The document provides an extensive overview of the human skeletal system, including the classification of bones into categories such as long, short, flat, and irregular bones, as well as their structure and functions. It discusses the adult human skeleton's composition of 206 bones, the roles of osteocytes, osteoblasts, and osteoclasts in bone remodeling, and the importance of joints in connecting these bones. Additionally, it outlines the axial and appendicular skeletons, detailing their components and the distinct features of various joint types.

1. Skeletal
System
SURESH BABU EMANDI M.Pharm
Vikas Institute of Pharmaceutical Sciences
Near Air Port, Rajahmundry,Andhrapradesh
emandi2008@gmail.com

2. Although bones are
often thought to be
static or permanent
they are highly
vascular living
structures that are
continuously being
remodelled

3. Types of bones
Bones are classified as
Long bones
Short bones
Irregular bones
Flat bones
Sesamoid bones.

4. Long bones. These consist of a shaft and two extremities.
As the name suggests the length is much greater than the
width. Examples include the femur, tibia and fibula.
Short, irregular, flat and sesamoid bones. These have
no shafts or extremities and are diverse in shape and size.
Examples include:
• short bones — carpals (wrist)
• irregular bones—vertebrae and some skull bones
• flat bones — sternum, ribs and most skull bones
• sesamoid bones — patella (knee cap).

5. Bone is a strong and durable type of
connective tissue.
It consists of:
• water (25%)
• organic constituents including osteoid
(the carbon containing part of the
matrix) and bone cells (25%)
• inorganic constituents, mainly calcium
phosphate (50%).

6. ⦁ The bones primarily give support to the appendages
and protect the fragile organs of the body such as
the brain, spinal cord, heart, and lungs.
⦁ They also store calcium and phoshorus in the hard
bone matrix, which can be released when needed
elsewhere.
⦁ The bumps, ridges, and grooves on the surface of
bones provide attachment sites for the skeletal
muscles.
⦁ Additionally, many bones contain a soft tissue called
marrow that produces new blood cells and stores fat

7. ⦁ Bone is one of the hardest parts of the body
⦁ Very lightweight
⦁ Can resist tension
◦ Calcium salts make it hard
◦ Collagen fibers make it strong and flexible

8. ⚫ Support
⚫ Internal framework of body
⚫ Ex: Legs support body trunk,
rib cage supports chest wall
⚫ Protection
⚫ Protects soft body organs (skull
protects brain, ribs protect
heart and lungs, etc)
⚫ Movement*
⚫ Muscles use bones as levers to
move body
⚫ NOT a function skeletal system
can do on it’s own
⚫ Storage
⚫ Fat storage
⚫ In yellow marrow
⚫ Mineral storage
⚫ Calcium, phosphorus, and
others.
⚫ Blood cell formation
⚫ Hematopoeisis
⚫ Occurs in bone marrow of long
bones

9. ⦁ The adult human skeleton is a framework of 206
bones and is anatomically divided into two parts,
◦ The axial skeleton
◦ The appendicular skeleton
⦁ Two types of bone
◦ Compact bone
🞄 Homogeneous appearance
🞄 Dense, looks smooth
◦ Spongy bone
🞄 Small needle-like pieces
🞄 Lots of open spaces
🞄 (Looks like a sponge, hence the name)

10. ⦁ In embryos…
◦ Skeleton made of hyaline cartilage
◦ Gets replaced by bone with age
⦁ Cartilage remains in a few places…
◦ Bridge of nose
◦ Parts of ribs
◦ Joints

11. ⚫ Epiphyseal plates allow for growth of long bone
during childhood
⚫New cartilage is continuously formed
⚫Older cartilage becomes ossified
⚫Cartilage is broken down
⚫Bone replaces cartilage
⚫ Bones remodeled, lengthened until growth stops
⚫Bones change shape somewhat
⚫Bones grow in width

14. ⦁ Osteocyte
◦ Mature bone cell
⦁ Osteoblast
◦ “Bone builders”
⦁ Osteoclast
◦ “Bone destroyers”
◦ Break down bone matrix to remodel and/or release
calcium

15. ⚫ Bone remodeling is done by osteoblasts and osteoclasts
⚫ Essential for bones to keep normal proportions and
strength
⚫ Bones get larger/thicker when…
⚫Large muscles are attached to them
⚫Need more bone to attach the large muscle to
⚫ Bones get smaller/weaker when…
⚫Physical inactivity
⚫Non-use of musclesatrophy
⚫Small muscles don’t need large bones to attach to
⚫ Bones remodeled to become smaller

16. ⚫ Long Bones
⚫Longer than wide
⚫Contain shaft with head at
each end
⚫Mostly compact bone
⚫Limbs (not ankle or wrist
bones)
⚫ Short Bones
⚫Cube-shaped
⚫Mostly spongy bone
⚫Wrist and ankle bones
⚫Patella (kneecap)
⚫ Flat Bones
⚫Thin, flat, usually curved
⚫Two layers of compact
bone with spongy bone in
between
⚫Skull, ribs, breastbone
⚫ Irregular Bones
⚫Don’t fit into the other
categories
⚫Vertebrae, hip bones

17. ⚫ Diaphysis
⚫Shaft
⚫Made of compact bone
⚫ Epiphyses
⚫Ends of long bone
⚫Made of compact
bone surrounding
spongy bone
⚫Covered with articular
cartilage
⚫Smooth, glassy, decreases
friction at joints

18. ⦁ Epiphyseal Line
◦ Line of bone tissue that
looks different from rest
of bone
◦ Remnant of epiphyseal
plate
🞄 Hyaline cartilage
🞄 Causes long bones to grow
lengthwise

19. ⦁ Periosteum
◦ Outer covering of shaft
◦ Like “skin” on chicken
bone
⦁ Sharpey’s fibers
◦ Attach periosteum to
bone
⦁ Arteries
◦ Supply nutrients to bone
cells

20. ⦁ Medullary Cavity
◦ In shaft
◦ Contains yellow marrow
(adipose) in adults
◦ Contains red marrow in
infants (for blood cell
formation)

21. ⦁ Osteon (Haversian system)
◦ A “unit” of bone
⦁ Central (Haversian) canal
◦ Opening in center of osteon
◦ Contains blood vessels
⦁ Perforating (Volkman’s) canal
◦ Perpendicular to central canal
◦ Contains blood vessels and nerves

23. ⚫ Lacunae
⚫Cavities that contain
osteocytes (bone cells)
⚫Arranged in concentric
rings (like tree rings)
⚫ Lamellae
⚫Rings around the central
canal
⚫Where the lacunae
can be found

24. ⦁ Canaliculi
◦ Tiny canals
◦ Radiate from central
canal to lacunae
◦ Transport nutrients to
bone cells

25. ⦁ The human skeleton can be divided into two
◦ The axial skeleton
◦ The appendicular skeleton.
⦁ The axial skeleton is formed by the vertebral
column, the rib cage, the skull and other associated
bones.
⦁ The appendicular skeleton, which is attached to the
axial skeleton, is formed by the shoulder girdle,
the pelvic girdle and the bones of the upper and
lower limbs.

27. ⦁ The core of the skeleton is referred to as the axial
skeleton. It consists of the following 80 bones.
⦁ The upright posture of humans is maintained by the
axial skeleton, which transmits the weight from the
head, the trunk, and the upper extremities down to
the lower extremities at the hip joints.
◦ Skull: 22 bones
◦ Hyoid: 1 bone
◦ Vertebrae: 32 -34 bones
◦ Ribs: 24 bones
◦ Sternum: 1 bone

29. ⦁ The skull consists of 22 bones and 7 associated
bones. All the larger skull bones are shown in this
exploded view. They fall into two main groups.
◦ One group (including the frontal, parietal, and temporal
bones) surrounds the brain and is fused together to form the
cranium.
◦ The remainder of the bones form the face.
⦁ Sutures
◦ Interlocking, immovable joints holding most skullbones
together
🞄 Mandible-only freely movable bone in skull

31. ⦁ This highly flexible structure, also called the
vertebral column, supports the head and body.
⦁ It also protects the delicate tissues of the spinal
cord.
⦁ It is made up of 32-34 bones called vertebrae,
separated by intervertebral discs, which act as shock
absorbers.
⦁ The bones of the spine are kept in place and
supported by attached ligaments and muscles.

32. ⦁ Hollow portions of bone around nasal cavity
◦ Named for bones they are found in
◦ Lighten skull
◦ Amplify sounds when speaking/ give resonance

33. ⦁ Large in comparison
to body length of
infant
⦁ Contains fontanelles
◦ Soft fibrous membranes
connecting cranial bones
🞄“Soft Spots”
🞄 Usually convert to bone
around 24 months after
birth

34. ⦁ Vertebrae named for
their location
◦ 7 cervical vertebrae
🞄 C1 = Atlas
🞄 C2 = Axis
◦ 12 thoracic vertebrae
◦ 5 lumbar vertebrae
◦ Sacrum
🞄 5 fused vertebrae
◦ Coccyx
🞄 4 fused vertebrae
⦁ Vertebrae separated by
fibrocartilage discs
◦ Cushions/absorbs shock

36. ⦁ Forms a cage to protect
organs
⦁ Three parts
◦ Sternum
🞄 Flat bone
🞄 3 fused bones
🞄 Manubrium
🞄 Body
🞄 Xyphoid process
🞄 Attached to first 7 pair of
ribs
◦ Rib Cage
🞄 12 pairs
🞄 True Ribs= 7 pair
🞄 False Ribs = 5 pair
🞄 Floating Ribs = 2 pair
◦ Thoracic vertebrae

37. The appendicular skeleton is
divided into six major regions:
⦁ Pectoral girdles (4 bones) –
◦ Left and right clavicle (2)
◦ Scapula (2).
⦁ Arms and forearms (6 bones) –
◦ Left and right humerus (2) (arm)
◦ Ulna (2)
◦ Radius (2) (forearm).
⦁ Hands (54 bones) –
◦ Left and right carpals (16) (wrist)
◦ Metacarpals(10)
◦ Proximal phalanges (10),
◦ Intermediate phalanges (8)
◦ Distal phalanges (10)
⦁ Pelvis (2 bones) –
◦ Left and right hip bone (2).
⦁ Thighs and legs (8 bones) –
◦ Left and right femur (2) (thigh)
◦ Patella (2) (knee)
◦ Tibia (2)
◦ Fibula (2) (leg).
⦁ Feet and ankles (52 bones)
⦁ Left and right tarsals (14) (ankle)
⦁ Metatarsals (10)
⦁ Proximal phalanges (10)
⦁ Intermediate phalanges (8)
⦁ Distal phalanges (10).

39. ⦁ Pectoral girdles (4 bones)
◦ Left and right clavicle (2)
◦ Scapula (2).

40. ⦁ Arms and forearms (6 bones) –
◦ Left and right humerus (2) (arm)
◦ Ulna (2)
◦ Radius (2) (forearm).

41. ⦁ Hands (54 bones) –
◦ Left and right carpals (16) (wrist)
◦ Metacarpals (10)
◦ Proximal phalanges (10),
◦ Intermediate phalanges (8)
◦ Distal phalanges (10)

42. ⦁ Three pairs of fused
bones
◦ Ilium
◦ Ischium
◦ Pubic bone
⦁ Carries total weight of
upper body
⦁ Protects
◦ Reproductive organs
◦ Bladder
◦ Part of large intestine

43. ⦁ Female inlet larger/more
circular
⦁ Female pelvis is shallower,
bones lighter/thinner
⦁ Female hip bones flare
wider
⦁ Female sacrum is
shorter/less curved
⦁ Female pubic arch is more
rounded/angle is greater

44. ◦ Left and right femur
(2) (thigh)
◦ Patella (2) (knee)
◦ Tibia (2)
◦ Fibula (2) (leg).

45. ⦁ Left and
right tarsals (14)
(ankle)
⦁ Metatarsals (10)
⦁ Proximal
phalanges (10)
⦁ Intermediate
phalanges (8)
⦁ Distal phalanges (10).

47. A joint is the site at which any two or
more bones articulate
or come together. Some joints have no
movement
(fibrous), some only slight movement
(cartilaginous) and
some are freely movable (synovial).

48. ⦁ Articulations of bones
⦁ Functions
◦ Hold bones together
◦ Mobility
⦁ Classified by
structure/function

49. ⦁ Fibrous joints or Immovable
🞄 EX: sutures of skull
⦁ Cartilaginous joints OR slightly movable
EX: Pubic symphysis and Vertebrae
Synovial joints
Freely movable

50. Fibrous /immovable/fixed Joints
 A fibrous joint is a fixed joint where collagenous
fibrous connective tissue connects two bones.
 Fibrous joints (synarthroses) are usually immovable and
have no joint cavity.
 They are subdivided further into sutures, gomphoses,
and syndesmoses.
 Sutures are immobile joints found only in the cranium.

51. Fibrous/immovable/fixed joints

52. Cartilaginous or slightly movable joints
 There is a pad of fibrocartilage between the ends of
the bones that form the joint which allows for very
slight movement where the pad of cartilage is
compressed.
 Examples include the symphysis pubis and the joints
between the vertebral bodies.

53. Cartilaginous or
Slightly movable joints

54. Synovial or freely movable joints
Synovial joints have characteristic features that
enable a wide range of movements.
They are classified according to the range of
movement possible or to the shape of the
articulating parts of the bones involved

55. Classification of synovial joints
Ball and socket
Hinge joints
Gliding joints
Pivot joints.
Condyloid
Saddle joints

56. Ball and socket.
The head or ball of one bone articulates with a
socket of another and the shape of the bones
allows for a wide range of movement.
Those possible are flexion, extension, adduction,
abduction, rotation and circumduction.
Examples are the shoulder and hip.

57. Hinge joints.
 These allow the movements of flexion
 and extension only. They are the elbow, knee, ankle, the
 joints between the atlas and the occipital bone, and the
 interphalangeal joints of the fingers and toes.

58. Gliding joints
 . The articular surfaces glide over each
 other, e.g. sternoclavicular joints, acromioclavicular joints
 and joints between the carpal bones and those between
 the tarsal bones.

59. Pivot joints.
Movement is round one axis (rotation),
e.g. proximal and distal radioulnar joints and
the joint between the atlas and the odontoid
process of the axis

60. Condyloid and saddle joints
 Movements take place round two axes, permitting
flexion, extension, abduction, adduction and
circumduction, e.g. the wrist,
temporomandibular,metacarpophalangeal and
metatarsophalangeal joints.

61. Characteristics of a synovial joint
 All synovial joints have certain characteristics in common.
 Articular or hyaline cartilage
 The parts of the bones which are in contact are always covered with
hyaline cartilage.
 It provides a smooth articular surface and is strong enough to absorb
compression forces and bear the weight of the body.

62.  The cartilage lining, which is up to 7mm thick in young
people, becomes thinner and less compressible with age.
 This leads to increasing stress on other structures in the
joint.
 Cartilage has no blood supply and receives its
nourishmentfrom synovial fluid.

63. Capsule or capsular ligament
 The joint is surrounded and enclosed by a sleeve of
fibrous tissue which holds the bones together.
 It is sufficiently loose to allow freedom of movement
but strong enough to protect it from injury.

64. Synovial membrane
This is composed of epithelial cells and is
found: lining the capsule covering those parts
of the bones within the joint not covered by
articular cartilage
covering all intra-capsular structures that do
not bear weight.

65. Synovial fluid
This is a thick sticky fluid, of egg-white
consistency, secreted by synovial membranes
into the synovial cavity.
Provides nutrients for the structures within
the joint cavity.

66. Synovial fluid
 contains phagocytes, which remove microbes and cellular
debris.
 Acts as a lubricant.
 Maintains joint stability.
 Prevents the ends of the bones from being separated, as
does a little water between two glass surfaces.

67.  Little sacs of synovial fluid or bursae are present in some joints, e.g.
the knee.
 They act as cushions to prevent friction between a bone and a
ligament or tendon, or skin where a bone in a joint is near the
surface.

68. Other intra-capsular structures
Some joints have structures within the capsule,
but outside the synovial membrane, which assist
in maintenance of stability, e.g. fat pads and
menisci in the knee joint.
When these structures do not bear weight they
are covered by synovial membrane.

69. Extracapsular structures
Ligaments that blend with the capsule provide
additional stability at most joints.
Muscles or their tendons also provide stability and
stretch across the joints they move.
When the muscle contracts it shortens, pulling one
bone towards the other

70. ⦁ Articulating bones
separated by joint cavity
◦ Articular cartilage covers
bone ends
◦ Joint surfaces enclosed by
fibrous capsule
◦ Cavity contains synovial
fluid
◦ Ligaments help reinforce
the joint
⦁ Associated Joint
Structures
◦ Bursae
🞄Flat fibrous sacs
🞄 Lined with synovial
membrane
🞄Contains synovial fluid
🞄 Common where ligaments,
muscles, skin, tendons rub
together
◦ Tendon sheath
🞄 Elongated bursa wrapping
around a tendon that deals
with lots of friction
🞄 Like a bun around hot dog

74. ⦁ A break in a bone
⦁ Types of Fractures
◦ Simple (closed) fracture
🞄 Bone breaks cleanly, does not penetrate skin
◦ Compound (open) Fracture
🞄 When bone ends penetrate through skin
⦁ Treated by reduction and immobilization
◦ Realignment of bone ends

76. ⚫ Hematoma forms
⚫Blood vessels rupture
when bone breaks
⚫Blood filled swelling
⚫Cells without nutrients die
⚫ Fibrocartilage callus
forms
⚫Made of connective tissue
⚫Splints the break
⚫Phagocytes dispose of dead
tissue
⚫ Bony callus forms
⚫Osteoblasts/clasts move in,
create callus of spongy
bone
⚫ Remodeling
⚫Osteoblasts/clasts remodel
in response to stress on the
bone
⚫Helps strengthen bone
⚫Creates a permanent “patch”
at the site
⚫Often, a healed fracture can
be stronger than the rest of
the bone

78. THANK YOU