2. Plan of the lecture
1. General concepts about skeleton
2. Bone as an organ
3. Functions of the skeleton
4. Classification of bones
5. Types of bone ossification
6. Development of bones
3. The Skeletal System!
Our First System
Cells (Osteocytes)
Tissues (Osseous Tissue)
Organs (Bones)
Systems (Skeletal)
4. THE LOCOMOTOR APPARATUS – ITS
COMPONENTS AND FUNCTIONAL ROLE
The skeleton is a complex of hard
structures that is of mesenchymal origin
and possesses a mechanical significance.
The term skeleton comes from a Greek word
meaning “dried up”.
NB: All the bones and articulations of the
body make up the passive part of the
locomotor apparatus.
5. The skeleton
The science concerned
with the study of bones is
termed osteology.
The skeletal system of an
adult is composed of
approximately 206 bones.
Each bone is an organ of
the skeletal system.
For the convenience of
study, the skeleton is
divided into axial and
appendicular parts.
6. The axial skeleton
The axial skeleton
consists of 80 bones that
form the axis of the body
and which supports and
protects the organs of the
head, neck, and trunk.
Skull
Auditory ossicles
Hyoid bone
Vertebral column
Thoracic cage
7. The appendicular The appendicular skeleton is composed of 126
bones of the upper and lower limbs and the
skeleton bony girdles, which anchor the appendages
to the axial skeleton.
The shoulder girdle (the scapula
and clavicle)
The upper limb (the humerus,
ulna, radius and bones of the hand)
The pelvic girdle (the hip bone)
The lower limb (the femur, tibia,
fibula and bones of the foot)
8. BONE AS AN ORGAN
STRUCTURE OF A BONE AND STRUCTURE OF THE
PERIOSTEUM
Bone (osis) is one of the hardest structures of
the body. It possesses also a certain degree of
toughness and elasticity. Its color, in a fresh
state, is pinkish-white externally, and red
within.
9. Types of bone tissue
There are two types of bone tissue:
a) compact bony tissue
b) spongy bony tissue
The names imply that the two types differ in density, or how tightly the
tissue is packed together.
There are three types of cells that contribute to bone homeostasis.
a) osteoblasts are bone-forming cell
b) osteoclasts resorb or break down the bone
c) osteocytes are mature bone cells.
An equilibrium between osteoblasts and osteoclasts maintains the bone tissue.
10. OSSIFICATION
OSTEOBLASTS
FORM NEW BONE
MATRIX OSTEOCLASTS
COLLAGEN
MAINTAIN SHAPE
STERNGTH
CALCIUM DEPOSITION
OSTEOCYTES
MAINTAIN BONE
11. Structure of bone
On examining a cross section of
any bone, it is composed of two
kinds of bony tissue:
Compact tissue, it is dense in
texture and it is always placed
on the exterior of the bone.
Cancellous tissue consists of
slender fibers and lamellae,
which join to form a reticular
structure and it is placed in the
interior of the bone
12. Macromicroscopic
structure of bone
The morphofunctional unit of
the bone is the osteon, or
Haversian system.
The osteon consists of a
system of bony lamellae
arranged concentrically around
a canal, which is called
Haversian canal and this canal
contains nerves and vessels.
The bone lamellae consist of
osteocytes, their lacunae, and
interconnecting canaliculi and
matrix.
13.
14. The spongy bone tissue
Spongy (cancellous) bone
is lighter and less dense
than compact bone.
Spongy bone consists of
plates (trabeculae) and bars
of bone adjacent to small,
irregular cavities that
contain red bone marrow.
The canaliculi connect to
the adjacent cavities,
instead of a central
haversian canal, to receive
their blood supply.
15. The spongy bone tissue
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.
16. The periosteum
Externally bone is covered by
periosteum (except articular
surfaces). The periosteum
adheres to the surface of the
bones.
It consists of two layers closely
united together:
a) The outer layer fibrous
layer
b) The inner layer or bone-
forming layer (cambial)
17. Structure of
the periosteum
The periosteum is rich in
vessels and nerves, and it
contributes to the nutrition
and growth of the bone in
thickness. Nutrients are
conveyed by blood vessels
penetrating in great number
the outer (cortical) layer of
the bone from the
periosteum through
numerous vascular
openings (foramina
nutricia).
18. The interior of
each long tubular
bone of the limbs
presents a
cylindrical cavity
named marrow
cavity and it is
lined with the
medullary
membrane called
endosteum.
23. Bone marrow
The bony compartments contain bony marrow,
medulla ossium. Two types of bone marrow can be
distinguished:
red bone marrow
white bone marrow
The white or yellow marrow fills up the medullary
cavities of the shafts of the long tubular bones.
The red marrow is located within the cancellous
tissue and extends into the larger bony canals
(Haversian canals) that contain blood vessels.
24. Haemopoiesis function
The bone marrow provides
haemopoiesis function and biological
protection of the organism. It takes NB: The
part in nutrition, development and bones of the
growth of the bone. The red marrow embryo and
concerned with haemopoiesis and bone new-born
formation, has an active role in the contain only
healing of fractures. Red marrow
predominates in infants and in
red marrow.
children, with growth of child the red
marrow is gradually replaced by
yellow marrow.
25. Haemopoiesis function
The red bone marrow of an adult produces white
blood cells, red blood cells, and platelets.
In an infant, the spleen and liver produce red blood
cells, but as the bones mature, the bone marrow
performs this task.
It is estimated that an average of 1 million blood
cells are produced every second by the bone marrow
to replace those that are worn out and destroyed by
the liver.
26. Mineral storage
The inorganic matrix of bone is
composed primarily of minerals
calcium and phosphorus. These
minerals give bone rigidity and
account for approximately two-
thirds of the weight of bone.
About 95% of the calcium and 90%
of the phosphorus, within the body,
are stored in the bones and teeth.
In addition to calcium and
phosphorus, lesser amounts of
magnesium and sodium salts are
stored in bones.
28. Support (weight bearing)
The skeleton forms a
rigid framework to
which are attached the
soft tissues and organs
of the body.
29. Protection
function
Protection is assured by the
property of the bones to form
body cavities which protects the
vital important organs.
The skull and vertebral column
enclose the central nervous system.
The thoracic cage protects the heart,
lungs, great vessels, liver and
spleen.
The pelvic cavity supports and
protects pelvic organs.
Even the site where blood cells are
produced is protected within the
central portion of certain bones.
30. Body movement
Bones serve as anchoring
attachments for most
skeletal muscles. In this
capacity, the bones act as
levers, with the joints
functioning as pivots, when
muscles, which are
regulated by the nervous
system, contract to cause
the movement.
31. Classification of bones by shape
Tubular bones
a) Long tubular bones b) Short tubular bones
humerus, metacarpal,
radius, ulna, metatarsal bones and phalanges
femur,
tibia, fibula
32. Classification of bones
Spongy bones
a) Long spongy bones
sternum,
ribs, etc
b) Short spongy bones
carpal and tarsal bones
c) Sesamoid bones
knee-cap
pisiform bone, etc.
33. Classification of bones
Flat bones
Skull bones
Bones of the vault of the
skull
Girdle bones
The scapula
The hip bone, etc.
34. Classification of bones
Mixed bones
The vertebrae are mixed, or
irregular bones (their bodies
are referred to spongy
bones, but their arches and
processes are referred to flat
bones).
35. Bone formation (osteogenesis)
Osteogenesis occurs throughout life but in different
ways
1. embryo responsible for laying down of bony
skeleton (ossification well started by 8th week)
2. bone growth continues until early adulthood
3. remodeling & repair continues for life
• Ossification - The process of replacing other
tissues with bone (endochondral and
intramembranous)
Calcification - The process of depositing calcium
salts
Occurs during bone ossification and in other
tissues
36. 2 types of ossification
1. Intramembranous (dermal ossification)
Formation of most of the flat bones of the skull and the
clavicles from a fibrous membrane
Fibrous connective tissue membranes are formed by
mesenchymal cells
2. Endochondral
Formation of bone in hyaline cartilage
Both lead to the same type of bone
Both begin with migration of mesenchymal cells from c.t. to
areas of bone formation
No blood supply chondroblasts
Blood supplyosteoblasts
37. Intramembranous Ossification: Step 1
Mesenchymal cells
aggregate:
differentiate into
osteoblasts
begin ossification
at the ossification
center
develop
projections called
spicules
38. Intramembranous Ossification: Step 2
Blood vessels grow
into the area:
to supply the
osteoblasts
Spicules connect:
trapping blood
vessels inside bone
39. Intramembranous Ossification: Step 3
Spongy bone develops and
is remodeled into:
osteons of compact bone
periosteum
or marrow cavities
40. Endochondral Ossification
Begins in the second month of
development
Uses hyaline cartilage “bones” as models
for bone construction
Requires breakdown of hyaline cartilage
prior to ossification
41. Endochondral Ossification: Step 1
Chondrocytes in the
center of hyaline
cartilage:
enlarge
form struts and calcify
die, leaving cavities in
cartilage
42. Endochondral Ossification: Step 2
Blood vessels grow
around the edges of the
cartilage
Cells in the
perichondrium change
to osteoblasts:
producing a layer of
superficial bone around
the shaft which will
continue to grow and
43. Endochondral Ossification: Step 3
Blood vessels enter the
cartilage:
bringing fibroblasts that
become osteoblasts
spongy bone develops at
the primary ossification
center
45. Endochondral Ossification: Step 5
Capillaries and
osteoblasts enter the
epiphyses:
creating secondary
ossification centers
46. Endochondral Ossification: Step 6
Epiphyses fill with
spongy bone:
cartilage within the
joint cavity is
articulation cartilage
cartilage at the
metaphysis is
epiphyseal cartilage
47. Primary centers of ossification
In the second month of the
intrauterine life, the
primary points of
ossification appear first, in
the shafts, or diaphyses of
tubular bones, and in the
metaphyses.
They ossify by
perichondral and
enchondral osteogenesis.
48. Secondary and accessory
points of ossification
The secondary points of
ossification appear shortly
before birth or during the
first years after birth and
they develop by encondral
osteogenesis.
The accessory points of
ossification appear in
children, adolescents, and
even adults in the
appophyses of bones (e.g.
tubercles, trochanters, the
accessory processes of the
lumbar vertebrae).
49. Blood Supply of Mature Bones
3 sets of blood vessels develop
Nutrient artery and vein:
a single pair of large blood
vessels enters the diaphysis
through the nutrient foramen
Metaphyseal vessels:
supply the epiphyseal cartilage
where bone growth occurs
Periosteal vessels provide:
blood to superficial osteons
secondary ossification centers
50. Effects of Hormones and Nutrition on Bone
1. Growth hormone
Single most important stimulus to the
epiphyseal plate (dwarfism/gigantism)
2. Thyroid hormone
Moderates growth hormone to insure proper
proportions of growth
3. Sex hormones (estrogens & androgens)
A great ‘rush’ at puberty = growth spurt
Lead to a breakdown of cartilage that leads
to a closure of plates …steroids!
4. Calcitriol
Made in kidneys; synthesis requires cholecalciferol
Helps absorb calcium & phosphorus from GI tract
51. Additional dietary regulators
Need adequate calcium, phophorus, magnesium,
flouride, iron, & manganese
Calcium is necessary for:
Transmission of nerve impulses
Muscle contraction
Blood coagulation
Secretion by glands and nerve cells
Cell division
Vitamin D – absorption of calcium from GI
Vitamin C – formation of collagen
Vitamin A – stimulates osteoblast activity
Vitamins K and B12 - help synthesize bone proteins
52. Bone Fractures (Breaks)
Bone fractures are classified by:
The position of the bone ends after fracture
The completeness of the break
The orientation of the bone to the long axis
Whether or not the bones ends penetrate the skin
53. Types of Bone Fractures
Nondisplaced – bone ends retain their normal position
Displaced – bone ends are out of normal alignment
Complete – bone is broken all the way through
Incomplete – bone is not broken all the way through
Linear – the fracture is parallel to the long axis of the bone
Transverse – the fracture is perpendicular to the long axis of the bone
Compound (open) – bone ends penetrate the skin
Simple (closed) – bone ends do not penetrate the skin
Comminuted – bone fragments into three or more pieces; common in the
elderly
Spiral – ragged break when bone is excessively twisted; common sports
injury
Depressed – broken bone portion pressed inward; typical skull fracture
Compression – bone is crushed; common in porous bones
Epiphyseal – epiphysis separates from diaphysis along epiphyseal line;
occurs where cartilage cells are dying
Greenstick – incomplete fracture where one side of the bone breaks and
the other side bends; common in children
56. Fracture Repair: Step 1
Bleeding:
produces a clot
(fracture hematoma)
establishes a fibrous
network
Bone cells in the area
die
57. Fracture Repair: Step 2
Cells of the endosteum
and periosteum:
Divide and migrate into
fracture zone
Calluses stabilize the
break:
external callus of
cartilage and bone
surrounds break
internal callus develops
58. Fracture Repair: Step 3
Osteoblasts:
replace central
cartilage of
external callus
with spongy bone
59. Fracture Repair: Step 4
Osteoblasts and
osteocytes remodel the
fracture for up to a year:
reducing bone
calluses
60. Osteoporosis
Bone reabsorption>bone Risk Factors
production Body build – short
Osteopenia begins between women have less bone
ages 30 and 40 mass
Women lose 8% of bone mass Weight – thinner at
per decade, men 3% greater risk
Decrease in bone Smoking – decreases
massincrease fracture risk estrogen levels
Decreased levels of estrogen
primarily
Lack of dietary calcium
Most important cause of fracture Exercise – decrease rate
in women>50 of absorption
35% of bone mass may be gone Drugs – alcohol,
by age 70 cortisone, tetracycline
Vertebrae & femur neck are Premature menopause
most affected
62. Homeostatic Imbalances
Osteomalacia
Bones are inadequately mineralized causing softened,
weakened bones
Main symptom is pain when weight is put on the affected
bone
Caused by insufficient calcium in the diet, or by vitamin D
deficiency
Rickets
Bones of children are inadequately mineralized causing
softened, weakened bones
Bowed legs and deformities of the pelvis, skull, and rib cage
are common
Caused by insufficient calcium in the diet, or by vitamin D
deficiency
63. Developmental Aspects of Bones
The embryonic skeleton ossifies in a predictable
timetable that allows fetal age to be easily determined
from sonograms
At birth, most long bones are well ossified (except for
their epiphyses)
By age 25, nearly all bones are completely ossified
In old age, bone resorption predominates
A single gene that codes for vitamin D docking
determines both the tendency to accumulate bone mass
early in life, and the risk for osteoporosis later in life