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List the functions of bone.
Identify human bones by name and location.
Identify the locations and types of joints.
Characterize several common disorders associated with the skeletal system.

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Many people currently suffer, or may one day suffer, from osteoarthritis, in which the joints between bones become stiff and painful due to the degeneration of the cartilage lining.
Conventional remedies range from pain relievers to supplements to injections of steroids.
More unconventional treatments employ combinations of various botanical extracts.

 Arthritis is a disorder of the skeletal system , the framework of bone, cartilage, and ligaments on which the body is built.

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 Should claims about “medicinal” exotic plant extracts have to be backed up by independent scientific testing?
 a. Yes, or companies could make any claim about their product.
 b. No, so long as the extract does no harm, let the buyer decide what to buy.

Bone – Mineralized Connective Tissue
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Bone is a connective tissue with living cells
( osteocytes ) and collagen fibers distributed throughout a ground substance that is hardened by calcium salts.
As bone develops, precursor cells called osteoblasts secrete collagen fibers and a ground substance of proteins and carbohydrates.
Eventually, osteocytes reside within lacunae in the ground substance, which becomes mineralized by calcium deposits.

Bone – Mineralized Connective Tissue
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Bones are surrounded by a sturdy membrane called the periosteum .
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There are two kinds of bone tissue.
Compact bone tissue forms the bone’s shaft and the outer portion of its two ends.
• Compact bone forms in thin, circular layers ( osteons or Haversian systems ) with small canals at their centers, which contain blood vessels and nerves.
• Osteocytes in the lacunae communicate by way of canaliculi (little canals).
Spongy bone tissue is located inside the shaft of long bones.

space occupied by living bone cell blood vessel compact bone tissue spongy bone tissue osteon
(Haversian system) spongy bone tissue compact bone tissue blood vessel outer layer of dense connective tissue Fig. 5.1, p. 88

Animation: Structure of the Human Thigh Bone
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Bone – Mineralized Connective Tissue
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A bone develops on a cartilage model.
Osteoblasts secrete material inside the shaft of the cartilage model of long bones.
Calcium is deposited; cavities merge to form the marrow cavity.
Eventually osteoblasts become trapped within their own secretions and become osteocytes
(mature bone cells).

Bone – Mineralized Connective Tissue
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In growing children, the epiphyses (ends of bone) are separated from the shaft by an epiphyseal plate (cartilage), which continues to grow under the influence of growth hormone until late adolescence.

Cartilage model of future bone in embryo
When organs form in embryo, blood vessel invades model; osteoblasts start producing bone tissue; marrow cavity forms
Remodeling and growth continue in newborn; secondary bone-forming centers appear at knobby ends of bone
Mature bone of adult
Forming bone collar epiphyses
Stepped Art
Fig. 5.2, p. 89

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Bone – Mineralized Connective Tissue
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Bone tissue is constantly “remodeled.”
Bone is renewed constantly as minerals are deposited by osteoblasts and withdrawn by osteoclasts during the bone remodeling process.
• Before adulthood, bone turnover is especially important in increasing the diameter of certain bones.
• Bone turnover helps to maintain calcium levels for the entire body.

Bone – Mineralized Connective Tissue
• A hormone called PTH causes bone cells to release enzymes that will dissolve bone tissue and release calcium to the interstitial fluid and blood; calcitonin stimulates the reverse.
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Osteoporosis (decreased bone density) is associated with decreases in osteoblast activity, sex hormone production, exercise, and calcium uptake.

a b
Fig. 5.3, p. 89

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 From ABC News, Human Biology in the Headlines, 2006 DVD.

The Skeleton:
The Body’s Bony Framework
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Bones are the main components of the human skeletal system.
There are four types of bones: long (arms), short (ankle), flat (skull), and irregular
(vertebrae).
Bone marrow fills the cavities of bones.
• In long bones, red marrow is confined to the ends; yellow marrow fills the shaft portion.
• Irregular bones and flat bones are completely filled with the red bone marrow responsible for blood cell formation.

The Skeleton:
The Body’s Bony Framework
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The skeleton: a preview.
The 206 bones of a human are arranged in two major divisions: the axial skeleton and the appendicular skeleton .
Bones are attached to other bones by ligaments ; bones are connected to muscles by tendons .

The Skeleton:
The Body’s Bony Framework
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Bone functions are vital in maintaining homeostasis.
The bones are moved by muscles; thus the whole body is movable.
The bones support and anchor muscles.
Bones protect vital organs such as the brain and lungs.
Bone tissue acts as a depository for calcium, phosphorus, and other ions.
Parts of some bones are sites of blood cell production.

Table 5.1, p. 90

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The skull protects the brain.
The skull consists of more than two dozen bones.
The cranial vault, or brain case , is a grouping of eight bones.
• The frontal bone makes up the forehead and contains the sinuses .
• Temporal bones form the lower sides of the cranium and surround the ear canals.
• A sphenoid bone and an ethmoid bone form the eye socket.

frontal sinus sphenoid sinus ethmoid sinus maxillary sinus
Fig. 5.6c, p. 93

• Parietal bones form a large part of the skull above the temporal bones.
• An occipital bone forms the back of the skull and encloses the foramen magnum , which is a passageway for the spinal cord.

parietal bone temporal bone frontal bone occipital bone external auditory meatus
(opening of the ear; part of the temporal bone) sphenoid bone ethmoid bone lacrimal bone zygomatic bone maxilla mandible
Fig. 5.6a, p. 92

 Facial bones support and shape the face.
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A mandible forms the lower jaw; two maxillary bones form the upper jaw.
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Zygomatic bones form the cheekbones; lacrimal bones form the inner eye sockets.
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Palatine bones make up the nasal cavity; a vomer bone forms the nasal septum.

hard palate maxilla palatine bone vomer temporal bone parietal bone maxilla zygomatic bone sphenoid bone jugular foramen foramen magnum occipital bone
Fig. 5.6b, p. 92

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The vertebral column is the backbone.
The vertebral column , or backbone, extends from the base of the skull to the hipbones.
The spinal cord extends through a cavity formed by the vertebrae .
Humans have 33 vertebrae: 7 cervical , 12 thoracic , and 5 lumbar , plus a sacrum formed of 5 fused vertebrae and a coccyx of 4 fused vertebrae.
Fibrocartilaginous intervertebral disks serve as shock absorbers; they may slip (herniate) or rupture, leading to pain and immobility.

Figure 5.7

cervical vertebrae (7) thoracic vertebrae (12) lumbar vertebrae (5) sacrum (5 fused) coccyx (4 fused)
4
3
3
2
1
4
5
6
7
1
2
3
4
5
6
9
7
8
10
12
11
1
2
5 intervertebral disks
Fig. 5.7, p. 93

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The ribs and sternum support and help protect internal organs.
Ribs (12 pairs) are attached to the vertebrae dorsally and serve as scaffolding for the upper body torso.
Most of the ribs are attached to the sternum ventrally.

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 From ABC News, Human Biology in the Headlines, 2006 DVD.

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The pectoral girdle and upper limbs provide flexibility.
The pectoral girdle includes the bones of, and is attached to, the shoulder.
• The scapula is a large, flat shoulder blade with a socket for the upper arm bone.
• The clavicle (collarbone) connects the scapula to the sternum.

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Each upper limb includes some 30 separate bones.
• The humerus is the bone of the upper arm.
• The radius and ulna extend from the hingelike joint of the elbow to the wrist.
• The carpals form the wrist; the metacarpals form the palm of the hand, and the phalanges the fingers.

humerus clavicle ulna radius sternum scapula carpals (8) metacarpals (5) phalanges (14)
Fig. 5.8, p. 94

 The pelvic girdle and lower limbs support body weight.
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The pelvic girdle includes the pelvis and the legs.
• The pelvis is made up of coxal bones attaching to the sacrum in the back and forming the pelvic arch in the front.
• The pelvis is broader in females than males; this is necessary for childbearing.

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The legs contain the body’s largest bones.
• The femur is the longest bone, extending from the pelvis to the knee.
• The tibia and fibula form the lower leg; the kneecap bone is the patella .
• Tarsal bones compose the ankle, metatarsals the foot, and phalanges the toes.

nutrient canal into and from marrow (for blood vessels and nerves) marrow cavity compact bone tissue spongy bone tissue
Fig. 5.4, p. 90

pelvis sacrum femur phalanges patella tibia fibula metatarsals tarsals pubic symphysis
Fig. 5.9, p. 95

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Skull bones cranial bones facial bones
Rib cage sternum ribs
Vertebral column (backbone) vertebrae intervertebral disks ligament bridging a knee joint, here sliced down through the middle, side view.
AXIAL
SKELETON
Pectoral girdle and upper limb bones clavicle ulna scapula humerus radius
APPENDICULAR
SKELETON phalanges carpals metacarpals
Pelvic girdle and lower limb bones pelvic girdle femur patella tibia fibula tarsals metatarsals phalanges
Fig. 5.5, p. 91

Animation: The Human Skeleton System
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Synovial joints move freely.
Synovial joints are the most common type of joint and move freely; they include the ball-andsocket joints of the hips and the hingelike joints such as the knee.
These types of joints are stabilized by ligaments.
A capsule of dense connective tissue surrounds the bones of the joint and produces synovial fluid that lubricates the joint.

ligament meniscus fibula femur posterior cruciate ligament anterior cruciate ligament ligament ligament (cut) tibia
Fig. 5.10a, p. 96

biceps femoris
(bends leg) femur cartilage ligament fibula quadriceps
(straightens leg) tendon (to thigh muscle) knee cap (patella) ligament
(to knee cap) tibia
Fig. 5.10b, p. 96

flexion at shoulder
© 2007 Thomson Higher Education extension at shoulder flexion at knee extension at knee
Fig. 5.11a (1), p. 97

© 2007 Thomson Higher Education hyperextension
Fig. 5.11a (2), p. 97

circumduction rotation
© 2007 Thomson Higher Education
© 2007 Thomson Higher Education
Fig. 5.11b, p. 97

abduction adduction abduction adduction adduction abduction
© 2007 Thomson Higher Education
Fig. 5.11c, p. 97

supination
© 2007 Thomson Higher Education pronation
Fig. 5.11d, p. 97

© 2007 Thomson Higher Education gliding movement between carpals
Fig. 5.11e, p. 97

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Other joints move little or not at all.
Cartilaginous joints (such as between the vertebrae) have no gap, but are held together by cartilage and can move only a little.
Fibrous joints also have no gap between the bones and hardly move; flat cranial bones are an example.

intervertebral disks
In-text Fig., p. 96

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Inflammation is a factor in some skeletal disorders.
In rheumatoid arthritis , the synovial membrane becomes inflamed due to immune system dysfunction, the cartilage degenerates, and bone is deposited into the joint.
Figure 5.12

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In osteoarthritis , the cartilage at the end of the bone degenerates.
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Tendinitis is the inflammation of tendons and synovial membranes around joints.
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Carpal tunnel syndrome is the result of the inflammation of the tendons in the space between a wrist ligament and the carpal bones, usually aggravated by chronic over use.

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Joints also are vulnerable to strains, sprains, and dislocations.
A strain results from stretching or twisting a joint suddenly or too far.
A sprain is a tear of ligaments or tendons.
A dislocation causes two bones to no longer be in contact.

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In factures, bones break.
A simple fracture is a crack in the bone; not very serious.
A complete fracture separates the bone into two pieces, which must be quickly realigned for proper healing.
A compound fracture is the most serious because it means there are multiple breaks with the possibility of bone fragments penetrating the surrounding tissues.

simple
© 2007 Thomson Higher Education complete compound
Fig. 5.13, p. 98

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Other bone disorders include genetic diseases, infections, and cancer.
Genetic diseases such as osteogenesis imperfecta can leave bones brittle and easily broken.
Figure 5.14

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Bacterial and other infections can spread from the blood stream to bone tissue or marrow.
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Osteosarcoma , bone cancer, usually occurs in long bones.
Figure 5.15

Table 5.2, p. 100