Download Bones

The Skeletal System
Chapter 6
p. 134-183
Osteology
Osteology: the study of bones
 Skeletal System includes:
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Bones: composed of osseous tissue
 Cartilage: connective tissue w/
rubbery matrix
 Ligaments: connect bones
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Functions of the Skeletal
System
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1) Support: hold body
upright, keep teeth in
place
2) Storage: of calcium
& phosphate ions and
energy in the form of
lipids
3) Blood Formation:
red & white blood cells
made in marrow
Functions of the Skeletal
System (con’t)
4) Protection: enclose brain, spinal
cord, lungs, heart, etc.
 5) Leverage: attach to muscles &
allow for movement
 Also plays role in:

Acid/Base Balance: prevents severe
pH changes
 Detoxification: removes heavy metals
from blood
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Features of Long Bones
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Diaphysis: shaft of long
bone
Epiphysis: ends of long
bone
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Epiphyseal Plate: btwn
diaphysis & epiphysis
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Covered in Articular
Cartilage to form joints
Area of growth in children &
teens
Marrow Cavity: contains
bone marrow, a loose,
conn. tissue
Shapes of Bones
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1) Long Bones: more long than wide
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2) Short Bones: equally wide & long
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Provide gliding motion
i.e.: wrists and ankles
3) Flat Bones: wide & flat
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Serve as levers for muscle movement
i.e.: arm, leg, hand, foot, forearm
Broad surface for muscle attachment
i.e.: skull, ribs, shoulder blade
4) Irregular: no common shape
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Many functions (depends on location)
i.e.: vertebrae, some skull bones
Types of Bone Tissue
Compact Bone: dense
cylinder enclosing shaft of
bone.
 Spongy Bone
“Cancellous”: loosely
packed tissue
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Found at ends of long
bones; in center of other
bones
Compact Bone

Composed of osteons (functional unit of
compact bone looks like a bullseye), which
contains:
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1) Lamellae formed in concentric circles around
central Haversian Canal (roadway)
2) contains blood vessels and nerves that feed bone
marrow and remove wastes
3) Perforating Canals: passageways that link
blood vessels btwm Havers. Canals, the
periosteum, & marrow cavity
Covers all bone surfaces except at joints
res Lacunae: small pockets where
osteocytes are located, btwn each
lamellae (space where osteon sits
inside)
 Lamellae: layers of calcified bone
matrix
 Canaliculi: small channels or
canals that connect lacunae to
each other & central canal to
blood vessels…allows blood to go
from one osteocyte to another
Spongy Bone

Contains :
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1) Lamellae formed in rods & plates called
trabeculae (wall)
• Help feed red bone marrow at center of bone
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2) Canaliculi radiate (likes spokes on a wheel)
from one lacunae to another connecting
osteocytes
Found in areas of bone that do not undergo
stress (i.e. epiphyses)
Lighter than compact bone (makes bones
easier to move)
Nutrients reach spongy bone by
diffusing thru canaliculi from marrow
Bone
Coverings
 Periosteum:
covers outer surface
Double layered membrane- Inner layer
consist of osteoblasts and osteoclasts.
Outer layer- dense irregular CT
Made of collagen & bone-forming cells
 Provides route for blood vessels & nerves
to reach bone
 Connects to ligaments & tendons
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Endosteum: lines marrow cavity &
internal surfaces
Plays active role on bone growth and repair
 Covers trabeculae of spongy bone
 Contains osteoblasts and osteoclasts
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Bone Cells
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1) Osteocytes: mature bone cells
 Signal bone formation & removal when needed
 Assist in repairs
 Recycles Ca+ salt in bony matrix
2) Osteoblasts: “bone-forming”
 Synthesize new bone matrix & mineralize bone
 Become osteocytes when fully surrounded by calcified matrix
3) Osteoclasts: “bone-dissolving”
 Dissolve small amounts of matrix to release Ca+, phosphate,
& minerals when needed (“Resorption aka osteolysis”)
NEGATIVE FEEDBACK LOOP: Rising Ca+ levels in blood 
thyroid gland to release hormone calcitionin  uptake of Ca+
deposit in bone. Falling Ca+ level in blood  Parathyroid
gland release PTH hormone  osteoclasts break down bone
matrix releasing Ca+…Summary PTH & Calcitonin operate in
a negative feedback loop to keep Ca+ homoestasis in blood.
Bone Matrix
Surrounds bone cells to make up
bone tissue
 ~2/3 calcium phosphate & minerals
 Many other foreign minerals can be
absorbed into matrix
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i.e.: radium – can be deadly
Also contains collagen (strength) &
minerals (resiliency)
TITLE THIS DESCRIPTION
ON YOUR QUIZ AT BOTTOM
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Rising Ca+ levels in blood
Thyroid gland to release hormone calcitionin
Uptake of Ca+ deposit in bone.
Falling Ca+ level in blood
Parathyroid gland release PTH hormone
osteoclasts break down bone matrix releasing
Ca+
Ossification (“Osteogenesis”)
Formation of bone
 A) Intramembranous: flat bones of
skull & clavicle

1) Thin layers of tissue (trabeculae)
(Recall Layers of calcified bone that form
the walls) become calcified
 2) Surface trabeculae keep calcifying &
form compact bone
 3) Osteoclasts (bone dissolvers) keep
inner trabeculae spongy
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Ossification (con’t)
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B) Endochondral: most bones
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1) Hyaline cartilage “model” forms; similar in shape to
bone
2) Osteoblasts calcify to form compact bone shell;
Osteoclasts open up space for marrow
3) Spongy bone forms from inner marrow space →
ends of bone until filled; blood vessels invade marrow
cavity
4) Osteoclasts open up marrow cavity further; new
cartilage is added to the ends of bones
5) Cartilage calcifies to form compact bone from
inside → out; ends of bone remain articular cartilage
(joints at end of long bones)
Bone Growth
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Interstitial Growth: length; new
cartilage added to ends of long bones
calcifies
Appositional Growth: diameter;
periosteum cells develop into
osteoblasts
Depends on:
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Hormones (esp. estrogen & testosterone)
Calcium salts (esp. as fetus)
Vitamin D3 – helps Ca absorption
Vitamins C & A – help osteoblast activity
Types of Bone Fractures
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1) Closed/Simple: is internal; surface is
skin is not broken
2) Open/Compound: projects thru skin
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Susceptible to infection & uncontrolled
bleeding
i.e.: Pott’s Fracture (at ankle); Colles’
Fracture (distal portion of radius)
3) Transverse: across shaft of long bone
4) Spiral: produced by twisting long bone
5) Communicated: shattering of bone
into many small fragments
Bone Fracture Repair
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1) Fracture Hematoma (blood clot)
forms to close off injured blood vessels
(kills surrounding osteocytes)
2) Periosteum & Endosteum cells
divide to form external callus &
internal callus (sections of hyaline
cartilage)
3) Osteoblasts transform hyaline cartilage
into spongy bone to form “brace”
4) Spongy bone slowly calcifies into
compact bone
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4 months → 1 year or longer
Bone Fracture Repair
Bone Remodeling
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1) Mineral Deposition: calcium
(Ca) & phosphate ions deposit in
bone tissue
Harden the matrix (“crystallization”)
 Ectopic Ossification: calcification of
non-osseous tissue
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• i.e.: Arteriosclerosis: hardening of
arteries
• Calculus: calcified mass in soft tissue
(lungs)
Bone Remodeling (con’t)
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2) Mineral Resorption: dissolving
of bone by osteoclasts
Releases minerals (Ca) into blood for
use
 How teeth are repositioned by braces
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Calcium and Phosphate
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Phosphate: found in DNA, RNA, ATP, &
other molecules
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Helps regulate acid/base balance
85-90% stored in bones
Normal: 3.5-4.0 mg/dL
Calcium: used for nervous system
communication, muscle contraction, blood
clotting, cell signaling
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99% stored in bones; only ~1% easily
released into blood
Normal: 9.2-10.4 mg/dL
Ca Imbalances
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1) Hypocalcemia: Ca deficiency in blood
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Causes excitability of nervous system &
muscle spasms
• Tetanus: inability of muscles to relax; may lead to
suffocation (4.0 mg/dL)
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Due to: vit D deficiency, diarrhea, thyroid
tumors, ↓ parathyroid activity
2) Hypercalcemia: excess Ca in blood
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↓ excitability of nerves & muscles
Causes emotional disturbace, muscle
weakness, sluggishnes; may lead to cardiac
arrest
RARE
Regulation of Calcium
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1) Calcitrol Hormone
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Inactive form of vit D
In general retains Ca levels in bones
Vit D deficiency may cause bones to soften
2) Calcitonin Hormone
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Secreted by thyroid gland when blood Ca
levels high
Inhibits osteoclasts (resorption) & stimulates
osteoblasts (deposition)
May prevent bone loss & osteoporosis
Regulation of Ca (con’t)
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3) Parathyroid Hormone
Released by parathyroid hormone when
blood Ca low
 Stimulates osteoclasts, inhibits
osteoblasts, ↓Ca excretion in urine, &
synthesizes Calcitrol
 Very sensitive to changes in Ca levels
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