Soriano Notes~Chapter 6~Anatomy & Physiology

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*Skeletal Cartilage

Back 1

1~ Contains no blood vessels or nerves

2~ Surrounded by perichondrium (dense irregular connective tissue) that resists outward expansion

3~3 types – hyaline, elastic, & fibrocartilage

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*Hyaline Cartilage

Back 2

1~Provides support, flexibility & resilience
2~Is most abundant skeletal cartilage
3~Is present in these cartilages:
a)Articular –Covers ends of long bones
b)Costal –Connects ribs to sternum
c)Respiratory –Makes up larynx, reinforces air passages
d)Nasal –Supports nose

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*Elastic Cartilage

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1~Similar to hyaline cartilage, but contains elastic fibers

2~Found in external ear & epiglottis

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*Fibrocartilage

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1~Highly compressed w great tensile strength

2~Contains collagen fibers

3~Found in menisci of knee & in intervertebral discs

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Growth of Cartilage

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1~Appositional – cells in perichondrium secrete matrix against external face of existing cartilage

2~Interstitial – lacunae-bound chondrocytes inside cartilage divide & secrete new matrix, expanding cartilage from within

3~Calcification of cartilage occurs
a)During normal bone growth
b)During old age

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Bones & Cartilages of Human Body
Classification of Bones

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1~Axial skeleton – bones of skull, vertebral column & rib cage

2~Appendicular skeleton – bones of upper & lower limbs, shoulder & hip

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Classification of Bones: By Shape

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1~Long bones – longer than they are wide
(ex humerus)

2~Short bones
a)Cube-shaped bones of wrist & ankle
b)Bones that form within tendons (ex patella)

3~Flat bones – thin, flattened & a bit curved (ex sternum & most skull bones)

4~Irregular bones – bones w complicated shapes (ex vertebrae & hip bones)

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*Function of Bones

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1~Support – form framework that supports body & cradles soft organs

2~Protection – provide a protective case for brain, spinal cord & vital organs

3~Movement – provide levers for muscles

4~Mineral storage – reservoir for minerals, especially calcium & phosphorus

5~Blood cell formation – hematopoiesis occurs within marrow cavities of bones

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Bone Markings

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1~Bulges, depressions & holes that serve as:
a)Sites of attachment for muscles, ligaments & tendons
b)Joint surfaces
c)Conduits for blood vessels & nerves

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Bone Markings: Projections – Sites of Muscle & Ligament Attachment

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1~Tuberosity – rounded projection
2~Crest – narrow, prominent ridge of bone
3~Trochanter – large, blunt, irregular surface
4~Line – narrow ridge of bone
5~Tubercle – small rounded projection
6~Epicondyle – raised area above a condyle
7~Spine – sharp, slender projection
8~Process – any bony prominence

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Bone Markings: Projections – Projections That Help to Form Joints

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1~Head – bony expansion carried on a narrow neck

2~Facet – smooth, nearly flat articular surface

3~Condyle – rounded articular projection

4~Ramus – armlike bar of bone

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Bone Markings: Depressions and Openings

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1~Meatus – canal-like passageway

2~Sinus – cavity within a bone

3~Fossa – shallow, basin-like depression

4~Groove – furrow

5~Fissure – narrow, slit-like opening

6~Foramen – round or oval opening through a bone

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Gross Anatomy of Bones: Bone Textures

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1~Compact bone – dense outer layer

2~Spongy bone – honeycomb of trabeculae filled w yellow bone marrow

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*Structure of Long Bone (Consists of 2)

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1~Diaphysis:
a)Tubular shaft that forms axis of long bones
b)Composed of compact bone that surrounds medullary cavity
c)Yellow bone marrow (fat) is contained in medullary cavity

2~Epiphyses:
a)Expanded ends of long bones
b)Exterior is compact bone & interior is spongy bone
c)Joint surface is covered w articular (hyaline) cartilage
d)Epiphyseal line separates diaphysis from epiphyses

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Bone Membranes

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1~Periosteum – double-layered protective membrane
a)Outer fibrous layer is dense regular connective tissue
b)Inner osteogenic layer is composed of osteoblasts & osteoclasts
c)Richly supplied w nerve fibers, blood & lymphatic vessels, which enter bone via nutrient foramina
d)Secured to underlying bone by Sharpey’s fibers

2~Endosteum – delicate membrane covering internal surfaces of bone

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Structure of Short, Irregular, and Flat Bones

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1~Thin plates of periosteum-covered compact bone on outside w endosteum-covered spongy bone (diploë) on inside

2~Have no diaphysis or epiphyses

3~Contain bone marrow between trabeculae

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Structure of a Flat Bone
Location of Hematopoietic Tissue
(Red Marrow)

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1~In infants:
Found in medullary cavity & all areas of spongy bone

2~In adults
Found in diploë of flat bones & head of femur & humerus

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Microscopic Structure of Bone:
Compact Bone

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1~Haversian system or osteon – structural unit of compact bone
a)Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen
b)Haversian or central canal – central channel containing blood vessels & nerves
c)Volkmann’s canals – channels lying at right angles to central canal, connecting blood & nerve supply of periosteum to that of Haversian canal

2~Osteocytes – mature bone cells

3~Lacunae – small cavities in bone that contain osteocytes

4~Canaliculi – hairlike canals that connect lacunae to each other & central canal

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*Chemical Composition of Bone: Organic

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1~Osteoblasts – bone-forming cells

2~Osteocytes – mature bone cells

3~Osteoclasts – large cells that resorb or break down bone matrix

4~Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins & collagen

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Chemical Composition of Bone: Inorganic

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1~Hydroxyapatites or mineral salts
a)65% of bone mass
b)Mainly calcium phosphates
c)Responsible for bone hardness & its resistance to compression

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Bone Development

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1~Osteogenesis & ossification – process of bone tissue formation, which leads to:
a)Formation of bony skeleton in embryos
b)Bone growth until early adulthood
c)Bone thickness, remodeling & repair

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Formation of Bony Skeleton

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1~Begins at week 8 of embryo development

2~Intramembranous ossification – bone develops from a fibrous membrane

3~Endochondral ossification – bone forms by replacing hyaline cartilage

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*Intramembranous Ossification

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1~Formation of most of flat bones of skull & clavicles

2~Fibrous connective tissue membranes are formed by mesenchymal cells

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Stages of Intramembranous Ossification

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1~An ossification center appears in fibrous connective tissue membrane

2~Bone matrix is secreted within fibrous membrane

3~Woven bone & periosteum form

4~Bone collar of compact bone forms & red marrow appears

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*Endochondral Ossification

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1~Begins in second month of development

2~Uses hyaline cartilage “bones” as models for bone construction

3~Requires breakdown of hyaline cartilage prior to ossification

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Stages of Endochondral Ossification

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1~Formation of bone collar

2~Cavitation of hyaline cartilage

3~Invasion of internal cavities by periosteal bud & spongy bone formation

4~Formation of medullary cavity; appearance of secondary ossification centers in epiphyses

5~Ossification of epiphyses, w hyaline cartilage remaining only in epiphyseal plates

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Postnatal Bone Growth

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*Growth in length of long bones:
1~Cartilage on side of epiphyseal plate closest to epiphysis is relatively inactive

2~Cartilage abutting shaft of the bone organizes into a pattern that allows fast, efficient growth

3~Cells of epiphyseal plate proximal to resting cartilage form 3 functionally different zones: growth, transformation & osteogenic

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Functional Zones in Long Bone Growth

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1~Growth zone – cartilage cells undergo mitosis, pushing epiphysis away from diaphysis

2~Transformation zone – older cells enlarge, matrix becomes calcified, cartilage cells die & matrix begins to deteriorate

3~Osteogenic zone – new bone formation occurs

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Growth in Length of Long Bone
Long Bone Growth & Remodeling

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1~Growth in length – cartilage continually grows & is replaced by bone as shown

2~Remodeling – bone is resorbed & added by appositional growth as shown

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*Hormonal Regulation of Bone Growth During Youth

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1~During infancy & childhood, epiphyseal plate activity is stimulated by growth hormone

2~During puberty, testosterone & estrogens:
a)Initially promote adolescent growth spurts
b)Cause masculinization & feminization of specific parts of skeleton
c)Later induce epiphyseal plate closure, ending longitudinal bone growth

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Bone Remodeling

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 Remodeling units – adjacent osteoblasts & osteoclasts deposit & resorb bone at periosteal & endosteal surfaces

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Bone Deposition

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1~Occurs where bone is injured or added strength is needed

2~Requires a diet rich in protein, vitamins C, D & A, calcium, phosphorus, magnesium & manganese

3~Alkaline phosphatase is essential for mineralization of bone

4~Sites of new matrix deposition are revealed by:
a)Osteoid seam – unmineralized band of bone matrix
b)Calcification front – abrupt transition zone between osteoid seam & older mineralized bone

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Bone Resorption

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1~Accomplished by osteoclasts

2~Resorption bays – grooves formed by osteoclasts as they break down bone matrix

3~Resorption involves osteoclast secretion of:
a)Lysosomal enzymes that digest organic matrix
b)Acids that convert calcium salts into soluble forms

4~Dissolved matrix is transcytosed across osteoclast’s cell where it is secreted into interstitial fluid & then into blood

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Importance of Ionic Calcium in Body

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*Calcium is necessary for:
1~Transmission of nerve impulses
2~Muscle contraction
3~Blood coagulation
4~Secretion by glands & nerve cells
5~Cell division

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*Control of Remodeling

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*2 control loops regulate bone remodeling

1~Hormonal mechanism maintains calcium homeostasis in blood

2~Mechanical & gravitational forces acting on skeleton

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Hormonal Mechanism

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1~Rising blood Ca2+ levels trigger thyroid to release calcitonin

2~Calcitonin stimulates calcium salt deposit in bone

3~Falling blood Ca2+ levels signal parathyroid glands to release PTH

4~PTH signals osteoclasts to degrade bone matrix & release Ca2+ into blood

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Hormonal Control of Blood Ca
Response to Mechanical Stress

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1~Wolff’s law – a bone grows or remodels in response to forces or demands placed upon it

2~Observations supporting Wolff’s law include:
a)Long bones are thickest midway along shaft (where bending stress is greatest)
b)Curved bones are thickest where they are most likely to buckle

3~Trabeculae form along lines of stress

4~Large, bony projections occur where heavy, active muscles attach

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Bone Fractures (Breaks)

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*Bone fractures are classified by:

1~Position of bone ends

2~Completeness of break

3~Orientation of bone to long axis

4~Whether or not bones ends penetrate skin

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Types of Bone Fractures

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1~Nondisplaced – bone ends retain their normal position
2~Displaced – bone ends are out of normal alignment
3~Complete – bone is broken all way through
4~Incomplete – bone is not broken all way through
5~Linear –Fracture is parallel to long axis of bone
6~Transverse –Fracture is perpendicular to long axis of bone
7~Compound (open) –Bone ends penetrate skin
8~Simple (closed) –Bone ends do not penetrate skin

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Common Types of Fractures

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1~Comminuted –Bone fragments into 3 or more pieces; common in elderly

2~Spiral –Ragged break when bone is excessively twisted; common sports injury

3~Depressed –Broken bone portion pressed inward; typical skull fracture

4~Compression –Bone is crushed; common in porous bones

5~Epiphyseal –Epiphysis separates from diaphysis along epiphyseal line; occurs where cartilage cells are dying

6~Greenstick –Incomplete fracture where one side of bone breaks & other side bends; common in children

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*Stages in the Healing of a Bone Fracture(4) ~Know all 6!!!

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1~Hematoma formation:
a)Torn blood vessels hemorrhage
b)A mass of clotted blood (hematoma) forms at fracture site
c)Site becomes swollen, painful & inflamed

2~Fibrocartilaginous callus forms:
a)Granulation tissue (soft callus) forms a few days after fracture
b)Capillaries grow into tissue & phagocytic cells begin cleaning debris
c)Fibrocartilaginous callus forms when:
Osteoblasts & fibroblasts migrate to fracture & begin reconstructing bone
a)Fibroblasts secrete collagen fibers that connect broken bone ends
b)Osteoblasts begin forming spongy bone
c)Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies

3~Bony callus formation:
a)New bone trabeculae appear in fibrocartilaginous callus
b)Fibrocartilaginous callus converts into a bony (hard) callus
c)Bone callus begins 3-4 weeks after injury & continues until firm union is formed 2-3 months later

4~Bone remodeling
a)Excess material on bone shaft exterior & in medullary canal is removed
b)Compact bone is laid down to reconstruct shaft walls

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*Homeostatic Imbalances

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*1~Osteomalacia
a)Bones are inadequately mineralized causing softened, weakened bones
b)Main symptom is pain when weight is put on affected bone
c)Caused by insufficient calcium in diet or by vitamin D deficiency

*2~Rickets
a)Bones of children are inadequately mineralized causing softened, weakened bones
b)Bowed legs and deformities of pelvis, skull & rib cage are common
c)Caused by insufficient calcium in diet or by vitamin D deficiency

~Rickets has been essentially eliminated in US

~Only isolated cases appear
Example: Infants of breastfeeding mothers deficient in Vitamin D will also be Vitamin D deficient & develop rickets

*3~Osteoporosis
a)Group of diseases in which bone reabsorption outpaces bone deposit
b)Spongy bone of spine is most vulnerable
c)Occurs most often in postmenopausal women
d)Bones become so fragile that sneezing or stepping off a curb can cause fractures

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Osteoporosis: Treatment

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1~Calcium & vitamin D supplements

2~Increased weight-bearing exercise

3~Hormone (estrogen) replacement therapy (HRT) slows bone loss

4~Natural progesterone cream prompts new bone growth

5~Statins increase bone mineral density

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*Paget’s Disease

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1~Characterized by excessive bone formation & breakdown
2~Pagetic bone w an excessively high ratio of woven to compact bone is formed
3~Pagetic bone, along w reduced mineralization, causes spotty weakening of bone
4~Osteoclast activity wanes but osteoblast activity continues to work
5~Usually localized in spine, pelvis, femur & skull
6~Unknown cause (possibly viral)
7~Treatment includes drugs Didronate & Fosamax

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Fetal Primary Ossification Centers
Developmental Aspects of Bones

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~Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes & cartilages that form embryonic skeleton

~The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms

~At birth, most long bones are well ossified (except for their epiphyses)

~By age 25, nearly all bones are completely ossified

~In old age, bone resorption predominates

~A single gene that codes for vitamin D docking determines both tendency to accumulate bone mass early in life & risk for osteoporosis later in life