The skeletal system has several important functions including support, protection, movement, mineral storage, and blood cell formation. The skeletal system is made up of 206 bones that are classified as long, short, flat, or irregular. Long bones have a diaphysis, epiphyses, and contain red or yellow marrow. Bones are made up of compact and spongy bone and have microscopic structures including osteons, lacunae, and canaliculi. The skeletal system includes the axial skeleton which is made up of the skull, vertebral column, and rib cage, as well as the appendicular skeleton consisting of the pectoral girdle, upper limbs, pelvic girdle, and lower limbs. Joint

1. By
Muhammad Iqbal Khan
SS Biology
Email ID: mikhan1313@yahoo.com
0923135448175
The Skeletal System

2. Function
 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

3. Bones
206 bones in the adult 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)

4. Bone Classification
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

5. Bone Classification

6. Long Bone Anatomy
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

7. Long Bone Anatomy
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

8. Long Bone Anatomy
Periosteum
Outer covering of shaft
Like “skin” on chicken
bone
Sharpey’s fibers
Attach periosteum to bone
Arteries
Supply nutrients to bone
cells

9. Long Bone Anatomy
Medullary Cavity
In shaft
Contains yellow marrow
(adipose) in adults
Contains red marrow in
infants (for blood cell
formation)

10. Microscopic Anatomy of Bone
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

11. Microscopic Anatomy of Bone

12. Microscopic Anatomy of Bone
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

13. Microscopic Anatomy of Bone
Canaliculi
Tiny canals
Radiate from central canal
to lacunae
Transport nutrients to
bone cells

14. Other Facts
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

15. Bone Formation
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

16. Bone Growth
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

17. Long Bone Growth

18. Long Bone Growth

19. Types of Bone Cells
Osteocyte
Mature bone cell
Osteoblast
“Bone builders”
Osteoclast
“Bone destroyers”
Break down bone matrix to remodel and/or release calcium

20. Bone Remodeling
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

21. Fractures
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

22. Common Fractures

23. Bone Repair
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

24. Bone Repair

25. Axial Skeleton
Makes up longitudinal part of the body
Three parts
Skull
Vertebral column
Bony thorax
**Note: notes on specific bones are not included. Make sure you
are using your textbook to help identify shapes/functions of
bones!!

26. Axial Skeleton **Shown in green

27. Skull
Formed by two sets of bones
Cranium
Encloses/protects brain
Facial bones
Holds eyes forward (anterior position)
Allow facial muscles to show feelings
Sutures
Interlocking, immovable joints holding most skullbones
together
Mandible-only freely movable bone in skull

28. Skull

29. Skull

30. Paranasal Sinuses
Hollow portions of bone around nasal cavity
Named for bones they are found in
Lighten skull
Amplify sounds when speaking/ give resonance

31. Fetal Skull
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

32. The Vertebral Column
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

33. Vertebrae Structure

34. Regional Characteristics

35. Regional Characteristics

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

37. Appendicular Skeleton
Limbs (appendages)
Pectoral girdle
Pelvic girdle
**shown in yellow

38. Pectoral Girdle (shoulder)
Two bones
Clavicle-collarbone
Scapula-shoulder blade

39. Upper Limb (arm)
Arm bone- humerus
Forearm bones-
Radius (thumb side)
Ulna
Hand bones
Carpals-wrist
Metacarpals-palm
Phalanges-fingers

40. Pelvic Girdle (hip bones)
Three pairs of fused bones
Ilium
Ischium
Pubic bone
Carries total weight of
upper body
Protects
Reproductive organs
Bladder
Part of large intestine

41. Gender Differences in Pelvis
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

42. Lower Limb (leg)
Thigh bone-femur
Two leg bones
Tibia (larger, medial bone)
Fibula (smaller, lateral
bone)
Foot
Tarsals-ankle
Metatarsals-sole
Phalanges-toes

43. Joints
Articulations of bones
Functions
Hold bones together
Mobility
Classified by
structure/function
**we’ll use structural classification
Fibrous joints
Immovable
EX: sutures of skull
Cartilaginous joints
Immovable OR slightly
movable
EX:Pubic symphysis and
Vertebrae
Synovial joints
Freely movable
**Be familiar with types of synovial
joints (illustrations to follow)

44. Synovial Joints
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

45. Synovial Joints

46. Types of Synovial Joints by Shape

47. Types of Synovial Joints by Shape