Bones: The Living Framework of

haplessuseUrban and Civil

Nov 25, 2013 (3 years and 11 months ago)

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Bones: The Living Framework of
the Human
Body

Eva L. Murdoch, PhD

Assistant Professor

Department of Natural Sciences

Joliet Junior College

http://
www.youtube.com
/
watch?v
=FufL80hJsP8

The Skeleton


Provides structural support for the entire body


Stores
minerals



Protects soft tissues


Houses red and yellow bone marrow


Serves as levers, on which skeletal muscles pull
to generate motion

Bone Formation and Growth


Bone formation


6 weeks (embryo 0.5”)


Bone
g
rowth



Continues during development in utero


Continues through childhood


Stops at about age 25


Hormonal
r
egulation


Growth hormone & Thyroxin


stimulate bone cells to produce bone
matrix


growth


Sex hormones (estrogen & testosterone) speed up bone synthesis at
puberty


growth stops within few years

The Human Body


The human body: collection of cells and cell
products

-
Cells
: smallest living unit performing vital functions

-
Cell products
: non
-
living, often proteins, also
perform vital functions

Bone Tissue


Living tissue composed of:

-
Several
cell

types


osteocytes, osteoblasts,
osteoclasts


-
Matrix
-

cell products

(collagen fibers) and
inorganic salts (calcium phosphate)



Matrix
:
Protein
-
Crystal
C
ombination:

-
Collagen
fibers: exceptionally
strong protein, when subjected to
tension


stronger than steel

-
Calcium phosphate crystals: very
hard, withstanding compression,
but brittle when exposed to
twisting



Bone C
ells:


-
Osteocytes:
maintain

protein and
mineral content of bone matrix

-
Osteoblasts:
produce

bone matrix

-
Osteoclasts:
remove

and recycle
bone matrix

Bone Tissue

Ca
3
(PO
4
)
2

Ca
2
+


Ca
2
+


Ca
2
+


Ca
2
+


Ca
2
+


Ca
2
+


Ca
2
+



Bone:



S
trong, somewhat flexible and
highly resistant to shattering.


On par with the best steel
-
reinforced concrete


Even better, bone undergoes
changes (
remodeling
), and can
repair itself after injury

Bone Tissue

Bone Remodeling


Maintaining bone mass is a balance between bone cells creating
bone matrix and bone cells dissolving bone matrix.


Recycle & renewal of bone matrix


Maintenance of mineral reserve, supply of minerals in body fluids (blood)


Involves
osteocytes, osteoblasts, and osteoclasts


Turnover
rate: varies


D
eposition
> removal, bone


stronger


D
eposition
<

removal,
bone


weaker


Heavy
-
metal ion deposition into bone matrix


Lead (
P
b
), cobalt (Co), uranium (U), plutonium (
Pu
)

Bone: Calcium Homeostasis


Calcium


essential ion for all cells


Bones: calcium reserve


Calcium homeostasis: maintenance of
sufficient calcium ion level in blood


1.
Calcium: high
in
blood


Calcitonin
: decrease of calcium in blood,
resulting in increased bone production

2.
Calcium: low
in
blood


Parathyroid
Hormone
:
increase of calcium in
blood, due to an increase in bone breakdown

The Effects of Exercise on Bone


Bone adapts to physical stress:


Mineral crystals in bone matrix create small
electrical currents


Osteoblasts: produce bone matrix


Electrical currents: repair of severe fractures


Bone surfaces change


Thicker, larger bumps & ridges: muscle
attachment

Bone and Aging


Bone: thinner & weaker


Osteopenia



b/n ages 30
&
40
women
lose
8% of bone
mass/decade
, men 3
%


Mainly at ends of long bones, vertebrae

&
jaws


Causing fragile limbs, reduction in height,
and tooth loss


Osteoporosis



age > 45, severe
bone
loss,
affects: 29% women & 18% man


Fractures due to normal physical activity
(standing)


Accelerated in women: loss of estrogen


Cancer (bone marrow, breast and other)


risk factor for osteoporosis


osteoclast activating factors

Normal spongy bone

Spongy bone in osteoporosis


Things I can do to slow
down the effects of aging
and assure optimum
bone mass.



Adequate diet


Weight bearing exercise (daily)


Monitor hormone levels
associated with bone mass