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29 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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FACT OR FICTION ?





YOUR SKELETON REPLACES
ITSELF EVERY 1O YEARS





IT’S A FACT!!


BONE IS

A


LIVING TISSUE!


Cells……
Osteoblast


Bone cell capable of synthesizing new
bone matrix


Usually found in growing portion of bone
Osteocyte


Main cell of mature bone tissue
Osteoclast


A multi-nucleate bone destroying cell


Usually found where bone is resorbed
during normal growth
Bone as a Tissue


Connective tissue with a matrix hardened by
minerals (
calcium phosphate)


Individual bones consist of bone tissue, marrow,
blood, cartilage and periosteum


Continually remodels itself


Functions of the skeletal system


support, protection, movement, electrolyte
balances,acid
-
base balance, and blood formation


Function:

1.
Support


2.
Protection

3.
Movement


4
. Hematopoiesis
(manufacture of blood cells)

5.

Storage of inorganic salts


THE FUNCTIONS OF BONE


Support the body with a by providing a frame


Protect softer tissues by shielding or encasing
them


Provide points of attachment for muscles
, so
that the skeleton can act as levers as forces are
generated by muscles. .


Houses blood
-
producing stem cells
, and


Stores inorganic minerals

necessary for
bioreactions in the body. Also, stored in bone
are
lipids
.


Storage of inorganic salts


Mostly
calcium phosphate


70% of weight of matrix
Calcium: Needed for


Blood clot formation


Nerve impulse conductor


Muscle contraction


HUMAN SYSTEMS


MAINTAIN


HOMEOSTATSIS

Negative Feedback
Mechanisms




The net effect of the response to
the stimulus is the
SHUT OFF

the
original stimulus
OR
reduce its
intensity
.

Negative Feedback


This is the
Most
common control
mechanism!

When Levels of
hormone in blood or
body return to Normal
levels homeostasis
shuts off
loop at the
hypothalamus and
pituitary ( Most
common Negative
Feedback Loop)


Positive Feedback

The initial stimulus

does
NOT

cause a switch to
be “shut off”. Rather, a
CASCADE

of
more ON
switches

in response to the initial response
occurs.


Examples: Giving Birth and Blood Clotting


An Example of Positive
Feedback: Giving Birth



Bone Homeostasis

Parathyroids regulate the homeostasis of blood
calcium

When blood calcium is low Osteoclasts tap into
reserves and Bone is “demineralized” Calcium
ions is released into blood

Too much calcium in the blood? This hormone
causes the deposition of Calcium into the
bone matrix by osteoblasts

Low Blood Calcium


Parathyroid gland
releases
parathyroid
hormone


Stimulates
osteoclasts
to
resorb
Ca++


Blood calcium rises
Feedback Inhibition
High Blood Calcium


Inhibits parathyroid gland

Homeostasis: the maintenance of




By releasing PO4 ions into the blood pH is
balanced.


When blood Ca levels are low; it is taken from
the bone; maintain blood Ca levels.


Bones

-
Organs
of the skeletal system.
Consist of several tissue types
Active Living Tissues


Bone


Cartilage


Fibrous connective tissue


Blood


Nerve
Non-living Material


Calcium phosphate


Calcium carbonate


Matrix proteins

The Types of Bones

Classification
:
1.
Long Bones
2.
Short Bones
3.
Flat Bones
4.
Irregular Bones
5.
Sesamoid Bones
6.
Accessory Bones
Long Bones


Long longitudinal axis and expanded ends
Arm


Humerus


Ulna - Radius


Metacarpels


Phalanges
Leg


Femur


Tibia - Fibula


Metatarsals


Phalanges
Short Bones of the arm
…….
The 8
carpel bones of the hand
1.
Scaphoid
2.
Trapezium
3.
Trapezoid
4.
Triquetral
5.
Pisiform
6.
Hamate
7.
Capitate
8.
Lunate
Short Bones of the leg
…….
The 7 tarsal bones of the foot
1.
Calcaneus
2.
Talus
3.
Cuboid
4.
Navicular
5.
Lateral (3rd) cuneiform
6.
Intermediate (2nd) cuneiform
7.
Medial (1st) cuneiform
Short Bones
Equal in length, width, thickness
Shaped irregularly
Flat Bones
Actually "Thin" or curved more often than flat
1.
Ribs
2.
Scapulae
(shoulder blades)
3.

Sternum
(breast bone)
4.

Clavicle
(collar bone)
5. Bones of the
cranium
(skull)


Frontal


Parietal
(2)


Temporal
(2)


Occipital


Sphenoid


Ethmoid
Irregular Bones
……..
1.

Vertebrae, Sacrum, Coccyx
2.
Hyoid
3. Facial bones


Zygomatic
(2)


Palatine
(2)


Lacrimal
(2)


Nasal
(2)


Vomer


Inferior nasal concha
(2)


Maxilla
(2)


Mandible
4.

Hip bones


Pubic bone


Ileum


Ischium
5.
Malleus, Incus, & Stapes
(Ear)
Sesamoid Bones……..


Small bones imbedded within certain tendons


Usually where tendons pass over the joint of a long
bone
patella
Within tendon of quadriceps femoris
pisiform carpel bone
Within tendons of flexor carpi ulnaris
Accessory Bones………
Most commonly found in feet


They occur where developing bones do not
fuse properly


May look like extra bones or broken bones in
x-rays
Sometimes small clusters of them between flat bones
of skull…


"Sutural" or "Wormian" Bones
ANATOMY

of a

BONE


Periosteum:





Tough vascular covering of fibrous tissue.



Surrounds bone



Fibers are continuous with ligaments and tendons



Functions in bone growth and repair


Medullary Cavity



Hollow portion of diaphysis of long bone



Continuous with spaces of spongy bone


Endosteum



Squamous epithelial lining of medullary cavity
and spaces in spongy bone



Surrounds marrow



Representative Bone Structures…….


Epiphypis


Articular Cartilage


Diaphysis


Periosteum


Compact bone


Spongy bone


Medullary Cavity


Endosteum

Compact bone:



Solid, strong, resistant to bending
Spongy bone:



"
Cancellous Bone"


Numerous branching bony plates ("Trabeculae")


Interconnecting spaces reduce weight
Both types are usually present in a bone
Short
Flat

These are "mostly" s
pongy
Irregular
Spongy Bone


It may appear that the
trabeculae
are arranged
in a haphazard manner, but
they are organized
to
provide maximum strength
similar to braces

that are
used to support a building.
The trabeculae of spongy
bone follow the lines of
stress and can realign if the
direction of stress changes
.





Compact Bone


Compact or cortical
bone
,
is made up many
rod
-
like units called
osteons or Haversian
systems which run
longitudinally within the
bone. Haversian systems
have a central Haversian
canal which carries blood
and lymphatic vessels and
nerve branches
.


Red Marrow
:


Forms
Erythrocytes
:



Forms
Leucocytes
:



Forms
Thrombocytes
:
Red color is due to hemoglobin
Location:


Skull


Ribs


Sternum


Clavicles


Vertebrae


Pelvis
General Features of Bones


Shaft (diaphysis) = cylinder of compact bone


marrow cavity (medullary cavity) lined with endosteum
(osteogenic cells and reticular connective tissue)


Enlarged ends (epiphyses)


spongy bone covered by compact bone


enlarged to strengthen joint and attach ligaments


Joint surface covered with articular cartilage


Shaft covered with periosteum


outer fibrous layer of collagen


inner osteogenic layer of bone forming cells


Epiphyseal plate (growth plate)

Matrix of Osseous Tissue


Dry weight = 1/3 organic and 2/3 inorganic matter


Organic matter


collagen, glycosaminoglycans, proteoglycans and glycoproteins


Inorganic matter


85% hydroxyapatite


10% calcium carbonate


other minerals (fluoride, potassium, magnesium)


Combination provides for strength and resilience


minerals resist compression; collagen resists tension


bone adapts by varying proportions


What is
Hydroxyapatite
?


This is the form that Calcium Phosphate takes on in
bone tissue.



Calcium Phosphate
Ca3(PO4)2

accounts for 2/3
weight of bone.


Calcium Phosphate interacts with
Ca(OH)2

to form
Ca10(P04)6(OH)2

(
hydroxyapatite)


Hydroxyapatite forms crystal that form plates and rods
that lock with the collagen fibers of bone matrix. This
allows for a flexable, yet shatter
-
resistant nature of
bone .






Maybe Superior to Concrete!


Better than concrete INDEED!


As bone is able to
REMODEL

itself and repair
itself after injury.


REMODELING: replacing old bone with new
bone
. Remodeling also allows bone to
respond to changes in mechanical forces


During childhood, the long bones (in the arms,
legs, and back) grow at the ends of the bones,
whereas the flat bones (such as the skull) have
a different pattern of growth.

Epiphyseal Plate

: a cartilaginous plate
Epiphyseal end
1. Zone of resting or reserve cartilage
2. Zone of proliferation
3. Zone of maturation
4. Zone of calcification
Diaphyseal end
THE

CELLS

OF


BONE

Cells……



Osteoprogenitor Cell
-

These are mesenchymal cells that
divide into daughter cells that differentiate into

Osteoblasts. (located in inner layer of periosteum and inner
layer of endosteum that lines marrow cavities)

Osteoblast



Bone cell
capable of synthesizing new bone matrix



Usually found in growing portion of bone


Osteocyte



Main cell of mature bone tissue


Osteoclast



A multi
-
nucleate bone destroying cell



Usually found where bone is resorbed during normal
growth



Figure 7.11



Our skeleton starts out
completely as hyaline
cartilage.


Ossification is the process of
cartilage turning to bone


ONLY places where you like
nasal septum, between tips
of ribs, between
bones(articular cart.) etc.
does HC remain.

General Features of Bones


Shaft (diaphysis) = cylinder of compact bone


marrow cavity (medullary cavity) lined with endosteum
(osteogenic cells and reticular connective tissue)


Enlarged ends (epiphyses)


spongy bone covered by compact bone


enlarged to strengthen joint and attach ligaments


Joint surface covered with articular cartilage


Shaft covered with periosteum


outer fibrous layer of collagen


inner osteogenic layer of bone forming cells


Epiphyseal plate (growth plate)

Osteogenesis
…..


Bone Development


Begins a few weeks after conception


Bones form by replacing existing connective
tissue
Osteogenesis
………
Two Types:
1. Intramembranous Ossification
2. Endochondral Ossification
Briefly Speaking…

I.
Mesenchymal Cells form Pericondrium which then
forms hyaline

II.
Formation of Primary Ossification Center, Bony
Collar and Periostium

III.
Formation of Secondary Ossification of Center,
Penetration of Blood Vessels into Bony Collar

IV.
A Secondary Marrow Cavity appears in the
epiphysis .

V.
Spongy Bone fills the epiphyses


NEXT LECTURE:


We will start with


OSTEOGENESIS: THE DETAILS