Skeletal System Overview S12 Mark Up-1
Transcript of 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
Basic Multicellular Units (BMUs) in Bone
Mature Bone
Osteoblasts move in and start secreting osteoid to form new bone
= Osteoclast = Osteoblast = Osteocyte
Basic Multicellular Units (BMUs) in Bone
Mature Bone
Some osteoblasts get surrounded by osteoid (new bone)
= Osteoclast = Osteoblast = Osteocyte
Osteoid
Basic Multicellular Units (BMUs) in Bone
Mature Bone
These trapped osteoblasts become osteocytes and communicate with the osteoblasts still making bone to lay down bone where it is needed
= Osteoclast = Osteoblast = Osteocyte
Osteoid
Basic Multicellular Units (BMUs) in Bone
Mature Bone
Result in the formation of new Haversian systems (osteons)
= Osteoclast = Osteoblast = Osteocyte
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
Intra-membranous Growth
2. Bone matrix (Osteoid) calcifies (turns to bone) trapped osteoblasts become osteocytes
Osteoblast
Osteocyte
Newly calcifiedbone matrix
Intra-membranous Growth
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
Intra-membranous Growth
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
Endochondral Growth Stage 2
#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
Endochondral Growth Stage 3
#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
Endochondral Growth Stage 4
• #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
Endochondral Growth Stage 5
#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
Endochondral Growth Stage 6
• #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]