Basics of the Skeletal System and Articulations Learn and - - PowerPoint PPT Presentation

Basics of the Skeletal System and Articulations

Learn and Understand

• Skeleton is more than just bone
• Functions go beyond support
• Bone grows upon existing bone or upon existing

cartilage, bone never grows by expanding existing bone from within

• The pattern of bone growth in the fetus aids in birth
• Bones exhibit a trade off between strength and

weight

• Many joints do not allow movement
• Synovial joints incorporate numerous adaptations

which protect them from damage even when frequently used

Functions of Bones Seven important functions

– Support – Protection – Movement – Mineral storage – Blood cell formation – Triglyceride (fat) storage – Hormone production

Components of Skeletal System

• Bone

– Compact or cancellous (spongy)

• Cartilage

– Hyaline – Fibrocartilage – Elastic

• Tendons – muscle to bone
• Ligaments – bone to bone

Figure 6.1 The bones and cartilages of the human skeleton.

Cartilage in external ear Cartilage in intervertebral disc Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Costal cartilage Articular cartilage

• f a joint

Cartilages in nose Epiglottis Thyroid cartilage Cricoid cartilage Larynx Trachea Lung Bones of skeleton Axial skeleton Appendicular skeleton Hyaline cartilages Elastic cartilages Fibrocartilages Cartilages Respiratory tube cartilages in neck and thorax

Hyaline Cartilage and Interstitial Growth

Interstitial Growth: An increase in the size of a tissue by cell division within the interior of a part or structure that is already formed

Daughter cells

Cells of Bone Tissue

Cell Type Location Function Osteo- progenitor cells Periosteum, endosteum When stimulated, divide into

• steoblasts or bone lining cells

– “osteogenic” Osteoblasts Initially on edge

• f existing

bone, then in matrix (become

• steocytes)

Form bone by secreting matrix components which assemble

• utside of blasts and

eventually entrap them in hard matrix Osteocytes Lacunae of bone matrix Monitor and maintain bone matrix, stimulate bone remodeling in response to physical stress Osteoclasts

(derived from macrophages)

Edges of existing bone, temporarily

• ccupy an area

Summoned to an area by

• steocytes or signaling

chemicals, have ruffled border that uses H+ and proteolytic enzymes to dissolve bone matrix

Chemical Composition of Bone

• Organic components include cells and

– Osteoid – up one-third of organic bone matrix – secreted by osteoblasts

• ground substance and collagen fibers
• Inorganic components

– Hydroxyapatites

• Makeup 65% of bone by mass
• Consist mainly of tiny calcium phosphate crystals
• Responsible for hardness and resistance to

compression

Figure 6.7 Microscopic anatomy

• f compact bone.

Compact bone Spongy bone Central (Haversian) canal Osteon (Haversian system) Circumferential lamellae Perforating (Volkmann’s) canal Endosteum lining bony canals and covering trabeculae Perforating (Sharpey’s) fibers Periosteal blood vessel Periosteum Lamellae Nerve Vein Artery Canaliculi Osteocyte in a lacuna Lamellae Central canal Lacunae Interstitial lamella Lacuna (with osteocyte)

Blood & Nervous Supply: good throughout compact bone, indirect supply to cancellous trabeculae

Figure 6.6 A single osteon.

Structures in the central canal Artery with capillaries Vein Nerve fiber Collagen fibers run in different directions Twisting force Lamellae

Structural unit of compact bone Hollow tubes of bone matrix called lamellae

• Collagen fibers in

adjacent rings run in different directions – Withstands stress – resist twisting

Figure 6.4c The structure of a long bone (humerus of arm).

Endosteum Yellow bone marrow Compact bone Periosteum Perforating (Sharpey’s) fibers Nutrient arteries

Periosteum

• White, double-layered

membrane

• Covers external surfaces

except joint surfaces

• Outer fibrous layer of

dense irregular connective tissue

– Sharpey's fibers secure to bone matrix

• Many nerve fibers and

blood vessels

• Anchoring points for

tendons and ligaments

Figure 6.4a The structure of a long bone (humerus of arm).

Articular cartilage Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) Proximal epiphysis Diaphysis Distal epiphysis

Epiphyseal line

• Remnant of childhood

bone growth at epiphyseal plate

Figure 6.3 Flat bones consist of a layer of spongy bone sandwiched between two thin layers of compact bone.

Spongy bone (diploë) Compact bone Trabeculae of spongy bone

Spongy Bone

• Trabeculae

– Align along lines of stress to help resist it – No osteons – Contain irregularly arranged lamellae and osteocytes interconnected by canaliculi – Capillaries in endosteum supply nutrients

Bone Development

• Ossification (osteogenesis)

– Process of bone tissue formation – Formation of bony skeleton

• Embryonic skeleton ossifies predictably
• Begins in 2nd month of fetal development

– Most long bones begin ossifying by 8 weeks – Primary ossification centers by 12 weeks

• At birth, most long bones well ossified (except epiphyses)
• At age 25 ~ all bones completely ossified and skeletal growth

ceases

– Bone remodeling and repair

• Lifelong

Approximate size of a human conceptus from fertilization to the early fetal stage

Fertilization 1-week conceptus 3-week embryo (3 mm) 5-week embryo (10 mm) Embryo 8-week embryo (22 mm) 12-week fetus (90 mm)

Bone Development: Two Types of Ossification Intramembranous

• ssification

Bone develops from fibrous connective tissue membranes

1. Ossification centers appear 2. Osteoid is secreted 3. Woven bone and periosteum form 4. Lamellar bone replaces woven bone & red marrow appears

Forms flat bones, e.g. clavicles and cranial bones

Endochondral

• ssification

Bone forms by replacing cartilage (endochondral) bones made of hyaline cartilage Forms most of skeleton

Figure 6.8 Endochondral

• ssification in a long bone.

Week 9 Month 3 Birth Childhood to adolescence Hyaline cartilage Bone collar Primary

• ssification

center Area of deteriorating cartilage matrix Spongy bone formation Blood vessel of periosteal bud Epiphyseal blood vessel Secondary

• ssification

center Articular cartilage Spongy bone Epiphyseal plate cartilage Medullary cavity Bone collar forms around the diaphysis of the hyaline cartilage model. Cartilage in the center of the diaphysis calcifies and then develops cavities. The periosteal bud invades the internal cavities and spongy bone forms. The diaphysis elongates and a medullary cavity

• forms. Secondary
• ssification

centers appear in the epiphyses. The epiphyses

• ssify. When

completed, hyaline cartilage remains

• nly in the

epiphyseal plates and articular cartilages. 1 2 3 4 5

Lengthening of Long Bones in Childhood and Adolescence

• Requires presence of epiphyseal cartilage
• Epiphyseal plate maintains constant thickness

– Rate of cartilage growth on one side balanced by bone replacement on other

• Concurrent remodeling of epiphyseal ends to

maintain proportion

• Result of five zones within cartilage

– Resting (quiescent) zone – Proliferation (growth) zone – Hypertrophic zone – Calcification zone – Ossification (osteogenic) zone

Growth in Length of a Long Bone Occurs at the Epiphyseal Plate

Figure 6.12 Growth in length of a long bone occurs at the epiphyseal plate.

(a) X-ray image of right knee, anterior

• view. Proximal epiphyseal plate of

the tibia enlarged in part (b).

Calcified cartilage spicule Osseous tissue

(b) Photomicrograph of cartilage in the epiphyseal plate (125x). (c) Diagram of the zones within the epiphyseal plate. Resting zone

Proliferation zone Cartilage cells undergo mitosis.

Hypertrophic zone Older cartilage cells enlarge. Calcification zone Matrix becomes calcified; cartilage cells die; matrix begins deteriorating. Ossification zone New bone is forming. 1 2 3 4

Growth in Length of Long Bones

• Near end of adolescence chondroblasts

divide less often

• Epiphyseal plate thins then is replaced by

bone

• Epiphyseal plate closure

– Bone lengthening ceases

• Requires presence of cartilage

– Bone of epiphysis and diaphysis fuses – Females – about 18 years – Males – about 21 years

Appositional Growth: Growth in Width

• Allows lengthening bone to widen
• Occurs throughout life
• Osteoblasts beneath periosteum secrete

bone matrix on external bone

• Osteoclasts remove bone on endosteal

surface

• Usually more building up than breaking

down

→ Thicker, stronger bone but not too heavy

Bone Homeostasis

• Recycle 5-7% of bone mass each week

– Spongy bone replaced ~ every 3-4 years – Compact bone replaced ~ every 10 years

• Older bone becomes more brittle

– Calcium salts crystallize – Fractures more easily

• Consists of bone remodeling and bone

repair

Figure 6.15 Stages in the healing of a bone fracture.

Hematoma Internal callus (fibrous tissue and cartilage) External callus New blood vessels Spongy bone trabecula Bony callus of spongy bone Healed fracture 1 A hematoma forms. 2 Fibrocartilaginous callus forms. 3 Bony callus forms. 4 Bone remodeling

• ccurs.

Stages of Bone Repair

Joints (Articulations)

• Site where two or more bones meet
• Functions of joints

– Give skeleton mobility – Hold skeleton together

• Two classifications

– Functional – based on amount of movement

• Synarthroses—immovable joints
• Amphiarthroses—slightly movable joints
• Diarthroses—freely movable joints

– Structural – based on binding materials and presence/absence of joint cavity

• Fibrous joints
• Cartilaginous joints
• Synovial joints – has a joint cavity

Fibrous Joints

• Bones joined by dense fibrous connective

tissue

• No joint cavity
• Most synarthrotic (immovable)

– Depends on length of connective tissue fibers

• Three types:

– Sutures – Syndesmoses – Gomphoses

Figure 8.1a Fibrous joints.

Suture

Joint held together with very short, interconnecting fibers, and bone edges

• interlock. Found only in the skull.

Dense fibrous connective tissue

Suture line

• Rigid, interlocking joints
• Immovable joints for

protection of brain

• Contain short connective

tissue fibers

• Allow for growth during

youth

• In middle age, sutures
• ssify and fuse

– Called Synostoses

Figure 8.1b Fibrous joints.

• Bones connected by

ligaments

• Fiber length varies so

movement varies

– Little to no movement at inferior tibiofibular joint – Large amount of movement at interosseous membrane connecting radius and ulna

• Interosseous

membrane

Radioulnar Syndesmosis

Figure 8.1c Fibrous joints.

Gomphosis “Peg in socket” fibrous joint. Periodontal ligament holds tooth in socket. Socket of alveolar process Periodontal ligament Root of tooth

• Peg-in-socket joints of

teeth in alveolar sockets

• Fibrous connection is the

periodontal ligament

Cartilaginous Joints

• Bones united by cartilage
• No joint cavity
• Not highly movable
• Two types:

– Synchondroses – Symphyses

Synchondroses Bones united by hyaline cartilage Epiphyseal plate (temporary hyaline cartilage joint) Sternum (manubrium) Joint between first rib and sternum (immovable)

Bar/plate of hyaline cartilage unites bones

– Temporary epiphyseal plate joints

• Become synostoses after plate closure

– Cartilage of 1st rib with manubrium – Many are synarthrotic

Cartilaginous Joints: Synchondroses

Symphyses Bones united by fibrocartilage Body of vertebra Fibrocartilaginous intervertebral disc (sandwiched between hyaline cartilage) Pubic symphysis

• Fibrocartilage unites bone

– Hyaline cartilage present as articular cartilage

• Strong, flexible amphiarthroses

Synovial Joints: Six Distinguishing Features

• 1. Articular cartilage: hyaline cartilage

– Prevents crushing of bone ends

• 2. Joint (synovial) cavity

– Small, fluid-filled potential space

• 3. Articular (joint) capsule

– Two layers

• External Fibrous layer

– Dense irregular connective tissue

• Inner Synovial membrane

– Loose connective tissue – Makes synovial fluid

Figure 8.3 General structure of a synovial joint.

Ligament Joint cavity (contains synovial fluid) Articular (hyaline) cartilage Fibrous layer Synovial membrane (secretes synovial fluid) Articular capsule Periosteum

Synovial Joints: Six Distinguishing Features

• 4. Synovial fluid

– Viscous, slippery filtrate of plasma and hyaluronic acid – Lubricates and nourishes articular cartilage – Contains phagocytic cells to remove microbes and debris

Synovial Joints: Six Distinguishing Features

• 5. Different types of reinforcing ligaments

– Capsular

• Thickened part of fibrous layer

– Extracapsular

• Outside the capsule

– Intracapsular

• Deep to capsule; covered by synovial membrane
• 6. Nerves and blood vessels

– Nerve fibers detect pain, monitor joint position and stretch – Capillary beds supply filtrate for synovial fluid

Other Features of Some Synovial Joints

• Fatty pads

– For cushioning between fibrous layer and synovial membrane or bone

• Articular discs (menisci)

– Fibrocartilage separates articular surfaces to improve "fit" of bone ends, stabilize joint, and reduce wear and tear

Structures Associated with Synovial Joints

• Bursae

– Sacs lined with synovial membrane

• Contain synovial fluid

– Reduce friction where ligaments, muscles, skin, tendons, or bones rub together

• Tendon Sheaths

– Elongated bursa wrapped completely around tendon subjected to friction

Bursae and Tendon Sheaths

Acromion

• f scapula

Subacromial bursa Fibrous layer of articular capsule A tendon sheath is an elongated fluid-filled sac that wraps around a tendon to decrease friction. Tendon of long head

• f biceps

brachii muscle Humerus Articular cartilage Joint cavity containing synovial fluid Synovial membrane Fibrous layer

(a) Frontal section through the right shoulder joint

Three Stabilizing Factors at Synovial Joints

• Shapes of articular surfaces (minor role)
• Ligament number and location (limited

role)

• Muscle tendons that cross joint (most

important)

– Muscle tone keeps tendons taut

• Extremely important in reinforcing shoulder and

knee joints and arches of the foot

• Largest, most complex joint of body
• Three joints surrounded by a single joint

cavity

– Femoropatellar joint

• Plane joint
• Allows gliding motion during knee flexion

– Lateral and medial tibiofemoral joints

• Femoral condyles with lateral and medial menisci
• f tibia
• Allow flexion, extension, and some rotation when

knee partly flexed

Knee Joint

Figure 8.8c The knee joint.

Anterior view of right knee Quadriceps femoris muscle Lateral patellar retinaculum Tibial collateral ligament Fibula Fibular collateral ligament Patella Tendon of quadriceps femoris muscle Patellar ligament Medial patellar retinaculum Tibia

Figure 8.8d The knee joint.

Tibia Arcuate popliteal ligament Oblique popliteal ligament Bursa Popliteus muscle (cut) Lateral head of gastrocnemius muscle Articular capsule Medial head of gastrocnemius muscle Fibular collateral ligament Tibial collateral ligament Tendon of semimembranosus muscle Posterior view of the joint capsule, including ligaments Femur Tendon of adductor magnus

Figure 8.8a The knee joint.

Patellar ligament Sagittal section through the right knee joint Anterior cruciate ligament Posterior cruciate ligament Tibia Femur Lateral meniscus Articular capsule Lateral meniscus Synovial cavity Infrapatellar fat pad Subcutaneous prepatellar bursa Patella Suprapatellar bursa Tendon of quadriceps femoris Deep infrapateller bursa

Figure 8.8e The knee joint.

Fibular collateral ligament Lateral condyle

• f femur

Lateral meniscus Tibia Fibula Anterior view of flexed knee, showing the cruciate ligaments (articular capsule removed, and quadriceps tendon cut and reflected distally) Posterior cruciate ligament Medial condyle Tibial collateral ligament Medial meniscus Patellar ligament Patella Anterior cruciate ligament Quadriceps tendon

Figure 8.8b The knee joint.

Articular cartilage on lateral tibial condyle Posterior cruciate ligament Lateral meniscus Superior view of the right tibia in the knee joint, showing the menisci and cruciate ligaments Anterior cruciate ligament Medial meniscus Articular cartilage

• n medial

tibial condyle Anterior

Anterior Knee

https://www.youtube.com/watch?feature=pl ayer_detailpage&v=_q-Jxj5sT0g

Posterior Knee

Optional Slides:

• Stages in bone repair that accompany a

Figure 6.15

• Structural and functional differences

between cartilage and bone

• Structural and functional differences

between cancellous bone and compact bone

Stages of Bone Repair: HEMATOMA Forms

• Torn blood vessels hemorrhage
• Clot (hematoma) forms
• Site swollen, painful, and inflamed

Stages of Bone Repair: Fibrocartilaginous Callus Forms

• Capillaries grow into hematoma
• Phagocytic cells clear debris
• Fibroblasts secrete collagen fibers to span

break and connect broken ends

• Fibroblasts, cartilage, and osteogenic cells

begin reconstruction of bone

– Create cartilage matrix of repair tissue – Osteoblasts form spongy bone within matrix

• Mass of repair tissue called

fibrocartilaginous callus

Stages of Bone Repair: Bony Callus Forms

• Within one week new trabeculae appear in

fibrocartilaginous callus

• Callus converted to bony (hard) callus of

spongy bone

• ~2 months later firm union forms

Stages of Bone Repair: Bone Remodeling Occurs

• Begins during body callus formation
• Continues for several months
• Excess material on diaphysis exterior and

within medullary cavity removed

• Compact bone laid down to reconstruct

shaft walls

• Final structure resembles original because

responds to same mechanical stressors

Cartilage Characteristics Bone Characteristics living components chondroblasts, chondrocytes

• steogenic cells, osteoblasts, osteoclasts,
• steocytes

matrix proteinaceous: packed collagen fibers, proteoglycan, water inorganic calcium hydroxyapatite and protein: CaPO4 – 65% (and related Ca minerals) collagen, proteoglycan – 35% sheath perichondrium, except articular surfaces periosteum, endosteum Not at articular surfaces growth interstitial and appositional Appositional: endochondral and intramembranous blood & nervous supply good blood supply at perichondrium, none within cartilage good throughout compact bone, indirect supply to cancellous trabeculae types hyaline, fibrocartilage, elastic Woven (temporary) and lamellar cancellous and compact benefits smooth articulation surfaces, flexible, resilient, strong but lighter than bone rigid strength, protection, reservoir

Cancellous (Trabecular, Spongy) Compact Trabeculae covered with endosteum, encased in compact bone Osteons cemented together by interstitial lamellae – endosteum internally, periosteum externally Creates a network of spaces for bone marrow Essentially a solid mass No direct blood supply to the bone matrix, rich blood supply to the marrow-containing cavities Network of blood vessels throughout Strong yet lighter than compact,

• rientation reflects lines of stress

Strongest, densest bone available Epiphyses of long bones, internal portions of short, flat, and irregular bones Shafts of long bones, thin outer covering of most bones