THE SKELETAL SYSTEM

HAP Unit 4th

THE SKELETAL SYSTEM

 Parts of the skeletal system include:
 Bones (skeleton)
 Joints
 Cartilages
 Ligaments

 Divided into two divisions:
1. Axial skeleton (skull, ribs and vertebra)
2. Appendicular skeleton (pelvis, extremities)

FUNCTIONS OF BONES

Support of the body

Protection of soft organs

Movement due to attached skeletal muscles

Storage of minerals and fats

Blood cell formation

BONES OF THE HUMAN BODY

The adult skeleton has 206 bones

Two basic types of bone tissue
 Compact bone

 Homogeneous

 Spongy bone
 Small needle-like

pieces of bone

 Many open spaces

CLASSIFICATION OF BONES ON THE BASIS OF SHAPE

CLASSIFICATION OF BONES

 Long bones

 Typically longer than wide

Have a shaft with heads at both ends

 Contain mostly compact bone

 Examples: Femur, humerus

 Short bones

Generally cube-shape

 Contain mostly spongy bone

Examples: Carpals, tarsals

CLASSIFICATION OF BONES
 Flat bones

 Thin and flattened, usually curved
 Thin layers of compact bone around a layer of

spongy bone
 Examples: Skull, ribs, sternum

 Irregular bones
 Irregular in shape
Do not fit into other bone classification categories

Example: Vertebrae and hip

GROSS ANATOMY
OF A LONG BONE

Diaphysis
 Shaft

 Composed of compact
bone

Epiphysis
 Ends of the bone

 Composed mostly of
spongy bone

Figure 5.2a

STRUCTURES OF A LONG BONE

 Periosteum
 Outside covering of the

diaphysis
 Fibrous connective tissue

membrane

 Sharpey’s fibers
 Secure periosteum to

underlying bone

 Arteries
 Supply bone cells with

nutrients

Figure 5.2c

STRUCTURES OF A LONG BONE

Articular cartilage
 Covers the external

surface of the
epiphyses

Made of hyaline
cartilage

Decreases friction at
joint surfaces

Figure 5.2a

STRUCTURES OF A LONG BONE

Medullary cavity
 Cavity of the shaft

 Contains yellow marrow
(mostly fat) in adults

 Contains red marrow
(for blood cell
formation) in infants

Figure 5.2a

BONE MARKINGS

Surface features of bones
 Projections and processes – grow out from the

bone surface

Depressions or cavities – indentations

Sites of attachments for muscles, tendons,
and ligaments

Passages for nerves and blood vessels

MICROSCOPIC ANATOMY OF BONE
Osteon (Haversian

System)
 A unit of bone

 Central (Haversian)
canal
 Carries blood vessels

and nerves

 Perforating
(Volkman’s) canal
 Canal perpendicular to

the central canal
 Carries blood vessels

and nerves

CHANGES IN THE HUMAN SKELETON

 In embryos, the skeleton is primarily hyaline
cartilage

During development, much of this cartilage is
replaced by bone

Cartilage remains in isolated areas
Bridge of the nose

 Parts of ribs

 Joints

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

BONE GROWTH

Bones are remodeled and lengthened until growth
stops

Bones change shape somewhat

Bones grow in width

LONG BONE FORMATION AND GROWTH

Figure 5.4b

TYPES OF BONE CELLS

Osteocytes
 Mature bone cells

Osteoblasts
 Bone-forming cells

Osteoclasts
 Bone-destroying cells

 Break down bone matrix for remodeling and release of
calcium

Bone remodeling is a process by both osteoblasts
and osteoclasts

THE SKELETAL SYSTEM (B)

BONE FRACTURES

A break in a bone
Types of bone fractures

 Closed (simple) fracture – break that does not
penetrate the skin

Open (compound) fracture – broken bone
penetrates through the skin

Bone fractures are treated by reduction and
immobilization
Realignment of the bone

COMMON TYPES OF FRACTURES

Table 5.2

REPAIR OF BONE FRACTURES

Hematoma (blood-filled swelling) is formed

Break is splinted by fibrocartilage to form a
callus

Fibrocartilage callus is replaced by a bony
callus

Bony callus is remodeled to form a permanent
patch

STAGES IN THE HEALING OF A BONE
FRACTURE

Figure 5.5

THE AXIAL SKELETON

Forms the longitudinal part of the body

Divided into three parts
 Skull

 Vertebral column

Bony thorax

THE AXIAL SKELETON

Figure 5.6

THE SKULL

Two sets of bones
 Cranium

 Facial bones

Bones are joined by sutures

Only the mandible is attached by a freely
movable joint

THE SKULL

Figure 5.7

BONES OF THE SKULL

Figure 5.11

HUMAN SKULL, SUPERIOR VIEW

HUMAN SKULL, INFERIOR VIEW

THE SKELETAL SYSTEM (C)

PARANASAL SINUSES

Hollow portions of bones surrounding the nasal
cavity

Figure 5.10

PARANASAL SINUSES

Functions of paranasal sinuses
 Lighten the skull

Give resonance and amplification to voice

THE HYOID BONE

The only bone that
does not articulate
with another bone

Serves as a moveable
base for the tongue

THE FETAL SKULL

The fetal skull is large
compared to the
infants total body
length

Figure 5.13

THE FETAL SKULL

Fontanelles – fibrous
membranes
connecting the
cranial bones
 Allow the brain

to grow

 Convert to bone
within 24 months
after birth

THE VERTEBRAL COLUMN

Vertebrae separated
by intervertebral
discs

The spine has a
normal curvature

Each vertebrae is
given a name
according to its
location

Figure 5.14

STRUCTURE OF A TYPICAL VERTEBRAE

Figure 5.16

REGIONAL CHARACTERISTICS OF VERTEBRAE

Figure 5.17a–b

REGIONAL CHARACTERISTICS OF VERTEBRAE

Figure 5.17c–d

THE SKELETAL SYSTEM (D)

THE BONY THORAX

Forms a cage
to protect
major organs

THE BONY THORAX

Made-up of
three parts
 Sternum

Ribs

 Thoracic
vertebrae

THE APPENDICULAR SKELETON

Limbs (appendages)

Pectoral girdle

Pelvic girdle

THE PECTORAL (SHOULDER) GIRDLE

Composed of two bones
 Clavicle – collarbone

 Scapula – shoulder blade

These bones allow the upper limb to have
exceptionally free movement

BONES OF THE SHOULDER GIRDLE

BONES OF THE SHOULDER GIRDLE

BONES OF THE UPPER LIMB

The arm is formed by
a single bone
Humerus

BONES OF THE UPPER LIMB

The forearm has two
bones
Ulna

Radius

BONES OF THE UPPER LIMB

The hand
 Carpals – wrist

Metacarpals – palm

 Phalanges – fingers

BONES OF THE PELVIC GIRDLE

Hip bones
 Composed of three pair of fused bones

 Ilium
 Ischium
 Pubic bone

 The total weight of the upper body rests on the pelvis
 Protects several organs

 Reproductive organs
 Urinary bladder
 Part of the large intestine

THE SKELETAL SYSTEM (E)

THE PELVIS

THE PELVIS: RIGHT COXAL BONE

GENDER DIFFERENCES OF THE PELVIS

BONES OF THE LOWER LIMBS

The thigh has one
bone
 Femur – thigh

bone

BONES OF THE LOWER LIMBS

The leg has two bones
 Tibia

 Fibula

Figure 5.24c

BONES OF THE LOWER LIMBS

The foot
 Tarsus – ankle

Metatarsals – sole

 Phalanges – toes

Figure 5.25

ARCHES OF THE FOOT

Bones of the foot are
arranged to form
three strong arches
 Two longitudinal

One transverse

JOINTS

Articulations of bones

Functions of joints
Hold bones together

 Allow for mobility

Ways joints are classified
 Functionally

 Structurally

FUNCTIONAL CLASSIFICATION OF JOINTS

Synarthroses – immovable joints

Amphiarthroses – slightly moveable joints

Diarthroses – freely moveable joints

THE SKELETAL SYSTEM (F)

STRUCTURAL CLASSIFICATION OF JOINTS

Fibrous joints
Generally immovable

Cartilaginous joints
 Immovable or slightly moveable

Synovial joints
 Freely moveable

FIBROUS JOINTS

Bones united by fibrous tissue
Examples

 Sutures
 Syndesmoses

 Allows more
movement than
sutures

 Example: distal
end of tibia and
fibula

CARTILAGINOUS JOINTS

Bones connected by cartilage

Examples
 Pubic

symphysis

 Intervertebral
joints

Figure 5.27d–e

SYNOVIAL JOINTS

Articulating
bones are
separated by a
joint cavity

Synovial fluid is
found in the joint
cavity

FEATURES OF SYNOVIAL JOINTS

Articular cartilage (hyaline cartilage) covers the
ends of bones

Joint surfaces are enclosed by a fibrous
articular capsule

Have a joint cavity filled with synovial fluid

Ligaments reinforce the joint

STRUCTURES ASSOCIATED WITH THE
SYNOVIAL JOINT

Bursae – flattened fibrous sacs
 Lined with synovial membranes

 Filled with synovial fluid

Not actually part of the joint

Tendon sheath
 Elongated bursa that wraps around a tendon

THE SYNOVIAL JOINT

TYPES OF SYNOVIAL JOINTS BASED ON
SHAPE

TYPES OF SYNOVIAL JOINTS BASED ON
SHAPE

INFLAMMATORY CONDITIONS ASSOCIATED
WITH JOINTS

Bursitis – inflammation of a bursa usually
caused by a blow or friction

Tendonitis – inflammation of tendon sheaths
Arthritis – inflammatory or degenerative

diseases of joints
Over 100 different types
 The most widespread crippling disease in the

United States

CLINICAL FORMS OF ARTHRITIS

Osteoarthritis
Most common chronic arthritis
 Probably related to normal aging processes

Rheumatoid arthritis
 An autoimmune disease – the immune system

attacks the joints
 Symptoms begin with bilateral inflammation of

certain joints
Often leads to deformities

CLINICAL FORMS OF ARTHRITIS

Gouty Arthritis
 Inflammation of joints is caused by a deposition of

urate crystals from the blood

 Can usually be controlled with diet

DEVELOPMENTAL ASPECTS OF THE
SKELETAL SYSTEM

At birth, the skull bones are incomplete

Bones are joined by fibrous membranes –
fontanelles

Fontanelles are completely replaced with
bone within two years after birth