Transcript Bone

WHERE AM I?
Online Anatomy Module 1
INTRO & TERMS
CELL
EPITHELIUM
BONE
MUSCLE
NERVOUS SYSTEM
AXIAL SKELETON
APPENDICULAR SKELETON
MUSCLES
EMBRYOLOGY
BONE
Bone is the hard supporting tissue that is used
to make the very many bones of the skeleton:
small, large; long, short; flat, rounded
Bones come together and are held at joints
which allow (& restrict) movement
Muscles act across joints to cause particular
movements, which are classified in relation to
the planes of the body - flexion, abduction,
rotation, etc. at that joint, e.g., extension of the
knee to kick
ENJOYABLE LIFE - - bones as the means to do
things; extended by the use of tools & devices
LIFE & ENJOYABLE LIFE: The BONE Connection
First things first - the most important activities:
BREATHE - respiratory muscles contract & relax
CIRCULATE BLOOD - heart & vessel muscles contract
muscle contractions
driven or timed by rhythm
generators in the brain
Nerve-cell firing & signaling + muscle contraction
& relaxation need Calcium ion
Blood Ca2+ level is held to a very precise and limited range
WHAT GUARANTEES Ca2+ STAYS AT THIS LEVEL
A very large store bone is about half crystalline
calcium salts (hydroxyapatite/bone mineral)
A way to get Ca2+ out of storage cells that
eat away bone & put its salts back into solution
A way to get Ca2+ into storage cells that
make
bone and build in the calcium
salts
Ways to get Ca2+ for the body calcium in the
diet; absorbed in the gut; not lost by the
kidneys into the urine
Ways to control the blood level
hormones
WHAT GUARANTEES Ca2+ STAYS AT THIS LEVEL
A very large store
bones are about half mineral
To get Ca2+ out of storage cells that eat
away bone & put its salts back into solution -
OSTEOCLASTS
To get Ca2+ into storage cells that make
bone and build in the calcium salts OSTEOBLASTS
Ways to get Ca2+ for the body calcium in diet;
absorbed in the gut; not lost by the kidneys
To control the blood level hormones &
helper materials (e.g. vitamin D, cytokines); use
SOME IDEAS 1
1 Bone is a hard material. How do cells make
something this hard?
2 Cells synthesize and release to their exterior
materials that will assemble to a strong, but soft
substrate - densely packed string-like collagen
fibers (fibril is the term used because they are small)
3 Also secreted outside the cell into the ECM/extracellular matrix (extra=outside) are other molecules
that cause calcium, phosphate, hydroxyl and opther
ions to precipitate as fine hydroxyapatite crystals
4 The densely packed fibrils make bone matrix
strong; the mineral crystals, also densely arranged,
confer hardness
SOME IDEAS 2
1 Construction/formation of bone is slower than
destruction/resorption
2 Construction & destruction need to be in balance,
or bone is lost
3 Many organs have to work together: gut, bone,
kidney, skin, endocrine glands, muscles & nerves
4 Complicated & vulnerable control systems
5 Some aspects under person’s control -- exercise,
diet, lactation; many things are not: genes, sex,
age, size
PURPOSE OF THE SKELETON
1 Mineral store for Ca2+
2 Protection skull - brain,
eyes
cord
heart
vessels
bone marrow
spine - spinal
rib cage lungs, great
bone -
Calls for a
living, hard,
strong
material with
Ca in it
}
3 Support & leverage
SKELETON -- many bones, connected by joints
(with ligaments), pulled on by muscles, covered by
skin & fat
ENJOYABLE LIFE - - bones as the means to do things;
extended by the use of tools & devices
PURPOSE OF THE SKELETON: Correlates
1 Mineral store for Ca2+
2 Protection skull, marrow
etc 3 Support & leverage
BONE MATERIAL/MATRIX
STRONG - densely packed-in collagen fibrils
HARD - calcium hydroxyapatite mineral
crystals
LIVING - osteocytes/bone cells living in
spaces/lacunae & extending long
processes in canaliculi
Contrast tooth enamel - 98 % mineral so very hard, but brittle
Where the bone cell
lives
LACUNA
(hole) for OSTEOCYTE
BODY
MATRIX
CANALICULUS
(tiny channel) for
Gap junction contact
with next osteocyte
OSTEOCYTE PROCESS
EXTRACELLULAR MATRIX ECM 3
Cells create and achieve control over their environment by
synthesizing combinations of types of macromolecule
which interact outside the cells
Cartilage collagens II &
Resilient firmness in joint, airway, IX aggregated
proteoglycans link
& fetal-skeletal cartilages
proteins & hyaluronan
cartilage glycoproteins
Collagens I & XII
Resilient hardness of bone
bone proteoglycans
bone glycoproteins
mineral crystals
STRUCTURES OF A WORKING JOINT
Articular cartilage
Marrow
Joint space
with synovium
Bone
Joint capsule
Ligament
Tendon
Nerve
Muscle
Periosteum
dense irregular
HARD/IMPOSSIBLE TO MOVE & ENJOY LIFE WHEN
Joints get inflamed Cartilage wears out Bones
break Bones grow out of shape Muscles weak or
painful
Brain, cord or nerves injured (paralysis)
Articular cartilage absorbs & spreads the load
Marrow
Joint space with
synovium
Bone
Joint capsule
Ligament
Tendon
Nerve
Muscle
Periosteum
dense irregular
BONE REGIONS & TYPES
Joint capsule
EPIPHYSIS
DIAPHYSIS/
SHAFT
Periosteum
marrow
Joint
cartilage
absorbs and
spreads load
Spongy bone with
struts/ trabeculae
Dense bone
BONE SURFACES
Fibrous
Periosteum
Osteoblastic
vessels
marrow
Joint
cartilage
Spongy bone with
struts/ trabeculae
Dense bone
Inner surfaces of both types lined by ENDOSTEUM
of resting cells, active osteoblasts, & osteoclasts
Endo = inside
Peri = around
BONE COMPONENTS
Joint capsule
EPIPHYSIS
DIAPHYSIS/
SHAFT
Fibrous
Periosteum
Osteoblastic
vessels
marrow
Joint
cartilage
Spongy bone with
absorbs
struts/ trabeculae
Dense bone
and spreads
Inner surfaces of both types lined by ENDOSTEUM
load
of resting cells, active osteoblasts, & osteoclasts
Bone matrix = collagen fibrils +
mineral crystals
BONE CELLS
Active Osteoblasts
Bone canal
vessels
Periosteum
Osteoclast
Resting cells
Osteocyte
Ca 2+
Osteon/Haversian system with
concentric lamellar/layered bone
DENSE BONE
REMODELING
Osteoblasts filling
in the tunnel
New bone start of new
osteon
Osteoclasts as a team eating out a resorption tunnel
BALANCE is vital in bone - bone destroyed
by osteoclasts has to be replaced close by
with new bone made by osteoblasts
1 Everything has to be done by cells*
2 Organs & tissues need to grow & to change
shape
3 Cells age , and control systems get out of
balance
4 Bone is always at the mercy of body’s need for
calcium - nerve-muscle priority
5 Bone needs to be loaded every day: use is
essential
BONE’S PROBLEMS
1 Everything has to be done by cells*
2 Organs & tissues need to grow & to change shape
3 Cells age , and control systems get out of balance
4 Bone is always at the mercy of body’s need for calcium nerve-muscle priority
5 Bone needs to be loaded every day: use is essential
*
Cells die & may not be replaced
Cells cannot respond to signals
Cells do not send signals
Supplies, e.g. of Ca , not adequate
Growth more demanding than
staying the same
DENSE BONE at less risk than spongy bone
1 A lot of bone to start with (less in women)
2 Only a few
tunnels made by
osteoclasts
3 Tunnels filled in at least a little by new bone
DENSE BONE OSTEOCLAST-osteoblast
imbalance leads to somewhat weaker bone
Larger holes
Narrower
SPONGY BONE at more risk than dense bone
1 Struts are thin to
start with ~ weak
2 Much surface
area for attack by
osteoclasts
3 Gap in a strut/trabecula cut right through is
usually too wide to be bridged by any new bone
SPONGY BONE OSTEOCLAST- osteoblast
imbalance & architecture lead to fragile bone
Thinner struts
Bigger holes
Fewer struts
=
much weaker framework
MAINLY SPONGY BONE LOSS causes fractures in
1 Bones that are mostly spongy, e.g.
vertebra
compression
fracture
2 Spongy part of long bones where leverage
“Wrist” end
concentrates loading
of radius
“Hip” fracture at
neck of femur
from falling
on the hand
FRACTURES KILL
Lung embolism - clot(s) not stopped
until lungs’ arteries
Infections - pneumonia, etc
Falls get Granma sent to a “home”,
where she is too depressed to live
How to get a better cell-activity balance
1 Get more bone built when young food,
exercise, vitamin D (sunlight)
2 Keep on eating properly, & boost needed
nutrients when older, or pregnant
3 Exercise - high rapid loads, as well as
lengthy lower loadings
4 Correct hormone deficiences - older
women especially
5 If at risk, have bone density measurements
taken, with a view to special drug therapy
Osteoblasts filling
in the tunnel
New bone
DENSE BONE
REMODELING*
REMODELING
Eaten-out hole is a
Howship’s lacuna
Sealing ring
of tight
attachment
to bone
Osteoclast
Ruffled border agitating
released enzymes & acid
Osteoclasts as a team eating Un-mineralized OSTEOID between
out a resorption tunnel
active osteoblasts & calcified bone
INTRAMEMBRANOUS OSTEOGENESIS
Osteoblast
Mesenchyme
Condensation
Differentiation
Osteoid deposition
Osteocyte incorporation
INTRAMEMBRANOUS OSTEOGENESIS
Condensations are
widely dispersed
and separated to
commit a territory
to becoming bone
Mesenchyme
Vessels present
Continued division
& recruitment to
osteoblast numbers
Mesenchyme
INTRAMEMBRANOUS OSTEOGENESIS
LESS
ACTIVE
CELLS
OSTEOCLAST
TRABECULA
OSTEOID
ACTIVE OSTEOBLASTS
Mesenchyme later turns
into marrow
IM & EC OSTEOGENESIS
Vessels : incorporated
from the start &
remodel with the bone
TRABECULAE
thicken by division &
recruitment of more
osteoblasts to
increase bone density
OSTEOCLASTS
active from the start to
remodel & reshape the
bone
SKELETON & CARTILAGE
Cartilage provides some flexibility &
recovery of shape at critical places
Cartilage participates as pieces that
develop, and stay attached to the skeleton
Other cartilage develops with bones
(indeed, it precedes the bone), then
remains at the ends to make the joint
surface or articular cartilage
Facial and skull vault/dome bones form
with negligible cartilage present
ENDOCHONDRAL OSTEOGENESIS
Recognizable, if
some of the
trabeculae have
cores of calcified
cartilage
SKELETAL DEVELOPMENT
Skeletal piece of
hyaline cartilage
Grows by internal
expansion and from the
surface
Cell
enlargement/hypertrophy
Matrix calcification
Calcified cartilage can be
resorbed like bone, and
be attached to bone
selective erosion into
mineralized cartilage
EARLY ENDOCHONDRAL OSSIFICATION
perichondrium
periosteum
Bony collar
provides support
as mineralized
cartilage is eaten
away
}
EPIPHYSIS
}
DIAPHYSIS/SHAFT
primary ossification
front
EARLY ENDOCHONDRAL OSSIFICATION: Cell activities
Expansive/interstitial
growth by cartilage
cell division and
matrix synthesis
Hypertrophy of
chondrocytes precedes
calcification
Bony collar
Chondroclasts & other
cells eating into calcified
cartilage
Bone laid down as a
seam on remnants of
calcified cartilage by
Marrow
osteoblasts
primary ossification
front
MIDDLE ENDOCHONDRAL OSSIFICATION
Secondary
ossification centers
start by repeating the
processes of the 1o
center
Bone would be larger
than in the previous
}
EPIPHYSIS
}
SHAFT
primary
ossification front
LATER ENDOCHONDRAL OSSIFICATION
Articular cartilage
Growth/epiphyseal plate
Secondary
ossification centers
-
+
Shaft bone grows by
deposition on the outside,
with mild resorption on
the inside surface, plus
osteonal remodelling in
the interior
Bone would be larger
than in the previous view
No surface
growth possible
on loaded surface
STRATEGIES FOR GROWTH WITH USE
Articular cartilage
Secondary
ossification center
Interstitial growth
to elongate bone
here
Erosion matching
cartilage’s
expansive growth
keeps plate same
width
Other growth
plate doubles
the ability to
grow in length
Growth/epiphyseal
plate
-
+
Shaft bone grows in
width by deposition on the
outside, & mild resorption
on the inside surface, with
osteonal remodelling in
the interior
Separation of function:
articular cartilage is
just for load-bearing
ZONES/LAYERS OF THE GROWTH
PLATE
}RESTING
}
PROLIFERATION
Expansion
}
HYPERYTROPHY
}
Matching erosion
Osteoclasts stop the
trabeculae from forever
extending
CALCIFICATION
}
OSSIFICATION
new bone on
calcified cartilage
Cartilage is replaced by bone. There is
no transformation of cartilage into bone
RICKETS - Expression in growth plate
Normal
Vitamin D & Ca2+ deficiencies
Cartilage cannot
mineralize
CARTILAGE LENGTHENS
& IS WEAK
V. little erosion &
bone substitution
WHERE AM I?
Online Anatomy Module 1
ORIENTATION
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