BCH 443
Biochemistry of
Specialized Tissues
3. Cartilage, Bone & Teeth Tissue
1
Types of Connective Tissue Found
in the Skeletal System


Cartilage
Bone

Each of these connective tissue types
consists of: living cells, nonliving
intercellular protein fibers, an
amorphous (shapeless) ground
substance
2
Cartilage

Location







Ear and nose
Respiratory system
Movable joints
Costal cartilage
Intervertebral disks
Pubic symphysis
Embryonic
3
Cartilage Tissue

Specialized CT






Chondrocytes in lacunae
Solid ground substance and fibers
Avascular
No nerves
Perichondrium
60-80% water –
resilient
4
Hyaline Cartilage


Most abundant
Locations




Joints
Trachea
Costal cartilages
Network of collagen fibers
5
Elastic Cartilage


Elastic fibers
Locations


External ear
Epiglottis
6
Fibrocartilage


Bundles of collagen fibers in rows
Locations



Intervertebral disks
Pubic symphysis
Menisci
7
Cartilage: Function


articular (or hyaline) cartilage covers
bone surfaces within the joint capsule
basic functions:




lubrication
prevents wear
despite common belief does not serve as a
“shock absorber”
 very thin
 capacity negligible compared to muscles and
bones
functions within a contact pressure range
of 2-11 MPa
8
Cartilage: Composition

Water+proteoglycan+collagen+ions
9
Cartilage: Composition


water contains dissolved inorganic salts
tissues with high proteoglycan content





high water content
low hydraulic permeability
high compressive stress
damage to proteoglycans will result in
increased water mobility and impaired
mechanical function
void (i.e. pore) dimension 50Å!
10
Cartilage: Composition

interaction between chemical and
mechanical factors

pH (potential of hydrogen, -log10[H+])



will affect numbers of negative charge
groups  change in bound water and
mobility
cations shields proteoglycan charges 
change in bound water and mobility
5% of tissue volume is
chondrocytes
11
Cartilage: Structure

Split line patterns (preferred collagen fiber orientation)
12
Cartilage: Structure
13
Cartilage: Structure

Superficial zone




densely packed
collagen fibrils
organized parallel
to articular surface
oblong
chondrocytes
Middle zone



fibers more or less
randomly arranged
greater fiber
diameter
round cells
14
Cartilage: Structure

Deep zone


Cells
arranged
in columns
along the
radial
direction
Calcified
cartilage and
subchondral
bone

large
fibers
from the
deep zone
anchor
into this
region
15
Cartilage: Structure

Collagen orientation




parallel to the surface on the superficial
layer
oblique in the middle layer
perpendicular to the surface in the
deep zone
Proteoglycan content

increases from surface till the middle
zone and diminishes towards the deep
zone
16
Cartilage: Structure

Water




proteoglycans can hold water up to 50
times their weight
70% of the water is bound to
proteoglycans
remaining 30% bound to collagen
inorganic ions such as Ca, Na, Cl and K
are dissolved

balance fixed charges on proteoglycans
and generate swelling pressure
17
Cartilage: Structure

proteoglycan-proteoglycan
interactions

aggregation
entropically favored
 cations are attracted to maintain
electroneutrality resulting in osmotic
swelling pressure (0.35 MPa)
 negative charges on the GAG chains exert
electrostatic repulsive forces on one
another

18
Aggregated Proteoglycans
19
Cartilage: Structure
20
Cartilage: Structure
21
A Rabbit’s Mojo and Proteoglycans…
22
Cartilage: Structure

collagen-proteoglycan
interactions

interactions involve


mechanical
entanglement
electrostatic bonds


excluded volume effects



negative charges of
GAGs and protein core
bind to collagen
a given molecule inhibits
neighboring molecules
from interacting with the
water in its
hydrodynamic domain
prevents proteoglycans
from passing in to solution
(PGs are water soluble)
balance and resist the
internal swelling forces of
proteoglycans
23
Cartilage: Properties

ultimate tensile strain varies from 60% to 120%
24
Bone

Definition



Connective tissue in which the
intercellular matrix has been
impregnated with inorganic calcium salts
Has great tensile and compressible
strength but is light enough to be moved
by coordinated muscle contractions
Composition

Two types of substances—organic matter
and inorganic salts
25
Bone Functions





Support body weight
Protect soft organs
Movement at joints
Storage of Ca++ and PO4-3
Hematopoiesis
26
Bone Composition


35% cells, fibers
(collagen), ground
substance
65% mineral salts,
mainly calcium
phosphate
precipitated
around collagen
fibers
27
Types of Bone

Cancellous (spongy) bone



Found in the interior of bones
Composed of trabeculae, or spicules, of
bone that form a lattice-like pattern
Compact (cortical) bone


Forms the outer shell of a bone
Has a densely packed calcified
intercellular matrix that makes it more
rigid than cancellous bone
28
Types of Bone Cells




Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts
29
Bone Formation







Osteogenesis – development of the skeleton
and growth through adolescence (~18 females,
~21 males)
Osteoblasts secrete osteoid
Osteoid is mineralized (calcium phosphate
precipitates)
Osteoblasts become osteocytes
Forms woven bone (immature)
Periosteum formed
Mature lamellar bone formed on surfaces
30
Bone Growth
Regulated by:



Growth hormone
Thyroid hormone
Sex hormones
31
Actions of Parathyroid Hormone








Increases intestinal absorption of calcium
Increases intestinal absorption of
phosphate
Decreases renal excretion of calcium
Increases renal excretion of phosphate
Increases bone resorption
Decreases bone formation
Promptly increases serum calcium levels
Prevents increase in serum phosphate
levels
32
Action of Calcitonin





Increases renal excretion of phosphate
Increases renal excretion of calcium
Decreases bone resorption
Decreases serum calcium levels with
pharmacologic doses
Decreases serum phosphate levels with
pharmacologic doses
33
Action of Vitamin D





Increases intestinal absorption of calcium
Increases intestinal absorption of
phosphate
Increases renal excretion of phosphate
Can increase bone resorption
Can increase bone formation
34
Classification of Bones

Long bones


Short bones


Found in the upper and lower extremities
Irregularly shaped bones located in the
ankle and the wrist
Flat bones


Composed of a layer of spongy bone
between two layers of compact bone
Found in areas such as the skull and rib
cage
35
Demineralization of enamel
Ca10(PO4)6(OH)2 + 2 H+ --> 10Ca2+ + 6 PO43- + 2 H2O
HYDROXYAPATATITE
(solid)
Dissolved ions
36
Tooth decay process




Bacteria in mouth convert sugars to
polysaccharides
Plaque = coating of bacteria +
polysaccharides
Other bacteria convert the carbohydrates in
plaque to carboxylic acids such as lactic acid
Tartar = plaque that combines with Ca2+ and
PO43- ions in saliva to form a hard yellow
solid
37
Protection of enamel by fluoride
Ca10(PO4)6(OH)2 + 2 F- --> Ca10(PO4)6(F)2 + 2 OHHYDROXYAPATATITE
(solid)
FLUOROAPATATITE
(solid)
Ca10(PO4)6(F)2 + 2 H+ --> no reaction
38
Chemical Composition of Bone
Bones composed of Organic matrix and Inorganic mineral component
Organic (35%): structure, flexibility, tensile strength, resists
stretching and twisting


Cells
 osteocytes
 osteoblasts
 osteoclasts
Osteoid
Inorganic (65%): hardness, strength, durability, resists compression
and tension


Hydroxyapatite (mineral salts)
Storage for Ca, P, Su, Mg, Cu
39
Regulation of Bone Growth
Vitamin C (ascorbic acid):






Lack of vitamin C leads to
poor structure, less
effective support, swollen &
painful connective tissues.
Wounds heal poorly (scar
tissue is rich in collagen
fibers). Gums bleed as
connective tissue around
teeth weakens
Scurvy is the vitamin C
deficiency disease
White line of Frankl: dense band in metaphysis
Wimberger’s ring: small epiphysis with sclerotic ring
Subperiosteal hemorrhage
Most common: Distal end of femur, proximal & distal tibia &
fibula, distal radius & ulna, proximal humerus, sternal ends of
ribs
40
Regulation of Bone Growth (Con’t)
Vitamin D




7-dehydrocholesterol located in the
skin: forms in the presence of
ultraviolet light
Becomes Vit. D3 (cholecalciferol) in
liver, Calcidiol in kidney
Calcitriol hormone + parathyroid:
stimulates bone deposition, reduced
excretion of Ca+ and increased
absorption of Ca+ from gut
Deficiency:


Osteomalacia is bone degeneration (similar to rickets) in the
elderly, who stay out of the sun.
Rickets is a softening and weakening of childrens’ bones




Calcification slows at epiphyses
Growth plate widens and appears frayed and cupped
Bones bend from stresses of weight bearing
Reduction in cortical bone density
41
Regulation of Bone Growth (Con’t)
Vitamin A




Retinol easist for the body to use. Found in animal foods (liver, eggs and
fatty fish). Beta-carotene is a precursor for vitamin A. The body needs
to convert it to retinol or vitamin A for use. Found in plant foods (orange
and dark green veggies: carrots, sweet potatoes, mangos and kale).
The body stores both retinol and beta-carotene in the liver, drawing on
this store whenever more vitamin A is needed.
Stimulates osteoblast activity, needed for cell division.
Too much vitamin A linked to bone loss and increased risk of hip
fracture. Excessive amounts of vitamin A triggers an increase in
osteoclasts and it may also interfere with vitamin D
42
Regulation of Bone Growth (Con’t)
Vitamin B-12




found in animal products (meat, shellfish, milk, cheese and eggs)
Important for blood formation and clotting
Low levels linked to loss of bone mass
However deficiency is uncommon in younger women who are also at
less risk of osteoporosis
Vitamin K


Important for protein synthesis in bone
Low intake of Vitamin K associated with osteopenia (reduction of bone
mass) and osteoporotic fracture (only in women?)
Calcium, Magnesium, Phosphorous, Potassium
43
Regulation of Bone growth (Con’t)
Hormones
 chemicals produced by the endocrine glands and secreted directly into the
bloodstream to their target organs to control the activity of that organ..
 Can stimulate cartilage formation, Vitamin D production, cause the release
of Ca & P from bone, and sex hormones play a role in the termination of
long bone growth


Estrogen: rapid and early growth
Androgens: later, slower growth
44
45
Hormonal Mechanism




Rising blood Ca2+ levels trigger the thyroid
to release calcitonin
Calcitonin stimulates calcium salt deposit in
bone
Falling blood Ca2+ levels signal the
parathyroid glands to release PTH
PTH signals osteoclasts to degrade bone
matrix and release Ca2+ into the blood
46
Hormonal Mechanism
47
Modified calcium phosphates in the
biological system of humans
Formula
Occurrences
(Ca,Z)10(PO4,Y)6(OH,X)2
HAp
enamel, dentine, bone, dental calculi,
stones, urinary calculi, soft tissue
calcifications
Ca8H2(PO4)6·5H2O
OCP
dental and urinary calculi
CaHPO4 ·2H2O
DCPD
dental calculi, chondrocalcinosis,
crystalluria, decomposed
(Ca,Mg)9(PO4)6
TCP
dental and urinary calculi, salivary
stones, dentinal caries, arthritic
cartilage, soft tissue calcification
(Ca,Mg)?(PO4,Q)?
ACP
soft tissue calcification
Ca2P2O7·2H2O
CPPD
pseudo-gout deposits in synovium
fluids
48
Tooth Structure
Periodontal
Ligaments
Enamel
Dentin
Dentinal
Tubules
Gingiva
Cementum
Pulp
Alveolar
Process
Cortical Plate
Spongy Bone
49
Tooth Structure




Two main regions – crown and the root
Crown – exposed part of the tooth above
the gingiva (gum)
Enamel – acellular, brittle material
composed of calcium salts and
hydroxyapatite crystals is the hardest
substance in the body
 Encapsules the crown of the tooth
Root – portion of the tooth embedded in
the jawbone
50
Tooth Structure (Con’t)
a. Enamel
(1) Makes up anatomic crown.
(2) Hardest material in the human
body.
(3) Incapable of remodeling and
repair.
51
Tooth Structure (Con’t)
b.
Dentin
(1) Makes up bulk of tooth.
(2) Covered by enamel on crown
and cementum on the root.
(3) Not as hard as enamel.
(4) Exposed dentin is often
sensitive to cold, hot, air, and
touch (via dentinal tubules).
52
Tooth Structure (Con’t)
c. Cementum
(1) Covers root of tooth.
(2) Overlies the dentin and joins
the enamel at the cementoenamel junction (CEJ).
(3) Primary function is to anchor
the tooth to the bony socket
with attachment fibers.
53
Tooth Structure (Con’t)
d. Pulp
(1) Made up of blood vessels
and nerves entering through the
apical foramen.
(2) Contains connective tissue,
which aids interchange
between pulp and dentin.
54
Tooth and Gum Disease

Dental caries – gradual demineralization of
enamel and dentin by bacterial action
 Dental plaque, a film of sugar, bacteria,
and mouth debris, adheres to teeth
 Acid produced by the bacteria in the
plaque dissolves calcium salts
 Without these salts, organic matter is
digested by proteolytic enzymes
 Daily flossing and brushing help prevent
caries by removing forming plaque
55
Tooth and Gum Disease:
Periodontitis




Gingivitis – as plaque accumulates, it
calcifies and forms calculus, or tartar
Accumulation of calculus:
 Disrupts the seal between the gingivae
and the teeth
 Puts the gums at risk for infection
Periodontitis – serious gum disease
resulting from an immune response
Immune system attacks intruders as well
as body tissues, carving pockets around the
teeth and dissolving bone
56
Proposed Mechanisms of Action of
Fluoride





 enamel resistance to acid
demineralization.
 rate of enamel maturation after eruption.
Remineralization of incipient lesions
 at the enamel surface.
 >1ppm fluoride needed to slow
demineralization process.
Interference with microorganisms
Improved tooth morphology.
57
How Does Dental Caries Begin?



Formation of acid by microorganisms in
plaque overly the enamel.
Requires the simultaneous presence of
three factors: (1) microorganisms, (2) a
diet for the microorganisms, (3) a
susceptible host or tooth surface.
If (1-3) are absent = no caries.
58
Remineralization



Remineralization: deposition of calcium,
phosphate, and other ions into areas of
previously demineralized by caries or other
causes.
Porous or slightly demineralized enamel has
a greater capacity to acquire fluoride than
adjacent sound enamel (3-5x more!)
Greater capacity of demineralized enamel
to absorb fluoride. =  enamel dissolution
59
Biochemical Basis

Enamel exposed to pH of  5.5 = enamel
dissolution:
Ca10(PO4)6(OH)2 + 8 H+ 
10 Ca++ + 6HPO2-4 + 2 H2O
60
Biochemical Basis (Con’t)

Fluoride exposure reduces enamel solubility
when fluorapatite is formed.
Ca10(PO4)6(OH)2 + 2 F-
Ca10 (PO4)6F2 + 2 OH-
61
Demineralization and
Remineralization

Caries dissolution of enamel

cyclic phenomenon with phases of
demineralization and reprecipitation.

Determined by changes in pH and ionic
concentrations within the plaque and the
lesion.
62