The Skeletal System

The Skeletal SystemParts of the skeletal system

Bones (skeleton)JointsCartilagesLigaments

Two subdivisions of the skeletonAxial skeletonAppendicular skeleton

Functions of BonesSupport the bodyProtect soft organsAllow movement due to attached skeletal

musclesStore minerals and fatsBlood cell formation

Bones of the Human BodyThe adult skeleton has 206 bonesTwo basic types of bone tissue

Compact boneHomogeneous

Spongy boneSmall needle-like

pieces of boneMany open spaces

Figure 5.2b

Classification of Bones on the Basis of Shape

Figure 5.1

Classification of BonesLong bones

Typically longer than they are wideHave a shaft with heads at both endsContain mostly compact boneExample:

FemurHumerus

Classification of Bones

Figure 5.1a

Classification of BonesShort bones

Generally cube-shapeContain mostly spongy boneExample:

CarpalsTarsals

Classification of Bones

Figure 5.1b

Classification of BonesFlat bones

Thin, flattened, and usually curvedTwo thin layers of compact bone surround a

layer of spongy boneExample:

SkullRibsSternum

Classification of Bones

Figure 5.1c

Classification of BonesIrregular bones

Irregular shapeDo not fit into other bone classification

categoriesExample:

Vertebrae Hip bones

Classification of Bones

Figure 5.1d

Anatomy of a Long BoneDiaphysis

ShaftComposed of compact bone

Epiphysis Ends of the boneComposed mostly of spongy bone

Anatomy of a Long BonePeriosteum

Outside covering of the diaphysisFibrous connective tissue membrane

Sharpey’s fibersSecure periosteum to underlying bone

ArteriesSupply bone cells with nutrients

Anatomy of a Long Bone

Figure 5.2c

Anatomy of a Long BoneArticular cartilage

Covers the external surface of the epiphysesMade of hyaline cartilageDecreases friction at joint surfaces

Anatomy of a Long BoneEpiphyseal plate

Flat plate of hyaline cartilage seen in young, growing bone

Epiphyseal lineRemnant of the epiphyseal plateSeen in adult bones

Anatomy of a Long Bone

Figure 5.2a

Anatomy of a Long BoneMedullary cavity

Cavity inside of the shaftContains yellow marrow (mostly fat) in adultsContains red marrow (for blood cell

formation) in infants

Anatomy of a Long Bone

Figure 5.2a

Bone MarkingsSurface features of bones

Sites of attachments for muscles, tendons, and ligaments

Passages for nerves and blood vesselsCategories of bone markings

Projections or processes—grow out from the bone surface

Depressions or cavities—indentations

Bone Markings

Table 5.1 (1 of 2)

Bone Markings

Table 5.1 (2 of 2)

Microscopic Anatomy of BoneOsteon (Haversian system)

A unit of bone containing central canal and matrix rings

Central (Haversian) canalOpening in the center of an osteonCarries blood vessels and nerves

Perforating (Volkman’s) canalCanal perpendicular to the central canalCarries blood vessels and nerves

Microscopic Anatomy of Bone

Figure 5.3a

Microscopic Anatomy of BoneLacunae

Cavities containing bone cells (osteocytes)Arranged in concentric rings

LamellaeRings around the central canalSites of lacunae

Microscopic Anatomy of Bone

Figure 5.3b–c

Microscopic Anatomy of BoneCanaliculi

Tiny canalsRadiate from the central canal to lacunaeForm a transport system connecting all bone

cells to a nutrient supply

Formation of the Human SkeletonIn embryos, the skeleton is primarily

hyaline cartilageDuring development, much of this cartilage

is replaced by boneCartilage remains in isolated areas

Bridge of the noseParts of ribsJoints

Bone Growth (Ossification)Epiphyseal plates allow for lengthwise

growth of long bones during childhoodNew cartilage is continuously formedOlder cartilage becomes ossified

Cartilage is broken downEnclosed cartilage is digested away, opening up a

medullary cavityBone replaces cartilage through the action of

osteoblasts

Bone Growth (Ossification)Bones are remodeled and lengthened until

growth stopsBones are remodeled in response to two

factorsBlood calcium levelsPull of gravity and muscles on the skeleton

Bones grow in width (called appositional growth)

Long Bone Formation and Growth

Figure 5.4a

Bone startingto replacecartilage

Epiphysealplatecartilage

Articularcartilage

Spongybone

In a childIn a fetusIn an embryo

New boneforming

Growthin bonewidth

Growthin bonelength

Epiphysealplate cartilage

New boneforming

Bloodvessels

Hyalinecartilage

New center ofbone growth

Medullarycavity

Bone collar

Hyalinecartilagemodel

(a)

Long Bone Formation and Growth

Figure 5.4b

Types of Bone CellsOsteocytes—mature bone cellsOsteoblasts—bone-forming cellsOsteoclasts—bone-destroying cells

Break down bone matrix for remodeling and release of calcium in response to parathyroid hormone

Bone remodeling is performed by both osteoblasts and osteoclasts