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Anatomy & PhysiologyUnit 5: The Skeletal System
5A: Skeletal Tissues & Basics
The Skeletal System
• Parts of the skeletal system– Bones (skeleton)– Joints– Cartilages– Ligaments
• Two subdivisions of the skeleton– Axial skeleton– Appendicular skeleton
The Axial Skeleton
• Forms the longitudinal axis of the body• Divided into three parts
– Skull– Vertebral column– Bony thorax
The Appendicular Skeleton
• Appendages that hang from axial• Girdles from which the appendages hang• Shoulder girdles—
– clavicle (collar bone)– scapula (shoulder blade)
• Arms hang from shoulder girdles• Pelvic girdle—coxal bones
– Coxal or pelvic bones are 3 fused bones
• Legs hang from pelvic girdle
Functions of Bones
• Support the body• Protect soft organs
– Skull and vertebrae for brain and spinal cord– Rib cage for thoracic cavity organs
• Allow movement due to attached skeletal muscles• Store minerals and fats
– Calcium and phosphorus– Fat in the internal marrow cavity
• Blood cell formation (hematopoiesis)
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 5.1
Spongybone
Compactbone
Classification of Bones on the Basis of Shape
• Bones are classified as:– Long– Short– Flat– Irregular
Figure 5.2
Classification of Bones
• Long bones– Typically longer than they are wide– Shaft with heads situated at both ends– Contain mostly compact bone– All of the bones of the limbs (except wrist, ankle,
and kneecap bones)– Example:
• Femur• Humerus
Figure 5.2a
Classification of Bones
• Short bones– Generally cube-shaped– Contain mostly spongy bone– Includes bones of the wrist and ankle– Sesamoid bones are a type of short bone which
form within tendons (patella)– Example:
• Carpals• Tarsals
Figure 5.2d
Classification of Bones
• Flat bones– Thin, flattened, and usually curved– Two thin layers of compact bone surround a layer
of spongy bone– Example:
• Skull• Ribs• Sternum
Figure 5.1
Spongybone
Compactbone
Figure 5.2c
Classification of Bones
• Irregular bones– Irregular shape– Do not fit into other bone classification categories– Example:
• Vertebrae • Hip bones
Figure 5.2b
Figure 5.3a
Distalepiphysis
Diaphysis
Proximalepiphysis
Articularcartilage
Spongy bone
EpiphyseallinePeriosteum
Compact boneMedullarycavity (linedby endosteum)
(a)
Anatomy of a Long Bone
• Diaphysis– Shaft– Composed of compact bone
• Epiphysis – Ends of the bone– Composed mostly of spongy bone
Anatomy of a Long Bone
• Periosteum– Outside covering of the diaphysis– Fibrous connective tissue membrane
• Perforating (Sharpey’s) fibers– Secure periosteum to underlying bone
• Arteries– Supply bone cells with nutrients
Figure 5.3c
Yellowbone marrow
Compact bone
Perforating(Sharpey’s)fibers
Nutrientarteries
Periosteum
Endosteum
(c)
Anatomy of a Long Bone
• Articular cartilage– Covers the external surface of the epiphyses– Made of hyaline cartilage– Decreases friction at joint surfaces
Figure 5.3b
Compact bone
Spongy bone
Articularcartilage
(b)
Anatomy of a Long Bone
• Epiphyseal plate– Flat plate of hyaline cartilage seen in young,
growing bone
• Epiphyseal line– Remnant of the epiphyseal plate– Seen in adult bones
Figure 5.3a
Distalepiphysis
Diaphysis
Proximalepiphysis
Articularcartilage
Spongy bone
EpiphyseallinePeriosteum
Compact boneMedullarycavity (linedby endosteum)
(a)
Anatomy of a Long Bone
• Marrow (medullary) cavity – Cavity inside of the shaft– Contains yellow marrow (mostly fat) in adults– Contains red marrow for blood cell formation in
infants
• In adults, red marrow is situated in cavities of spongy bone and epiphyses of some long bones
Figure 5.3a
Distalepiphysis
Diaphysis
Proximalepiphysis
Articularcartilage
Spongy bone
EpiphyseallinePeriosteum
Compact boneMedullarycavity (linedby endosteum)
(a)
Describe everything that is in this photograph.
Microscopic Anatomy of Compact 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 (Volkmann’s) canal– Canal perpendicular to the central canal– Carries blood vessels and nerves
Figure 5.4a
CompactbonePeriostealblood vesselPeriosteum
Perforatingfibers
Central (Haversian) canal
Perforating(Volkmann’s) canalBlood vessel
Spongy bone
Blood vessel continues intomedullary cavity containing marrow
Lamellae
(a)
Osteon(Haversian system)
Microscopic Anatomy of Bone
• Lacunae– Cavities containing bone cells (osteocytes)– Arranged in concentric rings called lamellae
• Lamellae– Rings around the central canal– Sites of lacunae
Figure 5.4b
Lamella
CanaliculusLacunaCentral (Haversian) canal
(b)
Osteocyte
Figure 5.4c
Osteon
Lacuna
Centralcanal
Interstitiallamellae
(c)
Microscopic Anatomy of Bone
• Canaliculi – Tiny canals– Radiate from the central canal to lacunae– Form a transport system connecting all bone cells
to a nutrient supply
Figure 5.4b
Lamella
CanaliculusLacunaCentral (Haversian) canal
(b)
Osteocyte
Describe everything that is in this photograph.
Bone Matrix (obj 5): 2 components—
• Organic• Collagen fibers• Reinforces bones• Gives bones some
degree of flexibility & resilience
• w/o collagen—brittle bone disease
• Inorganic• Inorganic salts
– Especially calcium salts but other minerals as well
• Makes bones hard & supportive
• w/o hard, supportive bones—rickets (soft bones)
Types of Bone CellsTypes of Bone Cells
Slide 5.15Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Osteocytes Mature bone cells
Osteoblasts Bone-forming cells
Osteoclasts Bone-destroying cells
Break down bone matrix for remodeling and release of calcium
Bone remodeling is a process by both osteoblasts and osteoclasts
Formation of the Human Skeleton
• In embryos, the skeleton is primarily hyaline cartilage
• During development, much of this cartilage is replaced by bone—Endochondral Ossification
• However, between flat bones of the skull arise from layers of dense connective tissue—Intramembranous Ossification
• Cartilage remains in isolated areas– Bridge of the nose– Parts of ribs– Joints
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
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)
Figure 5.5
In a fetusIn an embryo
Bone collar
Hyalinecartilagemodel
Bone startingto replacecartilage
In a child
Medullarycavity
New center ofbone growth
Hyalinecartilage
Epiphysealplate cartilage
Growthin bonelength
New boneforming
Invadingbloodvessels
Epiphysealplatecartilage
Articularcartilage
Spongybone
New boneforming
Growthin bonewidth
Figure 5.5, step 1
In an embryo
Bone collar
Hyalinecartilagemodel
Bone startingto replacecartilage
Figure 5.5, step 2
In a fetus
Medullarycavity
New center ofbone growth
Hyalinecartilage
Growthin bonelength
Invadingbloodvessels
Figure 5.5, step 3
In a child
Epiphysealplate cartilage
New boneforming
Invadingbloodvessels
Epiphysealplatecartilage
Articularcartilage
Spongybone
New boneforming
Growthin bonewidth
Figure 5.6
Bone growth
Bone grows inlength because:
Bone remodeling
Growing shaft isremodeled as:
Cartilagegrows here.
Cartilageis replacedby bone here.
Cartilagegrows here.
Cartilageis replaced by bone here.
1
2
3
4
1
2
3 Bone isresorbed here.
Epiphyseal plate
Articular cartilage
Bone isresorbed here.
Bone is addedby appositionalgrowth here.
Types of Bone Cells
• Osteocytes—mature bone cells• Osteoblasts—bone-forming cells• Osteoclasts—giant 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
Skeletal Changes Throughout Life
• Osteoporosis– Bone-thinning disease afflicting
• 50 percent of women over age 65 • 20 percent 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
Osteoporosis
Figure 5.36
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
Common Types of Fractures
• Comminuted—bone breaks into many fragments• Compression—bone is crushed• Depressed—broken bone portion is pressed
inward• Impacted—broken bone ends are forced into
each other• Spiral—ragged break occurs when excessive
twisting forces are applied to a bone• Greenstick—bone breaks incompletely
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
Figure 5.7
Internalcallus(fibroustissue andcartilage)
Hematomaforms.
Fibrocartilage callus forms.
Bony callus forms.
Bone remodeling occurs.
1 2 3 4
Hematoma
Bonycallus ofspongybone
Spongybonetrabecula
Newbloodvessels
Externalcallus
Healedfracture
Figure 5.7, step 1
Hematomaforms.
Hematoma
1
Figure 5.7, step 2
Internalcallus(fibroustissue andcartilage)
Hematomaforms.
Fibrocartilage callus forms.
Hematoma
Spongybonetrabecula
Newbloodvessels
Externalcallus
1 2
Figure 5.7, step 3
Internalcallus(fibroustissue andcartilage)
Hematomaforms.
Fibrocartilage callus forms.
Bony callus forms.
Hematoma
Bonycallus ofspongybone
Spongybonetrabecula
Newbloodvessels
Externalcallus
1 2 3
Figure 5.7, step 4
Internalcallus(fibroustissue andcartilage)
Hematomaforms.
Fibrocartilage callus forms.
Bony callus forms.
Bone remodeling occurs.
Hematoma
Bonycallus ofspongybone
Spongybonetrabecula
Newbloodvessels
Externalcallus
Healedfracture
1 2 3 4
Figure 5.8a(a) Anterior view
Phalanges
Metatarsals
Tarsals
Fibula
Tibia
Patella
Femur
Metacarpals
Phalanges
Carpals
UlnaRadius
Vertebra
Humerus
Rib
Sternum
Scapula
Clavicle
Facial bones
Cranium
Skull
Thoracic cage(ribs andsternum)
Vertebralcolumn
Sacrum
Figure 5.8b(b) Posterior view
Fibula
Tibia
Femur
Metacarpals
Phalanges
Carpals
RadiusUlna
Vertebra
Humerus
Rib
Scapula
Clavicle
Cranium
Bones ofpectoralgirdle
Upperlimb
Bones ofpelvicgirdle
Lowerlimb