The skeletal system comprises bones and cartilages that support the body, allow for movement, protect internal organs, and produce blood cells. There are two main types of bones - long bones in the limbs and flat/irregular bones in the skull, vertebrae, and pelvis. Bones form through either intramembranous or endochondral ossification and are constantly remodeled throughout life. The axial skeleton includes the skull, vertebral column, and thoracic cage, providing structure and protection to the head, neck and trunk.

1. SKELETAL SYSTEM
M.ASIYABI. M.pharm.,
ASSISTANT PROFESSOR
DEPT OF PHARMACOLOGY
1Skeletal system

2. Introduction
•Framework of joined bones.
•Helps to stand straight, to move, to perform any
physical activity
•Aids in breathing.
•It comprises of : Bones, cartilages, tendons,
and liagments.
•Bones comprise of salts like calcium phosphate
– gives stone like appearance.

3. Bones
 Osteology – study of bone and teeth.
 Applied in anthropology, forensic
science and archaeology.
 To determine nutritional value, health,
the position of bone.
3Skeletal system

4. Types of bones
1.) Long bones :
Shaft present. Length greater than
width.
Usually curved, imparts high strength
Eg : femur, tibia, ulna, humerus.
4Skeletal system

5. 2.) Short bones : Equal length and
width. Eg : Ankle and wrist. Cubical
in shape.
5Skeletal system

6. 3.) Flat bones: Thin, offer wide surface for
muscle attachment, provides mechanical
protection. Eg : Cranial bones (Protects brain)
6Skeletal system

7. 4.) Irregular bones : Assymetrical,
complicated shape. Shaped to fulfill certain
functions in body. Eg : Vertebrae and facial
bones.
7Skeletal system

8. 5.) Sesamoid bones: Present in Palms
of hand and soles of feet (Knee cap) .
Develop in some tendons under
stresses.
8Skeletal system

9.  6.) Sutural bones: Very small bones
found within sutural joints of cranium.
Categorised on basis of location not
shape.
9Skeletal system

10. Salient features
 Hard in consistency
 Light weighed tissue made of calcium
phosphate provides rigidity to bone.
 High compressive strength
 Lacks tensile strength.
 Brittle, but significant elastic due to the
presence of collagen.
 Made of living cells.
 Non-uniform structures.
10Skeletal system

11. Macroscopic structure of
bones
C.S of Compact and cancellous bone.
11Skeletal system

12. Compact / Cortical / Dense bone
 Hard outermost layer of bone.
 Minimum voids/spaces.
 Gives white , smooth and sturdy
outlook to bones.
 Harvesian system/osteons:
Cylindrical structure.
Has Concentric collagen layers called
Harvesian lamellae (Within this
Harvesian canal present which carry
blood vessels, lymph vessels and
nerve fibres). 12Skeletal system

13. Compact bone
 Volkmann’s canals : Connects
Harvesian systems.
 Lacuane – Small tiny spaces and has
tissue fluid and spider shaped
osteocytes (Has canaliculi, which joins
together to form network).
 Periosteum : Covers outer surface of
bone. Does not cover joints. Made of
vascularised connective tissue.
 Two layers : Internal (osteogenic) and
outer (fibrous).
13Skeletal system

14. Trabecular / cancellous /
Spongy bone
 Filled with trabecular bone tissue
which contains network of spongy
bones.
 Contains rod and plate like elements
which provides space for blood
vessels and bone marrow.
 20% lighter and 10 times greater
surface area than compact bone.
14Skeletal system

15. Microscopic structure
1.) Osteoblasts : Mononucleate cells
formed from osteoprogenitor cells.
Leads to formation of proteinaceous
mixture (osteoid, which gets
mineralised to form bone).
2.) Osteocytes : Mature bone cells
formed from osteoblasts.
Occupies specific space called lacuane.
Mechno-sensory receptor : Regulate
the response of bone to stress.
15Skeletal system

16. Microscopic structure
3.) Osteoclasts : Large multinucleated
cells that involved in re-modelling of
bone (Bone resorption).
Located on small depression on bone’s
surface called Howship’s lacunae/
resorption pits (Appear as scalloped
surfaces in case of bone fracture).
16Skeletal system

17. Molecular structure
INORGANIC CONSTITUENTS :
The organic constisuents of matrix are
usually mineralised salt and calcium in
crystaline forms ,that occurs as
hydroxypatite.
The oesteoblast get mineralised by
alkaine phosphate ,released secreting
vesicles.
17Skeletal system

18. Organic constituents:
Type I collagen - main part of organic
matrix .
its made up of tropocollagen
Glycosaminoglycans, bone
sialoproteins ,osteocalcin, oesteonectin
and cell attachment factor were also
present in organic matrix.

19. Based on pattern of collagen
formed by osteoid
1.) Woven bone: Weak, Little amount of
collagen fibres oriented randomly. It forms
quickly independent of previous structure at
the time of growth and repair.
2.) Lamellar bone : Layered and very strong.
Several layers are piled up on one another. It
consist of collagen fibres lying parallel to
other fibres. They withstand torsion forces
due to the lamellar bone arrangement (Opp in
each alternate layer)
Bony substitution : When fracture, lamellar
bone replaced by woven bone (at hyaline
cartilage). 19Skeletal system

20. Formation of bones :
During prenatal stage, bones developed
by two methods:
1.) Intramembranous ossification
2.) Endochondral ossification
20Skeletal system

21. Intramembranous ossification
 Ossification –formation of bones.
 Flat bones of cranium formed from
mesenchyme tissue by a process
called Intramembranous ossification.
 Steps :
1.) Ossification centre development
2.) Process of calcification
3.) Trabeculae formation
4.) Periosteum development.
21Skeletal system

22. Intramembranous ossification
showing :
22Skeletal system

23.  Membranous ossification : At
specific region, direct mineralisation of
vascularised connective tissue takes
place.
 At that centre, Osteoprogenitor cells
multiply and accumulate. Around
vessels, collagen fibres are present.
 Osteoprogenitor cells osteoblasts
osteoid Osteoblasts (bony matrix)
osteocytes (lined by active osteoblasts)
 This depostion, Primarily has
mesenchymal stem cells, later forms
the basic bone tissue. 23Skeletal system

24.  Thickness of trabeculae increases ad
spongy layer becomes narrowed.
Cancellous bone slows down the
process and occupied by hemopoitic
tissue.
 Mesenchyme become denser to form
fibrovascular periosteum. Peiosteum
grows and form woven bone.
 Stem cells from periosteum further
extends and is called ossification.
24Skeletal system

25. Endochondral ossification
 Long bones from limbs mainly formed from
cartlage by the process of endochondral
ossification.
Steps:
1.) Cartilage development model.
2.) cartilage growth model.
3.) Primary ossification development centre.
4.) Medullary cavity development.
5.) Secondary ossification development centre,
and
6.) Articular cartilage and epiphyseal plate
formation.
25Skeletal system

26. Endochondreal ossification
26Skeletal system

27. Endochondrial....
 Starting point – Primary ossification centre
formed (during fetal development and post
natal phase) – responsible for the formation
of short bones, diaphysis of long bones and
irregular bones.
 Secondary ossification : In post natal period,
epiphysis of long bones, extremities of flat
bones and other parts of irregular bones were
formed.
 Epiphyseal plate – zone for cartilage
formation. At age 18 to 25, all cartilages
ossified and converted to bones (Epiphysis
and diaphysis fuse together by epiphyseal
closure). 27Skeletal system

28. Regeneration and repair of
bones
28Skeletal system

29. Remodelling or bone turnover
 Removal of old bone cells and addition
of new bone cells.
 Lifelong process (if fractured, it will
reshape or replace the bone).
 The bone matrix is resorbed on one
surface of abone and deposited on other.
 It is continuous process.
 Takes place in conjuction with functional
and mechanical demands of body.
 Exercise , injury also involved in
remodelling.
Eg: Formation of new bone in at injured 29Skeletal system

30. Remodelling....
 Eg : Formation of sacrum (5) and coccyx
(4) from pelvic vertabrae (9).
 In adults, 10% remodelling occurs every
year.
 Hampers when bone resorption and
ossification imbalanced and results in
bone related metabolic diseases. (Eg:
Osteophoresis)
 Resorption : bone remodelling and bone
replacement.
 Facts : In the lifespan of person,There
are only minute changes in shape of 30Skeletal system

31. Calcium balance
 Osteoclast release stored Ca2+ into
systemic circulation and thus
helps in regulating Ca2+ .
 From bloodstream Ca2+ used to
fix damaged bone simultaneously
Ca2+ released by resorption.
 Both resorption and remodelling
interlinked and occurs at specific
site only. Eg: Fractured site .
31Skeletal system

32. Divisions of skeletal system
1.)Axial skeleton
2.) Appendicular skeleton
32Skeletal system

33. 33Skeletal system

34. Functions of bones:
 Shape and support.
 Protection : Protects internal organs (Eg :Skull
protects brain)
 Body Movement : Aids in physical movement of
body.
 Acid-Base balance : Alkaline salt Ca2+ either
released or absorbed and helps to maintain PH of
blood.
 Mineral storage : Eg - Ca2+ and P.
 Blood production: blood cells produced from
bone marrow.
 Detoxification : Toxin absorbed from blood and
excreted gradually.
 Sound transduction : Ear bones involved in
hearing. 34Skeletal system

35. 35Skeletal system

36. Axial skeleton
 Helps in the formation of body axis.
 Supports and protects skull, neck and
trunk.
 Adult : 80 bones ; Children : 87 bones
Bones Number
Skull
Cranium 8
Facial skeleton 14
Ear ossicles 6
Hyoid bone 1
Vertebral column 26 (33 in children)
Thorax
cage
Ribs 24 (12 pair)
Sterum 1
36Skeletal system

37. Skull
37Skeletal system

38. Skull
 Bones of head region forms skull.
 Located over vertebral column along vertical
axis.
 Skull of adult comprise of 28 bones
(Immovable , except mandible).
 Two regions : Cranium and facial bones
 Various cavities are formed by bones of skull
and face. Eg : Cranial cavity
 3 parts of sutures (Synarthroidal or
immovable joints) : Coronal suture,
Squamous suture and Lambdoid suture.
 Neurocranium (8 bones) supports brain
 Splanchocranium (14 bones) supports face. 38Skeletal system

39. Cranium
 Spherical box like structure –
Protective covering of brain.
 Basal region – numerous blood
vessels and nerves enter and exit the
cranial cavity.
39Skeletal system

40. Bones of cranium :
1.) Frontal bones :
i.) Frontal squama : thick plate like
structure that forms forehead
ii.) Supraorbital margin : Thick
region located above eyes
iii.) Frontal sinuses : Cavities in
frontal bone
2.) Parietal bones : Form the major
portion of both sides of the skull.
40Skeletal system

41. Cranium...
3.) Temporal bones : Present along the ear.
i) Temporal squama : temple of skull
ii) Zygomatic arch : part of jaw
iii) Carotid canal : Passage for carotid artery
and causes pulsation.
iv) Jugular foramen : passage for jugular vein
along with 3 cranial nerves.
v) Mandibular fossa : Forms Tempero-maibular
joint (TMJ).
vi) TMJ : articulates mandible with temporal
bone.
vii) Mastoid process : behind ear to which neck
muscles connects
viii) Styloid process : Keeps hyoid bone in its
place with the help of neck, muscles of tongue
and ligaments. 41Skeletal system

42. Cranium...
4.) Occipital bones : Back of skull
i) Foramen magnum : Site where
Spinal cord attached to brain.
ii) Occipital condyles : Articulates with
vertebrae and helps in nodding of head.
5.) Sphenoid : Bat like structure present in
the centre of skull.
i) Sella turcica : holds pituitary gland
ii) Greater (2 outer) and lesser (2
inner) wings
iii) Pterygoid process : Between
greater wings and body.
42Skeletal system

43. Cranium...
6.) Ethmoid : Anterior part of skull and
seperates nasal cavity from brain. It forms the
upper part of nasal cavity. Act as pivot
(center) for almost all the skull bones.
i) Cribriform plate : Perforate with
olfactory foramina through which 1st cranial
nerves passes. Forms roof of nasal cavity.
ii) Labyrinth or lateral mass : Contains
Thin walled cellular cavities, including
ethmoidal cells (sequenced in 3 groups :
Anterior, middle, posterior)
iii) Perpendicular plate : Consists of thin
flattened lamina and polygonal shaped
perpendicular plate. Forms nasal septum (via
cribriform plate)
43Skeletal system

44. Facial bones
Facial skeleton, also called as visceral skull,
attaches anterior and inferior surfaces of
cranium.
Different bones of face includes:
1.) Nasal bones : cartilaginous and provide
flexibility. Helps in formation of nasal
bridge.
2.) Nasal septum : seperates right and left
part of nose, composed of ethmoid, vomer
and cartilages. Three concho of nasal
cavity : middle concho, inferior concho,
superior concho.
3.)Maxillae : Paired bones of upper jaw.
Holds upper set of teeth and act as roof
for mouth and floor of nose and eye cavity.44Skeletal system

45. Facial bones..
4.) Cleft : Seperates oral and nasal cavity.
Roof of mouth.
5.) Zygomatic bones : Cheek
bones(articulate with maxilla, sphenoid
and temporal bones)
6.) Mandible : Strongest and largest bone.
Only movable bone of face. Forms lower
jaw and holds lower teeth.
7.) Vomer : Only unpaired bone of face
which forms nasal septum.
8.) Lacrimal bones : Smallest bone.
Lacrimal ducts present and responsible
for lacrimation.
9.) Orbit : The socket or cavity holding the 45Skeletal system

46. Hyoid bone • Horse shoe shaped bone
• Also known as lingual bone
• Located middle of neck, between
thyroid cartilage and chin
• Floor of oral cavity
46Skeletal system

47. Hyoid bone ..
 Thyroid ligament holds this bone.
 Only skeletal bone not attached to any
other bone.
 Act as point of attachment for : Muscles of
oral cavity and tongue (ventrally) , The
larynx (Dorsally).
 Posterior surface attached to epiglottis and
pharynx.
 Two parts :
- centrally loacted part (Body)
- Two pairs of cornu: Greater cornu (2) ,
lesser cornu
(2) 47Skeletal system

48. Functions of hyoid bone
 Anchoring structure for tongue and
larynx, anterior neck muscles.
 Aids in tongue movement.
 Helps in swallowing.
 Helps in production of sound and its
variations.
48Skeletal system

49. Vertebral column (vertebrae)
49Skeletal system

50. Vertebrae
 The backbone of human being
comprises of 33 vertebrae.
 Also known as spine
 Provides protection to spinal cord and
its membranes.
50Skeletal system

51. Basic structure of a vertebra
1.) Body : Anterior portion of vertebra
which is joined to the intervertebral disc.
2.) Vertebral arch : Arch of posterior part
of body and protects spinal cord. It has
pedicles and laminae.
3.) Vertebral foramen : Opening through
arch. Spinal cord passes through this
foramen.
4.) Processes : Projection or outgrowth of
tissue from vertebrae. Three types :
transverse process, spinous process and
superior articular process. Attachment 51Skeletal system

52. Parts of vertebrae
52Skeletal system

53. Parts...
1.) Cervical (7) : form neck region.
Presence of foramen in transverse
process.
2.) Thoracic (12) : Externally visible as
chest or thorax. Presence of facets (ribs)
3.) Lumbar (5) : Absence of facet and
foramen. Belove thoracic region and
above pelvic region. Larger and stronger
than other vertebrae.
4.)Sacral (5) : Formation of sacral region
or upper pelvis.
5.) Coccyx (1) : Fusion of 4 coccygeal
vertebrae, in lower part of pelvis.
53Skeletal system

54. Curvatures of vetebral column
 4 types :
1. The cervical curvature
2. The thoracic curvature
3. The lumbar curvature
4. The pelvic curvature.
54Skeletal system

55. Functions of vertebral column
 Maintain erect body posture
 Maintain body balance.
 Vertebral architecture : supporting framework
for the trunk of body.
 Support system : Supports upper limb and
head to make them move freely. Point of
attachment for various muscles, ribs and
organs.
 Protection : protects spinal cord, kidney and
liver.
 Other functions : Maintain and balance
distribution of weight. Haemopoiesis in foetus
or infants. Forms site of attachment for 55Skeletal system

56. Thoracic cage / thorax
 Lies between head and abdomen,
excluding upper limbs.
 It constitute of sternum, thoracic
vertebrae and ribs.
 Encloses and protects heart and lungs
as well as blood vessels and nerves.
 Three parts : Ribs, sternum, thoracic
vertebrae.
 Out of 12 pair of ribs, upper 10 pairs
attached to sternum via cartilage from
anterior end. From posterior end, all the
12 pairs are attached to thoracic 56Skeletal system

57. Functions of thoracic cage
 Motion : Mobility to thorax region.
 Costal breathing :Attached to costal
cartilages and helps in costal
breathing.
 Protection : Encapsulates several
organs like heart and lungs, and
protects from damage.
57Skeletal system

58. Ribs:
 Long semi- circular bones forming rib cage.
Encapsulate chest forming periphery.
 They also allow the expansion of lungs for
respiration by expanding the chest (thorax).
 Organs like heart and lungs prtoected by the
ribs.
Basic structure of ribs : 12 pairs of ribs
3 parts : 1. Head : Attaches rib to the vertebrae.
Neck lies adjacent to neck.
2. Shaft : Length of rib. It has costal
where the blood vessels and nerves pass.
3. Tubercle : Terminal parts of rib and
attached to vertebrae of thorax. 58Skeletal system

59. Central rib of the left side
59Skeletal system

60. Types of ribs
 Sub divided into 3 categories :
1. True ribs : Directly attached to
sternum (via cartilages)
2. False ribs : Not directly attached
to the sternum.
3. Floating ribs : Not attached to
the sternum.
60Skeletal system

61. Sternum
61Skeletal system

62. Sternum
 Sternum or breastbone is a T shaped
or dagger shaped long flat bone
located at the centre of thorax.
 Lies in the centre of thoracic cavity.
 Joins to the ribs with the help of
cartilages and forms the frontal part of
the rib cage.
 The rib cage protects the heart, lungs
and major blood vessels from physical
injury or damage.
62Skeletal system

63. Three main regions of
sternum
1. Manubrium : Uppermost part of the
sternum consisting of two notches. i.e.,
Jugular notch and clavicular notch.
Clavicle (collar bone) attached at
clavicular notch.
2. Body : Rins (12) gets attached to the
sternum.
3. Xiphoid process : At the time of birth,
xiphoid process occurs as a cartilage,
which hardens due to ossification.
i.) It act as the point of attachment of
muscles of abdomen
ii.) Main point for cardiopulmonary
resuscitation 63Skeletal system

64. Functions of sternum
 Protecting vital organs
 Providing flexibility (costal cartilages)
 Protects aorta, vena cava and thymus.
 Fills the space in the mid region of the
chest just above the lungs and the
heart.
64Skeletal system

65. Appendicular skeleton
 Bony framework of upper and lower
limbs and their supporting girdles
including 126 bones that anchor the
appendages to the axial skeleton.
65Skeletal system

66. Pectoral girdle
Divisions : Left and right halves
Each half contains : Scapula and
clavicle
66Skeletal system

67. Scapula : Large, irregular and triangular flat
bone. Attaches muscles with trunk and the
upper limb.
3 processes :
i.) Spinous process : Posterior surface of the
upper broader part of each scapula. Distinct
ridges or spines are present.
ii.) Acromian process : The lateral end
articlated with acromion process at acromio-
clavicular joint.
iii.) Coracoid process : Small projection which
extends out of the scapula. Tip of this
process forms the point of attachment of
biceps and coracobronchialis muscle.
Just benead coracoid, glenoid cavity (cup like
cavity) is present. 67Skeletal system

68. Clavicle (collar bone)
 S shaped subcutaneous bone.
 Present on both sides of neck and
connects upper limbs with trunk.
 Inner and outer end articulates with
sternum and acromian process (at
clavicular facet )
 No medullary cavity.
 Inner surface of lateral end shows
elevation called Conoid tubercle and
ridge known as trapezoid ridge.
68Skeletal system

69. Functions of pectoral girdle
 Support and suspension : for upper
extremities.
 Shock absorber : After the act of
jumping or leaping.
 Maintanence : Maintains shape of
thorax and provides space for
insertion of muscle of the back.
 Locomotor movement : It forms the
site of attachment for muscles of
upper limb and helps in movement.
69Skeletal system

70. Upper limb : 30 bones and divided into 3
parts (Humerus, forearm and carpals)
1.) Humerus or arm bone:
70Skeletal system
• Longest bone of fore limb
• Articulates with glenoid cavity
of scapula
• Joined with radius and ulna at
elbow joint
• To perform pull, push, lift and
rotation

71. Radius and ulna
Skeletal system 71

72. Ulna and Radius
Radius and ulna together forms forearm
Ulna : Forms medial bone in the fore limb.
It consist of following notches and
process:
i. Olecranon process
ii. Coronoid process
iii. Radial notch and
iv. Trochlear notch
Radius : Lateral bone of forearm of the
body. The upper surface of the radius
articulates with capitulum of the
humerus, distal end articulates with ulnar
Skeletal system 72

73. Carpals, metacarpals and
phalanges
Skeletal system 73

74.  Carpals: 8 irregularly shaped bones,
arranged in proximal (scaphoid,
lunate,triquetral and pisiform) and
distal (Trapezium, trapezoid, capitate
and hamate) rows.
 Metacarpals: 5, which are numbered
from lateral to medial side and have
the head, the shaft and base.
 Phalanges: There are 14 phalanges
present in single hand (2 in thumb, 12
in other four fingers 3 each).
Skeletal system 74

75. Pelvic girdle
 Irregular, arch shaped structure made
up of coxae or innominate bones.
 The arch of pelvic girdle is articulated
by highly flexible structure called
pubic symphysis.
 Pelvis : Ring like structure formed by
sacrum and coccyx.
 Pelvic girdle made of 3 distinct bones
(Ilium, Ischium and pubis), fused
completely in adult.
Skeletal system 75

76. Pelvic girdle
Skeletal system 76

77. Bones of pelvic girdle
1.) Ilium : Plate like structure Upper
expanded part of the hip bone. External
surface acts as an attachment site for
gluteus muscles such as Guteus
maximus, medius and minimus.
3 parts :
i.) Sacroiliac joint : Attach sacrum and
ilium
ii.) Greater sciatic notch : Pathway for
sciatic nerve passes towards the leg.
iii.) Iliac fossa : Flat surface of ilium
Skeletal system 77

78. 2.) Ischium : Posterior inferior region of hip
bone. It consists of body and Ramus along
with ischial spine and ischial tuberosity.
3 Parts:
i.) Obturator foramen : Large hole through
which blood vessel and nerve passes,
covered by fibrous network.
ii.) Ischial tuberosity : Rough and thicck
surface of ischial body. Strongest part of hip.
Supports whole weight of body, while sitting.
iii.) Acetabulum : Wide socket like cavity
that holds the head of femur (thigh).
3.)Pubis : Anterior-inferior part of the hip bone.
Three parts : Superior ramus, inferior ramus
and body. (together forms pubis). Meets to
form small area, called Acetabulum (like
deep socket).
Skeletal system 78

79. Difference
Skeletal system 79
Male pelvis Female pelvis
Massive size Comparatively
smaller
Iliac crests are
placed close
together
Placed farther apart
Less flexible More flexible
Variations in structure proves that the pelvis of female plays a vital
role in
pregnancy and delivery of child. During parturition, child passes
through
mother’s pelvis. If it is small, then caesarean is done

80. Functions of pelvic girdle
 Support : Weight of body from
vertebral column is supported by
pelvis
 Protection : Supports and protects the
organs related to reproduction and
urinary system as well as developing
fetus in pregnant females.
Skeletal system 80

81. Lower limb
Skeletal system 81

82. Lower limb comprises of 32
bones as given below :
1. Femur: Strongest and longest bone of
human body. Present at upper end of
femur. The lower condylar end present
two articular surfaces : Patellar surface
(patella) and tibial surface (tibia).
2. Patella : Sesamoid bone located right in
front of distal end of femur.
3. Tibia : larger bone of lower leg and
located medially.
4. Fibula : Lateral bone present in lower
limb , articulate with lateral condyle of
tibia. Skeletal system 82

83. Tibio-
fibula
Skeletal system 83

84. Femur
Skeletal system 84

85. Skeletal system 85
5. )Tarsal : Proximal (Talus and calcaneus) and distal (medial cuneiform,
internal
cuneiform, lateral cuneiform, cuboid and navicular bones) rows.
6.) Metatarsal : articulate proximally with uniform and cuboid bones, and
distally with phalanges.
7.) Phalanges : 14 phalanges in single foot (2 in great toe remaining in
other
fingers)
Foot contain two additional bones called sesamoid bones. Muscle of big

86. Skeletal system 86