipotent stem cells)
differentiate and begin to lay down bone around themselves,
forming early spicules.
Stages in intramembranous bone development
Occurs within a connective tissue membrane
Ø Begins with migration of mesenchymal stem cell which to the site
of bone formation and differentiate into osteoblasts
Ø Osteoblasts are clustered together in centers of ossification
Ø Osteoblasts secrete matrix material and collagenous fibrils
(ground substance or osteod)
Ø Mineralization occurs-(calcium and phosphate) the organic
strands once mineralized are called trabecula (little beam)
Endochondrial bone development
Most bones begin as a cartilage
model, with bone formation
spreading essentially from the
center to the ends
• Mesenchymal stem cell migrate to the site of
eventual bone development
• These cell are induced to become chondrocytes
(cartilage cells)
• Chondrocytes differentiate into very dense
avascular mass
• Cartilage forms in the shape of the bone
What happens after cartilage model of the bone is developed is long bone developement
ØThe cartilage is surrounded by periosteum (envelope of connective tissue) develops and enlarges Ø Osteoblasts which differentiate from the inner surface of the periosteum produce a collar of bone ØPrimary ossification center forms ØBlood vessel enters the cartilage at the midpoint of the diaphysis
ØBone grows in length as endochondral ossification progresses from the diaphysis toward each epiphysis
ØEpiphyseal plate remains between diaphysis and each epiphysis until bone growth in length is complete
Epiphyseal plate is composed of ___
4 layers:
- Zone of resting cartilage
- Zone of proliferation
- Zone of hypertrophy
- Zone of calcification
Epiphyseal plate allows long bones to grow in
Length
Bones grow in diameter by the
combined action of ___
osteoclasts
and osteoblasts
Osteoclasts enlarge the diameter of the medullary cavity • Osteoblasts from the periosteum build new bone around the outside of the bone
Symptoms of osteoporosis
fractures of the vertebrae, wrists or
hips, lower back pain, neck pain, bone pain or
tenderness, loss of height over time, or stooped
posture.
Treatment for osteoporosis
use of drugs such, raloxifene (It has estrogenic effects in bone), and calcitonin or
through estrogen replacement therapy.
• Another recommended treatment for osteoporosis is
exercise. Studies show that exercise can cause an
increase in bone density
Detailed role of estrogen in bones
Estrogen acts on osteoblast to stimulates the production of TGF-beta,
• TGF-β causes the osteoblast cells to make osteoprotegerin (OPG)
• OPG binds to RANKL and prevents it from binding to the RANK receptors on the
preosteoclasts. This prevents them from becoming osteoclasts and thus limits
bone resorption.
• When there are low levels of estrogen, the levels of OPG decline, leaving
RANKL to bind to RANK receptor and allowing differentiation of osteoclasts to
proceed and bone resorption increases
Spongy bonds looks the same as
compact inside trabeculae, but they are not so highly structured, no osteones
