chapter 6 osseous tissue and skeletal structure
TRANSCRIPT
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Osseous Tissue and Bone
Structure
Chapter 6
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Chapter Overview
1. Functions
2. A. Classification B. Structure C. Bone types
3. Bone tissue
A. Bone matrix
B. Bone cells
4. Bone StructureA. Compact
B. Spongy
5. Periosteum & Endosteum
6. Bone Formation and Growth7. Exercise, Hormones, and Nutrition
8. Calcium Homeostasis
9. Fractures
10. Osteopenia
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1. Skeletal System Functions
Skeletal system includes
Bones of the skeleton
Cartilages, ligaments, and connective tissues
5 Primary Functions: Support
Storage of minerals (calcium) & lipids (yellow marrow)
Blood cell production (red marrow- RBCs & WBCs)
Protection
Leverage (force of motion)
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2A. Classification of Bones
Bones are classified by
Shape
Internal tissue organization
Bone markings (surface features; marks)
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Long bonesLong and thin
Found in arms, legs,
hands, feet, fingers, toes
Flat bonesThin with parallel surfaces
Found in the skull,
sternum, ribs, scapulae
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c
Sutural bonesSmall, irregular bones
Found between the flat
bones of the skull
Irregular bonesHave complex shapes
Examples: spinal vertebrae,
pelvic bones
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c
c
c
c
Short bonesSmall and thick
Examples: ankle and wrist
bones
Sesamoid bonesSmall and flat
Develop inside tendons nearjoints of knees, hands, feet
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Bone Markings
Depressions or grooves
Along bone surface
Projections or elevations Where tendons and ligaments attach
At articulations with other bones
Tunnels
Where blood and nerves enter bone
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*You will learn these in lab! Not on your exam.
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2B. Structure of a Long Bone
Diaphysis- the shaft
Heavy wall of compact bone
Central space- medullary (marrow)
cavity
Epiphysis- wide part at each end Articulation with other bones
Mostly spongy bone covered with
compact bone
Metaphysis
Where diaphysis & epiphysis meet
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2C. Bone Types
Compact (dense) bone Relatively solid
Surrounds medullary cavity (marrow cavity)
Makes up diaphysis
Cancellous (spongy or trabecular)
bone
Open network of struts & plates
Resembles lattice work with thin coveringof compact bone called the cortex (cortical
bone)
Red bone marrow, no medullary cavity
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Compact
Bone
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Spongy Bone
Diploe- in cranium, layer of spongy bone between cortex
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3. Bone (Osseous) Tissue
Supportive connective tissue
Dense connective tissue
Cartilage
Bone
Periosteum-covers outer surfaces of bones, except atjoints (outer fibrous& inner cellularlayers)
Contains specialized cells & matrix
Matrix- extracellular protein fibers & groundsubstance
Solid matrix- calcium salt deposits around collagen
fibers
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3A. Matrix of Bone
Matrix Minerals
2/3 bone matrix- calcium phosphate, Ca3(PO4)2
Reacts with calcium hydroxide, Ca(OH)2to form
crystals of hydroxyapatite
As crystals form- incorporate other calcium salts(calcium carbonate, CaCO3) and ions (magnesium,
sodium, fluoride)
Matrix Proteins
1/3 bone matrix- protein fibers (collagen)
*You do not need to memorize the molecular formula of the minerals
calcium phosphate + calcium hydroxide hydroxyapatite
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Bone Matrix
Strong as steel reinforced concrete! Calcium phosphate- hard, withstand
compression, but not bending/twisting
Collagen fibers- flexible, withstandbending/twisting, little resistance to
compression
Together- strong, somewhat
flexible, shatter resistance bone
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3B. Types of Bone Cells
Make up only 2% of bone
mass, bone mostly matrix
most abundant
builders
CanaliculiForm pathways for blood vesselsExchange nutrients and wastes
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Osteocytes
Mature bone cells that maintain the bone matrix
Each osteocyte occupies a lacuna
Lacunae- pocket between layers of matrix (lamellae)
Osteocytes do NOT divide!
Canaliculi(narrow passageways) penetrate
lamellae - radiate through matrix, connecting
lacunae & nutrient sources Cytoplasmic extensions of osteocytes occupy
canaliculi
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Osteocytes Functions
To maintain protein and mineral content of matrix
Bones are dynamic- constantly changing!
Break down matrix & build it back again
To help repair damaged bone
*Can
convert to
less
specialized
cell type ifreleased
from lacuna.
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Osteoblasts- immature bone cells
1. Osteogenesis- secrete organic bone matrix
Proteins, etc. before calcium salts are deposited
Osteoid- matrix produced by osteoblasts, not yet calcified
2. Elevate local concentrations of calcium phosphate
above solubility limit, triggers deposition of calciumsalts
Converts osetoid to bone
Osteoblasts surrounded bybone become osteocytes
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Types of Bone Cells
break down (crack)Stem cells
Osteoprogenitor cell
osteoblast osteocyte
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Osteoprogenitor Cells
Mesenchymal stem cells that divide to produceosteoblasts
Are located in endosteum, the inner, cellular
layer of periosteum
Assist in fracture
repair
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Osteoclasts
Giant, multinucleate cells remove & recycle bone
matrix
Derived from stem cells that produce macrophages
Secrete acids & protein-digesting enzymes dissolve
bone matrix & release stored minerals (osteolysis) Important in maintaining calcium and phosphate
concentrations in body fluids
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Maintaining Bone
Homeostasis: building = breakdown Bone building (osteoblasts) and bone recycling
(osteoclasts) must balance
More breakdown than building,bones become weak
Exercise, particularly weight-bearing
exercise, causes osteoblasts to
build bone
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4A. Structure of Compact Bone
Osteon-basic functional unit in mature compact bone Haversian System
Osteocytes are arranged in concentric lamellae
around a central canal containing blood vessels
Run parallel to bone surgafe
Perforating Canals- run perpendicular to central canal
Canals of Volkmann Carry blood vessels into deep bone and marrow
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Histology of Compact Bone
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Histology of Compact Bone
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4A. Structure of Compact Bone
Interstitial lamellae- fill spaces between osteons
in compact bone
Remnants of osteons whose matrix have almost been
entirely recycled by osteoclasts
Circumferential Lamellae
Lamellae on outter/inner bone surface, covered
by periosteum & endosteum respectively Produced during growth of bone
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Structure of Compact Bone
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Structure of Compact Bone
Force applied along the axis of
alignment- will not bend bone
(the weight of your body will
not break your femur)
Collagen fibers spiral- adds
strength & resiliency
Force applied suddensideways force to femur- break
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4B. Structure of Spongy Bone
No osteons- struts & plates called trabeculae
Trabeculae have no blood vessels
Nutrients diffuse along canaliculi
Lighter than compact bone
Withstand stresses from many different directions
Red bone marrow -fills space between trabeculae
Blood vessels, forms red blood cells
Supplies nutrients to osteocytes, removes wastes
Yellow marrow- stores fat
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Structure of Spongy Bone
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5. c
Periosteum- superficial layer of compact bone
(except joint cavities)
2 layers- outer fibrous layer, inner cellular layer
Functions-
Isolates bone from surrounding tissues Provides route for circulatory and nervous supply
Participates in bone growth and repair
Joints- periosteum becomes continuous with
connective tissues (joint capsule, tendons,
ligaments)
Perforating fibers-collagen fibers of the periosteum
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The Periosteum
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5. Periosteum & Endosteum
Endosteum lines the medullary cavity & covers
trabecullae of spongy bone
Incomplete cellular layer
Active in bone growth and repair
Contains osteoblasts, osteoprogenitor cells, and
osteoclasts
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The Endosteum
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6. Bone Formation and Growth
Human bones grow ~25 yrs old
Osteogenesis-bone formation
Ossification- process of replacing
other tissues with bone
Calcification-process of depositing
calcium salts Occurs during bone ossification
Can occur in other tissues
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Ossification
Two main forms of ossification
Endochondral ossification- bone replaces cartilage
Most bones originate as hyaline cartilage
Intramembranous ossification- bone develops directlyfrom mesenchyme or fibrous connective tissue
Dermal ossification- occurs in dermis
Produces dermal bones-mandible (lower jaw) and
clavicle (collarbone)
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Endochondral Ossification
-cartilage enlarges
-chondrocytes
increase in size
-lacunae expand
-matrix reduces tothin struts that begin
to calcify
-chondrocytes
deprived of nutrients-
no diffusion
-chondrocytes
become surrounded
by calcified cartilage,
die
-blood vessels
grow into
perichondrium
-inner layer cells
differentiate into
osteoblasts,
-osteoblasts
begin producingthin layer of
bone
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Endochondral Ossification
-blood vessels
penetrate cartilage,central region
-fibroblasts migrate
in, differentiate into
osteoblasts
-osteoblasts produce
spongy bone
(primary ossification
center)
-bone formationspreads along shaft
-remodelingcontinues as growth
occurs
-osteoclasts appear
& degrade
trabeculae in thecenter of diaphysis
(medullary cavity)
-growth continues in
length & diameter
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Endochondral Ossification
-centers of
epiphyses begin to
calcify
-capillaries,
osteoblasts migrate
in, (secondaryossification center)
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-epiphysesbecome filled with
spongy bone
-articular cartilage
remains exposed
at joint cavity
-overtime reduces
to thin superficial
layer
-at metaphysis,
epiphyseal
cartilage
separates
epiphyses from
diaphysis
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Epiphyseal Lines
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Epiphyseal Lines
When long bone stops
growing, after puberty
epiphyseal cartilagedisappears
A i i l G h
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Appositional Growth
In early endochondral ossification, a superficial layer
of bone forms, then bone increase in diameter (outersurface)
Appositional Growth Cells of inner layer of periosteum differentiate into
osetoblasts, deposit superficial layers of bone matrix
Osteoblasts become surrounded by matrix- differentiate into
osteocytes Add series of layers form circumferential lamellae
I t b O ifi ti
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Intramembranous Ossification
-mesenchymal cells cluster
together and start secretingorganic components of matrix
-resulting osteoid becomes
mineralized as mesenchymal
cells differentiate intoosteoblasts
-developing bone grow
outward from ossification
center (where ossificationbegins) in spicules
-ossification trap osteoblasts,
differentiate into osteocyte
I t b O ifi ti
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Intramembranous Ossification
-Blood vessels grow into
the area
-Spicules grow and fuse
together, trap blood vessels
within developing bone
I t b O ifi ti
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Intramembranous Ossification
-Initially, intrmebraneous boneonly spongy bone
-Remodeling produce osteons
of compact bone
-Growth slows, periosteum
forms
-connetive tissue formsfibrous outer layer
-osteoblasts outer surface
become inner cellular layer
Bl d S l f M t B
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Blood Supply of Mature Bones
Bones very dynamic- constant remodeling
Three major sets of blood vessels develop
Nutrient artery and vein:
Single pair of large blood vessels, supply bood to diaphysis
Enter the diaphysis through the nutrient foramen during
endochondral ossification
Femur has more than one pair
Metaphyseal vessels:
Supply blood to the epiphyseal cartilage where bone growth
occurs
Periosteal vesselsprovide:
Blood to superficial osteons of the shaft
Blood to secondary ossification centers during endochondral
bone formation
Periosteum also contains
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Networks of lymphatic vessels
Sensory nerves
Bone injuries very painful!
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6 B R d li
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6. Bone Remodeling
Adult skeleton very dynamic- continually remodels,
recycles, and replaces
Replaces mineral reserves
Recycles and renews bone matrix
Involves osteocytes, osteoblasts, and osteoclasts Turnover rate varies
If deposition is greater than removal, bones get stronger
If removal is faster than replacement, bones get weaker
Store heavy metal ions in bone (lead, uranium,plutonium)
Cancer later in life as bone releases ions
7 E i Eff t B
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7. Exercise Effects on Bone
Bone is stressed, mineral crystals generate electrical
fields, attracts osteoblasts which produce bone
Mineral recycling allows bones to adapt to stress
Heavily stressed bones become thicker and stronger
Lifting weights highly beneficial
Bone Degeneration
Bone degenerates quickly
Up to one third of bone mass can be lost in a few weeks of
inactivity
Break leg, astronaut, paralyzed
7 H & N t iti l Eff t B
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7. Hormone & Nutritional Effects on Bone
Normal bone growth and maintenance requires nutritional
and hormonal factors Constant dietary source of calciumand phosphate salts
Small amounts of magnesium, fluoride, iron, manganese
Calcitriol-hormone made in the kidneys
Helps absorb calcium and phosphorus from digestive tract Synthesis requires vitamin D3(cholecalciferol)
Vitamin C- required for collagen synthesis, and stimulation of
osteoblast differentiation
Vitamin A- stimulates osteoblast activity
Vitamins K and B12help synthesize bone proteins
Calcitonin & parathyroid hormone regulate calcium &
phosphate levels
8 Calci m Homeostasis
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8. Calcium Homeostasis
Skeleton act as a calcium reserve
Bones store calcium and other minerals
Calcium is the most abundant mineral in the body
Calcium ionsare vital to:
Membranes & intracellular activities of neurons &muscle cells, especially heart cells
Too much calcium muscle & nerve cells unresponsive
Not enough calcium- neurons so excitable, convulsions50% reduction of calciumlead to death!
Calcium Homeostasis
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Calcium Homeostasis
Calcium tightly regulated in body
Calcitoninand parathyroid hormone
Control storage, absorption, and excretion
Calcitonin- thyroid gland
Parathyroid hormone- parathyroid gland Target
Bones- storage
Digestive tract- absorption
Kidneys- excretion
Calcium Homeostasis
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Calcium Homeostasis
Parathyroid Hormone (PTH)
Produced by parathyroid glands in neck
Increases calcium ion levels by
Stimulating osteoclasts, enhancing recycling of minerals by osteocytes
Increasing intestinal absorption of calcium
Decreasing calcium excretion at kidneys
Calcitonin
Secreted by C cells (parafollicular cells) in thyroid Decreases calcium ion levels by
Inhibiting osteoclast activity
Increasing calcium excretion at kidneys
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9 Fractures
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9. Fractures
Cracks or breaks in bones caused by physical stress
Major types of fractures:
Pott fracture- ankle, affects both bones
Comminuted fractures- shattered
Transverse fractures- break across access Spiral fractures- twisting stresses
Displaced fractures- abnormal bone arrangements
Colles fracture- break distal portion of radius
Greenstick fracture- 1 side of shaft broken, other bends
Epiphyseal fractures- where bone is undergoing calcification
Compression fractures- vertebrae under extreme stress
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-Extensive bleeding, large blood clot(fracture hematoma) closes off injured
-Cells of periosteum & endosteum rapiddivision & migrate in
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(fracture hematoma) closes off injured
vessels
-Establishes a fibrous network
-Bone cells in the area die
Fractures are repaired in 4 steps
division & migrate in
-External callus forms, stabalizes outer
edges
-Internal callus forms in medullary cavity
-Osteoblasts replace central cartilage ofexternal callus with spongy bone
-Cells continue remodeling ~1 yr
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external callus with spongy bone
-Struts of spongy bone unite broken ends
-Fragments of dead bone removed &
replaced
-Initially swelling
-Eventually calluses are removed
10 Osteopenia
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10. Osteopenia
Bones become thinner and weaker with age
Osteopenia-inadequate ossification
Begins between ages 30 and 40- osteoblast activity
drops, osteoclast activity remains constant
Women lose 8% of bone mass per decade, men 3%
Epiphyses, vertebrae, and jaws are most affected:
Resulting in fragile limbs
Reduction in height
Tooth loss
Osteoporosis- reduction in bone mass compromisesl f ti
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normal function
Severe bone loss & easily fractured
Over age 45, occurs in 29% of women,18% of men
Aging
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Aging
Hormones and Bone Loss
Estrogens and androgens help maintain bone mass
Bone loss in women accelerates after menopause
Cancer and Bone Loss
Cancerous tissues release osteoclast-activating
factor
Stimulates osteoclasts & produces severe
osteoporosis
Important Concepts
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Important Concepts
Skeletal functions
Bone shapes (dont need to memorize markings)
Bone structure
Difference between compact/spongy bone
Structure of each
What makes up bone matrix
Cell types/functions
Describe periosteum & endosteum
Important Concepts
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Important Concepts
Describe process of bone formation- endochondral
ossification & intramembranous ossification Describe how exercise affects bone formation
How do hormones/nutrients influence bone
formation
Describe calcium homeostasis by calcitonin and
parathyroid hormone
Describe how fractures are healed (do not need to
memorize fracture types)
Osteopenia/osteoporosis