Skeletal SystemChapter 5
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Skeletal System• Two divisions:• Axial Skeleton (“axis”)
• Head & trunk
• Appendicular Skeleton (“appendages”)• limbs & their
attachments to trunk
• Also includes:• Joints• Cartilages• Ligaments
Functions of Bones1. Support
• Internal framework, cradles soft organs
2. Protection• i.e. skull, vertebrae, rib cage
3. Movement• Used as levers by muscles
4. Storage• Fat is stored in yellow marrow (internal cavities)• Minerals stored in bone (calcium & phosphorus)
5. Blood Cell Formation• Hematopoiesis occurs
in red marrow
Classification of Bone• 206 bones in adult skeleton• Two types of osseous tissue:• Compact bone – dense, looks smooth & homogenous• Spongy bone – small needlelike pieces of bone & lots of open
space
Spongy & Compact Bone
Bone
Classification of Bones• Classified according to shape
• Long bones – longer than they are wide; contain mostly compact bone• i.e. Bones of the limbs
• Short bones – cube-shaped, contain mostly spongy bone• i.e. Bones of wrist and ankle, patella, sesamoid
bones (within tendons)• Flat bones – thin, flattened, usually curved;
compact bone sandwiches layer of spongy bones• i.e. Bones of the skull, ribs, sternum
• Irregular bones – do not fit into one of the preceding categories• i.e. Vertebrae and hip bones
Costume ideas??
metaphysis(disc)
Gross Anatomy of a
Long Bone(Hyaline)
(DCT)
Microscopic Anatomy of the Bone
• Osteocytes (mature bone cells)• Lacunae (cavities in matrix)• Lemellae (concentric circles
around central canal)• Central (Haversian) canal (carry
blood vessels and nerves to all areas of the bone)
• Osteon (Haversian System)• Canaliculi (radiate outward from
central canal to all lacunae)• Volkmann’s canal
(communication from exterior to interior of bone)
Bone Tissue• Connective Tissue: calcified matrix with
abundant collagen fibers• Four types of cells:
• Osteogenic cells: unspecialized from stem cells; found along periosteum and endosteum• Make osteoblasts
• Osteoblast: bone-building cells – synthesize and secrete collagen fibers
• Osteocyte: mature cells – maintain metabolism• Osteoclasts: huge collection of
white blood cells found in endosteum• release acids and enzymes that digest
bone matrix (resorption)
ANATOMICAL PUMPKINS!!
Bone Formation• Ossification (osteogenesis):
formation of bone• Begins in 6th week of pregnancy• Two patterns:• Intramembraneous ossification: flat
bones• i.e. skull & clavicles
• Endochondral ossification: most bones• i.e. long bones
Intramembraneous Ossification• Flat bones form on fibrous membranes• Mesenchymal cells cluster and form
osteoblasts which harden• Form ossification center in membrane
• Osteoblasts secrete bone matrix which mineralizes and traps cells in bones (become osteocytes)• Trabeculae then form followed by the
periosteum forming around bone• Trabeculae then thicken to form bone
collar and deeper remain distinct as spongy bone and eventually red marrow
Endochondral Bone Development• Most bones develop using a hyaline cartilage model• Fetal skeleton = hyaline cartilage (formed from mesenchyme)• Two phases (Fig 5.5, page 140):
1. hyaline cartilage model covered with bone matrix (bone “collar”) by osteoblasts
•Primary ossification: develops inward from outer surface & forms spongy bone (eventually compact bone)•Secondary ossification: develops outward (from center of epiphysis)
2. enclosed hyaline cartilage model digested away, opening up medullary cavity within newly formed bone
•Osteoclasts break down center to form medullary cavity
•By birth or shortly after, all cartilage converted to bone except articular cartilages (cover bone ends) and epiphyseal plates•Adult skeleton = cartilage exists in nose, parts of ribs, and joints
Bone Growth• Bones increase in length (interstitial growth) &
width (appositional growth)• Epiphyseal plate: layer of hyaline cartilage in
metaphysis of growing bone; new bone forms on diaphysis side
• Interstitial growth (length): from epiphyseal plate• Four zones; close around 18-21 (18-females, 21-
males)1. Resting cartilage: nearest epiphysis, anchor
plate to bone (not part of growing bone)2. Proliferating cartilage: cells divide & replace
dying cells3. Hypertrophic cartilage: matruing chondrocytes;
arranged in columns4. Calcified cartilage: cells harden & die; replaced
by bone tissue• Osteoclasts dissolve and osteoblasts
and blood vessels enter area
Interstitial Bone Growth
Appositional Bone Growth• Growth in thickness of the bone• Cells in periosteum differentiate
into osteoblasts while osteoclasts increase medullary cavity• Osteoblasts in periosteum add
bone tissue to external face of diaphysis as osteoclasts in endosteum remove bone from inner surface• Occur at about the same rate
Skull or lady in the mirror?
Bone Remodeling• Bone resorption & deposition used
to renew and replace injured bone• Affected by minerals, vitamins,
and hormones• Resorption: removal of minerals
and collagen fibers by osteoclasts• Deposition: addition of minerals
and collagen fibers by osteoblasts
Bone Remodeling• Bones are remodeled continually in response to changes in two
factors:1. Calcium levels in the blood
• Parathyroid gland releases PTH when blood calcium levels drop• PTH activates osteoclasts to break down bone matrix and release Ca2+ into blood• Hypercalcemia: Ca2+ is deposited into bone matrix as hard calcium salts
2. Pull of gravity and muscles on the skeleton• Shape of bone altered for stress• Osteoblasts lay down new matrix & become trapped within it (become osteocytes)
where bulky muscles attach (due to stress)• Bedridden/inactive: lose mass & atrophy (no stress)• Ongoing replacement of old bone tissue by new bone tissue
• PTH determines when/if bone broken down or formed in response to need for more or fewer Ca2+ ions in the blood; stress determines where bone matrix is to be broken down or formed• Helps maintain skeletal strength
Bone Fracture Repair• Repair involves four major
events:1. Hematoma forms
• From ruptured blood vessels, cells die that are deprived of oxygen
2. Fibrocartilage callus forms• growth of new capillaries
(granulation tissue) into clotted blood at site of damage and disposal of dead tissue by phagocytes.
• CT cells form mass of repair tissue which splints broken bone and closes gap (made up of bony matrix, collagen, collagen matrix)
Bone Fracture Repair3. Bony callus forms
• Fibrocartilage callus is gradually replaced by the bony callus (made of spongy bone) as more osteoblasts and osteoclasts migrate to area and multiply
4. Bone remodeling occurs• Bony callus is remodeled in
response to mechanical stresses placed on it
Skeletal System
Anatomy
Bone Markings
Can you see the hidden skull?
Skeletal System
Anatomy
206 total bones
Axial Skeleton• Three parts:• Skull• Vertebral column• Thoracic cage
Skull: 22 bones• Cranial (8), Facial
(13), Mandible (1)• Protects brain• Many paired bones• Page 148-149
• Teeth: 32 in adult (not part of 206 total)- considered part of digestive system
Skull• Infants have fontanels (soft spots)• Bones of the skull
are not fused yet
• Adults: skull bones fused with sutures • Immoveable joints
• Mandible: freely moving joint
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Middle Ear: 6 bones• Three in each ear• Stapes (stirrup)• Incus (anvil)• Malleus (hammer)
Hyoid Bone• Does not articulate
with any other bone• Often broken during
strangulation• CT attaches to
larynx & trachea
Vertebral Column: 26 bones• Strong, flexible, rotates• Protects spinal cord &
supports head• Intervertebral discs
between made of fibrocartilage• Shock absorption &
spine flexibility• High in water content
when young (spongy, compressible); discs harden with age
Vertebral Column: 26 bones• Born with 33 - fuse to 26• 7 cervical (neck)- smaller, bifed
clef• C1: atlas (articulates with
occipital condyle)• C2: axis
• 12 thoracic (chest)- stronger, long spine• 5 lumbar (lower back)- strongest,
short spine• Sacrum (5 fused by mid 20s)• Coccyx (4 fused by 30)- tail bone
Vertebral Column:Figure 5-1
Curvatures of the Spine• Four normal curvatures
• Fetus has 2 primary curvatures (thoracic and sacral)
• Secondary curvatures develop after birth
• Cervical (3 months) and lumbar (6 months)
• Cervical: concave (anterior)• Thoracic: convex (posterior)• Lumbar: concave (anterior)• Sacrum: convex (posterior)
• Exaggeration of the thoracic curve
Kyphosis: “Hunchback”
• Tuberculosis of spine- • vertebral bodies partially collapse
• Degeneration of discs• Rickets (lack of vitamin C)• Poor posture• Advanced osteoporosis
• Exaggeration of the lumbar curve
Lordosis: “Swayback”
•Exaggerated lumbar curve
• Result of increased weight gain• Pregnancy or extreme
obesity• Poor posture• Rickets• Tuberculosis of spine
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• Lateral bending of the vertebral column
• Lateralcurvature
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• Congenital malformed vertebrae (birth defect)• Chronic sciatica (pain down leg)• Paralysis of muscles on one side of
backbone• Poor posture• One leg shorter than other
Thoracic Cage: 25 Bones• Sternum: fusion of 3 bones,
attached to first 7 ribs• 12 pairs of ribs (1-7 increase in size,
8-12 decrease in size)• Attached by costal cartilage• True ribs (1-7)- direct
attachment• False ribs (8-12)- no anterior
attachment• Floating ribs (11-12)- no anterior
attachment• All have posterior attachment to
vertebrae
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Appendicular Skeleton
126 bones: limbs, pectoral & pelvic girdles (attach limbs to axial skeleton)
Pectoral Girdle: 4 bones• Attach arms; two of each• Clavicle: collar bones• s-shaped- weak juncture• Attaches to manubrium
and sternum medially and scapula posteriorly to form shoulder joint• Prevents dislocation
• Scapula: shoulder bones
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Upper Limbs: 60 bones• 8 carpals each• 5 metacarpals• 14 phalanges• 2 in thumb
• Radius (thumb side)• Ulna (pinky side)
1. Clavicle 1a. Sternal end1b. Acromial end2. scapula2a. Coracoid process2b. Acromion2c. Subscapular fossa2d. Infraspinous fossa2e. Spine of scapula2f. Supraspious fossa2g. Glenoid cavity3. Acromioclavicular4. Glenohumeral joint5. Humerus5b. Deltoid tuberosity5c. Head5d. Surgical neck5e. Anatomical neck5f. Greater tubercle5g. Lateral epicondyle5h. Medial epicondyle5i. Capitulum5j. Trochlea5k. Coronoid fossa6. Ulna6a. Olecranon7. Radius
1. Phalanges 1a. Distal1b. Medial1c. Proximal1d. Base1e. Head2 Interphalangeal joints3 Sesamoid bone4 Metacarpophalangeal joints5 Intermetacarpal joints6. Metacarpals6a. Base6b. shaft6c. Head
7. Carpometacarpal joint 8. Trapezium9. Trapezoid10. Capitate11. Hamate12. Pisiform13. Triquetrum14. Lunate15. Scaphoid16. Midcarpal join
•median nerve which runs through wrist to hand becomes compressed• involves narrow bony passage
in wrist called carpal tunnel, through which nine tendons and median nerve must pass
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Pelvic Girdle: 2 bones• Function: bearing weight (total
weight of upper body) & protects reproductive and urinary systems• United at pubic symphysis
(fibrocartilage; some flexibility)• Attached to axial skeleton via
sacral attachment to lower lumbar vertebrae• Three parts fuse at birth
• Ilium• Pubis• Ischium
Lower Limbs: 60 bones1. Hip joint 2.Femur2a. Head2b. Neck2c. Greater trochanter2d Lesse trochanter2e. Lateral epicondyle2f. Medial epicondyle2g. Adductor tubercle2h. Medial condyle2i. Lateral condyle2j. Intercondylar fossa2k. Linea aspera3. Patella
4. Knee joint 5. Tibia5a. Lateral condyle5b. Medial condyle5c. Tibial tuberosity5d. Medial malleolus6. Fibula6a. Head6b. Crest6c. Lateral malleolus7. Ankle joint8 Talus9. Calconeus
•Femur, tibia, fibula, patella
•7 tarsals, 5 metatarsals, 14 phalanges
•Carry our total body weight when erect
•much thicker/stronger than upper limbs
• Bones composing arch of foot held by ligaments and tendons• Weakened ligaments and tendons causes arch to “fall”• Caused by excessive weight, postural abnormalities,
weakened tissue, and genetic disposition
So easy a two year old can do it!!
So easy Miley Cyrus can do it!!
Name those bones
Male vs. Female• Males bones larger and
heavier• Angle of pubic symphysis
less for men• Page 163 lists differences
Fetal Skeleton• Arises from
mesenchymal cells (derived from mesoderm)• Intramembraneous
and endochondral ossification• 1st long bones =
hyaline cartilage• 1st flat bones of skull
= fibrous membranes
• 20 million people suffer from it (250,000 hip fractures a year)• Decreased bone mass• Increased susceptibility to fracture• Hormones effect osteoblast production• Afflicts entire skeletal system
• Body build (shorter females at greater risk)• Weight (adipose produces estrone)• Smoking (decreases estrogen levels)• Calcium deficiency or malabsorption• Vitamin D deficiency• Exercise (sedentary more at risk)• Certain drugs (alcohol, diuretics, cortisone, tetracycline)• Premature menopause• Family history
• Accelerated remodeling of bone tissue• Osteoclast resorption
massive• Osteoblast formation
extensive• Irregular thickening and
softening of bones• Greatly increased vascularity,
especially in skull, pelvis, and extremities link
Testicular tumor “face”
testicular tumor “face”
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