Chapter 6: Skeletal System
Theory Lecture Outline
Objectives
1. List the main function of the skeletal system
2. Explain the formation of bone
3. Name and locate the bones of the skeleton
4. Name and define the main types of joint movement
5. Identify common bone and joint disorders
6. Define the key words that relate to this chapter
Introduction
The skeletal system consists of 206 individual bones and the cartilage, ligaments and tendons associated
with the bones. It accounts for about 20% of the body weight. Bones are rigid structures that form the
framework for the body. Living bones in our bodies contain active tissues that consume nutrients, require
a blood supply, use oxygen and discharge waste products in metabolism, and change shape or remodel in
response to variations in mechanical stress. The skeletal system is strong but light weight. It is well
adapted for the functions it must perform.
Functions
The skeletal system gives form and shape to the body but also performs several other functions and plays
an important role in homeostasis
Five specific functions:
• Support - It supports body structures and provides shape to the body
• Protect - It protects the soft and delicate internal organs
• Movement and anchorage - It allows movement and anchorage of muscle
a. Ligaments are fibrous bands that connect bones to bones and cartilage and serve as
support for muscles
b. Tendons are fibrous cords that connect muscles to bone
• Mineral storage
It provides mineral storage such as calcium and phosphorus; storage and release of minerals is a
dynamic process that goes on almost continually; when mineral levels (i.e. calcium) exceed
normal, release from the skeletal system is inhibited. In this way the skeletal system helps to
maintain homeostasis
• Hemopoiesis
It is the site for hemopoiesis or blood cell formation
Structure and Formation of Bone
• Osteocytes
o Mature bone cell
Bone is made up of 35% organic material, 65% inorganic mineral salts and water
• Organic material (flexibility)
a. Collagen – fibrous protein material
b. Jellylike material – lays between the fibrous material
• Inorganic material (hardness and durability)
o Calcium phosphate, calcium carbonate, calcium fluoride, magnesium phosphate, sodium
oxide and sodium chloride
When pressure is applied to a bone, the flexible organic material prevents bone damage, while the mineral
elements resist crushing under pressure
Bone Formation
• Embryonic skeleton initially consists of collagenous protein fibers secreted by osteoblasts
• 8th week of embryonic development, ossification begins
o Mineral matter starts to replace previously formed cartilage, creating bone
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Long Bones
• Shaft or diaphysis
A hollow cylinder of hard, compact bone which makes it strong and hard yet light enough for
movement
• Each end is the epiphysis
o Covered by articular cartilage
This cartilage acts as a shock absorber between two bones that meet to form a joint
• In center is the medullary canal
a. Yellow bone marrow (mostly made of fat cells)
b. Endosteum (lining of the marrow canal)
• Red marrow
a. Ends of long bones
b. Manufacture some red blood cells and some white blood cells
• Periosteum
a. Covering on outside of the bone which contains blood vessels, lymph vessels and nerves
b. Necessary for bone growth, repair and nutrition
Growth
• Grow in length
o Bones grow in length at the growth zone (epiphyseal plate) located between the diaphysis
and epiphysis of a long bone
• Ossify from center outward causing the bone to lengthen
• Osteoblasts – bone cells that deposit the new bone
• Osteoclasts – immense bone cells that secrete enzymes that digest the bony material to be
absorbed by the surrounding fluid
• Growth stops when all the epiphyseal cartilage is ossified
Throughout life, bone is constantly renewed through a two step process called remodeling that
consists of resorption (osteoclasts) and formation (osteoblasts)
• Females grow until about 18 years of age
• Males grow until about 20-21 years of age
New bone growth can occur in a broken bone at any time
Bone Types
4 types classified on basis of their shape
• Long bones – found in both upper and lower arms and legs
• Flat bones – found in skull and ribs
• Irregular bones – represented by bones of the spinal column
• Short bones – found in the wrists and ankles
The degree of movement at a joint is determined by bone shape and joint structure
Skeletal System
The skeletal system consists of two main parts: the axial skeleton and the appendicular skeleton
• Axial skeleton
Includes the skull, spinal column, ribs, sternum (breastbone), and hyoid bone (U-shaped bone in
the neck)
a. Skull
1. Cranium houses and protects the delicate brain, while the facial bones guard and
support the eyes, ears, nose and mouth
2. Collectively there are 22 bones in the skull
(i.e. frontal forms the forehead, temporal houses the ears, maxilla make up upper
jaw, mandible forms lower jaw)
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
b. Spinal column/vertebra
1. Spine consists of small bones called vertebrae which are separated from each
other by pads of cartilage tissue called intervertebral disks
2. Spine is strong and flexible; supports the head, provides for the attachment of the
ribs and encloses the spinal cord of the nervous system
3. Five sections
o Cervical vertebrae – 7 vertebrae in the neck area
o Thoracic vertebrae – 12 vertebrae in the chest area
o Lumbar vertebrae – 5 vertebrae in the back
o Sacrum – 5 fused, wedge-shaped bones forming the posterior pelvic
girdle
o Coccyx – 4 fused bones known as the tailbone
Between each body of the vertebrae are fibrous disks; at the center of each
fibrous disk is a pulpy, elastic material which loses its resiliency with increased
usage and/or age
c. Ribs and sternum
1. 12 pairs of ribs (costal cartilages join 7 pairs of ribs directly to the sternum)
2. Sternum or breastbone divided into 3 parts: upper region, body and lower
cartilaginous part called the xiphoid process
The Skull (Handout Provided)
•
Appendicular skeleton (Handout Provided)
Includes the upper extremities (shoulder girdles, arms, wrists and hands) and lower extremities
(hip girdle, legs, ankles and feet)
a. Shoulder girdle
o Consists of 4 bones
1. 2 clavicles (collar bones)
2. 2 scapulae (shoulder bones)
b. Arms
1. Humerus – only bone in the upper arm and is the second largest bone in the body
2. Radius – lower arm bone runs up the thumb side of the forearm and can rotate
around the ulna
3. Ulna – largest bone in the forearm and fits with the humerus to form the hinged
elbow joint
c. Hand
1. 8 carpals (wrist bones)
2. 5 metacarpals
3. 14 phalanges (finger bones)
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
The thumb is the most flexible finger because the end of the metacarpal bone is more rounded and there
are muscles attached to it from the hand itself
d. Pelvic girdle
o Bones include:
1. Ilium
2. Ischium
3. Pubis
e. Legs
1. Femur (thigh bone) – upper leg bone; it is the longest and strongest bone in the
body
2. Tibia – largest of the two lower leg bones
3. Fibula – smaller of the two lower leg bones
4. Patella (kneecap) – attached to the tibia by a ligament
f. Ankle
1. 7 tarsal bones
2. Calcaneus (heel bone)
g. Foot
1. 5 metatarsal bones (foot bones)
2. 14 phalanges (toe bones)
Joints
• Called articulations
o Points of contact between two bones
• Classified into three main types according to degree of movement
a. Diarthroses (moveable) joints
b. Amphiarthroses (partially movable) joints
c. Synarthroses (immovable) joints
Diarthroses Joints (Moveable joints)
Most of the joints in our body are diarthroses and tend to have the same structure
• Movable joints consist of three main parts
a. Articular cartilage – smooth slippery cap of cartilage at the ends of opposing bones that
helps absorb shocks and prevent friction
b. Articular capsule
1. Synovial membrane – lines the articular capsule and secretes synovial fluid
2. Synovial fluid – lubricating substance
3. Synovial cavity – area between the two articular cartilages
c. Bursa sacs – fluid-filled sacs that act as cushions and help reduce friction located between
muscles, tendons, ligaments and bones
o Bursitis – inflammation of the bursa due to irritation or injury
• 4 types of diarthroses
a. Ball-and-socket joints – allows the greatest freedom of movement i.e. shoulders and hips
b. Hinge joints – move in one direction i.e. knees, elbows and outer joints of fingers
c. Pivot joints – those with an extension rotating in a second, arch-shaped bone i.e. radius
and ulna
d. Gliding joints – surfaces glide across each other i.e. vertebrae
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
Amphiarathroses Joints (Partially movable joints)
In this type of joint, the bones are connected by hyaline cartilage or fibrocartilage
• Cartilage between their articular surfaces
• Examples:
a. Ribs to the spine
b. Symphysis pubis
Synarthroses Joints (immovable joints)
• Connected by tough, fibrous connective tissue
• Example:
o Adult cranium
• Cranial joints called sutures
The bones are fused together in a joint which forms a heavy protective cover for the brain
Types of Motion
• Flexion – the act of bringing two bones closer together
• Extension – the act of increasing the angle between two bones
• Abduction – movement of an extremity away from the midline
• Adduction – movement toward the midline
• Circumduction – includes flexion, extension, abduction and adduction
• Rotation – movement allows a bone to move around one central axis
• Pronation – forearm turns the hand so the palm is downward or backward
• Supination – palm is forward or upward
Aging
•
•
•
•
Bone mass and density decline
External surfaces of bones thicken
Intervertebral cartilage disks shrink
Center of balance is altered
•
•
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Joints less mobile
Increased rigidity and decreased
flexibility
Fear of falling
Disorders of the Bones and Joints
• Fracture
The most common traumatic injury to a bone is a fracture
a. Common types of fractures
1. Greenstick – simplest type of fracture where bone is bent but never completely
separated
2. Closed/simple – bone is broken but the broken ends do not pierce through the
skin forming an external wound
3. Open/compound – most serious type of fracture, where the broken bone ends
pierce and protrude through the skin
4. Comminuted – bone is splintered or broken into many pieces that can become
embedded in surrounding tissue
b. Repairing Fractures
1. Closed reduction – bony fragments are brought into alignment by manipulation
and a cast or splint is applied
2. Open reduction - surgical intervention with wires, metal plates or screws to hold
the bone in alignment and a cast or splint may be applied
3. Traction – pulling force is used to hold the bones in place
Bone and Joint Injuries
• Dislocation – dislocation occurs when a bone is displayed from its proper position in a joint;
reduction or return to proper position is necessary
• Sprain – injury to a joint caused by any sudden or unusual motion; the ligaments are either torn
from their attachments to the bones or torn across but not dislocated
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition
•
•
Concussion – result of a severe blow to the head; it may be mild or severe and temporarily affect
memory, judgment, speech, balance and coordination
Hammer Toe – toe that’s curled due to bend in the middle joint of one or more toes
Treatment for bone, joint and muscle injuries
• RICE
a. Rest
b. Ice
c. Compression
d. Elevation
Recommended for the immediate treatment for bone, joint and muscle injuries
Diseases
• Arthritis – inflammatory condition of one or more joints, accompanied by pain and often by
changes in bone position
a. There are at least 20 different type, the most common:
1. Rheumatoid arthritis
o Chronic, autoimmune disease which affects the connective tissue and joints
o The pain causes muscle spasms which may lead to deformities in the joints
o Cartilage that separates the joints will degenerate and hard calcium fills the
spaces
o Its cause is unknown but affects three times more women than men
2. Osteoarthritis
o Degenerative joint disease
o The articular cartilage degenerates and a bony spur formation occurs at the
joint
o Occurs with aging and affects about 80% of Americans
b. There is no cure for arthritis, although there are many treatments to relieve pain and
increase mobility
• Gout – a joint disorder characterized by an acute inflammation caused by the accumulation of
uric acid crystals in the affected joint
• Rickets - caused by a lack of vitamin D resulting in bones that become soft, due to lack of
calcification
• Slipped (herniated) disc – condition where a cartilage disc ruptures or protrudes out of place and
places pressure on the spinal nerve
• Whiplash injury – trauma to the cervical vertebra
Abnormal Curvatures of the Spine
• Kyphosis (hunchback) – humped curvature in the thoracic area of the spine
• Lordosis (swayback) – exaggerated inward curvature in the lumbar region of the spine
• Scoliosis – side-to-side or lateral curvature of the spine
Other Disorders
• Osteoporosis
a. Porous bone disease, is characterized by low bone mass and structural deterioration of
bone tissue
b. Bone loss occurs without symptoms
c. Treatment is aimed at preventing or slowing the process by taking calcium supplements
or increasing calcium in the diet and exercising
• Osteomyelitis – infection which may involve all parts of the bone
• Osteosarcoma – bone cancer
Ann Senisi Scott & Elizabeth Fong: Body Structures & Functions 11th Edition