The Skeletal Systemcontents.kocw.or.kr/document/wcu/2012/Anatomy_and... · 2 Functions of Bones Support the body Protect soft organs Allow movement due to attached skeletal muscles

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5The Skeletal System

Yong Jeong, MD, PhD

Department of Bio and Brain Engineering

The Skeletal System

Parts of the skeletal system

Bones (skeleton)

Joints

Cartilages

Ligaments

Two subdivisions of the skeleton

Axial skeleton

Appendicular skeleton

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Functions of Bones

Support the body

Protect soft organs

Allow movement due to attached skeletal muscles

Store 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

Figure 5.2b

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Classification of Bones on the Basis of Shape

Figure 5.1

Classification of Bones

Long bones

Typically longer than they are wide

Have a shaft with heads at both ends

Contain mostly compact bone

Example:

Femur

Humerus

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Figure 5.1a


Short bones

Generally cube-shape

Contain mostly spongy bone

Example:

Carpals

Tarsals

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Figure 5.1b


Flat bones

Thin, flattened, and usually curved

Two thin layers of compact bone surround a layer of spongy bone

Example:

Skull

Ribs

Sternum

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Figure 5.1c


Irregular bones

Irregular shape

Do not fit into other bone classification categories

Example:

Vertebrae

Hip bones

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Figure 5.1d

Anatomy of a Long Bone

Diaphysis

Shaft

Composed of compact bone

Epiphysis

Ends of the bone

Composed mostly of spongy bone

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Figure 5.2a


Periosteum

Outside covering of the diaphysis

Fibrous connective tissue membrane

Sharpey’s fibers

Secure periosteum to underlying bone

Arteries

Supply bone cells with nutrients

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Figure 5.2c


Articular cartilage

Covers the external surface of the epiphyses

Made of hyaline cartilage

Decreases friction at joint surfaces

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Epiphyseal plate

Flat plate of hyaline cartilage seen in young, growing bone

Epiphyseal line

Remnant of the epiphyseal plate

Seen in adult bones


Medullary cavity

Cavity inside of the shaft

Contains yellow marrow (mostly fat) in adults

Contains red marrow (for blood cell formation) in infants

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Bone Markings

Surface features of bones

Sites of attachments for muscles, tendons, and ligaments

Passages for nerves and blood vessels

Categories of bone markings

Projections or processes—grow out from the bone surface

Depressions or cavities—indentations

Bone Markings

Table 5.1 (1 of 2)

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Bone Markings

Table 5.1 (2 of 2)

Notch Indentation at the edge of the structure

Microscopic Anatomy of Bone

Osteon (Haversian system)

A unit of bone containing central canal and matrix rings

Central (Haversian) canal

Opening in the center of an osteon

Carries blood vessels and nerves

Perforating (Volkman’s) canal

Canal perpendicular to the central canal

Carries blood vessels and nerves

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Figure 5.3a


Lacunae

Cavities containing bone cells (osteocytes)

Arranged in concentric rings

Lamellae

Rings around the central canal

Sites of lacunae

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Figure 5.3b–c


Canaliculi

Tiny canals

Radiate from the central canal to lacunae

Form a transport system connecting all bone cells to a nutrient supply

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Figure 5.3b

Formation of 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

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Bone Growth (Ossification)

Epiphyseal plates allow for lengthwise growth of long bones during childhood

New cartilage is continuously formed

Older cartilage becomes ossified

Cartilage is broken down

Enclosed cartilage is digested away, opening up a medullary cavity

Bone replaces cartilage through the action of osteoblasts

Long Bone Formation and Growth

Figure 5.4a, step 3

Bone startingto replacecartilage

Epiphysealplatecartilage

Articularcartilage

Spongybone

In a childIn a fetusIn an embryo

New boneforming

Growthin bonewidth

Growthin bonelength

Epiphysealplate cartilage

New boneforming

Bloodvessels

Hyalinecartilage

New center ofbone growth

Medullarycavity

Bone collar

Hyalinecartilagemodel

(a)

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Bone Growth (Ossification)

Bones are remodeled and lengthened until growth stops

Bones are remodeled in response to two factors

Blood calcium levels

Pull of gravity and muscles on the skeleton

Bones grow in width (called appositional growth)

Long Bone Formation and Growth

Figure 5.4b

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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 in response to parathyroid hormone

Bone remodeling is performed by both osteoblasts and osteoclasts

Bone Fractures

Fracture—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

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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

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Stages in the Healing of a Bone Fracture

Figure 5.5, step 4

Hematoma

Externalcallus

Bonycallus ofspongybone

Healedfracture

Newbloodvessels

Internalcallus(fibroustissue andcartilage)

Spongybonetrabecula

Hematomaformation

Fibrocartilagecallus formation

Bony callusformation

Bone remodeling

The Axial Skeleton

Forms the longitudinal axis of the body

Divided into three parts

Skull

Vertebral column

Bony thorax

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The Axial Skeleton

Figure 5.6a

The Axial Skeleton

Figure 5.6b

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The Skull

Two sets of bones

Cranium

Facial bones

Bones are joined by sutures

Only the mandible is attached by a freely movable joint

Human Skull, Lateral View

Figure 5.7

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Human Skull, Superior View

Figure 5.8

Human Skull, Inferior View

Figure 5.9

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Human Skull, Anterior View

Figure 5.11

Paranasal Sinuses

Hollow portions of bones surrounding the nasal cavity

Functions of paranasal sinuses

Lighten the skull

Give resonance and amplification to voice

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Paranasal Sinuses

Figure 5.10a

Paranasal Sinuses

Figure 5.10b

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The Hyoid Bone

The only bone that does not articulate with another bone

Serves as a moveable base for the tongue

Aids in swallowing and speech

The Hyoid Bone

Figure 5.12

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The Fetal Skull

The fetal skull is large compared to the infant’s total body length

Fontanels—fibrous membranes connecting the cranial bones

Allow the brain to grow

Convert to bone within 24 months after birth

The Fetal Skull

Figure 5.13a

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The Fetal Skull

Figure 5.13b

The Vertebral Column

Each vertebrae is given a name according to its location

There are 24 single vertebral bones separated by intervertebral discs

Seven cervical vertebrae are in the neck

Twelve thoracic vertebrae are in the chest region

Five lumbar vertebrae are associated with the lower back

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Nine vertebrae fuse to form two composite bones

Sacrum

Coccyx


Figure 5.14

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The spine has a normal curvature

Primary curvatures are the spinal curvatures of the thoracic and sacral regions

Present from birth

Secondary curvatures are the spinal curvatures of the cervical and lumbar regions

Develop after birth


Figure 5.16

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A Typical Vertebrae, Superior View

Figure 5.17

Regional Characteristics of Vertebrae

Figure 5.18a

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Figure 5.18b


Figure 5.18c

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Figure 5.18d

Sacrum and Coccyx

Sacrum

Formed by the fusion of five vertebrae

Coccyx

Formed from the fusion of three to five vertebrae

“Tailbone,” or remnant of a tail that other vertebrates have

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Sacrum and Coccyx

Figure 5.19

The Bony Thorax

Forms a cage to protect major organs

Consists of three parts

Sternum

Ribs

True ribs (pairs 1–7)

False ribs (pairs 8–12)

Floating ribs (pairs 11–12)

Thoracic vertebrae

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The Bony Thorax

Figure 5.20a

The Appendicular Skeleton

Composed of 126 bones

Limbs (appendages)

Pectoral girdle

Pelvic girdle

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Figure 5.6a


Figure 5.6b

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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

Figure 5.21a

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Figure 5.21b


Figure 5.21c–d

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Bones of the Upper Limbs

Humerus

Forms the arm

Single bone


Figure 5.22a–b

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The forearm has two bones

Ulna

Medial bone in anatomical position

Radius

Lateral bone in anatomical position


Figure 5.22c

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The hand

Carpals—wrist

Metacarpals—palm

Phalanges—fingers


Figure 5.23

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Bones of the Pelvic Girdle

Formed by two coxal (ossa coxae) bones

Composed of three pairs of fused bones

Ilium

Ischium

Pubis

Bones of the Pelvic Girdle

The total weight of the upper body rests on the pelvis

It protects several organs

Reproductive organs

Urinary bladder

Part of the large intestine

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The Pelvis

Figure 5.24a

The Pelvis: Right Coxal Bone

Figure 5.24b

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Gender Differences of the Pelvis

The female inlet is larger and more circular

The female pelvis as a whole is shallower, and the bones are lighter and thinner

The female ilia flare more laterally

The female sacrum is shorter and less curved

The female ischial spines are shorter and farther apart; thus the outlet is larger

The female pubic arch is more rounded because the angle of the pubic arch is greater

Gender Differences of the Pelvis

Figure 5.24c

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Bones of the Lower Limbs

The thigh has one bone

Femur

The heaviest, strongest bone in the body


Figure 5.25a–b

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The lower leg has two bones

Tibia

Shinbone

Larger and medially oriented

Fibula

Thin and sticklike


Figure 5.25c

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The foot

Tarsals

Two largest tarsals

Calcaneus (heelbone)

Talus

Metatarsals—sole

Phalanges—toes

Bones of the Lower Limb

Figure 5.26

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Arches of the Foot

Bones of the foot are arranged to form three strong arches

Two longitudinal

One transverse

Arches of the Foot

Figure 5.27

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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

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Structural Classification of Joints

Fibrous joints

Generally immovable

Cartilaginous joints

Immovable or slightly moveable

Synovial joints

Freely moveable

Summary of Joint Classes

[Insert Table 5.3 here]

Table 5.3

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Fibrous Joints

Bones united by fibrous tissue

Example:

Sutures

Syndesmoses

Allows more movement than sutures

Example: Distal end of tibia and fibula

Fibrous Joints

Figure 5.28a–b

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Cartilaginous Joints

Bones connected by cartilage

Example:

Pubic symphysis

Intervertebral joints

Cartilaginous Joints

Figure 5.28c–e

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Synovial Joints

Articulating bones are separated by a joint cavity

Synovial fluid is found in the joint cavity

Synovial Joints

Figure 5.28f–h

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Features of Synovial Joints

Articular cartilage (hyaline cartilage) covers the ends of bones

A fibrous articular capsule encloses joint surfaces

A joint cavity is 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

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The Synovial Joint

Figure 5.29

Types of Synovial Joints

Figure 5.30a–c

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Types of Synovial Joints

Figure 5.30d–f

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

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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 uric acid crystals from the blood

Can usually be controlled with diet

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Developmental Aspects of the Skeletal System

At birth, the skull bones are incomplete

Bones are joined by fibrous membranes called fontanels

Fontanels are completely replaced with bone within two years after birth

Ossification Centers in a 12-week-old Fetus

Figure 5.32

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Skeletal Changes Throughout Life

Fetus

Long bones are formed of hyaline cartilage

Flat bones begin as fibrous membranes

Flat and long bone models are converted to bone

Birth

Fontanels remain until around age 2


Adolescence

Epiphyseal plates become ossified and long bone growth ends

Size of cranium in relationship to body

2 years old—skull is larger in proportion to the body compared to that of an adult

8 or 9 years old—skull is near adult size and proportion

Between ages 6 and 11, the face grows out from the skull

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Figure 5.33a


Figure 5.33b

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Curvatures of the spine

Primary curvatures are present at birth and are convex posteriorly

Secondary curvatures are associated with a child’s later development and are convex anteriorly

Abnormal spinal curvatures (scoliosis and lordosis) are often congenital


Figure 5.16

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Osteoporosis

Bone-thinning disease afflicting

50% of women over age 65

20% of men over age 70

Disease makes bones fragile and bones can easily fracture

Vertebral collapse results in kyphosis (also known as dowager’s hump)

Estrogen aids in health and normal density of a female skeleton


Figure 5.34

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Figure 5.35

The Skeletal Systemcontents.kocw.or.kr/document/wcu/2012/Anatomy_and... · 2 Functions of Bones Support the body Protect soft organs Allow movement due to attached skeletal muscles

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