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”