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Why This Matters

Understanding bone anatomy and the process of bone remodeling allows you to work effectively with patients with bone diseases such as osteoporosis

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6.1 Skeletal Cartilages

The human skeleton initially consists of just cartilage, which is replaced by bone, except in areas requiring flexibility

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Basic Structure, Types, and Locations

Skeletal cartilage: made of highly resilient, molded cartilage tissue that consists primarily of water Contains no blood vessels or nervesPerichondrium: layer of dense connective tissue surrounding cartilage like a girdleHelps cartilage resist outward expansionContains blood vessels for nutrient delivery to cartilageCartilage is made up of chondrocytes, cells encased in small cavities (lacunae) within jelly-like extracellular matrix

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Basic Structure, Types, and Locations (cont.)

Three types of cartilage:Hyaline cartilageProvides support, flexibility, and resilienceMost abundant type; contains collagen fibers onlyArticular (joints), costal (ribs), respiratory (larynx), nasal cartilage (nose tip)Elastic cartilageSimilar to hyaline cartilage, but contains elastic fibersExternal ear and epiglottisFibrocartilageThick collagen fibers: has great tensile strengthMenisci of knee; vertebral discs

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Epiglottis

Larynx

Cartilage in

external ear

Cartilages in

nose

Trachea

Cartilage in

intervertebral

disc

Respiratory

tube cartilages

in neck and thorax

Pubic symphysis

Meniscus (

padlike

cartilage in

knee joint)

Cartilages

Articular cartilage

of a joint

Articular

cartilage

of a joint

Costal

cartilage

Thyroid

cartilage

Cricoid

cartilage

Lung

Axial skeleton

Appendicular skeleton

Bones of skeleton

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Figure 6.1 The bones and cartilages of the human skeleton

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Growth of Cartilage

Cartilage grows in two ways:Appositional growthCartilage-forming cells in perichondrium secrete matrix against external face of existing cartilageNew matrix laid down on surface of cartilageInterstitial growthChondrocytes within lacunae divide and secrete new matrix, expanding cartilage from withinNew matrix made within cartilage

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Growth of Cartilage (cont.)

Calcification of cartilage occurs during normal bone growth in youth, but can also occur in old ageHardened cartilage is not the same as bone

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6.2 Functions of Bones

There are seven important functions of bones: SupportFor body and soft organs ProtectionProtect brain, spinal cord, and vital organs MovementLevers for muscle action Mineral and growth factor storageCalcium and phosphorus, and growth factors reservoir

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6.2 Functions of Bones

Blood cell formation Hematopoiesis occurs in red marrow cavities of certain bones Triglyceride (fat) storageFat, used for an energy source, is stored in bone cavities Hormone productionOsteocalcin secreted by bones helps to regulate insulin secretion, glucose levels, and metabolism

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6.3 Classification of Bones

206 named bones in human skeletonDivided into two groups based on locationAxial skeletonLong axis of bodySkull, vertebral column, rib cageAppendicular skeletonBones of upper and lower limbsGirdles attaching limbs to axial skeleton

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Epiglottis

Larynx

Cartilage in

external ear

Cartilages in

nose

Trachea

Cartilage in

intervertebral

disc

Respiratory

tube cartilages

in neck and thorax

Pubic symphysis

Meniscus (

padlike

cartilage in

knee joint)

Cartilages

Articular cartilage

of a joint

Articular

cartilage

of a joint

Costal

cartilage

Thyroid

cartilage

Cricoid

cartilage

Lung

Axial skeleton

Appendicular skeleton

Bones of skeleton

Hyaline cartilages

Elastic cartilages

Fibrocartilages

Figure 6.1 The bones and cartilages of the human skeleton

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6.3 Classification of Bones

Bones are also classified according to one of four shapes: Long bonesLonger than they are wideLimb bones Short bonesCube-shaped bones (in wrist and ankle)Sesamoid bones form within tendons (example: patella)Vary in size and number in different individuals

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6.3 Classification of Bones

Flat bonesThin, flat, slightly curvedSternum, scapulae, ribs, most skull bones Irregular bonesComplicated shapesVertebrae and hip bones

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Figure 6.2 Classification of bones on the basis of shape.

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Flat bone

(sternum)

Long bone(humerus)

Irregular bone (vertebra),right lateral view

Short bone

(talus)

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6.4 Bone Structure

Bones are organs because they contain different types of tissuesBone (osseous) tissue predominates, but a bone also has nervous tissue, cartilage, fibrous connective tissue, muscle cells, and epithelial cells in its blood vesselsThree levels of structureGrossMicroscopicChemical

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Gross Anatomy

Compact and spongy boneCompact bone: dense outer layer on every bone that appears smooth and solidSpongy bone: made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculaeOpen spaces between trabeculae are filled with red or yellow bone marrow

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Gross Anatomy (cont.)

Structure of short, irregular, and flat bonesConsist of thin plates of spongy bone (diploe) covered by compact boneCompact bone sandwiched between connective tissue membranesPeriosteum covers outside of compact bone, and endosteum covers inside portion of compact boneBone marrow is scattered throughout spongy bone; no defined marrow cavityHyaline cartilage covers area of bone that is part of a movable joint

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

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Spongy bone

(diploë)

Compact

bone

T

rabeculae of

spongy bone

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Gross Anatomy (cont.)

Structure of typical long boneAll long bones have a shaft (diaphysis), bone ends (epiphyses), and membranesDiaphysis: tubular shaft that forms long axis of boneConsists of compact bone surrounding central medullary cavity that is filled with yellow marrow in adultsEpiphyses: ends of long bones that consist of compact bone externally and spongy bone internallyArticular cartilage covers articular (joint) surfacesBetween diaphysis and epiphysis is epiphyseal lineRemnant of childhood epiphyseal plate where bone growth occurs

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

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Articular

cartilage

Proximal

epiphysis

Diaphysis

Distal

epiphysis

Spongy bone

Epiphyseal

line

Periosteum

Compact bone

Medullary

cavity (lined

by

endosteum

)

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

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Articular

cartilage

Compact

bone

Endosteum

Spongy

bone

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Gross Anatomy (cont.)

Membranes: two types (periosteum and endosteum)Periosteum: white, double-layered membrane that covers external surfaces except jointsFibrous layer: outer layer consisting of dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrixOsteogenic layer: inner layer abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cellsContains many nerve fibers and blood vessels that continue on to the shaft through nutrient foramen openingsAnchoring points for tendons and ligaments

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Gross Anatomy (cont.)

Membranes (cont.)EndosteumDelicate connective tissue membrane covering internal bone surfaceCovers trabeculae of spongy boneLines canals that pass through compact boneLike periosteum, contains osteogenic cells that can differentiate into other bone cells

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

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Endosteum

Yellow

bone marrow

Compact bone

Periosteum

Perforating

(Sharpey’s)

fibers

Nutrient

artery