Skeletal System Overview S12 Mark Up-1

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Chapter 6Skeletal System Overview:

Osseous Tissue

and Skeletal Structure

Lindsey L. Jenny, PhD

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Introduction, p1

• Medical Morphemes:– chondro- = cartilage– osteo- = bone

• Osteology – the study of the human skeletal system– Histology – study bone as a tissue– Gross Anatomy – study bones as organs– Physiology - study of regulation of bone

tissue– Physical Anthropology- uses bones to

study life experiences of individuals

Components of the Skeletal System, p1

• Bones — are composed of all four primary tissue types, thus an organ

• Cartilage – located b/t bones

• Ligaments – connects bones at joints

• Nerves and vessels – nourish & maintain bone tissue

Composition of bone tissue, p2

• 70% Inorganic – (Hydroxyapatite crystals) Ca10(PO4)6(OH)2)– Hard, brittle calcium mineral salts, 98% of body’s Ca– Accounts for 2/3 of bone weight

• 30% Organic – Osteoid – newly formed bone matrix prior to

calcification, 90% is collagen, very flexible– Cells – Account for only ~3% weight of bone

tissue

• What happens to bone if you remove the inorganic component? the organic component?

Bone Cells

– 3 types of bone cells• Osteoblasts – build / deposit

new bone by secreting osteoid

• Osteocytes – osteoblasts that become trapped in the osteoid

• reside in small spaces called lacunae, act as control centers to maintain bone quality

• Osteoclasts – break down and absorb old bone

Osteoblast

Osteocyte

Osteoclasts

Figure 6.6 (modified)

Basic Multicellular Units (BMUs) in Bone

Mature Bone

Osteoclasts resorb mature bone leaving a cavity

= Osteoclast = Osteoblast = Osteocyte


Mature Bone

Osteoblasts move in and start secreting osteoid to form new bone



Mature Bone

Some osteoblasts get surrounded by osteoid (new bone)


Osteoid


Mature Bone

These trapped osteoblasts become osteocytes and communicate with the osteoblasts still making bone to lay down bone where it is needed


Osteoid


Mature Bone

Result in the formation of new Haversian systems (osteons)


Osteoid-New Bone

BMUs results in Haversian systems

Figure 6.8

Properties of bone, p3

• Strong —difficult to break, but also lightweight• Tensile strength - Poor

– Tolerates some stretching & twisting; from collagen

• Compressive strength - High– Withstands compression but NOT stretching &

twisting; from mineral salts

• Rigid —resists compression (bending) but not stretching/twisting

• Highly vascular – good blood supply• Impermeable - substances do not diffuse

through bone tissue – must travel thru vascular channels

Functions of the skeletal system

• 1) Support and movement

• 2) Encasement and protection – Examples?

Functions of the skeletal system

• 3) Hemopoiesis – Production of blood cells in bone marrow

• 4) Lipid storage in bone marrow

• 5) Mineral balance and storage – Balance levels of Calcium by hormone

action and physical activity– Calcitonin hormone released from thyroid

gland production of new bone– PTH hormone released from parathyroid

gland destruction of bone

Two main types of bone tissue, p3

(Figures 6.4 and 6.8)• 1) Cortical bone

– composed of compact bone or Haversian bone– Relatively dense, forms the outer layer of all

bones

• 2) Spongy bone – a.k.a. cancellous bone or trabecular bone– Very porous, found inside bones, on the ends of

long bones– Affected by osteoporosis

• These two types of bone differ with respect to their function, metabolism, and mechanical properties.

Figure 6.8 Components of Bone

Cortical and Spongy Bone

Figure 6.9

Bone Types, p4

• Based on shape, 6 types• 1) Long bones

– Characteristics: longer than they are wide, tubular, all limb bones are long bones

Architectural features of a typical long bone • Diaphysis (shaft) – mainly compact bone• Metaphysis – flared region• Epiphysis

– proximal & distal ends; contains spongy bone in adults

• -physis – growth; epiphyseal plate

Long Bone Features

Figure 6.4 Gross Anatomy of a Long Bone

Long Bone Features cont.• Periosteum

– outer covering of bone cortex– 2 layers: 1) fibrous – support; 2) cellular - growth

• Endosteum– Inner lining of hollow bones; cellular function

• Medullary cavity (marrow cavity)– Hollow center of long bones– Red marrow – produces blood cells; found in spongy

bone of adults • children have red marrow in all bones

– Yellow marrow – stores lipids (fats); found only in long bones of adults

• Nutrient foramen – openings in the cortex for blood vessels

Figure 6.5 Periosteum and Endosteum

Periosteum & Endosteum; Marrow Cavity

Figure 6.14 Arterial Supply to a Mature Bone

Figure 6.3 Classification of Bone by Shape

Classification of Bones, p 5

2) Flat Bones• Characteristics: spongy

bone sandwiched between two layers of cortical bone

• Examples: Skull bones, Ribs, Sternum

3) Short Bones• Characteristics: boxlike,

shell of cortical bone surrounding spongy bone

• Examples: Wrist bones (carpals) & Ankle bones (tarsals)

Other Bone Types

• 4) Irregular bones– Characteristics: complex, irregularly shaped bones

with combined characteristics of other bone types– Examples: Vertebrae & Facial bones

• 5) Sesamoid bones– Characteristics: bones that develop within a muscle

tendon; generally variable in number– Examples: Patella & misc. bone in wrist

• 6) Wormian or sutural bones– Characteristics: islands of bone that develop within

cranial sutures - variable

I Clicker Time

The black arrow is pointing to the

A. Diaphysis

B. Proximal epiphysis

C. Distal epiphysis

D. Metaphysis

I clicker

Osteoblasts:

A. deposit new bone

B. remove old bone

C. act as communication centers

I Clicker

What type of bone is the patella?

A. long

B. flat

C. short

D. sesamoid

E. wormian/sutural

Growth & Development of the Skeletal System, p5

• Osteogenesis – Production of new bone

• Calcification– Process of deposition and hardening of calcium salts

in bone and teeth

• Ossification – the replacement of cartilage or mesenchymal

(embryonic) tissue with bone

• There are two general types of ossification:– 1) Intramembranous ossification– 2) Endochondral ossification

Figure 7.34

Fetal Bone Development

Intramembranous Ossification

• Intra- = within• Highly vascular

membranespongy bone formed in membrane

• Over time, compact bone forms on the outer surface while spongy bone develops in the middle

• Examples: flat bones of the skull

Intra-membranous Growth

1. Ossification centers form within the mesenchymea. Osteoblasts develop and begin to secrete osteoid

Mesenchymalcell

Ossificationcenter

Osteoid

Osteoblast


2. Bone matrix (Osteoid) calcifies (turns to bone) trapped osteoblasts become osteocytes

Osteoblast

Osteocyte

Newly calcifiedbone matrix


3. Newly calcified bone is unorganized and immature- called woven bone. Periosteum begins to form around woven bone.

Mesenchymecondensingto form theperiosteum

Blood vessel

Trabecula ofwoven bone


4. Over time, woven bone is replaced by compact boneand spongy bone

Periosteum

Compact bone

Spongy bone

Endochondral Ossification

• Endo- = Inside• Formation of bone within a cartilage model• Mesenchymal cells form a Cartilaginous

model (anlage) ossifies as bone replaces cartilage

• Most bones of the body are formed by this process, especially long bones

Endochondral Growth Stage 1

#1 – Fetal hyaline cartilage model develops – (8-12 weeks in utero)

Perichondrium

Hyalinecartilage


#2 Cartilage model calcifies forming a bone collar around diaphysis of bone– cartilage cells become larger and lose their nutrients and

die- creating a space inside the model– outer layer of cartilage is invaded by osteoblasts and

becomes periosteum Deterioratingcartilage matrix Developing

periosteum

Periostealbone collar

Hyalinecartilage


#3 – Primary ossification center forms in diaphysis (appear by 12th week fetal development)– Capillaries and osteoblasts form a periosteal bud that

extends into the cartilage shaft– Calcified cartilage acts a template for new bone cells– Starts at center of diaphysis and moves out in both

directions

Primaryossificationcenter

Bloodvessel ofperiostealbud


• #4 – Secondary Ossification Centers appear (beginning around birth)– hyaline cartilage in epiphysis calcifies, replaced with bone

cells– In the Diaphysis

• Medullary cavity forms in diaphysis• Compact bone develops in diaphysis

Epipysealblood vessel

Calcified cartilage

Secondaryossificationcenters

Medullarycavity

Developingcompactbone


#5 Bone replaces most of the cartilage• cartilage is present at:

– articular surfaces– epiphyseal plates (to allow for growth)

Epipyseal plate

Articularcartilage

Spongybone

Compact bone

Periosteum

Epiphysealplate

Medullarycavity


• #6 Fusion of primary and secondary centers, growth in length stops– most epiphyseal plates fuse between 10-25

years

Epiphyseal line(remnant ofepiphyseal plate)

Medullarycavity

Spongy bone

Epiphyseal line

Articular cartilage

Compact bone

Periosteum

Centers of Ossification, p6

• Primary centers– First part of the bone to ossify,

typically occurs about the 8th fetal week for most bones

– Located in the middle of the shaft– 806 ossification centers in 11th fetal

week; 450 at birth

• Secondary centers– Develop after birth anywhere from 2

months to 18 years– These secondary centers are the

“epiphyses”– Most bones have multiple secondary

centers

Primary and Secondary Centers

Fused b/t 17-20

Fused b/t 18-23

p6

• Union/fusion of primary centers with secondary centers– The growth plates closes, uniting

the epiphysis to the diaphysis in a long bone

– This occurs at regular sequence from infancy early adulthood

– This “pattern” allows physical anthropologists to age juvenile skeletons very precisely

– Females mature skeletally 1-2 years before males

– Once fusion occurs there is no more growth in length!

• Clinical Correlate: It is essential to know the age of an individual when interpreting X-rays, so that a line of fusion is not misinterpreted as a fracture or vice versa.

Timing of epiphyseal union “EHAKWS”

• Elbow 14 to 18 years

• Hip 14 to 18 years

• Ankle 16 to 19 years

• Knee 17 to 20 years

• Wrist 18 to 20 years

• Shoulder 14 to 20 years

• What is final epiphysis to close?

(Stewart, 1979)

E-1 H-2 A-3

K-4W-5S-6

Review

• What is bone composed of?

• What do the following bone cells do?– Osteoblasts

– Osteoclasts

– Osteocytes

Review

• How are intramembranous ossification and endochondral ossification different?

• In general, what types of bones ossify from– Intramembranous

– Endochondral

Review

• For the exam, you should be able to put the stages of endochondral growth in order.– 1.– 2.– 3.– 4.– 5.– 6.

Review

• What is a primary center of ossification?

• How is it different from a secondary center of ossification?

• For the exam, know the general order of epiphyseal fusion

E-1 H-2 A-3

K-4W-5S-6

Can activity affect epiphyseal fusion?

• Medieval English warship the Mary Rose sank off the coast of Portsmouth in 1545 with a crew of 415– Skeletons of ½ the crew recovered

– 13.6% had unfused acromion epiphyses– Suggested that these individuals were archers

• Began training @ 6 years• Stress of training prevented fusion?

Stirland and Waldron, 1997. Evidence for Activity Related Markers in the Vertebrae of the Crew of the Mary Rose. Journal of Archaeological Science 24:329-335

Bone changes over a lifetime, p7

• What is bone remodeling?• Continuous process of “turning over bone”

through lifetime• Osteon (aka Haversian systems) – functional

unit of bone; microscopic• Resorption – osteoclasts destroy old bone• Deposition – osteoblasts make new bone

• Remodelling maintains structural integrity• Influenced by hormones & physical activity

Osteons

Figure 6.8

Figure 6.9

Microscopic Age Determination (add to c-pack)

• As age increases, so does number of Osteons/Haversian Systems

• Can be used by physical anthropologists to age skeletal remains

• Also used to ID bone as human or nonhuman

Fig 8.10

How do bones increase in length

• Growth occurs at the epiphyseal plate

• Cartilage is replaced by bone at each end of the bony shaft a longer shaft

• This stops at skeletal maturity after puberty ~18-20 years

The “V” Principle p7

• Important concept for growth of facial skeleton– bone is resorbed on the

outer surface – bone is deposited on the

inner surface– example: Mandible widens

as it grows

Adult Mandible from Butt Road CemeteryPhoto: Lindsey Jenny

--

---

+++

+

+

After Figure 29 from Orthodontic Diagnosis, Rakosi et al. 1993

Figure 6.13 Appositional Bone Growth

How do bones increase in diameter?

Growth in width (Appositional Growth)• at Periosteum – osteoblasts deposit new bone• at Endosteum – osteoclasts destroy bone• Stops at ~20-25 years

Degenerative Changes of Bone, p7

• Bone density decreases with age after 35 y/o– Osteopenia – normal age-related

decrease in bone density– Osteoporosis – pathological

decrease in bone density

• Normal bone density - within 1 S.D. of mean bone mineral density of a 25 y/o female

• Osteopenia – b/t 1 and 2.5 S.D. lower than mean

• Osteoporosis – greater than 2.5 S.D. lower then mean– Dramatically increases fracture

risk

p. 167

Degenerative Changes of Bone, p7 • 3 factors contribute to osteoporosis

– Genetics– insufficient dietary intake of calcium and Vitamin D– insufficient weight-bearing physical activity (e.g.

walking, resistance training, but NOT swimming)

Clinical View, p. 167

Osteoporosis– Osteoporosis can predispose a patient to:

• Hip Fractures – most occur at neck of femur, ~90% are related to osteoporosis (>60 yrs)

– resulting immobility leads to (5-20%) increase in death and decreases the chance of living independently

• Wedge Fractures of Vertebra– leads to abnormal thoracic curvature ("hunchback")– can impinge nerves entering/exiting spinal cord resulting in pain and loss of

motor function

Figure 6.16 Fracture Repair

Bone Injury and Repair Steps, p8

Terminology of bone surface features, p9

• Bony projections/processes; “bumps”– Function: attachment sites for tendons and

ligaments– Categories

• trochanter—large, rough projection• tuberosity—smaller, rough projection• tubercle—small, rounded projection• spine—pointed projection• line—low ridge• crest—prominent ridge

Figure 6.17 Bone Markings

Examples of Bony Projections

Bone Openings and Depressions• Openings: allow the passage of vessels and nerves• Depressions:

–house/protect a structure like the pituitary gland –allow a full range of motion at a joint like the olecranon fossa of the elbow.

• Categories–foramen (pl. foramina) —a hole which transmits

vessels or nerves–fossa (pl. fossae) —a shallow, rounded depression

where something sits or projects into–Groove / sulcus —a long, narrow depression–canal —a longer enclosed passageway through a bone

which transmits vessels or nerves–alveolus —the socket into which a tooth fits (found only

in the maxilla and mandible)

Articular features

•These features are associated with joints–Facet —a small, flat articular surface;

• where 2 or more bones touch–Condyle —a smooth, rounded articular process;

• at the ends of some of the long bones–Head —expanded articular region of a bone; ex. femur & humerus

–Neck —a constricted region that separates the head from the major portion of the bone

Examples of Bony Features, F7.33, 8.11

Specific Examples of•Head•Neck•Facet•Condyle•Fossa•Groove•Tubercle

The “Typical” Adult Human Skeleton, p10• 206 separate bones • Some are paired – R. & L. copy • Some are unpaired – usually in

midline• Axial Skeleton = 80 bones

(Figure 7.1)– The central axis of the

body– Skeletal elements

• skull and associated bones = 22 + 7 bones

• ribs = 24 bones

• sternum = 1 bone

• vertebral column = 26 bones Figure 7.1

Appendicular Skeleton• Appendicular Skeleton = 126

bones (all paired)–pectoral girdle = 4 bones–upper limb = 60 bones–pelvic girdle = 2 bones–lower limb = 60 bones

Figure 8.1 Appendicular Skeleton

Skeletal System Checklist Study characteristics, properties, and functions of bone Know different types of bones (Figure 6.3) Study Figures 6.4c, 6.17- These could appear on the exam Spend some time looking at Figures 6.10 and 6.11,

Compare/contrast ossification types Know the order of stages for endochondral ossificationKnow examples of each ossification type

Know the general order of epiphyseal fusion (no need for age ranges)

Know steps of fracture repair Be familiar with terminology on pp11-12 of coursepack Typical adult skeleton (p13)

How many bones are there? How is the skeleton divided up? (Figures 7.1 and 8.1)

Clinical Correlates- osteoporosis, interpreting x-rays based on age

HERE ARE YOUR NEXT STEPS1) Review your lecture note packet and power point slides

2) As needed, review the textbook images, tables, figures etc. to fill in gaps and reinforce knowledge

3) As needed, review pertinent pages in Anatomy Coloring Book.

4) start working on the course pack's Sample Questions (answers at end of coursepack)

5) Go to Connect and complete any available practice assignments and go to LearnSmart and complete chapter 6 module

Questions regarding my anatomy lecture content? Post to the Unit #1 Discussion Forum on ANGEL

Questions regarding course administration, enrollment, grading, or exam procedure & policy? Email Michael Koot at [email protected]

Skeletal System Overview S12 Mark Up-1

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