The Skeletal System

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SkeletonBones Skeletal System

THE SKELETAL SYSTEM - NOTES

• Skeletal System Parts:

• bones, cartilage, tendons, ligaments

• Functions: • maintain body shape - support• protects organs

• provides levers for movement• mineral and fat storage• blood cell formation

• Skeletal System connective tissues:

• living cells in a matrix

LIVING CELLS MATRIX

• bone cells • calcium, phosphorus, collagen

• cartilage cells • collagen and ground tissue

• tendons & ligaments

• parallel collagen fibers

Skeletal Cartilages

Hyaline Cartilage – most abundant Frosted glass Support with flexibility and resilience Fine collagen fibers in matrix Articular, costal, respiratory, nasal

Skeletal Cartilage Elastic – resembles hyaline but has

elastic fibers. External ear and epiglottis.

Fibrocartilage – highly compressible with great strength. Seen in areas with pressure and stretch – pad like cartilages. Menisci in knee, discs between vertebrae.

Parts of the skeleton

Axial Skeletonskull, spine, rib cage

Appendicular Skeletonupper and lower limbs and

girdles (shoulders and hips)

• Bone Classification by Shape• LONG BONE • EX: humerus

• SHORT BONE • EX: trapezoid (bone in wrist)

• FLAT BONE • EX: sternum

• IRREGULAR BONE

• EX: vertebra

• SESAMOID BONE • patella (knee cap)

• Anatomical Features of Long Bones• DIAPHYSIS • shaft

• EPIPHYSIS • end of the bone

• EPIPHYSEAL PLATE (or EPIPHYSEAL LINE)

• site of bone growth – bones grow from their ends

diaphysis

epiphysis epiphyseal plate

• MEDULLARY CAVITY• location: • in diaphysis

• filled with yellow marrow (adipose tissue)

• PERIOSTEUM • outer covering of bone – tough connective tissue (dense irregular)• contains blood vessels & nervesInner layer – osteogenic cells

• Anatomical Features of COMPACT BONE

• location: diaphysis• solid matrix & tightly packed cells

• made up of OSTEONS or HAVERSIAN SYSTEMS

Microscopic Anatomy of Bone

Figure 5.3a

Microscopic Anatomy of Bone

Figure 5.3b–c

• OSTEOCYTES • bone cells – supplied by Haversian Canals with blood

• CANALICULI • tiny canals that connect osteocytes together

• LAMELLAE • thin rings of bone that serve to anchor bone cells

• Anatomical Features of SPONGY BONE

• bone is not really “spongy” or soft, it only “looks” spongy• Location: • epiphysis

• made of TRABECULAE

• interconnecting rods of bone

• spaces in trabeculae filled w/red marrow

• no Haversian Canals• lighter than compact bone

Cell Types

Osteogenic cells – mitotically active cells in periosteum

Osteoblasts – bone-forming cells that secrete bone matrix.

Osteocytes – mature bone cells that occupy spaces (lacunae)

Osteoclasts – giant cells – job is bone resorption

• BONE MARROW • cells produced from within bones

• red marrow • produces blood cells• yellow marrow • adipose tissue – stores fat (energy)

Bone Markings

Projections, depressions, and openings on the bones. Sites of muscle, ligament and tendon attachment.

Formation of the Human Skeleton In embryos, the skeleton is primarily

hyaline cartilage During development, much of this

cartilage is replaced by bone Cartilage remains in isolated areas

Bridge of the nose Parts of ribs Joints

Developmental Aspects of the Skeletal System At birth, the skull bones are

incomplete Bones are joined by fibrous

membranes called fontanelles Fontanelles are completely replaced

with bone within two years after birth

Ossification Centers in a 12-week-old Fetus

Figure 5.32

© 2013 Pearson Education, Inc.

Figure 6.17 Fetal primary ossification centers at 12 weeks.

Parietalbone

Occipitalbone

Clavicle

Scapula

Ribs

Vertebra

Ilium

Frontalboneof skull

Mandible

Radius

Ulna

Humerus

Femur

Tibia

Skeletal Changes Throughout Life Fetus

Long bones are formed of hyaline cartilage

Flat bones begin as fibrous membranes Flat and long bone models are converted

to bone Birth

Fontanels remain until around age 2

Skeletal Changes Throughout Life Adolescence

Epiphyseal plates become ossified and long bone growth ends

Size of cranium in relationship to body 2 years old—skull is larger in proportion to

the body compared to that of an adult 8 or 9 years old—skull is near adult size

and proportion Between ages 6 and 11, the face grows

out from the skull

Skeletal Changes Throughout Life

Figure 5.33a

The Fetal Skull

The fetal skull is large compared to the infant’s total body length

Fontanels—fibrous membranes connecting the cranial bones Allow the brain to grow Convert to bone within 24 months after

birth

The Fetal Skull

Figure 5.13a

The Fetal Skull

Figure 5.13b

Skeletal Changes Throughout Life Curvatures of the spine

Primary curvatures are present at birth and are convex posteriorly

Secondary curvatures are associated with a child’s later development and are convex anteriorly

Abnormal spinal curvatures (scoliosis and lordosis) are often congenital

The Vertebral Column

Figure 5.15

Bone Growth (Ossification) Epiphyseal plates allow for

lengthwise growth of long bones during childhood New cartilage is continuously formed Older cartilage becomes ossified

Cartilage is broken down Enclosed cartilage is digested away,

opening up a medullary cavity Bone replaces cartilage through the action

of osteoblasts

Bone Growth (Ossification) Bones are remodeled and

lengthened until growth stops Bones are remodeled in response to two

factors Blood calcium levels Pull 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)

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings

Long Bone Formation and Growth

Figure 5.4a, step 1

Bone startingto replacecartilage

In an embryo

Bone collar

Hyalinecartilagemodel

(a)

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings

Long Bone Formation and Growth

Figure 5.4a, step 2

Bone startingto replacecartilage

In a fetusIn an embryo

Growthin bonelength

Bloodvessels

Hyalinecartilage

New center ofbone growth

Medullarycavity

Bone collar

Hyalinecartilagemodel

(a)

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings

Long Bone Formation and Growth

Figure 5.4a, step 3

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)

© 2013 Pearson Education, Inc.

Figure 6.10 Growth in length of a long bone occurs at the epiphyseal plate.

Resting zone

1 Proliferation zoneCartilage cells undergomitosis.

2 Hypertrophic zoneOlder cartilage cellsenlarge.

3 Calcification zoneMatrix calcifies; cartilagecells die; matrix beginsdeteriorating; bloodvessels invadecavity.

4 Ossification zoneNew bone forms.

Calcifiedcartilage spicule

Osteoblastdepositing bonematrix

Osseous tissue (bone) coveringcartilage spicules

Long Bone Formation and Growth

Figure 5.4b