General anatomy of bone lecture notes for written exam and viva
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Bone
Definition:
bone is a highly vascular, hard form of special connective
tissue.
Composition of bone
1.
Cells :
Osteoprogenitor
cells: they are stem cells. They
can convert to any types of cells
Osteoblast:
calcification of bone matrix
Osteoclast:
remodeling of bone
Osteocyte
: maintenance of calcification
2.Extracellular
matrix:
Organic:
collagen fibres, chondroitin sulphate
Inorganic: Ca, Mg, and
PSO4
Function of bone
- Structural support,
- Protection of vital organs,
- Storage of calcium and magnesium
- Bone contain red bone marrow responsible for
blood cell formation
Periosteum
It is a thick
fibro-vasculo-cellular layer that covers the outer surface of bone except the
articular surfaces which are covered by articular cartilage (hyaline
cartilage).
It consists of two layers:
Outer fibro vascular layer –is
composed of collagen fibres and fibroblast
and blood vessels
Inner osteogenic layer – Inner
cellular layer or osteogenic layer (containing osteoprogenitor cells which form
osteoblasts).
It is united to the underlying
bone by Sharpey’s fibers (collagen fibers).
It has very rich nerve supply and
therefore it is the most pain sensitive part of bone.
Normally this layer responsible
for increasing width of bone. By intramembranous ossification, it increase the
width of bone
Functions
of periosteum
1.
It receives the attachments of muscles
2.
Gives nutrition to the outer part of
the compact bone by the periosteal vessels
3.
It is important in the repair of
fractures
4.
During fetal development, this is
responsible for appositional growth of bone
Sharpey's fibers (bone fibers,
or perforating fibres): are a
matrix of connective tissue consisting of bundles of strong collagenous fibres
connecting periosteum to bone. They are part of the outer fibrous layer of
periosteum, entering into the outer circumferential and interstitial lamellae
of bone tissue
Macroscopically
bones (without microscope) are two types –
1. Compact (bony tissue without cavity ) and
2. spongy (bony tissue contain numerous cavities )
Cross section of long bone, we fine outer compact bone and inner spongy
bone
Cross section of flat bone of skull: we find Inner
& outer table (compact bone) and middle diploe spongy bone)
Each haversian system contain a haversian canal,
Lamina-thin plate of bone surrounded by haversian canal,
Lacuna (depressed area within the lamina contain osteocyte)
Canaliculi (very tiny canal contain processes of osteocytes
Volkman’s canal connect two separate haversian canal
Classification
of bone:
1.
According to the position-
Axial bone : skull bones, vertebrae
Appendicular bone: bones of
upper and lower limb
2.
Classification of bone according to
mechanism of ossification
Membranous
ossification:
EX:
head and neck: parietal bone,
frontal bone, maxilla, zygomatic,
Superior extremity: clavicle
Cartilaginous
ossification:
Ex: all vertebrae, all ribs, sternum,
scapula, all bones of upper limb except clavicle, all bones of lower limb
Membrano-cartilaginous
ossification:
Occipital: membranous
ossification area above the highest nuchal line, rest of the parts arises from
cartilaginous ossification
Sphenoid: membranous
ossification above the lateral part of greater wing and pterygoid process except
the hamulus, rest of the part arises from cartilage,
Temporal: membranous
ossification – squamous part and tympanic part, rest of the parts arises from
cartilage,
Mandible:
cartilaginous ossification anterior part of body and part of ramus above mandibular
foramen, rest of the body arises from membranous ossification
3.
According to the shape (Morphological
classification of bone)
Long bone: they are three types
a. typical long bone: Ex: femur ,
b. Modify
long bone:Ex: clavicle (because it is
the only bone lies horizontally, has no medullary cavity, and ossify in
membrane)
c. Miniature
long bone: Ex: metacarpal bone , shape long but size smaller than the typical
long bone
Short bone: cuboid shaped, presents six surfaces, 4 surface form
joint and 2 surface for articulation
Flat bone: this bone form by two plates of compact bone and
middle spongy bone. Ex: parietal bone
Irregular bone : irregular in shape. They mostly form by spongy bone
and red marrow with thin outer covering of compact bone Ex: vertebrae
Pneumatic bone : these bone contain air filled cavity, it makes bone
lighter, act as an air conditioning chamber and helps in resonance of voice.
Ex: Maxilla
Sesamoid bone : it is developed in the tendon of muscle, act as
pulley, has no haversian system and periosteum
Parts of an adult long bone
Adult long
bone has two ends: upper end and lower end
and an intervening shaft.
• Shaft
(diaphysis) The shaft of the long bone is composed of the following from
outside to inside
• Cortex (cortical
bone): It is made up of dense
compact/cortical bone.
• Marrow
cavity: deep to the cortex is the medullary cavity. It is lined by endosteum
and is filled with bone marrow (depending upon age of the individual it can be
red or yellow marrow).
• Ends of long bone (Epiphysis): Are made up
of cancellous bone (having bony trabeculae and marrow spaces (filled with red
bone marrow)). The articular surfaces at the ends are covered by articular (hyaline) cartilage).
Parts
of growing long bone:
Epiphysis (E)
Epiphyseal
cartilage (EC) ,
Metaphysis
(M) (it is the part of diaphysis near the epiphyseal cartilage ) and
Diaphysis(D)
Diaphysis:
it is the part of growing long
bone which ossify from primary ossification centre and form shaft of bone.
Epiphysis:
parts of a growing long bone which
ossify from secondary ossification center
Types of epiphysis:
Pressure epiphysis: it transmits body weight. Ex: head of femur
Traction epiphysis: it is produce by pull of muscles
EX: trochanter of femur
Atavistic epiphysis: coracoid process of scapula.
Coracoids process is independent bone unit with scapula for nutrition.
Epiphyseal cartilage: it
is the plate of hyaline cartilage situated between the epiphysis and diaphysis.
The plate is found in children and adolescents; In
adults, who have stopped growing, the plate is replaced by an epiphyseal
line.
One of the steps of Intracartilaginous ossification
occurs in epiphyseal
cartilage of growing long bone:
Histologically, there are some zone present in epiphyseal cartilage.
These zone explain how a bone grow in length.
Zone of
reserve
No proliferation of chondrocytes
Zone of
proliferation Chondrocytes undergo rapid mitosis under influence of
growth hormone
Zone of
hypertrophy Chondrocytes stop mitosis, and begin to hypertrophy by
accumulating glycogen, lipids, and alkaline phosphatase
Zone of
cellular death Cartilagenous matrix begins to calcify- so chondrocytes do
not get nutrition-- death of chondrocytes leaving empty spaces.-- Periosteal bud with Blood vessels begin to
grow through the empty spaces
Zone of ossification Periosteal
buds contain osteoblast which calcify the bone matrix and blood vessel form red
bone marrow. This newly form zone of ossification add as metaphysis of growing
long bone and bone increase in length
Metaphysis:it
is part of diaphysis near the epiphyseal cartilage
Clinical
importance of metaphysis
It is the most actively growing area of long bone
Profuse blood supply, contain hair pin loops like vessels so it is the
common sites of infection
Muscle, ligament and capsule of joint are attached close to it
Metaphysis is common site of osteomyelitis in children
Growing end of the long bone : the epiphysis which appear first and unit last with the diaphysis
The growing end is situated against the direction of
the nutrient foramen
Upper end of
humerus and lower end of Radius and ulna is the growing end
Lower end of femus and upper end of tibia and fibula
is the growing end
Clinical importance: injury or infection of this end
makes the bone stunted in growth
Blood
supply of Developing long bone /growing long bone
•
Nutrient artery: It enters the shaft through the nutrient foramen, pass obliquely through
the cortex of shaft. Then, it enters medullary cavity and divides into
ascending and descending branches.
These branches reach the metaphysis and form ‘hair
pin loops’ branches which are anastomose with the metaphyseal and epiphyseal
arteries.
Supply
areas of the nutrient artery
·
The medullary cavity,
·
Inner 2/3rd of cortical bone of diaphysis,
·
Metaphysis
•
Periosteal arteries:
Are branches of neighbouring muscular arteries and
therefore they are especially numerous beneath the muscular attachments.
They ramify beneath the periosteum and reach the
underlying cortical bone through the Volkman’s canals.
Supply
area of periosteal arteries
Periosteum
outer 1/3rd of the cortical bone of shaft.
•
Epiphyseal arteries:
They are
derived from the peri-articular (around the joint) anastomosis present around
the non-articular surface of ends of long bones.
They enter
the epiphyseal ends through the numerous foramina present in the non articular
part. The number and size of these foramina gives an idea of the vascularity of
the ends of long bones.
•
Metaphyseal arteries:
Numerous arteries arise from the anastomosis around
the joint and pierce the metaphysis along the attachment of the joint capsule
Ossification
It is the process of new
bone formation. Two Mechanism of ossification – intra cartilaginous and
intramembranous ossification
How a cartilaginous model of bone converted into
adult bone?
Cartilaginous model of a long bone
Bone formation is started at diaphysis of growing
long bone. This area is known as primary ossification centre
After formation of diaphysis, bone formation is
started at epiphyseal ends. These areas
known as secondary ossification centres
So upper and lower end plus central part of growing
long bone converted into bone from cartilage
but epiphyseal cartilage remain unchanged
until the end of growth
In adult, Epiphyseal cartilages converted into bone and form epiphyseal line,
Adult bone is formed by fusion of epiphysis and diaphysis
S N: Ossification of long bone: occur by both
intracartilaginous and intramembranous ossificatin process
Length of long bone increase by intracartilaginous
ossification (location : epiphyseal cartilage of growing long bone )
Width of long bone increase by intra membranous ossification
(location : periosteum of growing long bone- osteogenic layer of periosteum is
responsible for membranous ossification )
Intra membranous ossification:
1.
Mesenchyme (fetal
connective tissue membrane) contain mesenchymal sterm cell , they proliferate
and condense to primary ossification centre
2.
The mesenchymal
stem cells are converted into osteoblast
3.
Osteoblasts
begin to secrete un-calcify bone matrix away from the blood vessel .
4.
Soon matrix
become calcify and some of osteoblast tapped
in calcifies matrix become osteocyte.
5.
By this
process small bone spicules are form. Bone spicules are unite with each other and form spongy bone/ trabecular bone
6.
embryonic
blood vessels grow within spaces between bone spicules and ultimately form red
bone marrow which is formed by hematopoietic
stem cells, reticular cell and fibres and fibroblast and blood vessels
7.
the middle
part of spongy bone remain spongy but outer and inner part of spongy bone
remodel and form compact bone
8.
Outer and
inner vascular mesenchyme do not take part in ossification process are
converted into periosteum, endosteum or endosteal dura
Classification
of ossification centre
1.
A primary ossification center is the first area of
a bone to start ossifying.
It
usually appears during intra-uterine life in the central part of each
developing bone.
Exception: carpal bones of hand
In long bones the primary ossification
centers appear in the diaphysis/shaft and in irregular bones the primary
centers appear usually in the body of the bone.
All long bones have only one primary
center but some irregular bones such as the hip bone and vertebrae have
multiple primary centers.
2.
Secondary ossification centre: A secondary
ossification center is the area of ossification that appears after the primary
ossification center has already appeared - most of which appear during the
postnatal and adolescent years. Most bones have more than one secondary
ossification center. In long bones, the secondary centers appear in the epiphyses
(upper and lower end).
Name of bone |
Primary
ossification center |
Secondary
ossification center |
|
Clavicle |
Two |
One for sternal end |
|
Humerus |
One for shaft |
Three for upper end – head , greater & lesser tubercle & Four
for lower end – lateral & medial epicondyle, capitulum, trochlear |
|
Radius |
One for shaft |
One for upper end & One for lower end |
|
Ulna |
One for shaft |
One for upper end & One for lower end |
|
Carpal bone |
One center which appear after birth |
No secondary ossification centre |
|
Metacarpal bone |
One center for shaft |
One 2nd ossification centre : base of 1st metacarpal bones is ossified
from 2nd ossification center& Heads of 2-5 metacarpal bone are ossified from 2nd
ossification center |
|
Phalanges |
One center for shaft & head |
One 2nd ossification center for base of each phalanx |
Lower limb
|
Name of bone |
Primary
ossification center |
Secondary
ossification center |
|
Hip bone |
Three – ilium, ischium, pubis |
5 secondary ossification center |
|
Femur |
One for shaft |
Three for upper end – head , greater & lesser trochanter & One
for lower end |
|
Tibia |
One primary ossification center for shaft |
One for upper end & One for
lower end |
|
Fibula |
One primary ossification center for shaft |
One for upper end One for lower end |
|
Tarsal bone (except
calcaneus) |
One primary ossification center |
No secondary ossification centre |
|
Calcaneus |
One primary ossification center |
One secondary ossification centre |
|
Metatarsal bone |
One primary ossification center for shaft |
One 2nd ossification centre : base of 1st metatarsal bones is ossified
from 2nd ossification center & Heads of 2-5 metatarsal bone are ossified from 2nd
ossification center |
|
Phalanges |
One for shaft and head |
One center for base of each
phalanx |
Bone marrow: It is a soft tissue which fills the medullary cavity of long bone and the
trabeculae of spongy bone
Types : Yellow bone marrow: location: medullary cavity of long bone
Red bone marrow : Location :
In new bone, it is occupied in whole skeleton
By the 7th year , medullary cavity of long bone contain white
bone marrow
By the age of 20, red bone marrow found in upper and lower end of long, diploe of skull
bone, sternum, rib, vertebra
Function : red bone marrow responsible for blood cells formation
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