This document provides an overview of the skeletal system chapter from an anatomy and physiology textbook. It covers the following key points in 3 sentences: It defines the components of the skeletal system as bones, cartilages, tendons, and ligaments. It describes the functions of the skeletal system as support, protection, movement, storage, and blood cell production. It provides details on the structure of bones, including their extracellular matrix composition, bone cell types, and the processes of bone formation, growth, remodeling and repair.

1. Seeley’s
ESSENTIALS OF
Anatomy &
Physiology
Tenth Edition
Cinnamon Vanputte
Jennifer Regan
Andrew Russo
See separate PowerPoint slides for all figures and tables
pre-inserted into PowerPoint without notes.
© 2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education.

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Chapter 6
Skeletal System:Bones
and Joints
Lecture Outline

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Components of Skeletal System
Bones
Cartilages
Tendons
Ligaments

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Bones of the Skeletal System
Figure 6.11

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Skeletal System Functions
1. Support
2. Protect
3. Movement
4. Storage
5. Blood cell production

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Extracellular Matrix1
Bone, cartilage, tendons, and ligaments of the
skeletal system are all connective tissues.
Their characteristics are largely determined by
the composition of their extracellular matrix.
The matrix always contains collagen, ground
substance, and other organic molecules, as well
as water and minerals.

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Extracellular Matrix2
Collagen is a tough, ropelike protein.
Proteoglycans are large molecules consisting of
many polysaccharides attaching to and encircling
core proteins.
The proteoglycans form large aggregates and
attract water.
The extracellular matrix of tendons and ligaments
contains large amounts of collagen fibers, making
these structures very tough, like ropes or cables.

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Cartilage Extracellular Matrix
The extracellular matrix of cartilage contains
collagen and proteoglycans.
Collagen makes cartilage tough, whereas the
water-filled proteoglycans make it smooth and
resilient.
As a result, cartilage is relatively rigid, but it
springs back to its original shape after being
bent or slightly compressed.
It is an excellent shock absorber.

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Bone Extracellular Matrix
The extracellular matrix of bone contains collagen
and minerals, including calcium and phosphate.
The ropelike collagen fibers lend flexible strength
to the bone.
The mineral component gives bone compression
(weight-bearing) strength.
Most of the mineral in bone is in the form of
calcium phosphate crystals called hydroxyapatite.

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Shape Classification of Bones1
There are four bone shape classifications: long,
short, flat, and irregular.
Long bones are longer than they are wide;
examples are upper and lower limb bones.
Short bones are approximately as wide as they
are long; examples are the bones of the wrist and
ankle.

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Shape Classification of Bones2
Flat bones have a relatively thin, flattened shape;
examples are bones of the skull and sternum.
Irregular bones include the vertebrae and facial
bones, which have shapes that do not fit readily
into the other three categories.

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Long Bone Structures1
Diaphysis:
Shaft
compact bone
tissue (on outside)
Epiphysis:
ends spongy bone tissue
Articular cartilage:
covers epiphyses
reduces friction Figure 6.2a

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Long Bone Structures2
Epiphyseal plate:
site of growth
between
diaphysis and
epiphysis
Medullary cavity:
center of
diaphysis red or
yellow marrow
Figure 6.2b

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Long Bone Structures3
Periosteum:
membrane around
bone’s outer
surface
Endosteum:
membrane that
lines medullary
cavity
Figure 6.2a

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Structure of Long Bone
Figure 6.2

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Bone Marrow1
Bones contain cavities, such as the large
medullary cavity in the diaphysis, as well as
smaller cavities in the epiphyses of long bones
and in the interior of other bones.
These spaces are filled with soft tissue called
marrow.
Red marrow is the location of blood forming
cells.
Yellow marrow is mostly fat.

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Bone Marrow2
In newborns most bones have blood making red
bone marrow.
In adults red marrow in the diaphysis is replaced
by yellow bone marrow.
In adults most red bone marrow is in the flat
bones and the long bones of the femur and
humerus.

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Compact Bone Tissue1
Location:
outer part of
diaphysis (long bones)
and thinner surfaces
of other bones
Osteon:
structural unit of
compact bone
includes lamella,
lacunae, canaliculus,
central canal, osteocytes
Lamella:
rings of bone matrix
Figure 6.2c

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Compact Bone Tissue2
Lacunae:
spaces between lamella
Canaliculus:
tiny canals
transport nutrients
and remove
waste
Central canal:
center of osteon
contains blood vessels Figure 6.2c

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Structure of Bone Tissue
Figure 6.3
(a) ©Trent Stephens

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Spongy (Cancellous) Bone Tissue
Spongy bone
• It is located at the epiphyses of long bones
and center of other bones.
• It has trabeculae, which are interconnecting
rods, and spaces that contain marrow.
• It has no osteons.

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Spongy Bone Tissue
Figure 6.4

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Bone Cells
Osteoblasts: responsible for the formation of
bone and the repair and remodeling of bone.
Osteocytes: cells that maintain bone matrix and
form from osteoblast after bone matrix has
surrounded it.
Osteoclasts: contribute to bone repair and
remodeling by removing existing bone, called
bone reabsorption.

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Bone Formation
Ossification is the formation of bone by
osteoblasts.
Bone formation that occurs within connective
tissue membranes is called intramembranous
ossification.
Bone formation that occurs inside hyaline
cartilage is called endochondral ossification.
Both types of bone formation result in compact
and spongy bone.

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Intramembranous Ossification1
Intramembranous ossification occurs when
osteoblasts begin to produce bone within
connective tissue.
This occurs primarily in the bones of the skull.
Osteoblasts line up on the surface of connective
tissue fibers and begin depositing bone matrix
to form trabeculae.

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Intramembranous Ossification2
The process begins in areas called ossification
centers and the trabeculae radiate out from the
centers.
Usually, two or more ossification centers exist in
each flat skull bone and mature skull bones result
from fusion of these centers as they enlarge.
The trabeculae are constantly remodeled and
they may enlarge or be replaced by compact
bone.

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Bone Formation in the Fetus
Figure 6.5
(b) ©Biophoto Associates/Science Source

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Endochondral Ossification
Endochondral bone formation is bone formation
within a cartilage model.
The cartilage model is replaced by bone.
Initially formed is a primary ossification center,
which is bone formation in the diaphysis of a
long bone.
A secondary ossification center is bone
formation in the epiphysis.

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Steps in Endochondral Ossification
1. Chondroblasts build a cartilage model, the
chondroblasts become chondrocytes.
2. Cartilage model calcifies (hardens).
3. Osteoblasts invade calcified cartilage and a
primary ossification center forms diaphysis.
4. Secondary ossification centers form epiphysis.
5. Original cartilage model is almost completely
ossified and remaining cartilage is articular
cartilage.

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Endochondral Ossification of a Long
Bone
Figure 6.6

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Bone Growth in Width
Bone growth occurs by the deposition of new
bone lamellae onto existing bone or other
connective tissue.
As osteoblasts deposit new bone matrix on the
surface of bones between the periosteum and
the existing bone matrix, the bone increases in
width, or diameter.
This process is called appositional growth.

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Bone Growth in Length1
Growth in the length of a bone, which is the
major source of increased height in an
individual, occurs in the epiphyseal plate.
This type of bone growth occurs through
endochondral ossification.
Chondrocytes increase in number on the
epiphyseal side of the epiphyseal plate.

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Bone Growth in Length2
Then the chondrocytes enlarge and die.
The cartilage matrix becomes calcified.
Much of the cartilage that forms around the
enlarged cells is removed by osteoclasts, and the
dying chondrocytes are replaced by osteoblasts.

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Bone Growth in Length3
The osteoblasts start forming bone by
depositing bone lamellae on the surface of the
calcified cartilage.
This process produces bone on the diaphyseal
side of the epiphyseal plate.

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Endochondral Bone Growth
Figure 6.7
(a) ©Ed Reschke/Photolibrary/Getty Images; (c) ©Biophoto Associates/Science Source

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Bone Remodeling
Bone remodeling involves:
• removal of existing bone by osteoclasts and
• deposition of new bone by osteoblasts
• occurs in all bones
• responsible for changes in bone shape, bone
• repair, adjustment of bone to stress, and
• calcium ion regulation

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Bone Repair1
1. Broken bone causes bleeding and a blood clot
forms.
2. Callus forms which is a fibrous network
between 2 fragments.
3. Cartilage model forms first then, osteoblasts
enter the callus and form cancellous bone
this continues for 4-6 weeks after injury.
4. Cancellous bone is slowly remodeled to form
compact and cancellous bone.

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Bone Repair2
Figure 6.8
(a) (top and bottom) ©Andrew F. Russo

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Bone and Calcium Homeostasis
Bone is a major storage site for calcium
Movement of calcium in and out of bone helps
determine blood levels of calcium
Calcium moves into bone as osteoblasts build
new bone
Calcium move out of bone as osteoclasts break
down bone
Calcium homeostasis is maintained by
parathyroid hormone (PTH) and calcitonin

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Calcium Homeostasis
Figure 6.10

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Bone Anatomical Terms1
Foramen:
• hole
• Example - foramen magnum
Fossa:
• depression
• Example - glenoid fossa
Process:
• projection
• Example - mastoid process

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Bone Anatomical Terms2
Condyle:
• smooth, rounded end
• Example - occipital condyle
Meatus:
• canal-like passageway
• Example - external auditory meatus
Tubercle:
• lump of bone
• Example - greater tubercle

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Axial Skeleton1
The axial skeleton is composed of the skull, the
vertebral column, and the thoracic cage.
The skull has 22 bones divided into those of the
braincase and those of the face.
The braincase, which encloses the cranial cavity,
consists of 8 bones that immediately surround
and protect the brain.
The bony structure of the face has 14 facial
bones.

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Axial Skeleton2
Thirteen of the facial bones are rather solidly
connected to form the bulk of the face.
The mandible, however, forms a freely movable
joint with the rest of the skull.
There are also three auditory ossicles in each
middle ear (six total).

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Cranial Bones1
Frontal bone
• Anterior part of cranium
Parietal bones
• Sides and roof of cranium
Occipital bones
• Posterior portion and floor of cranium
Temporal bones
• Inferior to parietal bones on each side of the cranium
• Temporomandibular joint

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Cranial Bones2
Sphenoid bone
• Forms part of cranium floor, lateral posterior
portions of eye orbits, lateral portions of cranium
anterior to temporal bones
• Sella turcica
Ethmoid bone
• Anterior portion of cranium, including medial
surface of eye orbit and roof of nasal cavity
• Nasal conchae

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Facial Bones1
Maxillae
• Form upper jaw, anterior portion of hard palate,
part of lateral walls of nasal cavity, floors of eye
orbits
• Maxillary sinus
Palatine bones
• Form posterior portion of hard palate, lateral wall of
nasal cavity

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Facial Bones2
Zygomatic bones
• Cheek bones
• Also form floor and lateral wall of each eye orbit
Lacrimal bones
• Medial surfaces of eye orbits
Nasal bones
• Form bridge of nose

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Facial Bones3
Vomer
• In midline of nasal cavity
• Forms nasal septum with the ethmoid bone
Inferior nasal conchae
• Attached to lateral walls of nasal cavity
Mandible
• Lower jawbone
• Only movable skull bone

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The Skull1
Figure 6.12

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The Skull2
Figure 6.13
(b) ©Eric Wise

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The Skull3
Figure 6.15
(b) ©McGraw-Hill Education/Christine Eckel

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The Skull4
Figure 6.16
(b) ©McGraw-Hill Education/Christine Eckel

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Paranasal Sinuses1
Several of the bones associated with the nasal
cavity have large cavities within them, called the
paranasal sinuses which open into the nasal
cavity.
The paranasal sinuses are:
• Frontal
• Ethmoid
• Sphenoid
• Maxillary

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Paranasal Sinuses2
Figure 6.14

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Hyoid Bone1
The hyoid bone is an unpaired, U-shaped bone
that is not part of the skull and has no direct bony
attachment to the skull or any other bones.
The hyoid bone has the unique distinction of
being the only bone in the body that does not
articulate with another bone.
The hyoid bone provides an attachment for some
tongue muscles, and it is an attachment point for
important neck muscles that elevate the larynx.

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Hyoid Bone2
Figure 6.17

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Vertebral Column1
The vertebral column, or spine, is the central axis of the
skeleton, extending from the base of the skull to slightly
past the end of the pelvis.
In adults, it usually consists of 26 individual bones,
grouped into five regions.
The adult vertebral column has four major curvatures:
cervical, thoracic, lumbar and sacrococcygeal.
The cervical region curves anteriorly.
The thoracic region curves posteriorly.
The lumbar region curves anteriorly
The sacral and coccygeal regions together curve
posteriorly

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Vertebral Column2
7 cervical vertebra
12 thoracic vertebra
5 lumbar vertebra
1 sacrum
1 coccyx
Atlas:
• 1st vertebra
• holds head
Axis:
• 2nd vertebra
• rotates head

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Functions of Vertebral Column
Supports body weight
Protects the spinal cord
Allows spinal nerves to exit the spinal cord
Provides a site for muscle attachment
Provides movement of the head and trunk

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Vertebral Column3
Figure 6.18

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Vertebra
Figure 6.19

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Regional Differences in Vertebrae
Figure 6.20
(a) ©McGraw-Hill Education/Christine Eckel

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Sacrum
Figure 6.21
(c) ©McGraw-Hill Education/Christine Eckel

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Thoracic Cage1
Protects vital organs
12 pair of ribs
Sternum:
• breastbone
True ribs:
• attach directly to sternum by cartilage
False ribs:
• attach indirectly to sternum by cartilage
Floating ribs:
• not attached to sternum

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Thoracic Cage2
Figure 6.22

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Bones of the Pectoral Girdle
Scapula:
• shoulder blade
Clavicle:
• collar bone

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Pectoral Girdle
Figure 6.23

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Scapula and Clavicle
Figure 6.25
(d) ©Trent Stephens

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Upper Limb Bones1
Humerus:
• upper limb
Ulna:
• forearm
Radius:
• forearm
Carpals:
• wrist
Metacarpals:
• hand

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Upper Limb Bones2
Figure 6.23

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The Humerus
Figure 6.27
(c) ©McGraw-Hill Education/ Christine Eckel

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Ulna and Radius
Figure 6.28
(b) ©McGraw-Hill Education/Christine Eckel

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Bones of the Wrist and Hand
Figure 6.29

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Pelvic Girdle
Where lower limbs attach to the body
Pelvis:
• includes pelvic girdle and coccyx
Ischium:
• inferior and posterior region
Ilium:
• most superior region
Acetabulum:
• hip socket (joint)

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Pelvis
Figure 6.32

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Hip Bones
Figure 6.33
(c) ©McGraw-Hill Education/Christine Eckel

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Comparison of the Male Pelvis
to the Female Pelvis
Figure 6.34

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Lower Limb Bones1
Femur:
• thigh
Patella:
• knee cap
Tibia:
• large lower leg
Fibula:
• small lower leg

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Lower Limb Bones2
Tarsals:
• ankle
Metatarsals:
• foot
Phalanges:
• toes and fingers

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Lower Limb Bones3
Figure 6.31

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Bones of the Thigh
Figure 6.35
(b) ©McGraw-Hill Education/Christine Eckel

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Bones of the Leg
Figure 6.36
(b) ©McGraw-Hill Education/Christine Eckel

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Bones of the Foot
Figure 6.37

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Articulations
Articulations (joints) are where two bones come
together.
Joints can be classified structurally as fibrous,
cartilaginous, or synovial, according to the major
connective tissue type that binds the bones
together and whether a fluid-filled joint capsule is
present.
Joints are also be classified in functional categories
according to their degree of motion as
synarthroses, amphiarthroses, or diarthroses.

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Structural Classification of Joints
Fibrous joint:
• united by fibrous connective tissue
• subclasses are sutures, syndesmosis, and gomphoses
Cartilaginous:
• united by means of cartilage
• subclasses are synchondroses and symphysis
Synovial:
• joined by a fluid cavity
• Most joints of the appendicular skeleton

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Functional Classification of Joints
Synarthrosis:
• non-movable joint
• Example – skull bone articulations
Amphiarthrosis:
• slightly movable joint
• Example - between vertebrae
Diarthrosis:
• freely movable joint
• Example - knee, elbow, and wrist articulations

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Fontanels and Sutures
Figure 6.39

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Structure of a Synovial Joint
Figure 6.40

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Types of Synovial Joints
Figure 6.41

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Types of Movement1
Flexion: bending
Extension: straightening
Abduction: movement away from midline
Adduction: movement toward the midline
Pronation: rotation of the forearm with palms down
Supination: rotation of the forearm with palms up
Rotation: movement of a structure about the long axis

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Types of Movement2

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Effects of Aging on the Skeletal System
and Joints
1. Decreased Collagen Production
2. Loss of Bone Density
3. Degenerative Changes