Chapter 5 Skeletal System

Biology 112

Tri-County Technical College

Pendleton, SC

Skeletal System Functions

• Functions of the skeletal system are:– Support– Protection (limited to be sure)– Movement (because of muscular system)– Storage – Blood cell formation (hematopoiesis)

Divisions of the Skeletal System

• AXIAL SKELETON consists of bones that form longitudinal axis of body (skull, bones associated with skull, thoracic cage, and vertebral column

• APPENDICULAR SKELETON includes all the bones of the limbs and the PECTORAL and PELVIC girdles that attach limbs to the trunk

Summary of Bone Functions

• Support-form internal framework that supports and anchors are soft organs; are the girders and concrete of body

• Protection-protect soft organs• Movement-skeletal muscles attached to bones by

tendons; use bones as levers to move body and its parts• Storage-used to store fat and minerals (most important

are calcium and phosphorous• Hematopoiesis-blood cell formation occurs within

marrow of certain bones

CLASSIFICATION OF BONES

• Two basic types of OSSEOUS tissue– Compact bone is dense; looks smooth and

homogeneous– Spongy bone composed of small needlelike

pieces of bone and lots of open spaces

• BONES are classified according to SHAPE• LONG bones are longer than they are wide

– Have shaft with heads at both ends– Mostly compact bone– All bones of limbs (except wrist/ankle bones)

Classification, cont.• SHORT bones generally cube shaped and contain

mostly spongy bone– Bones of wrist and ankle are short bones

• FLAT bones are thin, flattened, and usually curved

• Have two layers of compact bone sandwiching layer of spongy bone between– Most bones of skull, ribs, and sternum are flat bones

• IRREGULAR bones are those that do NOT fit one of the above– Vertebrae and hip bones are irregular bones

Gross Anatomy of Long Bone

• DIAPHYSIS (shaft)-makes up most of bone’s length; composed of compact bone

• PERIOSTEUM-fibrous connective tissue membrane that covers/protects diaphysis– 100s of connective tissue fibers (Sharpey’s fibers)

secure periosteum to underlying bone

• EPIPHYSES-the ends of long bone– Each epiphysis consists of layer of compact bone

enclosing area filled with spongy bone

Long Bone Anatomy, cont.

• ARTICULAR CARTILAGE-covers external surface of epiphysis (instead of periosteum that covers the shaft)– Glassy hyaline cartilage provides smooth, slippery surface

that decreases friction at joint surfaces

• EPIPHYSEAL PLATE-flat plate of hyaline cartilage seen in young, growing bones– Responsible for lengthwise growth of long bone

– By end of puberty, hormones stop long bone growth and epiphyseal plates have been completely replaced by bone

Long Bone Anatomy, cont.

• EPIPHYSEAL LINE-thin line of bone tissue spanning epiphysis; different appearance from rest of bone there– Is the remnant of epiphyseal plate– Marks the previous location of the epiphyseal plate

• MEDULLARY CAVITY-cavity of shaft of long bones– Also called yellow marrow cavity– In adults, primarily storage area for adipose (fat) tissue

Long Bone Anatomy Visual

Red Bone Marrow

• MEDULLARY cavity of long bones of infants contains RED bone marrow and blood cells are formed there

• In adults, red marrow confined to cavities of spongy bones of flat bones and epiphyses of long bones

• Hematopoiesis is a function of RED bone marrow

Hard Bone MS Anatomy

• Compact bone laced with passageways carrying nerves/blood vessels which provide living bone cells with nutrients/route waste disposal

• OSTEON-is complex of central canal and matrix rings (Haversian system)

• OSTEOCYTES-are mature bone cells• LUCUNAE-tiny cavities within matrix that

contain osteocytes• LAMELLAE-concentric circles around

Haversian canal containing the lucunae

Microscopic Anatomy, cont.

• HAVERSIAN CANAL-is another name for “central canal”– Central canals running lengthwise through bony

matrix carrying blood vessels/nerves to all areas of bone

• CANALICULI-tiny canals that radiate outward from central canal to all lucunae– Form transport system that connects all bone cells to

nutrient supply through hard bone matrix

Microscopic Anatomy, cont.• VOLKMANN’S CANALS (perforating canals)

run into compact bone at right angles to shaft– Part of communication pathway

Ossification and more…

• OSSIFICATION is process of bone formation• There are two major forms (types)• INTERMEMBRANEOUS-bone develops from

mesenchyme or fibrous connective tissue – Roofing bones of skull, mandible, and clavicle

• ENDOCHONDRAL-occurs when bone replaces existing cartilage

• Except for flat bones which form on fibrous membranes, MOST bones develop using hyaline cartilage structures as their models

Ossification, cont.

• ENDOCHONDRAL ossification involves two major steps

• 1. Hyaline cartilage model is completely covered with bone matrix by bone forming cells called OSTEOBLASTS

• 2. Enclosed hyaline cartilage model is digested away– Opens up medullary cavity within newly formed

bone

Ossification Visual

Bone Destruction

• Bones are continually remodeled in response to changes in TWO factors– Calcium levels in blood– Pull of gravity and muscles on the skeleton

• If blood levels of calcium drop BELOW homeostatic levels, parathyroid glands release PTH into blood

• PTH activates OSTEOCLASTS (giant bone-destroying cells in bones) to break down bone matrix and release the calcium ions into blood

Bone Destruction, cont.

• HYPERCALCEMIA (too much calcium in blood) results in calcium being deposited in bone matrix as hard calcium salts

• Bone remodeling essential if bones are to retain normal proportions and strength during maturation process

• Bones become thicker and form larger projections in areas where bulky muscles are attached

Bone Destruction, cont.

• At such sites, osteoblasts deposit new matrix and become trapped

• Once trapped, they differentiate into osteocytes (mature bone cells)

• **PTH determines when or if bone is to be broken down or formed in response to need for more or fewer calcium ions in blood

• **Stresses of muscle pull/gravity determine where bone matrix is to be broken down or formed

Formation and Growth Visual

Fracture Repair

• Repair of bone fracture (break) involves FOUR major events

• 1. Blood vessels ruptured when bone breaks & results in blood-filled swelling called HEMATOMA– Bone cells deprived of nutrition DIE

• 2. New capillaries (granulation tissue) grow into clotted blood at site of damage– Connective tissue of all types form mass of repair

tissue called FIBROCARTILAGE CALLUS

Fracture Repair, cont.• FIBROCARTILAGE CALLUS composed of cartilage

matrix, some bony matrix, and collagen fibers) acts to SPLIT the broken bone thereby closing the gap

• 3. BONY CALLUS forms as more osteoblasts and osteoclasts migrate into area and multiply– Fibrocartilage gradually replaced by bony callus

– Bony callus composed of spongy bone

• 4. Bony callus remodeled in response to mechanical stresses placed upon it– Forms strong permanent patch at fracture site

Fracture Repair Visual

What’s a Joint?

• Joints are classified FUNCTIONALLY and STRUCTURALLY

• Functional classification focuses on amount of movement allowed by joint

• SYNARTHROSES-immovable joints• AMPHIARTHROSES-slightly moveable joints• DIARTHROSES-freely moveable joints• Freely moveable joints predominate in limbs• Immovable/slightly moveable joints restricted to axial

skeleton where firm attachments and protection of internal organs are priorities

Diarthrotic Joint• As general rule, synovial joints (joint cavity) are freely

moveable (diarthrotic)• SYNOVIAL joints-articulating bone ends are separated

by joint cavity containing synovial fluid• ARTICULAR (hyaline) cartilage covers ends of bones

forming the joint• FIBROUS articular capsule-joint surfaces enclosed in

sleeve or capsule of fibrous connective tissue and capsule is lined with smooth SYNOVIAL MEMBRANE

• JOINT CAVITY enclosed by articular capsule and contains lubricating synovial fluid

Diarthrotic Joint, cont.

• Reinforcing ligaments reinforce the fibrous joint capsule

• Bursae and tendon sheaths often found closely associated with synovial joints (ball bearings..)

• BURSAE are flattened fibrous sacs lined with synovial membrane and contain thin film of synovial fluid– Common where ligaments, muscles, skin, tendons, or

bones rub together

• TENDON sheath is elongated bursa that wraps completely around tendon subjected to friction

The Joint

Structural Joints

• Classified as fibrous, cartilaginous, or synovial based on whether fibrous tissue, cartilage, or joint cavity separates bony regions at joint

• Fibrous joints-immovable (sutures of skull)• Cartilaginous joints-both immovable and slightly

moveable examples (cartilaginous joints between first ribs and sternum/pubic symphysis of pelvis)

• Synovial joints-freely moveable (shoulder/hand joints)

Joint Visual

Bone Disorders• ARTHRITIS term given more than 100 different

inflammatory or degenerative diseases that damage the joints

• OSTEOARTHRITIS most common form of arthritis and is chronic degenerative condition that typically affects the aged– “wear and tear” arthritis– Over years, cartilage softens, frays, and breakdowns;

exposed bone thickens, extra bone tissue (bone spurs) grows around margins of eroded cartilage

– Spurs protrude into joint cavity restricting movement– Affects fingers, cervical/lumbar joints of spine, knees/hips– Progression slow but rarely crippling– Aspirin, exercise, and rest

Disorders, cont.• RHEUMATOID arthritis-chronic inflammatory

disorder that is autoimmune disease– Usually occurs between ages of 40 and 50– Affects 3X as many women as men– Fingers, wrists, ankles, and feet usually affected– Course varies with remissions and flareups– Begins with inflammation of synovial membranes– Joints swell as fluid accumulates– WBCs enter joint and produce PANNUS (abnormal tissue

that clings to and erodes articular cartilages– Cartilage destroyed, scar tissue formed and connects bone

ends– Scar tissue ossifies and bone ends become firmly fused

(ankylosis) and often deformed

Disorders, cont.• Treatment for rheumatoid arthritis include aspirin,

exercise, cold packs, heat, methotrexate/cyclosporin (anti-inflammatory drugs), and joint replacement

• GOUTY arthritis (gout)-is disease in which uric acid deposited as needle-shaped crystals in soft tissues of joints– Very painful and destructive

– Bone ends fuse/joint becomes immobilized

– Treated with colchicine/other drugs

– Weight loss, restrict intake of organ meat, & avoid alcohol

– Alcohol inhibits secretion of uric acid by kidneys

Rickets/Osteoporosis

• Rickets-disease of children when bones fail to calcify– Bones soften and bow where weight bearing (legs)– Lack of calcium in diet or lack of vitamin D which is needed

to absorb calcium into bloodstream– Not very common in US, but problem elsewhere

• Osteoporosis-loss of bone mass leading to thin, fragile bones (especially in spine/neck of femur)– Estrogen deficiency at menopause strongly implicated– Diet poor in calcium, lack of vitamin D, smoking, and

insufficient weight-bearing exercise to stress bone are also factors