Chapter 5
THE SKELETAL SYSTEM
Introduction
The adult skeleton is composed of 206 bones
The skeletal system is subdivided into 2 divisions:
◦ Axial skeleton
◦ Appendicular skeleton
The skeletal system includes joints, cartilages, & ligaments
Bones: An Overview
Functions of the bones
◦ Storage—fat is stored in the internal cavities of bones, and bone serves as a
storehouse for minerals such as calcium
◦ Blood cell formation—this process is also called hematopoiesis & occurs
within the marrow of certain bones
◦ Movement- used by the muscles to provide leverage for movement
◦ Protection- protect the organs from physical damage
◦ Support-provides the basic framework of our internal structure.
Classification of Bones
There are 2 basic types of bone tissue
◦ Compact bone—dense & looks smooth
◦ Spongy bone—composed of small needlelike pieces of bone & lots of open
space
Bones are classified into 4 groups according to shape
Classification of Bones
Bones are classified into 4 groups according to shape
◦ Long bones—longer than they are wide; mostly compact bone; includes all the
bones of the limbs
◦ Short bones—cube-shaped; mostly spongy bone; includes all the bones of the wrist
& ankle & also the patella
◦ Flat bones—thin, flat, & curved; 2 thin layers of compact bone with a layer of
spongy bone in between; includes the bones of the skull, ribs, & sternum
◦ Irregular bones—bones that do not fit any of the above categories; includes the
bones of the hip & vertebrae
◦ Sesamoid bones-formed within a tendon, act to alter the pull of a tendon, ex:
patella
Classification of Bones
Structure of a Long Bone
Diaphysis
◦ Shaft of the bone
◦ Makes up most of the bone’s length & is composed of compact bone
Epiphyses
◦ Bones ends covered with cartilage—proximal & distal ends
◦ Consists of a thin layer of compact bone that encloses an area filled with
spongy bone
◦ Between the end and the diaphysis is a thin line called the epiphyseal line,
AKA the growth plates
Structure of a Long Bone
Periosteum
◦ Fibrous connective tissue membrane
◦ Covers & protects the diaphysis
Articular cartilage
◦ Covers the external surface of the epiphyses
◦ It provides a smooth, slippery surface that decreases friction at joint surfaces
Medullary cavity
◦ The cavity of the shaft that is primarily a storage area for adipose tissue
◦ Also known as the yellow marrow cavity
Structure of a Long Bone
Bone Formation, Growth, &
Remodeling
The skeleton is formed from two of the strongest & most supportive
tissues in the body—cartilage & bone
In embryos, the skeleton is primarily made of hyaline cartilage, but in
the young child most of the cartilage has been replaced by bone.
Bone Formation, Growth, &
Remodeling
Ossification—process of bone formation & involves 2 phases:
◦ The hyaline cartilage is completely covered with bone matrix by boneforming cells called osteoblasts.
◦ The hyaline cartilage is digested away, opening a medullary cavity within the
newly formed bone.
Bone Formation, Growth, &
Remodeling
Bone Formation, Growth, &
Remodeling
Bones are always changing & are remodeled in response to changes in 2
factors:
◦ Calcium levels in the blood
◦ If blood calcium levels are too low, osteoclasts (bone-destroying cells) break down bone matrix & release
calcium into the blood.
◦ If blood calcium levels are too high, calcium is deposited in bone matrix as hard calcium salts.
◦ The pull of gravity & muscles on the skeleton
Bone Formation, Growth, &
Remodeling
Bone remodeling is essential if bones are to retain normal proportions
& strength during long-bone growth as the body increases in size &
weight
Bone Fractures
Bones are susceptible to fractures, or breaks, all through life.
During youth, most fractures result from exceptional trauma that twists
or smashes the bones. In old age, bones thin and weaken so fractures
occur more often.
Bone Fractures
2 common types of fractures:
◦ Simple (closed) fractures = a fracture in which the bones breaks cleanly but
does not penetrate the skin
◦ Compound (open) fractures = when the broken bone ends penetrate
through the skin
Fractures are treated by reduction—realignment of the broken bone
ends
Greenstick fracture- occurs in preadolescents- Periosteum does not
separate.
Simple fracture
Compound fracture
Pictures too gross to put in slide show…blech!…
Green stick fracture
Bone Fractures
Axial
Skeleton
Forms the longitudinal axis of the body
Divided into 3 parts
◦ Skull—formed by 2 sets of bones
◦ Cranium—encloses & protects the brain tissue; made up of several smaller bones (pp 126-127)
◦ Frontal bone—forms the forehead
◦ Parietal bones—forms the superior & lateral walls
◦ Temporal bones—inferior to the parietal bones
◦ Occipital bone—forms the back of the cranium
◦ Sphenoid bone—butterfly-shaped & forms part of the floor of the cranial cavity
◦ Ethmoid bone—lies anterior to the sphenoid & forms the roof of the nasal cavity
Axial Skeleton
◦ Facial bones—hold the eyes in position & allow the facial muscles to show our feelings (p 129)
◦ Maxillae—upper jaw
◦ Palatine bones—form the posterior part of the hard palate
◦ Zygomatic bones—cheekbones
◦ Lacrimal bones—medial walls of the eyes & has a groove that serves as a passageway for tears
◦ Nasal bones—forms the bridge of the nose
◦ Vomer bone—single bone in the median line of the nasal cavity (nasal septum)
◦ Inferior conchae—curved bones projecting from the lateral walls of the nasal cavity
◦ Mandible—lower jaw; the largest & strongest bone of the face!!!
Axial Skeleton
◦ Fetal skeleton—the skull of a fetus or newborn infant is different from an adult skull. When a
baby is born, its skeleton is unfinished. The skull also has regions that yet to be converted to
bone which are called fontanels. These are also known as the “soft spots.”
Axial Skeleton
◦ Vertebral Column (p 131)
◦ Extends from the skull to the pelvis
◦ Formed from 26 irregular bones
◦ Running through the central cavity of the vertebral column is the spinal cord
◦ The vertebrae are separated by pads of cartilage-intervertebral discs-cushion the vertebrae
◦ The spinal cord curves & forms an S-shaped structure
◦ Abnormal spinal curvatures (p 132)
◦ Scoliosis
◦ Kyphosis
◦ lordosis
Axial Skeleton
◦ 3 main types of vertebrae
◦ Cervical vertebrae
◦ Identified as C1 to C7
◦ Form the neck region to the spine
◦ Thoracic vertebrae
◦ Identified as T1 to T12
◦ Larger than cervical vertebrae
◦ Lumbar vertebrae
◦ Identified as L1 to L5
◦ Where most of the stress on the vertebral column occurs
◦ Sacrum—formed by the fusion of 5 vertebrae
◦ Coccyx—formed by the fusion of 3-5 tiny vertebrae; also known as the human “tailbone”
Axial Skeleton
Axial Skeleton
Axial Skeleton
◦ Bony thorax—aka the thoracic cage (p 135)
◦ Sternum
◦ Aka the breastbone
◦ A flat bone & the result of the fusion of 3 bones:
◦ Manubrium
◦ Body
◦ Xiphoid process
◦ Ribs
◦ 12 pairs
◦ Males DO NOT have 1 rib less than females!!!
◦ 3 types of ribs:
◦ True ribs—the 1st 7 pairs that are attached directly to the sternum
◦ False ribs—the next 5 pairs that are attached to the sternum
◦ Floating ribs—the last 2 pairs of false ribs that lack sternal attachment
Axial Skeleton
Appendicular Skeleton
Composed of 126 bones of the limbs & pectoral & pelvic girdles
Bones of the shoulder girdle (p 139)
◦ Clavicle—aka the collarbone
◦ Scapula—aka the shoulder blades
Bones of the upper limbs (pp 140-141)
◦ Arm—formed by a single bone=humerus
◦ Forearm—2 bones:
◦ Radius—on the thumb side
◦ Ulna—on the pinky side
Appendicular Skeleton
Appendicular Skeleton
Appendicular Skeleton
◦ Hand—3 sets of bones
◦ Carpals—8 bones that make up the wrist
◦ Metacarpals—the palm of the hand
◦ Phalanges—bones of the fingers
Bones of the pelvic girdle (p 142)
◦ Formed by 2 coxal bones called hip bones
◦ Each hip bone is formed by the fusion of 3 bones:
◦ Ilium
◦ Ischium
◦ pubis
Appendicular Skeleton
Appendicular Skeleton
◦ Differences between the male & female pelvis:
◦ Female pelvis is shallower
◦ Female bones are lighter & thinner
◦ Female sacrum is shorter & less curved
Bones of the lower limbs (pp 144-145)
◦ Thigh—formed by a single bone=femur
◦ Leg—2 bones
◦ Tibia—shinbone=larger & more medial
◦ Fibula—lies next to the tibia
Appendicular Skeleton
Appendicular Skeleton
◦ Foot—3 sets of bones
◦ Tarsals—7 bones that make up the posterior foot
◦ Metatarsals—the sole of the foot
◦ Phalanges—the bones of the toes
Appendicular Skeleton
Joints
Also called articulations
2 main functions
◦ Hold bones together securely
◦ Give the skeleton mobility
Classified in 2 ways
◦ Functionally
◦ Structurally
Joints
Functional classification--focuses on the amount of
movement allowed by the joint
◦ Immovable joint
◦ Slightly movable joints
◦ Freely movable joints
Structural classification—focuses on the type of tissue
◦ Fibrous joints—bones are united by fibrous tissue
◦ Cartilaginous joints—bones are united by cartilage
◦ Synovial joints—joint cavity contains synovial fluid
Joints
Types of synovial joints based on shape
◦ Plane joint—short slipping or gliding; ie joints of the wrist
◦ Hinge joint—movement in one direction; ie elbow, ankle, & the joints between the
bones of the fingers
◦ Pivot joint—rotating movement; ie between the radius & ulna
◦ Condyloid joint—bones move from side to side or back & forth; ie your knuckles
Joints
◦ Saddle joint—same movement as condyloid; ie twiddling your thumbs
◦ Ball-and-socket joint—head of one bone fits into a round socket; ie shoulder
& hip joint
Joints
Joints
Inflammatory disorders of joints
◦ Arthritis
◦ Inflammation of the joint
◦ Most widespread disease in the U.S.
◦ Symptoms=pain, stiffness, & swelling of the joint
◦ Osteoarthritis
◦ Most common type of arthritis
◦ Chronic degenerative condition that affects the aged
Joints
◦ Rheumatoid arthritis
◦ Chronic inflammatory disorder
◦ Affects more women than men
◦ The body’s immune system attempts to destroy tissues
◦ Gout
◦ Uric acid accumulates in the blood & may be deposited as needle-shaped crystals in the soft tissues of
joints
◦ Usually affects the great toe