Bone anatomy

1. Anatomy of bone and
its functions
Dr.Navaneesh
Moderator:Dr.Anna mohan

2.  Contents
 Formation of bone
 Classification of bones
 Structure of bone
 Blood supply
 Composition of bone

3.  Bone(syn os-osteon)
 Osseous tissue,a specialized form of
dense connective tissue consisting of bone
cells(osteocytes)
 Embedded in a matrix of calcified
intercellular substance
 Bone matrix contains collagen
fibers,minerals like calcium phosphate and
calcium carbonate

4. Formation of bone
 All bone is of mesodermal origin
 Two types of ossification
 Intramembranous ossification
 Endochondral ossification

7. Intramembranous ossification
 Mesenchymal condensation
 Highly vascular
 Laying down of bundle of collagen fibers in
mesenchymal condensation
 Osteoblast formation-osteiod
 Calcium salts deposition-lamellus of bone

9. Enchondral ossification
 Ossifies bone that originate as hyaline
cartilage
 Most bones originate as hyaline cartilage
 Growth and ossification of long bones
occur in 6 steps

11. Skeletal organization
 The actual number of bones in human
skeleton varies from person to person
 Typically there are about 206 bones
 For convenience the skeleton is divided
into the
 Axial skeleton
 Appendicular skeleton

13. Classification of bones by shape
 Long bones
 Short bones
 Irregular
 Pnuematised
 Sesamoid bones

14. Long bones
 Diaphysis-shaft
 Epiphysis-Expanded
ends
 Shaft-3 surfaces,3
borders,medullary
cavity and a nutrient
foramen directed away
from growing end
 Ex-
Humerus,radius,ulna,fe
mur,etc

15. Short bones
 Are small and thick
 Their shape is usually
cuboid,cuneiform,trap
ezoid or scaphoid
 Ex-Carpal and Tarsal
bones

16. Flat bones
 Are thin with parallel
surfaces
 Are found in the
skull,sternum ,ribs
and scapula
 Form boundaries of
certain body cavities
 Resembles a sandwich
of spongy bone
 Between 2 layers of
compact bone

17. Pnuematic bones
 Certain irregular bones contain large air
spaces lined by epithelium
 Make the skull light in weight ,help in
resonance of voice and act as air
conditioning chambers for inspired air.
 Ex –Maxilla,Sphenoid,Ethmoid,etc

18. Sesamoid bones
 Resembling a grain of
sesame in size or shape
 Bony nodules found
embedded in the tendons
or joint capsules
 No periosteum and ossify
after birth
 Related to an articular or
non articula bony surface
 Ex:patella,pisiform and
fabella

19. Irregular bones
 Have complex shapes
 Examples:
 Spinal vertebrae
 Pelvic bones

21. Developmental classification
 Membrane (dermal ) bones
 Cartilaginous bones
 Membrano-cartilaginous bones

22.  Membrane(dermal )bones
 Ossify in membrane(intramembranous of
mesenchymal.
 Derived from mesenchymal condensations
 Ex-bones of the vault of skull and facial
bones
 Defect-Cleidocranial dysostosis

23. Cartilaginous bones
 Ossify in cartilage(intracartilagenous or
endochondral)
 Derived from preformed cartilaginous
models
 Ex-Bone of limbs,Vertebral column and
thoracic cage
 Defect-Common type of dwarfism called
achondroplasia.

24. Membrano-cartilaginous bones
 Ossify partly in cartilage and partly in
membrane
 Ex-clavicle,mandible,Occipital etc

25. Structure of bone
◦ It consists of bone cells or osteocytes
seperated by intercellular substance
◦ 1.Osteoblast-Bone producing cells
◦ 2.Osteoclasts-Bone removing cells
◦ 3.Osteoprogenitor cells-From which osteoblasts
and osteoclasts derived

27. Osteoprogenitor cells
 Mesenchymal stem cells that divide to
produce osteoblasts
 Are located in inner,cellular layer of
periosteum(endosteum)
 Assist in fracture repair

28. Osteoblasts
 Immature bone cells that secrete matrix
compounds(osteogenesis)
 Matrix produced by osteoblasts,but not yet
calcified to form bone
 Osteoblasts surrounded by bone become
osteocytes

29. Osteocytes
 Mature bone cells that maintain the bone
matrix
 Live in lacunae
 Are between layers (lamellae)of matrix
 Connect by cytoplasmic extensions
through canaliculi in lamellae
 Do not divide

30. Osteoclast
 Secrete acids and protein digesting
enzymes
 Giant,multinucleate cells
 Dissolve bone matrix and release stored
minerals(osteolysis)
 Are derived from stem cells that produce
macrophages

32. Structural classification
 Macroscopically
 1.Compact bone
 2.Cancellous bone

33. Compact bone
 Strong dense-80 % of
skeleton
 Consists of multiple
osteons(haversian
systems) with intersitial
lamellae.
 Best developed in cortex of
long bones
 Osteons are made up of
concentric bone lamellae
with central canal
containing osteoblasts and
an arteriole supplying the
osteon

34.  Lamellae are connected
by canaliculi
 Cement lines mark
outer limit of
osteon(bone resorption
ended
 Volkmanns
canals:radially
oriented,have arteriole
and connect adjacent
osteons
 This is an adaptation to
bending and twisting
forces
(compression,tension
and shear)

35. Osteon
 The basic unit of mature compact bone
 Osteocytes are arranged in concentric
lamellae
 Around a central canal containing blood
vessels

38. Cancellous bone(spongy or
trabecular)
 Open in texture-Meshwork of trabeculae(rods
and plates)
 Crossed lattice structure ,makes up 20% of
skeleton
 High bone turnover rate
 Bone is resorbed by osteoclasts in howship
lacunae and formed on the opposite side of
trabeculae by osteoblasts
 Osteoporosis is common in cancellous
bones,making it susceptible to fracture.

39.  Commonly found in the metaphysis and
epiphysis of long bones
 Adaptation to compressive forces.
 Does not have osteons
 The matrix forms an open network of
trabeculae
 Trabeculae have no blood vessels

40.  Microscopically
 1.Lamellar bone
 2.woven bone

42. LAMELLAR BONE
 Bone is made up of layers or lamellae
 Lamellae is a thin plate of bone consisting
of collagen fibers and mineral
salts,deposited in gelatinous ground
substance
 Between adjoining lamellae we see small
flattened spaces-lacunae

43.  Lacunae
 contains one osteocyte
 Have fine canals or canaliculi that
communicate with those from other
lacunae
 Fibers of one lamellus run parallel to each
other ,but those of adjoining lamellae run
at varying angles to each other

44. Woven bone
 Found in all newly formed bone –later
replaced by lamellar bone
 Collagen fibers are present in bundles –
run randomly –interlacing with each other
 Abnormal persistence-pagets disease

45.  Shaft
 Composed of
 1.periosteum
 2.cortex
 3.medullary cavity

46. periosteum
 External surface of any bone covered by a
membrane –periosteum
 Two layer
 Outer-fibrous membrane,inner –cellular
 In young bones-inner layer-numerous
osteoblasts-osteogenitic layer
 In adults-osteoblasts are not
conspicuous,but osteoprogenitor cells
present here can form osteoblasts when
need arises

47. functions
 Medium through which muscles,tendons
and ligaments attached
 Forms a nutritive function
 Can form bone when required
 Forms a limiting membrane that prevents
bone tissue from spilling out into
neighbouring tissues

48. cortex
 Is made up of a compact bone which gives
the desired strength
 Can withstand all possible mechanical
strains

49. ENDOSTEUM
 An incomplete cellular layer
 Lines the marrow cavity
 Covers trabeculae of spongy bone and lines
central canals
 Contains osteoblasts,osteoprogenitor cells
and osteoclasts
 Is active in bone growth and repair

50. Medullary cavity
 Filled with red or yellow bone marrow
 Red-at birth-heamopoiesis
 Yellow-as age advance-atrophies-fatty
 Red marrow persists in the cancellous
ends of long bones

51. Parts of young bone
 It ossifies in 3 parts
 The two ends from the secondary centers
 Intervening shaft from a primary center

52. EPIPHYSIS
 The ends of a bone which ossify from
secondary centers
 Types
 1.Pressure epiphysis-Transmission of
weight .Ex:head of femur
 2.Traction epiphysis-Provide attachment
to one or more tendons which exerts a
traction on the epiphysis.Ex-Tronchanters
of femur

53.  Atavistic epiphysis-phylogenitically an
independent bone,which fuses to another
bone.Ex-corocoid process of scapula.
 Aberrant epiphysis-not always
present .Ex-head of 1 st metacarpal and
base of other metacarpal

54. DIAPHYSIS
 It is the elongated shaft of a long bone
which ossifies from a primary center
 Made of thick cortical bone
 Filled with bone marrow

55. Metaphysis
 Epiphysial ends of a diaphysis
 Zone of active growth
 Typically made up of cancellous bone
 Hair pin bends of end arteries

56. Epiphysial plate of cartilage
 It seperates epiphysis from metaphysis
 Proliferation-Responsible for length wise
growth of long bone.
 Epiphysial fusion-Can no longer grow
 Nourished by both epiphysial and
metaphysial arteries.

58. Blood supply of bones
 Long bones-derived from
 1.Nutrient artery
 2.Periosteal artery
 3.Epiphysial artery
 4.Metaphysial artery

60. Nutrient artery
 Enters through nutrient foramen
 Divides into ascending and descending branches in
medullary cavity
 Brach divides –small parallel channels-terminate in
adult metaphysis
 Anatomosing with the epiphysial,metaphysial and
periosteal arteries
 Supplies the medullary cavity,inner 2/3 rd of the
cortex and metaphysis
 Nutrient foramen is directed away from the
growing end of the bone

61. Periosteal artery
 Numerous beneath the muscular and
ligamentous attachments
 Ramify beneath the periosteum and enter
the volkmanns canals to supply the outer
1/3 rd of the cortex

62. Epiphyseal artery
 Derived from periarticular vascular
arcades(circulus vasculosus)
 Out of the numerus vascular foramina in
this region –few admit arteries and rest
venous exits
 Number size-idea of the relative
vascularity of two ends of the long bone.

63. Metaphysial artery
 Derived from the neighbouring systemic
vessels
 Pass directly into the metaphysis and
reinforce the metaphysial branches from
the primary nutrient artery

64. Homeostasis of bone tissue
 Bone resorption –action of osteoclasts and
parathyroid hormone aka PTH
 Bone deposition-Action of osteoblasts and
calcitonin
 Occurs by direction of the thyroid and
parathyroid glands

67. Factors affecting bone tissue
 Deficiency of vitamin a –retards bone development
 Deficiency of vitamin c-results in fragile bones
 Deficiency of vitamin D-Rickets,osteomalacia
 Insufficient growth hormone-dwarfism
 Excessive growth hormone –gigantism,acromegaly
 Insufficient thyroid hormone-delays bone growth
 Sex hormones-promote bone formation,stimulate
ossification of epiphyseal plates
 Physical stress-stimulates bone growth

68. References
 Miller’s review of orthopaedics-seventh
edition
 Netter’s atlas

69. Thank you